AN ABSTRACT OF THE THESIS OF
Frank Paul Almeida
in
Fisheries
for the degree of
presented on
Master of Science
September 25, 1984
Title: An Analysis of the Stock Structure of Silver Hake,
Merluccius bilinearis, off the Northeast Coast of the
United States
Abstract approved:
Redacted for privacy
Howard F. Horton, Ph.D.
The stock structure of silver hake, Merluccius
bilinearis, was examined utilizing data from research
vessel bottom trawl surveys, U.S. and distant water fleet
commercial fishery statistics, and morphometric data
collected during bottom trawl surveys in 1978-1979.
Seasonal distribution, as evinced front survey and
commercial fishery data, indicated a discontinuous pattern
during all seasons.
Linear discrintinant function analysis performed on
standardized morphometric data indicated that silver hake
inhabiting the waters off the northeast coast of the
United States comprise two stocks, although intermixture
on Georges Bank may occur between the stocks. Analyses
performed on individuals in spawning and post-spawning
condition indicated greater separation during the spawning
season than during other times throughout the year.
Proposed stock groupings include a northern stock,
made up of silver hake found on northern Georges Bank and
in the Gulf of Maine, and a southern stock, comprised of
fish inhabiting the waters of southern Georges Bank south
to Cape Hatteras, NC.
An Analysis of the Stock Structure of Silver Hake,
Merluccius bilinearis, off the Northeast Coast of the
United States
by
Frank P. Almeida
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Completed September 25, 1984
Commencement June 1985
APPROVED:
Redacted for privacy
Professor of Fisheries in charge of major
Redacted for privacy
Head of Departnientof FIsheries and Wildlife
Redacted for privacy
Dean of Gradua
School
Date Thesis is presented
September 25, 1984
Typed by researcher for
Frank P. Almeida
ACKNOWLEDGMENT
I wish to express my appreciation to the staff of the
Northeast Fisheries Center, Woods Hole, Mass., for their
continuing efforts in the collection and maintenance of
the data used in this project. I am also grateful to Drs.
Howard Horton, my major professor, and James Hall for
their critical review of the manuscript and their
patience. Drs. Michael Sissenwine and Steven Murawski also
provided suggestions and helpful assistance during the
preparation of the manuscript. Special thanks go to Dr.
Emory Anderson for his friendship and guidance.
I wish to thank Joseph Wade, Jeffrey Floyd, Stephen
Morrison, William Burns, and other members of the NEFC
staff who participated intermittently in the preparation
of the morphometric data, for their diligence and patience
during the many hours required to obtain the measurements
used in the analysis.
This work is dedicated to my wife, Denise, and my
family, for without their support and understanding, the
project would not have been possible.
TABLE OF CONTENTS
INTRODUCTION
Previous Studies
....................
GENERAL BIOLOGY
Trophic Relations ....................
Gonadal Development and Spawning ...........
Egg and Larval Development ...............
Larval Distribution ...................
1
7
17
18
21
22
SEASONAL DISTRIBUTION PATTERNS
Introduction .......................
......
Methods........................
Results ........................
Adults .......................
Research Vessel Bottom Trawl Survey Data
Prerecrujts ....................
Commercial Fishery Catch Statistics .........
Methods........................
Results........................
Distribution of U.S. Commercial Catch
Distribution of Distant Water Fleet Catch
.
.
.
.
25
25
25
32
38
54
72
72
75
75
88
DISCRIMINANT FUNCTION ANALYSIS
Introduction....................... 97
Methods.......................... 99
Results .......................... 107
Complete Sample Analysis .............. 107
Analysis of Spawning and Post-spawning Samples
.
110
................. 122
LITERATURE CITED ....................... 133
APPENDIX ............................ 141
DISCUSSION AND CONCLUSIONS
LIST OF FIGURES
Figure .............................. Page
1. Current stock boundaries for silver hake based on
Northwest Atlantic Fisheries Organization (NAFO)
divisions and subdivisions .................
4
2. Stock boundaries proposed by the authors of previous
studies............................
8
3. Location of silver hake samples collected for
morphometric analysis by Conover et al. (1961). Open
symbols represent samples from northern group, closed
symbols, from southern group ................ 10
4. Survey area off the northeast coast of the United
States............................. 28
5. Research vessel bottom trawl survey sampling strata.
28
6. Spatial coverage (by 10-minute square) by U.S.,
1963-1981 (A) and foreign, 1967-1977 (B) bottom trawl
surveys during the winter ................. 34
7. Spatial coverage (by 10-minute square) by U.S.,
1963-1981 (A) and foreign, 1967-1977 (B) bottom trawl
surveys during the spring ................. 35
8. Spatial coverage (by 10-minute square) by U.S.,
1963-1981 (A) and foreign, 1967-1977 (B) bottom trawl
surveys during the summer ................. 36
9. Spatial coverage (by 1O-minute square) by U.S.,
1963-1981 (A) and foreign, 1967-1977 (B) bottom trawl
surveys during the autumn ................. 37
10. Distribution of adult silver hake (numbers) from U.S.
(A) and foreign (B) bottom trawl surveys during the
winter, 1964-1981 ...................... 39
11. Bottom temperature distribution (7.) at stations where
adult silver hake were collected from U.S. bottom trawl
surveys during winter, 1964-1981 ............. 41
12. Distribution of adult silver hake catches (7.) by depth
from U.S. bottom trawl surveys during winter 1964-1981.42
13. Distribution of adult silver hake (numbers) from U.S.
(A) and foreign (B) bottom trawl surveys during the
spring, 1968-1981 ...................... 44
14. Bottom temperature distribution (7.) at stations where
adult silver hake were collected from U.S. bottom trawl
surveys during spring, 1968-1981.
45
15. Distribution of adult silver hake catches (%) by depth
from U.S
bottom trawl surveys during spring,
1968-1981 ............................ 46
16. Distribution of adult silver hake (numbers) from U.S.
(A) and foreign (B) bottom trawl surveys during the
summer, 1963-1981
..................... 48
17. Bottom temperature distribution (%) at stations where
adult silver hake were collected from U.S. bottom trawl
surveys during summer, 1963-1981. ............ 49
18. Distribution of adult silver hake catches (%) by depth
from U.S bottom trawl surveys during summer,
1963-1981 ........................... 51
19. Distribution of adult silver hake (numbers) from U.S.
(A) and foreign (B) bottom trawl surveys during the
autumn, 1963-1981 ...................... 52
20. Bottom temperature distribution (%) at stations where
adult silver hake were collected from U.S. bottom trawl
surveys during autumn, 1963-1981. ............ 53
21. Distribution of adult silver hake catches (%) by depth
from U.S. bottom trawl surveys during autumn,
1963-1981
.......................... 55
22. Distribution of prerecruit silver hake (numbers) from
U.S. (A) and foreign (B) bottom trawl surveys during
the winter, 1964-1981 ................... 56
23. Bottom temperature distribution (%) at stations where
prerecruit silver hake were collected from U.S. bottom
trawl surveys during winter, 1964-1981
58
24. Distribution of prerecruit silver hake catches (%) by
depth from U.S. bottom trawl surveys during winter,
1964-1981 ........................... 59
25. Distribution of prerecruit silver hake (numbers) from
U.S. (A) and foreign (B) bottom trawl surveys during
the spring, 1968-1981 .................... 60
26. Bottom temperature distribution (%) at stations where
prerecruit silver hake were collected from U.S. bottom
trawl surveys during spring, 1968-1981 .........
27. Distribution of prerecruit silver hake catches (%) by
depth from U.S. bottom trawl surveys during spring,
62
1968-1981.. 63
28. Distribution of prerecruit silver hake (numbers) from
U.S. bottom trawl surveys during the summer, 1963-1981.
Data from foreign surveys was not available ....... 64
29. Bottom temperature distribution (Z) at stations where
prerecruit silver hake were collected from U.S. bottom
trawl surveys during summer, 1963-1981 ......... 66
30. Distribution of prerecruit silver hake catches (%) by
depth from U.S. bottom trawl surveys during summer,
1963-1981 ........................... 67
31. Distribution of prerecruit silver hake (numbers) from
U.S. (A) and foreign (B) bottom trawl surveys during
the autumn, 1963-1981
.................. 68
32. Bottom temperature distribution (%) at stations where
prerecruit silver hake were collected from U.S. bottom
trawl surveys during autumn, 1963-1981
........ 70
33. Distribution of prerecruit silver hake catches (U by
depth from U.S. bottom trawl surveys during autumn,
1963-1981
.......................... 71
34. Fishery statistical areas and northeast regional port
agent office locations ................... 73
35. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
January for combined years 1965-1980. .......... 77
36. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
February for combined years 1965-1980. ......... 78
37. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
March for combined years 1965-1980 ............ 79
38. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
April for combined years 1965-1980. ........... 81
39. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
May for combined years 1965-1980. ............ 82
40. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
June for combined years 1965-1980. ............ 83
41. Distribution of U.S. commercial catch per unit effort
by lO-minute square obtained from interview data during
July for combined years 1965-1980 ............ 84
42. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
August for combined years 1965-1980 ........... 85
43. DistributIon of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
September for combined years 1965-1980. ........ 86
44. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
October for combined years 1965-1980. ......... 87
45. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
November for combined years 1965-1980. ......... 89
46. Distribution of U.S. commercial catch per unit effort
by 10-minute square obtained from interview data during
December for combined years 1965-1980. ......... 90
47. Distribution of catches by month from the U.S.S.R.
distant water fleet during 1962-1976. (Taken from
Sauskan 1964, Sarnits and Sauskan 1966, Noskov 1976 and
annual U.S.S.R. Research Report series.)
....... 91
48a. Fishing areas and gear restrictions by area fo.r the
distant water fleet off the northeast coast of the U.S.
in effect during 1977-1978. Shaded months indicate open
fishing seasons ...................... 94
48b. Fishing areas and gear restrictions by area for the
distant water fleet off the northeast coast of the U.S.
in effect since 1979. Shaded months indicate open
fishing seasons ...................... 95
49. Location of samples collected during bottom trawl
surveys used In the discriminant function analysis of
morphometric characters, ................. 100
50. Morphometric characters utilized in discriminant
function analysis
....................
101
51. Territorial map of discriminant scores for male and
female silver hake during summer 1978. ( A indicates
group centroid) ...................... 114
52. Territorial map of discriminant scores for male and
female silver hake during autumn 1978. ( A indicates
group centroid) ...................... 115
53. Territorial map of discriminant scores for male and
female silver hake during spring 1979. ( A indicates
group ceñtroid) ........................ 116
54. Stock biomass and total international catch of silver
hake off the northeast coast of the U.S. (Almeida and
Anderson 1981) ........................ 128
55. Distribution of U.S. catch on Georges Bank by
statistical area for 1962-1982 ..............
131
56. Distribution of distant water fleet catch on Georges
Bank by statistical area for 1962-1976. ........ 131
LIST OF TABLES
Table.............................
Page
1. Research vessel bottom trawl surveys conducted off the
northeast coast of the United States during 1963-1981.26
2. Summary of U.S. and foreign research vessel bottom
trawl surveys, both inshore and offshore, conducted
between Nova Scotia and Cape Hatteras, NC during
1963-1981
.......................... 33
3. Results of analysis of covariance of males versus
females with all areas and all seasons combined. Values
listed are the results of F tests for equality of
adjusted group means .................... 103
4. Correlation coefficients between morphometric
characters and length for male and female silver hake
before and after removal of linearity .......... 103
5. Discriminant function coefficients utilizing data from
all maturity stages from samples collected in
1978-1979, mean C-values, and tests of significance for
eachsex ...........................
108
6. Summary results of discriminant analyses performed on
data from samples collected in the summer and autumn of
1978 and the spring of 1979.
.............. 111
7. Summary results of discriminant analyses performed on
data from samples collected In the summer and autumn of
1978 and the spring of 1979.
.............. 112
8. Summary results of discriminant analyses performed on
data from samples collected in the summer and autumn of
1978 and the spring of 1979.
.............. 113
9. Discriminant function coefficients utilizing data from
silver hake in spawning condition from samples
collected in 1978-1979, mean C-values, and tests of
significance for each sex. ................ 118
10. Summary results of discriminant analyses performed on
data from spawning and post-spawning individuals from
samples collected in the summer and autumn of 1978.
119
.
11. Summary results of discriminant analyses performed on
data from spawning and post-spawning individuals from
samples collected In the summer and autumn of 1978.
120
.
12. Total international catch (mt) of silver hake off the
northeast coast of the United States during 1955-1982
.
127
13. Total international catch (nit) from the Georges Bank
area during 1962-1982 by sampling area. (+ indicates a
catch of less than .5 nit) ................. 130
An Analysis of the Stock Structure of Silver Flake,
Merluccius bilinearis, off the Northeast Coast of the
United States
INTRODUCTION
The silver hake or whiting, Merluccius bilinearis, is
a widely distributed, slender, swiftly swimming gadid
species that inhabits the continental shelf waters of the
Northwest Atlantic between South Carolina and
Newfoundland, but is most abundant from New Jersey to Nova
Scotia. The abundance and availability of silver hake have
made it important to domestic, commercial, and
recreational fisheries as well as to distantwaterfleet
fisheries.
This resource has supported a commercial fishery
since the 1930s when catches averaged about 900 metric
tons (mt) annually. By the early 1940s, catches increased
to over 18,000 mt due to an increase in demand, primarily
from consumers in midwestern states (Carson 1943). In the
1950s, catches increased to an average of about 65,000 mt
during 1955-1961. With the introduction of the
distantwaterfleet in 1962, catches increased
dramatically to a peak of over 353,000 mt in 1965.
However, due primarily to a sharp decline in the total
biomass of silver hake because of overfishing and poor
recruitment over a period of about five successive years,
2
catches dropped steadily to 55,000 tnt in 1970. By 1973,
catches had increased again to 137,000 tnt, but declined
thereafter due largely to restrictions placed upon the
fishery, and totaled only 19,900 tnt in 1980 (Almeida and
Anderson 1981).
Catches of silver hake have been utilized in a
variety of ways, including use as mink food, canned pet
food, and fish meal as a supplement to poultry and cattle
feed. Large quantities of silver hake have also been
processed for human consumption in the headed and gutted
form as well as fillets and fresh fish (Anderson et al.
1980).
Total biomass of the resource, derived from virtual
population analysis, averaged 440,000 tnt during 1955-1960,
before rising to a peak of 1,334,000 tnt in 1964. Indeed,
Edwards (1968) estimated that silver hake comprised the
largest standing crop of any species in the New York Bight
- Nova Scotian Shelf area during 1963-1965. Under heavy
pressure by the distantwaterfleet, biomass dropped
steadily to only 280,000 tnt in 1970 (a 79% decrease from
the 1964 level). Biomass increased to 528,000 tnt in 1975,
but, due to poor recruitment, declined to low levels in
the late 1970s and early 1980s (Almeida and An4erson
1981). Although current assessments indicate that silver
hake no longer holds the supremacy in biomass it held in
the early 1960s, a significant amount of biômass remains
3
available to the fisheries within the U.S. Fishery
Conservation Zone (FCZ).
Silver hake in U.S. waters from Cape Hatteras, NC to
the Gulf of Maine have, since the early 1970s, been
grouped into three stocks. The boundaries of the three
stocks were the divisions and subdivisions of the
International Commission for the Northwest Atlantic
Fisheries (ICNAF, replaced in 1980 by the Northwest
Atlantic Fisheries Organization, NAFO). These stocks are
the Gulf of Maine (Division 5Y), Georges Bank (Subdivision
5Ze), and Southern New England - Middle Atlantic
(Subdivision 5Zw and Subarea 6) (Figure 1). The
delineations were based upon the scientific information
available when management of silver hake through ICNAF
quotas began in 1973, but also conformed to the areas by
which catch statistics were reported to ICNAF, thus
facilitating the assessment and management of the
fisheries in those areas.
Since the passage of the Magnuson Fishery
Conservation and Management Act of 1976 (MFCMA, PL 94-265
as amended by PL 95-354 and H.R. 5570), foreign catch
statistics have been reported on a finer area basis (U.S.
catches have, for many years, been reported at least by
30minute latitude by 30minute longitude squares). The
Act specifies that "to the extent practicable, an
individual stock of fish shall be managed as a unit
4
76
I,
6A
5Zw
5ZE
6B
6C
9S
I
I
I
I
6
55
6
Figure 1. Current stock boundaries for silver hake based on
Northwest Atlantic Fisheries Organization (NAFO)
divisions and subdivisions.
5
throughout its range, and interrelated stocks of fish
shall be managed as a unit or in close coordination (Sec
301 [al[3}). The Act further defines a stock of fish as "a
species, subspecies, geographical grou ping, or other
category of fish capable of management as a unit" (Sec 3
[24}).
There have, in fact, been several definitions of the
term stock in the past, from DarwinTh use referring to a
single "wild stock" from which all races descended, to
simply a related group of organisms (Booke 1981). These
two widely divergent definitions demonstrate the
flexibility with which the term has been used and the
confusion surrounding its use depending upon discipline.
The term has been used to describe species, and within
species, races, populations, and subpopulations (Booke
1981). In its broadest sense, a stock is a group or
population of fish that sustains itself over time (through
reproduction) in a reasonably definable area. An important
characteristic of a stock is its uniform reaction to
exploitation and management throughout its range. In this
sense, unit stocks of a given population could be treated
separately throughout their range.
The necessity for a clear understanding of stock
structure in a single species context has been illustrated
for several species, such as the Alaskan herring (Clupea
harengus pallasi) fishery (Rounsefell 1975) and for
several species of trout (Salmo sp.) and salmon
(Oncorhynchus sp.) (Everhart and Youngs 1981) where
fishermen have concentrated effort on specific locations
or spawning stocks of these species. In the management of
fisheries, it is important to understand what the effects
of fishing in a particular locality or on a particular
group of fish will be on the abundance of that species in
other areas throughout its range.
Biological definitions, however, are often
impractical in the context of the management of a fishery
where a non-selective gear such as an otter trawl is used.
The silver hake fishery is a prime example of this type of
fishery where greater than 95% of the annual catch is
taken by otter trawl. In the U.S. silver hake fishery in
the Gulf of Maine, for example, up to 31% of the total
annual catch may be taken as by-catch in other directed
fisheries (Anderson and Marchesseault 1980). Single
species management of stocks exploited in multiple species
fisheries, by definition, does not account for biological
(eg. predator-prey) or technological (eg. fishing gear)
interactions taking place in the ecosystem. However,
a
clear understanding of the stock structure of the
exploited species is still necessary in assessing the
effects of fishing on a given resource and for providing
the biological parameters required in the complex
multispecies management models being developed.
7
In the case of silver hake in U.S. waters, the New
England Fishery Management Council, while in the process
of developing a hake management plan, expressed concern
with the current stock boundaries, Indicating that
questions raised by fishermen, managers, and scientists
warranted renewed Investigation of the stock
Identification of this species. In general, there is
sufficient information available on distributional
patterns and seasonal shifts in availabilty to suggest
that the present stock configuration may not constitute
discrete groups of silver hake.
Previous Studies
Several methods have been used in the past by
scientists in both the U.S. and U.S.S.R. to examine the
stock identity of silver hake. These methods have included
an analysis of morphometric characters, examination of
otolith formation, tagging studies, serological analyses,
and descriptions of seasonal distribution patterns. The
results of each of the studies indicated the presence of
at least two stocks of silver hake inhabiting the waters
off the northeast coast of the U.S. although with varying
stock boundary lines (Figure 2). However, none of the
studies have provided a comprehensive examination of fish
from the entire area or conclusive evidence with which to
define the stock structure. The following brief
description of each of the studies outlines the method
8
U
a
(1974)
NJQ{Y' (1969)
\
\
\
\
\------aNMER El AL (1961)
KThST1WFI1Ew &
SIW (1969)
'S
3S
Figure 2. Stock boundaries proposed by the authors of
previous studies
used and its results and identifies potential problem
areas which were addressed in the analysis of silver hake
stock structure in U.S. waters presented herein.
Conover et al. (1961) examined morphometric
characteristics of 1,265 individuals collected during
1955-1956 from the Gulf of Maine, both inshore and
offshore, and the coastal waters from Cape Cod, MA to New
Jersey. Statistical methods used to differentiate between
groups included analysis of covariance and examinations of
the distance between regression lines using T-tests. The
results of the analyses indicated that four characters
--head length, eye diameter, pelvic fin length, and the
length of the first ventral fin, contributed to the
separation of groups. No statistically significant
differences in the characteristics of fish collected from
the inshore and offshore waters of the Gulf of Maine were
found. However, approximately 40% of those individuals
measured from waters designated offshore Gulf of Maine
were collected on the northern edge of Georges Bank
(Figure 3). No differences were found between silver hake
collected in the southern New England area, primarily
south of Rhode Island, and those from the Middle Atlantic
off the New Jersey coast.
Highly significant differences (p<O.Ol) between fish
collected from the Gulf of Maine - northern Georges Bank
area and those from southern New England - Middle Atlantic
ic
£5
l
-7
0
21
Location
Symbol
0
1'
Gulf of Maine - Offshore
Gulf of Maine - Inshore
Southern New England
Long Island Area
Middle Atlantic
0
)
(
A
U
35
I
IS
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
Figure 3. Location of silver hake samples collected for
morphometric analysis by Conover et al. (1961).
Open symbols represent samples from northern
group, closed symbols, from southern group.
53 S
11
waters were found. The study suggested that two distinct
stocks populate the region, one in the Gulf of Maine,
including northern Georges Bank, and another from southern
New England to New Jersey with Nantucket Shoals considered
to be somewhat of a dividing line between the two stocks
(Figure 2).
In the analysis by Conover et al. (1961), two areas
of potential bias were identified. The first was the
distribution of samples. While the Gulf of Maine area was
relatively well represented in the sample collection,
virtually no samples were collected from the offshore,
continental slope waters along the southern edge of
Georges Bank and south to Cape Hatteras (Figure 3). These
areas will be identified in subsequent sections of this
study as major overwintering and spawning area for silver
hake, and their exclusion from the analysis by Conover et
al. (1961) resulted in an incomplete data set.
Silver hake have been shown to be sexually dimorphic
with respect to growth (Schaefer 1960, Nichy 1969).
However, since sexes were grouped by Conover et al. (1961)
differences found between groups may have been partially
due to the effect of the grouped sexes.
Nichy (1969) examined growth patterns on otoliths
from immature male and female silver hake (ages 0 and 1)
from Gulf of Maine and southern New England waters and
12
found differences in zonal formation and length at age
between fish collected during research vessel bottom trawl
surveys in each area. He suggested using 41030_ N latitude
as the division line between what he considered to be the
two stocks in the areas (Figure 2). This line was chosen
because silver hake abundance both north and south of the
line was found to be much higher than in the area near the
line.
U.S. tagging studies in continental shelf waters
between Massachusetts and New Jersey and also in the Gulf
of Maine began in 1946 and continued, with limited
success, until 1958. Between 1945 and 1956, approximately
2,100 fish were tagged with otter trawis and trap nets and
a variety of tags. Those studies produced only a 0.6% rate
of recapture (Fritz 1959, 1962, 1963, and unpublished NEFC
data). During 1957-1958, approximately 2,200 fish were
tagged using a plastic tube tag (Wilson 1953), which was
primarily a modified version of the tag judged to be
superior in the previous attempts. The methods of capture
in this study were otter trawls, trap nets, and hook and
line. The rate of recapture was 6.0%, but all fish were
recaptured within 65 km of the tagging site. Due to the
very low recapture levels in the first study and the
restricted recapture area in the second, no conclusions
were drawn concerning movements and distribution.
In 1964, U.S.S.R. scientists tagged 5,050 silver hake
13
taken by otter trawl on Cultivator Shoal on the
northwestern part of Georges Bank between depths of 20-50
m (Noskov 1970). Returns included 44 tags with no
accompanying information and 12 (0.2%) with recapture
locations. Of the 12 with recapture locations, 8 were
caught very near the tagging site, with the remaining 4
recaptured on the northern edge of Georges Bank or the
southern edge of Browns Bank. It is uncertain whether the
returns attributed to Browns Bank were, in fact, caught
there or on Georges Bank due to the uncertainty of the
catch location of the processed product. The migration
patterns indicated by the result of this study give little
insight into the makeup or distribution of stocks between
the Gulf of Maine and the Middle Atlantic region.
A third study was conducted jointly by scientists
from the U.S. and U.S.S.R. in the autumn of 1979. The
sampling area included Cultivator Shoal in depths of 55-60
m and Nantucket Shoals in depths of 31-50 m. Silver hake
were collected utilizing an otter trawl and were placed in
observation tanks prior to tagging. However, no fish were
tagged during the 6-day study because most fish died
within 45 minutes of capture and none survived longer than
4 hours.
The probable reasons for the 100% mortality rate in
the latest attempt and very low recapture rates in the
previous studies were 1) excessive swim bladder pressure
14
caused by bringing this physoclist species to the surface
faster than the fishs circulatory system could
equilibrate the pressures and 2) shock due to excessive
scale loss caused by the abrasive actions of the net
during haulback.
Methods employed in processing silver hake in both
the U.S. and distantwaterfleet fisheries probably also
contribute to the very low recapture rates reported in
previous studies. A high percentage of silver hake are
processed to fish meal or are mechanically processed into
the headed and gutted form with a minimum of human
contact, providing little opportunity for the recovery of
tags. Therefore, tagging holds little promise as a means
to investigate the stock structure of silver hake.
Four types of immunoserological methods were used to
examine blood serum and erythrocyte antigens of silver
hake from samples collected in the Sable Island, Georges
Bank, and Middle Atlantic areas by Konstantinov and Noskov
(1969). Their results indicated that a separate stock
could be distinguished in each area. Konstantinov and
Noskov (1969) stated that the division between the Georges
Bank and Middle Atlantic stocks was in the Nantucket
Shoals area (Figure 2), and that significant amounts of
intermixture occurred between stocks during the fall and
winter, with 14
of the Middle Atlantic stock found on
Georges Bank and 35% of the Georges Bank stock intermixed
15
with the Middle Atlantic. Additionally, the blood serum
antigens from fish collected in each area differed
slightly by sex, age, and size. Unfortunately, the
locations of the samples collected for use in this study,
particularly in the Georges Bank area, are unknown, and,
given the stock boundary lines suggested by other authors,
this area is of primary importance.
A recent study, examining tissue samples of spawning
silver hake collected from commercial fishing vessels both
south of Point Judith, RI and east of Gloucester, MA
during the summer of 1978, indicated that fish from these
two areas are genetically distinct (Schenk 1981). The
samples were examined using an isoelectric focusing
techinque and the data analysed using chisquare
evaluation. Highly significant chisquare values were
found between areas when males and females were treated
separately. Although this method of analysis showed great
promise, the limited sample area, made it impossible to
indicate any stock boundaries associated with the groups.
Anderson (1974) examined the seasonal distribution of
silver hake from research vessel bottom trawl survey data
and suggested a stock structure which placed fish on
northern Georges Bank and in the Gulf of Maine in one
group and fish from the southern part of Georges Bank
south to Cape Hatteras in another (Figure 2). This
proposed stock structure was based upon the discontinuous
16
distribution of silver hake and their general absence from
the shoal portions of the Bank during all seasons.
The objective of the present study was to analyze
fisheries and research vessel data to more clearly define
the stock structure of silver hake inhabiting the FCZ off
the northeast coast of the U.S. from Cape Hatteras to the
Gulf of Maine. Three sources of data were utilized in the
study: research vessel bottom trawl survey data during the
period 1963-1980, domestic and distant-water-fleet catch
statistics from 1962-1980, and morphometric data collected
in 1978-1979 for use in a multivariate statistical
analysis.
17
GENERAL BIOLOGY
The successful examination of the stock structure of
any marine fish species depends In large part on a clear
understanding of its general biology, including its
trophic relations, reproductive strategy, early life
history, and seasonal distribution. In this chapter, the
biology pertinent to the stock definition of silver hake
Is reviewed, with the exception of prerecruit and adult
seasonal distribution, which Is presented in the
succeeding chapter.
Trophic Relations
Silver hake, by virtue of its abundance and position
in the food web, plays an Important role In the Northwest
Atlantic continental shelf ecosystem. As a predator, It
feeds primarily on shrimplike crustaceans and the
juvenile fish of many species. As prey, juvenile silver
hake is a part of the diets of species such as mackerel
(Scomber scombrus) and American shad (Alosa sapidlssima)
while pollock (Pollachius virens), bluefish (Pomatomus
saltatrix), and mackerel among others feed on larger
individuals. Cannaballsm has also been shown to be more
significant among silver hake than many other species
(Langton and Bowman 1977).
Several studies have Indicated that the food habits
IF:]
of silver hake vary with fish size. Bowman and Michaels
(1982) reported that silver hake less than about 21 cm ate
primarily crustaceans, while larger silver hake preyed
more heavily upon fish and squid. Vinogradov (1972) found
that silver hake larger than about 40 cm, mainly females,
ate fish almost exclusively.
Gonadal Development and Spawning
Silver hake inhabiting the waters from Cape Hatteras,
NC to Nova Scotia have a protracted spawning season
beginning in early May in southern New England and Middle
Atlantic waters and proceeding through November in the
Gulf of Maine (Bigelow and Schroeder 1953, Colton and St.
Onge 1974, Fahay 1974). While adult life is primarily
demersal, silver hake spawn mainly in the upper 10 m of
the water column (Kendall and Naplin 1981). The range in
spawning temperatures for silver hake is quite wide and
apparently decreases with increasing latitude. Bigelow and
Schroeder (1953) reported a temperature range of 5 to 13°C
in the Gulf of Maine, while Fahay (1974) reported that
newly hatched eggs in the Middle Atlantic were collected
in waters with surface temperatures between 13 and 22°C.
Spawning occurs in May-June in the waters of southern
New England and the Middle Atlantic Bight, primarily in
the area of Nantucket Shoals and south of Marthas
Vineyard, and, to a lesser extent, as far south as Cape
19
Hatteras (Fahay 1974). Indeed, most of the eggs (887.) and
the densest concentration of larvae collected during
ichthyoplankton surveys conducted in 1966 between Marthas
Vineyard and Cape Lookout, NC were found between Nantucket
Shoals and the Hudson Canyon.
Spawning takes place on the southern slopes of
Georges Bank primarily during July and August (Sauskan
1964, Silverman 1982); however, spawning has been observed
in this area as early as late May (Marak et al. 1962a).
The northern and northwestern slopes of Georges Bank are
secondary spawning and important post-spawning feeding
areas based on an examination of the relative fullness of
silver hake stomachs collected in late July and August in
this area (Sauskan 1964, S. Koch, NEFC, Statistics Branch,
pers. comm.).
Spawning areas in the Gulf of Maine include the
coastal region from Cape Cod to Grand Manan Island, with
depths less than 90 m along the eastern side of Cape Cod
to Cape Ann, being the most important (Bigelow and
Schroeder 1953). Peak spawning is generally during July
and August.
Sexual maturity in silver hake is initiated at age 2
and all fish are capable of spawning by their third or
fourth year. Bigelow and Schroeder (1953) reported mature
fish to be age 2 in the Gulf of Maine. Sauskan (1964)
20
reported that first-time spawners collected from the
southeast portion of Georges Bank during 1962-1963, were
29-33 cm in length (age 2-3). Doubleday and Halliday
(1975) examined specimens collected on the Scotian Shelf
and found that males greater than 25 cm and females
greater than 30 cm (age 2 and older) were sexually mature.
It is assumed that silver hake inhabiting the southern New
England and Middle Atlantic waters are also mature by
about age 2-3.
The annual cycle of ovarian development of female
silver hake is characterized by asynchronous
vitellogenesis (Sauskan and Serebryakov 1968). During the
overwintering period, the ovaries begin to develop the
first of three generations or "batches" of eggs that will
be released during the protracted spawning season. By late
spring, the three generations of oocytes are clearly
distinguishable and the gonads almost completely fill the
body cavity, making up approximately 35% of the fishs
total body weight. After the first batch of eggs is
spawned, the gonads shrink and make up only about 5% of
the body weight. About half of the annual production of
eggs is released In the first batch, with the remainder
divided about equally between the second and third
batches. At the end of the spawning season, the gonads
account for only about 2% of the total body weight; any
unshed oocytes are apparently resorbed.
21
The asynchronous oogenesis of the female silver hake
is not paralleled by asynchronous spermatogenesis. Sperm
are released gradually during the spawning period from May
to late autumn, but most heavily in June in the southern
and offshore areas and in August in the Gulf of Maine.
Egg and Larval Development
When spawned, silver hake eggs are spherical, almost
transparent, and contain one oil droplet. The eggs are
pelagic and are generally found in the upper 10 m of water
(Bigelow and Schroeder 1953, Kendall and Naplin 1981).
Average egg diameters, reported by several authors, range
between .79 mm and .95 mm, however, Sauskan and
Serebryakov (1968) reported minimum and maximum egg sizes
to be .70 mm and 1.11 mm, respectively, the widest range
of all species of hake that have been investigated.
Kendall and Naplin (1981) reported a total incubation time
of about 39 hours at a mean surface temperature of 22.7°C
based on an examination of the distribution of
developmental stages from icthyoplankton survey samples
taken at 3-hour intervals in Middle Atlantic Bight waters.
Kuntz and Radcliffe (1917) reported the incubation period
to be not more than 48 hours though no accompanying
temperature data were given. Optimum incubation
temperatures reported by Bigelow and Schroeder (1953) were
13-16°C, with a range for normal development between 10
22
0
and 21 C in the Gulf of Maine.
Newly-hatched larvae range in size from 2.8 mm (Kuntz
and Radcliffe 1917) to 3.2 mm (Fritz 1962). Assuming that
M. bilinearis development is similar to the Pacific hake,
M. productus, young larvae live off food reserves stored
in the yolk sac until they reach about 9 mm in length. At
this point, the Jaws are sufficiently developed to support
active feeding. Pelagic life continues for about two
months, after which the larvae, now measuring 17-20 mm,
descend to the bottom and begin a more demersal life
(Fahay 1974).
Larval Distribution
The seasonal distribution of silver hake larvae
between 1953 and 1980 has been studied by several authors.
The spring distribution of larvae (primarily
February-June) in the Gulf of Maine - Georges Bank area
during the early-to-mid 1950s was described by Marak and
Colton (1961) and Marak et al. (1962a and 1962b). Colton
and Byron (1977) discussed the autumn distribution
(September-December) during 1971-1974. Larval distribution
in southern New England
Middle Atlantic waters was
described by Fahay (1974) based on eight surveys in 1966
between Martha's Vineyard, MA and Cape Lookout, NC.
Silverman (1982) presented the results of synoptic
bimonthly surveys in the shelf and slope waters from Nova
23
Scotia to Cape Hatteras, NC during 1977-1980.
In general, larvae are first available in May in the
offshore (60-90 m) southern New England waters south of
Block Island, RI. During June-July, the area of larval
distribution expands and extends both southwestward toward
Cape Hatteras and easterly to southern Georges Bank; this
widespread distribution usually persists through about
November. While the most dense concentrations of larvae
are found in the offshore waters from late July to
September, the time period encompassing the major spawning
activities, significant quantities can be found in the
shallow inshore waters south of Long Island, NY. Lesser
concentraions of larvae can also be found on the northern
and northwestern edge of Georges Bank and also along the
Massachusetts
Maine coast. By December, the shallow
water aggregations apparently move to the deeper, offshore
slope and central Gulf of Maine waters.
Silver hake larvae exhibit a bimodal dlel-depth
distribution occupying the upper 15 m during the nighttime
hours but moving to as deep as 30 in during the day
(Kendall and NaplIn 1981). During the pelagic stage, eggs
and larvae are susceptible to drifting with the prevailing
currents. Eggs and larvae drift generally in
a
southwesterly direction during their first summer along
the coasts of Maine and Massachusetts in Gulf of Maine
waters and along the continental shelf in the offshore
24
Georges Bank and southern New England waters (Colton and
Byron 1977, Silverman 1982). Maximum drift distances have
been calculated by Fahay (1974) and Sauskan and
Serebryakov (1968) to be 77 km (41.5 nautical miles) and
111 km (59.9 nautical miles), respectively. It has been
estimated that approximately 60-90% of the water
circulating along the outer continental shelf waters of
Georges Bank move into the southern New England area
(Butman et al. 1984). Given these prevailing currents
during the pelagic stage, the majority of silver hake
larvae inhabiting the outer shelf waters of southern
Georges Bank probably remain in the offshore waters. Those
occupying the northern edge of Georges Bank may either
remain on the Bank or drift in a northeasterly direction
following the counterclockwise flow in the Gulf of Maine.
25
SEASONAL DISTRIBUTION PATTERNS
i!t rod u c t ion
The delineation of the distributional patterns of
silver hake was important in this examination of their
stock structure for two basic reasons. The first and most
obvious reason was that, by simply displaying the
locations of major concentrations of silver hake during
the year, important qualitative inferences could be drawn
concerning the possibility of discrete stocks. The second
reason was that, having determined the probability of
multiple stocks, research vessel bottom trawl survey and
commercial fishery data were used in determining the
location of proposed stock boundaries. The stock boundary
definitions were necessary for assigning group membership
to sample data used in the multivariate statistical
procedures to quantify the stock structure.
Research Vessel Bottom Trawl Survey Data
Methods
The seasonal distribution of adult and prerecruit
silver hake was determined by examining catch data from
bottom trawl surveys of the fishery resources of the
northwest Atlantic continental shelf. These surveys have
been conducted by U.S. and foreign research vessels since
the summer of 1963 (Table 1). The U.S. surveys initially
'C
z
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;;;; ;,
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:
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27
covered the area extending from Nova Scotia south to the
Hudson Canyon in depths of 27
in
to approximately 366 in,
however, greater depths were occasionally encountered in
the deep canyons along the continental shelf break. In the
autumn of 1967, coverage was extended southward to include
the area from New Jersey to Cape Hatteras, NC (Figure 4).
The survey program was again expanded in 1968 with the
addition of spring surveys covering the same area. Inshore
surveys, from depths of 5 to 27
in,
and covering primarily
the waters of the southern New England - Middle Atlantic
areas were added to the program in 1972. In 1978, inshore
survey coverage was extended to include the Gulf of Maine
area (Table 1).
During 1967-1977, additional cooperative research
vessel surveys were conducted periodically with the
U.S.S.R., Poland, Federal Republic of Germany (F.R.G.),
German Democratic Republic (G.D.R.), and France. These
cruises were oriented primarily toward species specific
and/or ecological considerations and therefore sampled
only selected areas between Nova Scotia and Cape Hatteras
and utilized various types of commercial fishing gear.
Trawl stations during each of the U.S. surveys were
selected utilizing a stratified random design which
provided unbiased estimates of the availability of silver
hake to the trawl gear in relation to their distribution.
The entire survey area was stratified with the major
iT
N
N
N
NNN
1'QP
stratum boundaries determined by depth and biological
considerations, primarily the location of the fishing
grounds of the major species sought in the early surveys
(Figure 5). The number of stations allocated to each of
the strata was roughly proportional to the strata areas.
However, to permit the calculation of within-stratum
variance, at least two stations were sampled in each
stratum. Therefore, in the smaller inshore and offshore
strata, sampling intensity was greater than in larger
strata. Station selection was carried out using the
following procedure. Each of the strata was divided into
5- by 10-minute areas with each of these areas further
subdivided into 2- by 2.5-minute blocks. Only one station
was selected in each of the 5
by 10-minute rectangles by
choosing one 2- by 2.5-minute block at random. This
sampling scheme provides for about 400-450 stations per
survey or roughly one station for each 200 square nautical
miles (Grosslein 1974, Azarovitz 1981).
During U.S. offshore surveys conducted in the autumn,
a No. 36 Yankee bottom trawl, rigged with 41 cm rollers to
prevent net damage on rough bottom and with a 1.25 cm
stretched mesh cod end, was towed at each station for 30
minutes at an average speed of 3.5 knots. Operations were
conducted 24 hr/day. The No. 36 Yankee trawl used during
1968-1972 in offshore spring surveys was replaced by a
larger, high-opening No. 41 Yankee trawl during 1973-1981.
30
inshore surveys during 1972-1975 used either a modified
3/4 size No. 36 Yankee trawl rigged with a chain sweep or
a standard No. 36 Yankee trawl, depending upon the vessel
conducting the survey. Since 1976, the No. 36 and No. 41
Yankee trawis have been used inshore in the autumn and
spring, respectively. Research vessel surveys conducted in
the winter and summer have employed the No. 36 Yankee
trawl throughout the series.
The cooperative foreign research vessel surveys were
also conducted using a stratified random design of station
selection with the exception of the F.R.G. R/V Walther
Herwig survey in 1973 which used a non-random station
selection. Tow durations during these surveys were 30
minutes at speeds ranging from 3.5 to 5 knots (Table 1).
Sampling was conducted only during the daylight hours,
except during the R/V Khronometer survey in 1974 which
sampled 24 hr/day.
At each station during all surveys, all fish and
major invertebrates were sorted by species, weighed,
measured, and sampled for other analyses. A complete log
for each station, including total catch of each species by
weight and number, length frequency data by species,
location, depth, and surface and bottom temperature, was
prepared and processed ashore for later computer analysis.
Silver hake catches (in numbers) from each survey
31
were divided into prerecruits (age 0 for summer and autumn
surveys and age 1 for winter and spring surveys) and
adults (ages 1 and older for summer and autumn and 2 and
older for winter and spring). This was accomplished by
examining either age-length data (available for 1973-1981
from U.S. surveys) or length frequency data. For each
season/year, the maximum length for age 0 or 1 individuals
was determined; the breakdown was generally:
Summer
Autumn
Winter
Spring
surveys
surveys
surveys
surveys
-
10 cm fork length (FL)
13 cm FL
18 cm FL
21 cm FL,
although in some years the "cutoff" lengths varied up to
about 3 cm. Fish above and below these lengths were
designated adults or prerecruits, respectively. Numbers at
length data for each group were summed for each
country/season/station by 10-minute square and divided by
the total number of stations in each square to obtain mean
catch per square per country/season. All foreign research
vessel surveys were grouped together by season and no
attempt was made to standardize the catches from the
variety of gears used by the vessels in the time series.
The data were plotted by 10-minute squares and contoured
to produce cumulative seasonal distribution maps of
prerecruit and adult silver hake during the period for
both U.S. and foreign surveys.
Bottom temperatures and depths from stations where
32
prerecruit and adult silver hake were collected were also
summarized by season. To determine the relative
frequencies of occurrence, percentages of the total number
of stations at each 1°C temperature interval and 10 m
depth interval were calculated and displayed in histogram
form.
Results
A total of 16,732 bottom trawl stations were occupied
during the 92 surveys in the time series (Table 2).
Virtually all of the more than 1,030 10minute squares
between Cape Hatteras, NC and Halifax, NS were sampled at
least once during the spring and autumn surveys (the two
major time series maintained by the NEFC), with only
slightly fewer in the summer. During the winter surveys,
coverage was less intensive, with approximately 78% of the
total number of 1Ominute squares in the survey area
sampled by U.S. and/or foreign surveys (Figures 6-9).
Adult silver hake were collected at 9,321 stations (56%)
throughout the survey area, while prerecruits were
captured at 5,134 stations (31%). Silver hake sizes ranged
between 2 and 67 cm FL. Bottom temperatures were recorded
at 8,769 stations where adults were collected and at 4,572
stations where prerecruits were collected. Depth data was
obtained at 9,284 and 5,115 stations where adult and
prerecruit silver hake were collected, respectively.
33
Table 2. Summary of U.S. and foreign research vessel bottom
trawl surveys, both inshore and offshore, conducted between Nova Scotia and Cape Hatteras, NC
during 1963-1981.
Season
Winter
Spring
Summer
Number of
Surveys
Number of
Stations
U.S.
4
Foreign
3
927
320
Foreign
23
10
4,749
823
U.S.
13
2,041
1
102
24
14
6,010
1,760
92
16,732
Country
U.S.
Foreign
Autumn
U.S.
Foreign
Total
Dates (inclusive)
6
Jan
-
8
Apr
28 Jan - 23 Mar
3
2
Mar - 4 Jun
Mar - 16 Apr
23 Jun 9
3
7
1
Sep
- 26 Aug
Sep - 16 Dec
Sep - 11 Dec
34
A:a
/
35 4
'6
4
35
'3
63
4
'S
is
38
83
Figure 6. Spatial coverage (by 10-minute square) by U.S.,
1963-1981 (A) and foreign, 1967-1977 (B) bottom
trawl surveys during the winter.
35
$3
'S
r
A
4 35
6
'6
63
4
J
3$
35
63
Figure 7. Spatial coverage (by 10-minute square) by U.S.,
1963-1981 (A) and foreign, 1967-1977 (B) bottom
trawl surveys during the spring.
36
'6
45
t
'A
35
35
'6
'6
63
63
.5
45
35
35
'6
63
Figure 8. Spatial coverage (by 10-minute square) by U.S.,
1963-1981 (A) and foreign, 1967-1977 (B) bottom
trawl surveys during the summer.
37
63
A
35
63
63
'6
is
B4.:.::.::::
35
4
'6
35
.3
Figure 9. Spatial coverage (by 10-minute square) by U.S.,
1963-1981 (A) and foreign, 1967-1977 (B) bottom
trawl surveys during the autumn.
38
Adults
Adult silver hake inhabiting the waters
from Cape Hatteras, NC to Nova Scotia were found
throughout their distributional range during all seasons
with only major concentrations of fish varying, primarily
in response to hydrographic changes. They occupied
a
variety of depths ranging from shallow inshore areas to
depths greater than 400 m. They are able to tolerate a
rather wide bottom temperature regime ranging from 1°C (19
occurrences) to 20°C (2 occurrences). They were found
generally in the deep basins of the Gulf of Maine and
along the outer continental shelf south of Georges Bank to
Long Island, NY during the winter and early spring. With
the onset of warmer late spring and summer temperatures,
a
general movement to the more shallow inshore waters of the
Gulf of Maine and somewhat shallower waters of Georges
Bank was evident. In southern New England and Middle
Atlantic waters, the seasonal pattern differed In that
fish were present both Inshore and offshore from eastern
Long Island south to Cape Hatteras during late autumn to
early spring, with a general northerly movement in the
spring and summer.
The distribution of catches during both the U.S. and
foreign winter surveys (6 Jan - 8 Apr) (Figure 10) showed
that although they were taken in shallow strata, the major
concentrations of fish (averaging greater than 100
fish/lO-minute square in U.S. surveys) were located in the
39
/
SILVER HAKE / 10 SQUARE
6/
)
O
ainninn
1-100
- 101-1000
111011
)I000
35
Js
'6
16
63
63
Figure 10. Distribution of adult silver hake (numbers) from
U.S. (A) and foreign (B) bottom trawl surveys
during the winter, 1964-1981.
40
deep basins of the Gulf of Maine, along the continental
slope from Georges Bank to Cape Hatteras, and also in the
near shore waters from eastern Long Island to Cape
Hatteras. Georges Bank was virtually devoid of all adults.
Bottom temperatures at stations where adults were
collected during the winter ranged from 1.5 to 12.9°C. The
preferred temperature range (defined as the range in
bottom temperatures from which 60% or greater of the
catches were taken) was 4.6 to 7.5°C (Figure 11). The
depth range from which adults were captured during the
winter was from 18 to 392 m. There did, however, appear to
be two modes, one with a median depth of 60-70 m,
representing primarily those individuals inhabiting the
more temperate Middle Atlantic waters, and a second with a
peak at about 170 m, representing those inhabitants of the
offshore slope waters and the deep basins of the Gulf of
Maine (Figure 12). The distribution during this season was
the most restricted due to hydrographie conditions and the
availablity of prey.
During the spring surveys (2 Mar - 4 Jun), the
distribution of major concentrations of adults was similar
to the winter in that there were two general areas of
habitation in U.S. waters, one in the deeper waters of the
Gulf of Maine and a second along the continental shelf
break from southern Georges Bank to Cape Hatteras. A third
41
WINT
5UrVr6
ROULTS ONLY
36. C
30. C
25. C
20. C
16.0
10. a
5.0
0.
0
30.0
LJ
rE:,1P (C)
Figure 11. Bottom temperature distribution (%) at stations
where adult silver hake were collected from U.S.
bottom trawl surveys during winter, 1964-1981.
42
wINrE:r 5VEY6 NOTI1EPN STPTR ONLY,)
PQULT6
ONLY
16.
14.
-
12.
IC. -
8.6.
-
4.
2
-
0.n
0.
nfl
50.
iCC].
150.. 2C]0
n
250. 300. 350. 400. 460
DEPTH (ti)
WINTEI 5UVEY6 (SOUTI-IEPN 5T)RTP ONLY)
FIOULTS ONLY
16.
n27I
14.
12.
10.
8.
a-
6.
4.
2.
0
Iu..uI.I.u.uuuuII
OEPTt4 (ti)
Figure 12. Distribution of adult silver hake catches (%) by
depth from U.S. bottom trawl surveys during
wInter 1964-1981.
43
area of dense concentration also was located in the
offshore waters of the Scotian Shelf, with the very deep
Fundian Channel which separates Georges and Browns Banks
acting as a boundary (Figure 13).
By the time of the spring surveys, fish in the Gulf
of Maine had begun a slight inshore movement with more
fish collected in the nearshore areas along the coasts of
Maine and southwestern Nova Scotia. There were also
consistent, though somewhat smaller, catches (averaging
10-100 fish/lO-minute square in U.S. surveys) in the very
shallow inshore waters from Long Island south to the
Chesapeake Bay. In fact, these nearshore Inhabitants
support an Important spring recreational fishery in this
area. The shallow areas of Georges Bank (strata 13,16,19
and 20) were devoid of adults even though bottom
temperatures averaged 5.8°C for those strata during the
spring period.
The range In bottom temperatures at stations where
silver hake were collected was slightly broader in the
spring, from 1.9 to 18.4°C (Figure 14). The preferred
range was between 4.6 and 8.5°C, similar to that in the
winter. Depths at which silver hake were encountered
ranged between 9 and 402 m, with two modes in each of the
areas (Figure 15). In the northern waters, a peak at
approximately 80 m represented those fish in the inshore
waters of the Gulf of Maine and along the northern edge of
44
-5
SILVER HAKE / 10 SQUARE
oii:ii
i-so
fllflIffiflTh
11-100
- 101-1000
IDUR
>1000
I
135
'6
63
/5
5l
35
76
35
63
Figure 13. Distribution of adult silver hake (numbers) from
U.S. (A) and foreign (B) bottom trawl surveys
during the spring, 1968-1981.
45
5r?UNO &JeVY6
ROULTS
ONLY
35.0
n 2,879
90.0
25.0
20.0
-.
15.0
10.0
5.0
5.0
10.0
15.0
20.0
raie (C)
25.0
30.0
35.. 0
Figure 14. Bottom temperature distribution (%) at stations
where adult silver hake were collected from U.S.
bottom trawl surveys during spring, 1968-1981.
46
51NG 5UVY6 (NOfTNN 5TTR ONLY)
POULTS
ONLY
16.
ncI,301
14.
12.
lcL
B.
6.
4.
2.
IUUUIUr.
uu.uuuu.uuu.II...
MI11III1V2
orrti (N)
5FIN0 SLVEY6 (5QUThNN 6TRTR ONLY)
FOULT6
ONLY
16.
nt,798
14.
12.
10.
4.
2.
-
0.
60.
100. 160. 200. 260. 300. 350. 400. 460
DEPTH (II)
Figure 15. Distribution of adult silver hake catches (%) by
depth from U.S. bottom trawl surveys during
spring, 1968-1981.
47
Georges Bank. A second mode, with an average of about 165
in, represented the major concentration of individuals in
the deep basins of the Gulf. In the southern waters, a
large percentage of individuals located in waters 50
in
or
less, while another mode representing the offshore
concentration was at approximately 230
m.
A migration of fish to shallower waters within the
northern area and a northern migration in the southern
area was clearly evident from the summer surveys
(conducted during 23 Jun
-
I Sep) (Figure 16). These
surveys also provided evidence of the major spawning areas
discussed previously. In the Gulf of Maine, silver hake
were located in the coastal areas between Cape Ann, MA and
Grand Manan Island. On Georges Bank, concentrations were
found on the southern and southeast parts, and in southern
New England - Middle Atlantic waters, concentrations of
fish were found from south of Nantucket to eastern Long
Island and also in the Hudson Canyon area. Only small
average catches (less than 10 fish/lO-minute square)
occurred south of the Hudson Canyon.
Bottom temperatures ranged from 2.5 to 21.0°C during
the summer, while the preferred range was between 4.6 and
10.5°C (Figure 17). This range in preferred temperatures
is similar to that for Scotian Shelf silver hake. Scott
(1982) reported that 7 to 100C was the range for Scotian
48
63
a)
SILVER HAKE / 10 SQUARE
aiiitn
i-to
UflIfllluII
11-100
UHID
>1000
- 101-1000
35 F
35
'6
63
76
(3
SILVER HAKE / 0 SQUARE
IIIIIJ3
1-10
amnninj
11-100
101-1000
>1000
is
76
63
Figure 16. Distribution of adult silver hake (numbers) from
U.S. (A) and foreign (B) bottom trawl surveys
during the summer, 1963-1981.
49
5Ut1t1
POULT
5UNVY5
ONLY
3G.O
n=(,269
30.0
.0
20.0
a is.o
10.0
0.c
C
Li]
TEfIP (C)
Figure 17. Bottom temperature distribution (%) at stations
where adult silver hake were collected from U.S.
bottom trawl surveys during summer, 1963-1981.
kiøJ
Shelf silver hake. Depth ranged between 10 and 348
in
during the summer surveys, with two distinct peaks in the
northern area representing fish in the shallow inshore
waters as well as a component that remained offshore in
depths primarily between 140 and 170
in.
In the southern
area, silver hake were predominantly in waters less than
90 in (Figure 18).
By autumn (surveys conducted during 3 Sep - 16 Dec),
the offshore migration of fish in the Gulf of Maine was
indicated by a shift in concentrations from the coastal
waters to the deeper areas of the Gulf (Figure 19). On
Georges Bank, although small catches averaging less than
10 fish/lO-minute square, occured in all parts, major
concentrations were located on the northern and southern
edges. Adults were distributed over the entire shelf from
Nantucket Shoals to south of the Hudson Canyon, but the
southern migration of fish in this area was also indicated
by concentrations of fish on the outer shelf and slope
waters south to Cape Hatteras. A wider range of
temperatures was found in the autumn than in the other
seasons, with temperatures ranging from 2.6 to 21.2°C
(Figure 20). There was also a slightly wider range of
preferred temperatures in autumn, ranging between 5.6 and
12.5°C. The more stable hydrographic conditions prevailing
during the autumn also allowed for a wide range In depths.
The range in depths during this season was between 9 and
51
5UNr1
51JIVY5 (NOTt-4EN 5TPTP ONLY)
OULT6
c,r4_Y
16.
n857
14.
12.
10.
La
a-
6.
4.
-I-
1OO
160. 200. 260.
0O.
6O. 400. 450.
oPTH (N)
5Uf-1r1EI S*VY6 6OUTI-INN 5TIRTP ONLY)
ONLY
ROtJLTS
16.
-
n4T8
14. -
12.
-
10.
4.
2.
-
a. 0.
. ...................
100. 160. ZOO. 250.
60.
OO.
O. 400. 4c3.
0EPTP$ (fl)
Figure
18. Distribution .of adult silver hake catches (Z) by
depth from U.S. bottom trawl surveys during
summer, 1963-1981.
52
7 C
SILVER HAKE /10' SQUARE
riinn
IflhIlflflUIl
i-to
11-100
- 101-1000
WIlU
>1000
35
I-
'6
63
76
35
35
76
'3
Figure 19. DistributIon of adult silver hake (numbers) from
U.S. (A) and foreign (B) bottom trawl surveys
during the autumn, 1963-1981.
53
AUTUMN 5UNVeY5
AOULT
ONLY
35.0
n=4,125
90.0
25.0
20.0
a-
10.0
6.0
rErip (C)
Figure 20. Bottom temperature distribution (Z) at stations
where adult silver hake were collected from U.S.
bottom trawl surveys during autumn, 1963-1981.
54
393 m. Modes representing the inshore and offshore
components in the northern area and the predominantly
shallower component of the southern area were evident
(Figure 21).
Prerecruits
The seasonal geographic distribution
of prerecruit silver hake in the survey area was also very
widespread and similar to that of adults with two major
exceptions. These exceptions were: 1) the maximum depths
of major concentrations of prerecruits were generally less
than those of adults, and 2) their preferred temperature
range, especially in the northern areas, was usually
narrower and cooler than for the adults. Edwards et al.
(1962) and Edwards (1965) also reported this relationship
between temperature and size for fish collected in
southern New England waters during the 1950s, and found
that adults were usually more abundant in deeper, more
temperate water while youngoftheyear fish were taken in
the shallower, colder water.
During winter surveys (Figure 22), areas of
prerecruit concentrations were in the deeper waters of the
Gulf of Maine north and west of Georges Bank, along the
southern edge of Georges Bank, and in southern New England
and Middle Atlantic waters primarily between Nantucket
Shoals and the Hudson Canyon. None were found in the
shallowest waters of Georges Bank. While there was some
55
PUTLJMN 6UI!Ve:Ys (Norrt-1e:rN STRTP ONLY I
ONLY
RIJULT6
16.
-
14.
-
12.
-
10.
-
n2,662
.
0.
60.
I
100. 160. 200. 250. 300. 360. 400. 460.
OTH CM)
AUTUMN 6UlVEY6 (6OUTHN 5TTR ONLY)
OULT6
Ot&Y
16.
n=I,756
14.
12.
10.
a.
6.
4.
2.
0.
60
10C1
1Efl
20Q
250
300. 350. 400. 450.
OrTH (N)
Figure 21. Distribution of adult silver hake catches (%) by
depth from U.S. bottom trawl surveys during
autumn, 1963-1981.
56
76
SILVER HAKE / 10 SQUARE
ci
,J
lItlIuJ
1-10
IflhtllflflTh
11-100
£111111
>1000
- 101-1000
76
4'
SILVER HAKE / (0 SQUARE
U1
I
k
1.1
1-10
WIIflhIBO
11-100
101-1000
AfI
W1H1
))
35
OIIIED
>1000
55
I
I
Figure 22. Distribution of prerecruit silver hake (numbers)
from U.S. (A) and foreign (B) bottom trawl
surveys during the winter, 1964-1981.
57
degree of commonality in the distribution of prerecruit
and adult silver hake, the locations of major
concentrations of the two groupings generally abutted, but
did not overlap. On Georges Bank and in southern New
England
Middle Atlant'ic waters, prerecruits were taken
in depths usually less than 100 m, while the largest
concentrations of adults were found in depths between 100
and 200 m. In the Gulf of Maine, prerecruits were
generally found in waters shallower and nearer shore than
adults. During the winter, prerecruits were taken in
waters with bottom temperatures between 1.4 and 11.4°C
with preferred temperatures between 2.8 and 5.5°C
(compared to 4.6
7.5°C for adults) (Figure 23).
The depth range for prerecruits during the winter
surveys was between 9 and 275 m (Figure 24). In the
northern area, peaks in their distribution by depth were
found at about 80 m, representing the inshore component,
and at approximately 170-190 m, representing the deeper,
offshore component. In the southern area, while
prerecruits were obtained in waters as deep as 234 m, they
were taken primarily in waters less than 50 m.
Results from spring surveys indicated a
distributional pattern very similar to that in the winter,
with major differences found in the size of the average
catches and the further movement to shoaler waters (Figure
25). In the Gulf of Maine area, while catches of 10-100
WINTt! 5UrVY5
PRERECRU ITS ONLY
36.0
n=220
90.0
25.0
20.0
a
15.0
10.0
5.0
0-c
0
C
30.0
35.0
TEMP (C)
Figure 23. Bottom temperature distribution (Z) at stations
where prerecruit silver hake were collected from
U.S. bottom trawl surveys during winter,
1964-1981.
UINT
SUVEYS
NOTt-4EIN STPTR ONLY)
PRcRECRUIT
ONLY
16.
nII7
14.
12.
10.
8.
6.
4.
2.
3.
OrTH
WINT
cr1)
5UNVEYS (80UTHN ST?PTR ONLY)
RERECRU1T6 Ot&Y
16.
nI22
14.
12.
10.
8.
6.
4.
2.
(1
3.
OErTN (11)
Figure 24. Distribution of prerecruit silver hake catches
(%) by depth from U.S. bottom trawl surveys
during winter, 1964-1981.
SILVER HAKE / 10' SQUARE
cttIJII3
I-to
ainniiiuii
1-100
- 101-1000
WJIU
>1000
6
35 4-
3,5
76
63
76
53
[:1
0
SILVER HAKE / 10 SQUARE
UIEIIU
1-10
üIIWflIfl
11-100
imm
>1000
- 101-1000
35 476
4-
35
63
Figure 25. Distribution of prerecruit silver hake (numbers)
from U.S. (A) and foreign (B) bottom trawl
surveys during the spring, 1968-1981.
61
fish/lU-minute square were common, the largest catches
(101-1,000 fish/lO-minute square) were primarily at depths
of 100 m or less along the coastal waters of I4aine and
Massachusetts and on the northwestern edge of Georges
Bank. In southern waters, major areas of concentration
were south of MarthaTh Vineyard to eastern Long Island.
The overall temperature range during the spring was 1.4 16.1°C with 3.6
-
7.5°C the preferred temperature range
(compared to 4.6 - 8.5°C for adults) (Figure 26). Depths
ranged from 6 to 404 m (Figure 27), and, like winter, the
northern area demonstrated two peaks at approximately 80 m
and 180 m. In the southern area, the depth range with the
highest percentage of prerecruits was between 5 and 15 m.
The summer distribution of prerecruits (age 0 fish)
primarily defined the location of spawning grounds for
silver hake since the prerecruits collected during the
spring surveys (age 1 fish spawned the previous year) had
grown sufficiently to be included in the adult (or
postrecruit) category by summer. The summer collection of
prerecruits was quite sparse due mainly to the timing of
spawning (early summer in southern waters to early autumn
In northern waters) and the timing of the surveys (23 Jun
- 1 Sep) (Figure 28). Although Individuals as small as 1-2
cm are collected by the trawl gear, these individuals are
generally just beginning their demersal life stage and are
less susceptible to the trawl gear than larger 3-10 cm
62
5Pr1N0 5UVY5
PIEFECRU ITS ONLY
35.0
n=2,OII
30.0
2 .0
20.0
a..
15.0
10.0
6.0
0.0
0.0
6.0
10.0
16.0
20.0
ZG.O
30.0
35.0
TtIIP (C)
Figure 26. Bottom temperature distribution (%) at stations
where prerecruit silver hake were collected from
U.S. bottom trawl surveys during spring,
1968-1981.
63
SPIINO SUIVYS (NOThN 6TTR ONLY 3
PRERECRUIT6 ONLY
16.
-
nI,I74
14.
12. 10_ -
0.
50.
100. 150. ZOO. Z60. 300. 350. 400. 450
OPTH
((I)
SPI'UNO 5UrVY6 (SOUTt1NN STRRTR ONLY)
PRERECRUIT6 ONLY
16.
n 1,029
14.
12.
10.
1)
a-
6.
4.
2.
uIuuIuIIuIuIu.
orn-i UI)
Figure 27. Distribution of prerecruit silver hake catches
(%) by depth from U.S. bottom trawl surveys
during spring, 1968-1981.
64
63
Figure 28. Distribution of prerecrult silver hake (numbers)
from U.S. bottom trawl surveys during the summer,
1963-1981. Data from foreign surveys was not
available.
65
fish. For this reason, very few prerecruits were collected
in the Gulf of Maine. However, those individuals caught in
the Gulf of Maine were mainly concentrated in coastal
waters from Cape Ann, MA to Monhegan Island, ME.
Prerecruit silver hake in the southern waters were more
vulnerable to the trawl gear due to the earlier spawning
season. These individuals were located on the southwestern
portion of Georges Bank and south to approximately the
Baltimore Canyon, generally in waters less than 100 m.
The temperature range during the summer surveys was
5.1 - 17.3°C, with a preferred temperature range of 4.4 to
10.5°C (very similar to adults) (Figure 29). The overall
depth range in which prerecruits were collected ranged
from 6 to 210 m (Fig ure 30).
During the autumn, prerecruits were collected from
virtually the entire survey area, with the exception of
the southernmost inshore waters (Figure 31). Although
adults were generally caught in very small numbers from
the shoal waters of Georges Bank (strata 12, 16, 19, 20),
large catches of prerecruits were taken in these strata
where bottom temperatures averaged 12.10 C. Concentrations
of prerecruits were also located south of Marthas
Vineyard and Block Island to depths of approximately 100
m, and in the inshore waters off central New Jersey and
south of the Hudson Canyon. The overall temperature range
was 3.6 - 21.2°C with a preferred temperature range of 6.6
66
5UrV1
5UfVY5
REIECIUXT5 ONLY
36.0
n 72
30.0
25.0
20.0
Q_.
5Q
10.0
5.0
0.
.0
30.0
TCMP CC
Figure 29. Bottom temperature distribution (7.) at stations
where prerecruit silver hake were collected from
U.S. bottom trawl surveys during summer,
1963-1981.
67
5UNt1E
6UVEY5 (NOITt-1N 5TAT ONLY)
PRERECRUIT6 ONLY
16.
n40
14.
12.
10.
Li
-
a-
6.
4.
2.
0.
50.
.L
100. 160. ZOO
Z60. 300. 360. 400. 450
0PTH (N)
SU11NJ 5%JfVfY6 (S0UTHEJN 6TIRT1 ONLY I
PREREcRU! T 0!&Y
16.
n 35
14.
12.
10.
a.
a.
6.
4.
2.
n
uuuuuuuuuuui
3.
OEP'TtS (II)
Figure 30. Distribution of prerecruit silver hake catches
(%) by depth from U.S. bottom trawl surveys
during summer, 1963-1981.
68
63
76
4-
SILVER HAKE / 10' SQUARE
nirmj
fllin1mii
I-io
n-ioo
- 101-1000
UUh11
1000
35
'3
3$
'6
6
'S
45
35
63
35
76
(numbers)
Figure 31. Distribution of prerecruit silver, hake
(B)
bottom
trawl
from U.S. (A) and foreign
surveys during the autumn, 1963-1981.
-
12.5°C (Figure 32). Depths from which prerecruits were
taken ranged from 8 to 385 in (Figure 33).
70
F1UTIJIIN 5*JfV't5
PRERECRU ITS ONLY
35.0
n2,449
30.0
25.0
20.0
15.0
10.0
5.0
0.
inn
ari
tLr1
TEMP (C)
Figure 32. Bottom temperature distribution (%) at stations
where prerecruit silver hake were collected from
U.S. bottom trawl surveys, during autumn,
1963-1981.
71
RUTUrIN SUfVEY5 (NoftTHrN 5TITf ONLY)
PRERECRUITG ONLY
16.
,539
n
14.
12.
O.
8.
0
6.
4-
2.
iuuu..uuuiu
r.1l-i.Ie-
p
OTt1 (NI
RUT&JNN sU,Ver6 (SOUTI1N GTI!ATR ONLY I
PRERECRUITG ONLY
16.
______________________________________
nI,O59
14.
12.
ici.
8.
a-
6.
4.
2.
0.0.
.
. .
60.
1
100. 160. ZOO. 260. 300. 360. 400. 4Cp
OErTa-i
cr1)
Figure 33. Distribution of prerecruit silver hake catches
(Z) by depth from U.S. bottom trawl surveys
during autumn, 1963-1981.
72
Commercial Fishery Catch Statistics
Methods
Commercial fishery landings statistics and biological
samples have been collected in the northeast by port
agents of the National Marine Fisheries Service and its
predecessor agencies since the 1930s. The original
program was designed to collect information on individual
species such as haddock and Atlantic cod in major ports;
however, the program was gradually modified and expanded
so that by the 1960s most ports In the northeast had
agents assigned to them (Figure 34). The agents
responsibilities include the collection of landings data,
fishing area, effort data, and biological samples (lengths
and scales or otoliths for ageing) for all species landed
in each port (Burns et al. 1983).
Detailed landings statistics for the U.S. silver hake
fishery, collected through a system of vessel captain
interviews, are available in computer format from New
England ports since 1965 and from ports located in the
Middle Atlantic region (primarily in New Jersey) since
1974. The primary data obtained from the interviews and
used in this analysis Include landings, fishing effort,
and area of catch by 10-minute square. In order to
evaluate the traditional fishing patterns of the U.S.
fleet, catch-per-unit effort values (ie. interviewed
73
y
£/I
(0
'
:
',:
/
'-4-'
4,-'
4-!
4,
-
<i-c,
/
(0
44)
0'
k,4,
-p.
/
(01
Office IocoiOflS
Figure 34. Fishery statistical areas and northeast regional
port agent office locations.
74
catch/days fished, CPUE) from trips in all ports in which
silver hake were assumed to be the main species sought
(le. the silver hake catch made up at least 50% of the
total catch of a trip), were summarized by 10-minute
square for the period 1965-1980 and plotted by month (all
years combined). These data were used to identify the
location of persistently high seasonal concentrations of
silver hake.
The number of interviewed trips in which silver hake
was the main species sought averaged approximately 38% of
the total trips landing silver hake each year. The
interviews were primarily from the New England ports of
Portland, ME, Gloucester and Provincetown, MA, whose
vessels fished mainly in the Gulf of Maine and on northern
Georges Bank, and from Pt. Judith and Newport, RI vessels
fishing in the southern New England waters off Rhode
Island.
A fishery for silver hake off the northeast coast of
the U.S. by distant-water-fleets began in 1962. Although
several countries have participated in the fishery,
including Bulgaria, Canada, Cuba, the Federal Republic of
Germany, the German Democratic Republic, Italy, Japan,
Poland, Romania, Spain, and the U.S.S.R., catches by the
U.S.S.R. clearly dominated the fishery, averaging 73% of
the total annual international catch during 1962-1976.
After the implementation of MFCMA in 1977, the
75
distant-water-fleet catch dropped sharply and has remained
at a very low level. An examination of the
activity of the
U.S.S.R. was conducted to determine the fishing
patterns
of the largely offshore fleets with respect to silver
hake. Summaries of these activities were obtained from the
ICNAF Research and Summary Document series for the years
1962-1976 (Noskov et al. 1963; Anon. 1964; Bogdanov et al.
1965; Konstantinov and Noskov 1966, 1967, 1968, 1969,
1970, 1971, 1972, 1973, 1974, 1975, 1976). A composite
distribution map was prepared from the narrative
descriptions and plots contained in Sauskan (1964),
Sarnits and Sauskan (1966), and Noskov et al. (1976).
Results
Distribution of U.S. Commercial Catch
The
distribution of monthly catch-per-unit-effort from the
U.S. commercial fleet reflects both the distribution of
the major seasonal concentrations of silver hake,
as
evinced by research vessel bottom trawl
survey data, and
the composition of the fleet. The data, summarized for the
period 1965-1980 are presented in Figures 35-46.
The fleet
is comprised of small to medium sized vessels (less than
150 gross registered tons) without freezing
capabilities
which fish chiefly day trips or trips with a maximum
length of approximately 5 days. The trip length
restrictions are due to the fact that silver hake have
relatively soft flesh which deteriorates rapidly if not
76
frozen soon after being caught. These restrictions were
evident in the distribution of monthly catches which
indicated very little effort from the eastern or southern
parts of Georges Bank or the eastern Gulf of Maine and
intensive effort only in fishing areas of consistently
high concentrations of silver hake.
During the winter months of January through March
(Figures 35-37) when weather and sea conditions are most
harsh, effort was primarily concentrated in three
nearshore areas. The deep, nearshore waters east of
Steliwagon Bank in the western Gulf of Maine, exploited by
vessels from Gloucester and Provincetown, MA, produced the
highest levels of catch (greater than 25 mt/day) while the
inshore waters off the central and southern coast of New
Jersey ranked second. The inshore waters south of Block
Island, RI and the continental slope waters south of Rhode
Island southwestward to the Baltimore Canyon to depths up
to 200 m also produced consistent catches during these
months. Vessels primarily from Pt. Judith, RI, supporting
an industrial fishery mainly for fish meal and pet foods,
fished these grounds year round.
During April and May, the fishery continued in the
areas described above, but expanded in the Gulf of Maine
northward along the Maine coast and further inshore, and
in southern New England waters the offshore area stretched
further eastward from the Hudson Canyon to the Great South
77
COTITIERCIAL CATCH PER DAY
'6
(INTERVIEW DATA)
63
JANUARY
:
I E ) F ND
SYMBOL
SIZE
J
DATA RANGE
(TONS)
.00
10.00
25.00
35
-
,.
I
'0
GE
LT
IT
GE
GE X
.<
0.00
25.00
I
.55
63
Figure 35. Distribution of U.S. commercial catch per unit
effort by 1O-minute square obtained from
interview data during January for combined years
1965-1980.
CO)IrIERC!AL CATC)1 PER DAY
76
(INTERVIEW DMA)
a.'
63
FEBRUARY
(I,
V
SYMBOL
SIZE
35
I
I
I4
*
LEGEND
.30
0.00
2530
DMA RANGE
(TONS)
CE X iT
GE V iT
CE X
0.00
25.00
.55
6
63
Figure 36. Distribution of U.S. commercial catch per unit
effort by 10-minute square obtained from
interview data during February for combined years
1965-1980.
79
'6
COMMERCIAL CATCH PER OAY
(INTERVIEW DATA)
C S
.c s
35
'6
63
Figure 37. Distribution of U.S. commercial catch per unit
effort by lO-minute square obtained from
interview data during March for combined years
1965-1980.
Channel (Figures 38-39). With the warming of the inshore
waters and the northerly migration of silver hake, the
New
Jersey coastal waters began to lessen in
importance while
the area south of Rhode Island increased.
By June and July, spawning concentrations in
the
southern New England shelf waters from eastern Long
Island, NY to the Great South Channel
were heavily fished
by the Pt. Judith fleet, while the coastal
area from Casco
Bay, ME to Cape Cod increased in importance, with
much of
the region producing catches greater than 10 mt/day
(Figures 40-41).
In June, vessels primarily from
Gloucester, MA began to exploit post-spawning
concentrations of silver hake along the northwestern slope
of Georges Bank. By August-September,
this area of Georges
Bank produced the highest catch rates, with rates commonly
greater than 25 mt/day (Figures 42-43). Although
this area
was the furthest offshore, the generally calm
summer
weather and promise of high catch rates made it an
attractive location for vessels from Gloucester in spite
of the approximate 13-20 hours of travel
each way.
Fishing activity on Georges Bank was reduced
greatly
by October due to the migration of post-spawning fish
off
the northwest portion of the Bank (Figures 44).
The areas
south of Rhode Island and along the coast
from Cape Cod to
Maine were important through December, however,
and while
the size of the areas diminished, there
were commercially
81
COMMERCIAL CATCH PER OAT
(INFFRVIEI4 nrA
45
APRI L
I
I.
Jr.
I
...
.
w
a
LEGEND
SYMBOL
I
J
SIZE
.
*
.00
10.00
25.00
DAYA RANGE
TEONSI
CE X LI
CE X LT
CE X
10.00
25.00
.55
-4-
.5 S
63
Figure 38. Distribution of U.S. commercial catch per unit
effort by lO-minute square obtained from
interview data during April for combined years
1965-1980.
82
COMMERCIAL CATCH PER DAY
(INTERVIEW DATA)
1)
MAY
U
1'
SYIIBOL
SIZE
I
I
35
--
LEGEP4O
DATA RANGE
.00
10.00
25.00
.
a
(IONS)
0
C
C
XLI
X LI
X
000
25.00
I
35
I
63
Figure 39. Distribution of U.S. commercial catch per unit
effort by 10-minute square obtained from
interview data during May for combined years
1965-1980.
83
COMMERCIAL CATCH PER DAY
45
(INTERVIEW DATA)
45
*
JUNE
I
1::
a.
...iu.
1.
7.
a
3,
/5L2
LEGEND
SYMBOL
SIZE
-
W
35 r
DATA RANGE
(TONS)
GE X LI
GE X IT
GE X
.00
I
,.
0.00
25.00
I
I
1000
25.00
35
*
63
Figure 40. Distribution of U.S. commercial catch per unit
effort by 10-minute square obtained from
interview data during June for combined years
1965-1980.
84
COMMERCIAL CATCH PER DAY
4
*
(INTERVIEW DATA)
45
$
______+_____+__JuL Y
(
V
LEGEND
SYMBOL
SIZE
100
a
10.00
25.00
I
_J
35
I-
4
I
I
4
t
I
76
DATA RANGE
(TONS)
CE X LI
CC X LI
CE X
10.00
25-00
35
I
63
Figure 41. Distribution of U.S. commercial catch per unit
effort by 10-minute square obtained from
interview data during July for combined years
1965-19 80.
C0SERC)AL CATCH PER DAT
'S
4
-.
-,
()NTERVIEW DATA)
&3
4
4
AUGUST
C?
(I
I
STII8OL
'.
SUE
t.00
10.00
25-00
I
35
LEGEND
4
I
-f
*
I-
I
4
DATA RANGE
(TONS)
GE X t.T
GE X LT
GE X
10-00
25-00
I
4
4
I
4
I
4
4
35
Figure 42. Distribution of U.S. commercial
catch per unit
effort by 10-minute square obtained from
interview data during August for combined years
1965-1980.
COMrIERCIAI CATCH PER DAY
6
(INTERVIEW DATA)
63
45
15
SEP TES8ER
,
17
*
(
fr
SYTIBOL
LEGEND
DATA RANGE
SIZE
-
(IONS)
GE X LI
GE X LI
GE X
1.00
10.00
25.00
35
1
'6
-.
4
I
10.00
25.00
I
-I-
-4
I
I
1
35
4
63
Figure 43. Distribution of U.S. commercial catch per unit
effort by 10-minute square obtained from
interview data during September for combined
years 1965-1980.
87
(INTERVIEW DATA)
COY1TIERCIAL CATCH PER DAY
63
4'
45
OCTOBER
(I
V
SYMBOL
SIZE
LEGEND
-
*
35
I
DATA RANGE
(TONS)
.00
0.00
25.00
GE X Li
GE X Li
CC X
10.00
25.00
35
I
63
6
Figure 44. Distribution of U.S. commercial catch per unit
effort by 1O-minute square obtained from
interview data during October for combined years
196 5-19 80
exploitable concentrations in these two areas year-round
(Figures 45-46). During the late fall, as silver hake
migrated south, the fishery along the New Jersey coast
again increased.
Distribution of Distant-Water-Fleet Catch
The
distribution of landings by month reported by the U.S.S.R.
is summarized in Figure 47. The time periods assigned to
each of the areas generally encompass the entire range of
months during which the fleet prosecuted the fishery. Some
areas were fished more intensively than others in
different years depending upon hydrological conditions and
the variability in the size of the fishable biomass.
Examination of the pattern of this fishery showed
that effort was directed primarily toward the offshore
concentrations of silver hake along the slopes of the
continental shelf, but was not confined to this area. The
large vessels that comprised this fleet (gross tonnages
ranging from 500 to over 2,000 nit) exploited
concentrations of silver hake overwintering in the deep
offshore waters south and southwest of Georges Bank. They
also directed effort towards spawning concentrations along
the southern portion of the Bank and in the Nantucket
Shoals region and towards post-spawning concentrations on
the northwestern edge of the Bank.
During the winter months from January to March,
76
COIIMERCIAL CATCH PER DAY
45 -4-.--
)INTERVIEW DATA)
63
4.
45
NOV EMBER
4"y.
.-__,/______C-
SYTIBOL
SLE
*
35 -4-.-
'6
LEGEND
.00
000
2500
DATA RANGE
(TONS)
CCXLI
GE X LI
GE X
I 0.00
25.00
63
35
Figure 45. Distribution of U.S. commercial catch
per unit
effort by 10-minute square obtained from
interview data during November for combined years
1965-1980.
COMMERCIAL CATCH PER DAY
76
(INIERVIEW DATA)
45
£3
45
DECEMBER
y
\
SthBOL
SIZE
/
I
I
)
A /
*
35
4
76
DATA RANGE
(IONS)
.00
I
I
LEGEND
0.00
25.00
I
GE X LI
CE X LI
GEX
10.00
25.00
4
.55
63
Figure 46. Distribution of U.S. commercial catch per unit
effort by 1O-minute square obtained from
interview data during December for combined years
1965-1980.
91
76
(AA.
I
I
cy
DEC-JAN
NOV-FEB
t1jJ1Jj1JJ
________
JtJL-
JUN-DEC"
OCT
UL -DEC
'JAN-JUt
fMAY
35
I
I
I
I
4
I
I
I
I
I
I
I
I
I
Figure 47. Distribution of catches by month from the
U.S.S.R. distant water fleet during 1962-1976.
(Taken from Sauskan 1964, Sarnits and Sauskan
1966, Noskov 1976 and annual U.S.S.R. Research
Report series.)
92
effort was directed primarily over the
shelf slopes from
southwestern Georges Bank south to about
the Hudson Canyon
usually in depths of 150-300
m (Noskov et al. 1976).
However, during 1963 and the
early-to-mid 1970s, the
fleet reported some landings from the
basins of the Gulf
of Maine in depths of
waters 240-280 m. From March through
May in some years, the fleet also
caught silver hake in
the more southern slope waters off
the Deltuarva Peninsula.
Pre-spawning and spawning aggregations
of silver hake
along the southern and southeastern
slopes of Georges Bank
in depths of 100-300 m provided
the fleet with sizeable
catches during March
July during all years. Peak catches
in this area usually occurred
during July at the height of
the spawning season, after which
the concentrations of
silver hake dispersed. During
late spring - autumn in the
early years of the fishery
(1962-1968), the fleet also
reported large catches in the
shallow shelf waters, (40-70
in depth) from Nantucket Shoals
to the eastern end of
Long Island, an area identified
as a major spawning
ground. This was also an area in which
distant-water-fleet
vessels competed directly with
smaller U.S. vessels for a
local resource. However, in 1970,
ICNAF regulations
restricting the use of bottom tending
trawls in the shelf
waters were imposed upon the distant-water--fleet.
The
regulations banned the use of bottom
trawis by vessels
larger than 47 m (155 ft) in
waters less than 40 fathoms,
93
thus confining the fleet to the offshore waters along the
slope break.
In late summer and autumn of most years, the fishery
shifted effort to the north and northwestern edges of
Georges Bank, an area which was described as an intensive
post-spawning feeding ground (Noskov et al. 1963, Sauskan
1964) but which also contained spawning individuals. The
depths at which silver hake were caught in this area
ranged between 40 and 110 m.. The area was fished, with
varying degrees of success, through December.
The Hudson Canyon area, in relatively shallow depths
of 50-100 m, supported large catches during the late fall
and early winter, primarily in years when water
temperatures remained relatively mild. This area was also
"closed", however, when gear restrictions were imposed in
the shelf waters in 1969.
Since the implementation of MFCMA in 1977, fishing
operations by the distant-water-fleet have been further
restricted with respect to area and time. Foreign fishing
is now confined to fishing areas or "windows" located in
the offshore slope waters from southern Georges Bank (west
of 67°W latitude) to Cape Hatteras (north of 35°13N
longitude), mainly during the winter months (Figures 48a
and 48b). These restrictions effectively eliminated the
fishery on spawning aggregations on both the southern and
94
35
Figure 48a. Fishing areas and gear restrictions by area for
the distant water fleet off the northeast coast
of the U.S. in effect during 1977-1978. Shaded
months indicate open fishing seasons.
95
75
I&5
-'s
1-
5
4
2
I
P.I..4.
I-fl
II
I
I
I
35
35
Figure 48b. Fishing areas and gear restrictions by area for
the distant water fleet off the northeast coast
of the U.S. in effect since 1979. Shaded months
indicate open fishing seasons.
96
northwestern slopes of Georges Bank as well as the Inshore
waters off southern New England.
97
DISCRIMINANT FUNCTION ANALYSIS
Introduction
Discriminant analysis is a multivariate statistical
technique that employs a set of measurements or counts to
discriminate between groups and provides the best function
to separate morphotypes (Fisher 1936). The discriiuinant
analysis method used in this study consists of two steps.
The objective of the first step is to determine the best
linear combination of a set of measurements to distinguish
between populations and, using statistical tests, analyze
the constructed functions to measure their discriminating
success. Two assumptions must be made at this step even if
the analysis performed is solely descriptive (without the
application of statistical tests to examine the function):
1) the data collected to construct the function must be
able to be classified correctly (Lachenbruck 1975) and 2)
individuals to be classified based on the function must
belong to one of the groups in the analysis (Reyment
1966). The success of the function depends upon the
discriminating characteristics
ability to recognize
patterns that differ between the groups (Cook and Lord
1978). Theoretically, two further assumptions must be
made: 1) the variables being analyzed must have
a
multivariate normal distribution, and 2) there must be
equal variancecovariance matrices within each group.
Adherence to these assumptions was tested a posteriorly,
98
but, according to Kiecka (1975), need not be strictly
followed due to the robustness of the technique.
The second step in the technique involves
classifying
"unknown" individuals using the functions
constructed and
tested in the previous step. The precision
and accuracy of
the classification depends upon the precision
of the
inherent separation between the groups (Cook and Lord
1978) and the accuracy of the classification
of the data
used to construct the function.
In previous applications of discriminant analysis
in
marine fisheries, anadromous species such
as American shad
(Alosa sapidissima) (Hill 1959), sockeye salmon
(Oncorhynchus nerka) (Fukuhara et al. 1962, Anas and Mural
1969), pink salmon (Oncorhynchus gorbuscha)
(Amos et al.
1963, Pearson 1964), and Atlantic salmon (Salmo
salar)
(Lear and Sandeman 1974) were primarily
examined. In these
studies, samples of fish collected in home rivers were
used to construct the functions which
were applied to
samples of the high seas catch to determine
proportions of
the catch from particular home rivers
or countries of
origin. High percentages of correct
classification
generally resulted using this technique on anadromous
species. The stock structure of other species
such as
Atlantic herring (Clupea harengus harengus) (Nessieh
1975,
Parsons 1972), capelin (Mallotus villosus) (Sharp
et al.
1978), and summer flounder (Paralichthys
dentatus) (Wilk
99
et al. 1980) has also been examined successfully with
discriminant analysis although percentages of correct
classification were generally lower than for the
anadromous species.
In this study, a set of measurements was obtained
from silver hake collected from research vessel survey
catches from the waters of the northwest Atlantic from
Cape Hatteras, NC to Nova Scotia. These data were then
subjected to a discriminant function analysis to
statistically separate the stocks of silver hake.
Methods
During the summer and autumn of 1978 and the spring
of 1979, a total of 3,015 silver hake were collected from
catches made by research vessels during bottom trawl
surveys (Figure 49). Specimens were frozen and returned to
the NMFS, Woods Hole Laboratory for analysis. Fork length
was measured to the nearest millimeter and sex, age, and
maturity were determined. A total of 13 morphometric
characters, the same characters used by Conover et al.
(1961), were measured to the nearest 0.1 mm using vernier
calipers (Figure 50). All measurements were made on the
right side of each individual according to criteria
detailed by Hubbs and Lagler (1947). Of the original
number of specimens collected and measured, data from
1,112 males and 1,370 females (age 1 and older) were used
100
76
45
35
63
Figure 49. Location of samples collected during
bottom trawl
surveys used in the discriminant function
analysis of morphometric characters.
101
Head
Length
Length of
First
Snout
Length
Third
Second
Dorsal
Fin
Dorsal
Dorsal
Fin
Fin
Eye
Diameter
..S
I
-
Snout to
Insertion
of Pelvic
First
Ventral
Fin
Fin
Snout to
Insertion
of Pectoral
Pelvic
Fin
Length
Second
Ventral
Fin
Pectoral
Fin Length
Snout to
Anal
Opening
Fin
Figure 50. Morphometric characters utilized in discriminant
function analysis.
102
in subsequent analyses. All data were transferred to
computer files for retrieval and analysis.
Due to the sexual dimorphism in the growth of silver
hake, an analysis of covariance was performed on the
morphometric measurements for males and females (all areas
combined), using length as the covariate, to test for
differences in characters between sexes. Significant
differences (p
0.01) were evident in 9 of the 13
characters (Table 3); therefore, data were treated
separately by sex. Additionally, each of the characters
was plotted against fork length, and linear regressions
were calculated both as a quality control measure and to
examine the correlation between each character and length
using the program BMDP1R, Multiple Linear Regression
(Dixon et al. 1981). Strong linear correlations were found
between each of the morphometric characters and length,
with correlation coefficients (r) averaging 0.943 for
females (range = 0.858 to 0.979) and 0.906 for males
(range = 0.842 to 0.957) (Table 4). Examination of
residuals indicated the absence of any non-linear trends.
To remove the linear effect, two methods were considered.
The first method involved constructing discriminant
functions for individuals from each age category assuming
that the range of lengths within ages was sufficiently
narrow to eliminate the bias accompanying unstandardized
data. This method was not used, however, because of small
103
Table
3. Results of analysis of covarimace of alc
versus female silver hake froa the northwest
Atlantic during 1978-1979 with all areas and
all seasons combined. Values listed are the
results of F tests for equality of adjusted
group means.
Source of Variance
F-value
Read Length (ci)
Eye Diameter (c2)
Snout Length (c3)
Snout to Anal Opening (c4)
Snout to Insertion of Pelvic Fin (c5)
Snout to Insertion of Pectoral Fin (c6)
Pelvic Fin Length (c7)
Pectoral Fin Length (c8)
First Dorsal Fin Length (c9)
Second Dorsal Fin Length (dO)
Third Dorsal Fin Length (cli)
First Ventral Fin Length (c12)
Second Ventral Fin Length (c13)
30.8204CC
78.3902CC
76.3027CC
17.2411CC
53.1674CC
71.1146**
15.0922CC
26.0644**
.2524
1.8875
2.5637
1O.7971**
4.6207
Degrees of Freedom
2482
** Indicates significance at the 11 level.
Table 4. Correlation coefficients between .orphoaetric
characters and length for male and female silver
hake from the northwest Atlantic during 1978-1979
before and after removal of linearity.
)iales
Morphometric
Character
Females
Size
Linear
Independent
Linear
Size
Independent
ci3
.954
.842
.900
.954
.944
.957
.906
.919
.861
.897
.860
.912
.868
.112
.407
.005
.143
.044
.094
.001
.062
.115
.148
.002
.120
.006
.944
.952
.930
.943
.917
.947
.915
.079
.035
.022
.133
.072
.017
.076
.031
.048
Average
.906
.094
.943
.083
ci
c2
c3
c4
c5
c6
c7
c8
c9
dO
cli
c12
.975
.858
.953
.977
.970
979
.115
.171
.147
.1.36
104
sample sizes, especially at the older ages (4 and older),
and wide variations in lengths at age were sufficient to
maintain the bias caused by the linear effect. The second
method, used by Ehrich and Rempe (1980) in their
examination of Pacific hake (Merluccius
stocks,
removed the linear effect by calculating auxiliary
variables and applying these to logged measurement data
(see Appendix I for method). Logarithms of the variables
were used because morphometric characters are continuous
variables and multivariate normality is more closely
approximated by their logarithms (Piemental 1979, Bliss
1970). After removing the linear effects, correlation
coefficients averaged 0.094 and 0.083 for males and
females, respectively (Table 4).
The initial selection of parent groups required in
the construction of the discriminant functions was based
on the examination of composite plots of catches of silver
hake from both seasonal bottom trawl surveys and the
commercial fishery. The plots indicated a clear separation
of fish into components north and south of Georges Bank,
with the shoal portions of the Bank generally devoid of
fish. Hypothesizing that fish from these two components
constituted different stocks by virtue of their
discontinuous distributional pattern, individuals from
each of the sample periods were divided into northern and
southern groups. The northern group contained fish
105
collected in the Gulf of Maine and on northern Georges
Bank, while the southern group was made up of fish
collected on the southern portion of Georges Bank south to
Cape Hatteras (Figure 49).
After removal of the linear effect the data from each
survey were used in the SPSS Discriminant Analysis program
(Kiecka 1975). A stepwise analysis was performed to select
the characters that would best distinguish between the
groups, evaluate the relative contribution of each
character, construct the discriminant function, and
finally assign individuals to either of the groups.
Because the same data set was used to both construct and
evaluate the functions, the rates of correct
classification may have been optimistically biased. Due to
the migratory behavior of silver hake and the possibilty
of intermixture between groups, prior probabilities of
group membership were assigned such that the probability
of classifying individuals into either of the groups was
equal.
The important concept of reproductive isolation as a
criterion in the successful separation of a population
into unit stocks was investigated by the examination of
only those individuals in the sample collection that were
in spawning condition. Five maturity stages were
identified from the collection made for morphometric
analysis:
106
Naturity Stage
1) Immature
2) Developing
3) Ripe
Description
Gonads small relative to the body
cavity, usually colorless, translucent with no prominent blood
vessels.
Gonads enlarged, firm, with blood
vessel network developing. Ovary
has granular appearance with yolked
eggs becoming visible.
Gonads enlarged and in female fill
almost entire body cavity. Ovary
has mixture of yolked eggs and
clear, undeveloped eggs.
In later
stages, milt or eggs flow from vent
with little abdominal pressure
applied.
4) Spent
5) Resting
Gonads flaccid with blood vessel
network diminishing, often reddish
in color.
Ovary may contain fluid
with unspawned, unresorbed eggs.
Testes with little or no milt.
Gonads diminished in size relative
to ripe stage but larger than
immature.
No prominent blood vessel
network, eggs, or niilt present.
A stepwise discriininant analysis was performed on those
individuals in spawning or postspawning condition (i.e.,
stages 3 and 4). A total of 273 females and 145 males from
the summer and autumn collections were used in the
analysis.
The criterion used for selecting variables for
inclusion in the functions was the maximization of the
Generalized Mahalonobis Distance (D2) between the groups
on each variable. The discriminating power of the
variables, indicating their ability to successfully
recognize differing patterns between the groups, was
measured using Wilks lambda. Details of the statistical
107
procedures used are described by Fisher (1936),
Mahalanobis (1936), Rao (1952), Fukahara et al. (1962),
and Amos et al. (1963).
Results
Complete
Analysis
Stepwise discriminant analysis applied to
standardized morphometric data from individuals
representing all maturity stages collected during
1978-1979 resulted in 12 characters contributing to the
functions for males and 13 characters for females (Table
5). For males, two characters (head length and the length
from the tip of the snout to the insertion of the pectoral
fin) contributed to all three functions(summer, autumn,
and spring). Three characters (the length from the tip of
the snout to the insertion of the pelvic fin, the length
from the tip of the snout to the insertion of the pectoral
fin, and the second ventral fin length)
contributed to all
three functions for females. It was unclear why the
significant characters differed between sexes and seasons.
The relative contribution by each of the characters to the
function was shown by an examination of the standardized
discriminant function coefficients (Table 5). The absolute
value of the standardized coefficients (coefficients
calculated with variables in standard form (zscores)
where:
Table
5.
Diacriminant function coefficient, utilizing data from all maturity
stages fros silver hake sample, collected in 1978-1979, mean
C-value,, and tests of significance for each sex. See Table 3 for
definitions of coefficients (c-values).
Males
Summer
Autumn
1978
1978
Females
Spring
1979
Summer
1978
Autumn
1978
Spring
1979
Discriminant
function
coefficients
11.830
ci
c2
c3
c4
cS
c6
c7
-
18.802
34.267
19.992
-
-
c8
c9
-32.626
-8.252
-
28.545
14.600
-12.551
dO
cii
-
c12
c13
9.148
-88.407
Constant
Group centriods
(C-values)
North
South
mean
F-value
degrees of freedom
Wilks lambda
.302
18.522
-
8.168
-12.790
-31.602
13.938
19.212
-10.186
-
10.409
-7.406
.368
-
-7.554
.219
-.463
-.080
-.304
7.763*5
7.0305* 5.372*5
6,375
8,440
5,275
.876
.032
-35.911
10.932
52.570
-
-
-
-5.102
-
-
-.445
.113
.899
.911
-.624
.420
-4.067
10.006
-53.433
.476
-.530
-.027
12.076*5
5,237
.797
-23.177
10.465
-
-
-11.463
30.407
10.783
-7.855
-9.635
-9.925
11.692
5.190
-6.112
.334
-.189
.073
8.240
9.250
-37.183
36.577
12.474
-4.951
-6.138
-7.893
-
-
10.409
-33.631
.342
-.561
-.110
3.928
10,620
.940
i0.402**
-.503
.284
9,486
.838
Standardized
coefficients
ci
c2
c3
c4
c5
'.214
-
.705
.292
-
c9
dO
cli
dl
cl3
*5 Imdicst.s
.645
-
.537
.412
-.225
-.380
-
-
-
-.211
-.251
-
-
.327
-.328
-.766
.340
.621
-
-.616
.221
.782
-
-
-
-
-
-.356
-
-
-
.192
igmific*m. et the .001 level.
-
-.169
-
.372
.441
-
.318
-
-
-.262
-.939
-
-.147
-.261
-.250
.373
.206
-
.565
.305
-.304
-.342
-.394
.828
.357
-
.412
109
z-score = (variable value - variable group mean)
group standard deviation
represent its contribution to the function. In each
function, the contribution of only one to three variables
clearly dominated the function. The lengths from the tip
of the snout to the insertion of the pelvic and pectoral
fins contributed significantly during all seasons while
head length and eye diameter added contributions primarily
during the fall sample collection. The classification
functions constructed by the stepwise discriminant
analysis were in the form:
C(i)
c(il)X(l)+c(i2)X(2)...+c(i13)X(13)+ constant
where:
C(i)
= the classification value for each group
(by sex by season),
c(il) = the classification coefficient for
character 1 in group i,
X(1)
= the size-independent raw value o.f
character 1.
In order to assign group membership, mean C-values for
each sex from the two areas were determined by
substituting the respective X-values into the appropriate
functions. Classification coefficients and mean C-values
for each sex, by season are presented in Table 5. To
discriminate between the groups, individuals with C-values
greater than the mean for each season were classified as
belonging to the southern group and those with values less
than the mean were classified as belonging to the northern
group. Significant differences (at the 1% level) were
110
found to exist between the groups during each season for
both males and females (Table 5).
The probability of "correctly" classifying
individuals (i.e., an individuals chances of being
assigned to the group from which it was originally
captured) averaged 66.1% (range 61.8 - 71.2) for males
(Table 6) and 67.1% (range 63.0 - 72.4) for females (Table
7). Overall, the percentage of correctly classified
individuals was 66.5% (Table 8). The separation of the
groups during each of the seasons are shown graphically in
Figures 51-53.
The results of the analyses indicated the presence of
two groups in the study area during all seasons, but the
functions were not able to identify a clearcut separation
between the groups. The highest levels of correct
classification came during the spring sample collection
when silver hake were occupying their overwintering
grounds and demonstrating their widest annual spatial
separation.
Analysis of §pwning and Post-spawning Samples
A stepwise discriminant analysis applied to
morphometric data from spawning and post-spawning
individuals collected during the 1978 spawning season
(summer and autumn) resulted in 9 characters contributing
to the functions for males and 12 characters for females.
111
Table 6. Summary results of discriminant analyses performed on silver hake
data from aaeples collected in the summer and autuwn of 1978 and
the spring of 1979.
HALES ONLY
Z of fish classified as belonging to the:
Season 6 Location
of aaaple
southern Georges Bank and
Southern New England Gulf of Maine and
Sample
Middle Atlantic
northern Georges Bank
size
Group
Group
Summer 1978
Gulf of Maine and
northern Georges Bank
61.8
38.2
170
southern Georges Bank and
Southern New England Middle Atlantic
27.9
72.1
111
Gulf of Maine and
northern Georges Bank
65.3
34.7
173
southern Georges Bank and
Southern New England Middle Atlantic
35.9
64.1
209
Gulf of Maine and
northern Georges Bank
66.8
33.2
301
southern Georges Bank and
Southern New England Middle Atlantic
32.4
67.6
148
65.1
34.9
644
32.9
67.1
468
Autumn 1978
Spring 1979
Combined Summer/Autumn 1978
and Spring 1979
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
112
Table 7. Summary results of discriminant analyses performed on silver hake
data from samples collected in the summer and autumn of 1978 and
the spring of 1979.
FEMALES ONLY
I of fish classified as belonging to the:
Season & Location
of sample
Gulf of Maine and
northern Georges Bank
Group
southern Georgea Bank and
Southern New England Middle Atlantic
Sample
Group
size
Summer 1978
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
68.0
32.0
128
27.8
72.2
115
64.5
35.5
228
37.0
63.0
403
72.4
27.6
308
34.0
66.0
188
68.8
31.2
664
34.7
65.3
706
Autuan 1978
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
Spring 1979
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
Combined Summer/Autumn 1978
and Spring 1979
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
113
Table 8. Summary result, of di.cri.inant analyse. performed on silver hske
data from samples collected in the summer and autumn of 1918 and
the spring of 1979.
SEXES COMBINEO
B of fish classified as belonging to the:
Season 6 Location
of Sample
southern Georges Bank and
Southern New England Gulf of Maine and
Sample
Middle Atlantic
northern Georges Bank
size
Group
Group
Summer 1978
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
64.4
35.6
298
27.9
72.1
226
64.8
35.2
401
36.6
63.4
612
69.6
30.4
609
33.3
66.7
336
67.0
33.0
1,308
34.0
66.0
1,174
Autumn 1978
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New Englsnd Middle Atlantic
Spring 1979
Gulf of Maine and
northern George. Bank
southern Georges Bank and
Southern New England Middle Atlantic
Combined Summer/Autumn 1978
and Spring 1979
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
114
t1ftES
1
C
z
'I
3
a
'4-
Ia
DISCRININANT SCORE
NOR7H
FEMALES
3-
U
'a
3
0
'a
10
I
Z
3
DISCRIMINANT SCORE
Figure 51. Territorial map of discriminant scores for male
and female silver hake during summer 1978. ( A
indicates group centroid)
115
NH
MRLES
4-
U
z
a
¶4
WSCRIMNANT SCORE
4-
0
z
a
'a
SXI1H
4'
3
C
U
I
Z
3
'
DISCRIMINANT SCORE
Figure 52. Territorial map of discriminant scores for male
and female silver hake during autumn 1978. ( A
indicates group centroid)
116
NORTH
NfLCS
scxjm
C)
z
a
A
:4
OISCRIUINAIIT SCOM
rEtiLES
NORTH
CI-,
3
a
SIYJIH
14
O($CIUCNANT SCOAE
Figure 53. Territorial map of discriminant scores for male
and female silver hake during spring 1979. ( A
indicates group centroid)
117
Four characters (head length, snout length, pelvic fin
length, and pectoral fin length) contributed to the
functions during both summer and autumn for males. For
females, four different characters (lengths from the tip
of the snout to the anal opening and to the insertion of
the pelvic and pectoral fins, and second dorsal fin
length) contributed to both functions (Table 9). Head
length contributed significantly to three of the four
functions, primarily in the autumn, as it did in the
analysis of all maturity stages. Others with strong
contributions to the separation of the groups included eye
diameter, lengths from the tip of the snout to the anal
opening and insertion of the pelvic fin, and pectoral fin
length.
The functions were able to detect significant
differences between the groups (at the 1% level) for both
sexes as demonstrated by their F-statistics (Table 9).
Percentages of correctly classifying these individuals
were substantially higher than for all maturity stages
combined. For spawning and post-spawning males, the
functions
ability to correctly classify an individual
into the group from which it was sampled averaged 79.9%
(range 68.2 - 91.4) (Table 10). For females, the average
correct classification was 75.9% (range 72.9 - 80.4)
(Table 11).
These results indicated that while the discriminant
118
Table
9.
Discri.inant function coeffici.ntp utilizing data fro. silver
hake in spawning condition from samples collected in 1978-1919.
See
mean C-values, and tests of significance for each sex.
Table 3 for definitions of coefficients (c-values).
Females
Males
Summer
Autumn
36.991
45.513
-10.134
Summer
Autumn
Disc riminant
function
coefficients
ci
c2
c3
c4
c5
c6
c7
c8
c9
dO
cii
c12
c13
Constant
Group centriods
(C-values)
North
South
mean
F-value
degrees of freedom
Wilks lambda
-
8.401
-
16.314
-
9.552
-18.744
-
14.415
-
-61.664
16.420
13.297
9.437
-
-
-99.969
-15.141
-15.008
.442
-.855
-.206
6.340**
5,82
.721
37.971
-
-
-12.870
-
-12.905
23.708
-14.922
-7.321
-8.740
45.163
-13.281
-29.646
9.604
-
11.454
11.828
- 8.878
- 7.816
-
-
6.083
-
-
-31.604
-44.834
-.584
-.591
-.587
4.597**
8,48
.566
7.645**
9,122
.639
6.741**
7,133
.138
1.266
.341
.939
.174
.596
.005
Standardized
coefficients
ci
c2
c3
c3
c5
c6
c7
c8
c9
.730
-
.263
-
.418
-
.248
-.506
dO
-
c12
c13
-
cli
.714
-
.483
-.251
.768
-.287
-.480
-.421
-
-.894
.393
.451
.430
-
-
-.625
Indicate. significance at the .001 level.
-
.239
-
.394
.473
-.230
-.215
.631
-.547
-.244
.484
-.270
-.251
-
.211
-
119
Table 10. Summary results of discriminant analyses performed on silver hake
data from spawning and post-spawning individuals from eamples
collected in the summer and autumn of 1978.
MALES ONLY
1 of fish classified as belonging to the:
Season & Location
of sample
southern Georges Bank and
Golf of Maine and
Southern Mew England northern Georges Bank
Middle Atlantic
Sample
Group
Group
size
Summer
Gulf of Maine and
northern Georges Bank
83.3
16.7
30
22.4
77.6
58
68.2
31.8
22
8.6
91.4
35
76.9
23.1
52
17.2
82.8
93
sthetn Georges Bank and
Southern New England Middle Atlantic
Autumn
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
Combined Summer/Autumn
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
120
Table 11. Su..ary result, of discriminant analyse. perfor.ed on silver hake
data fro. spawning and postspawning individuals fro. sa.plea
collected in the summer and autumn of 1978.
FEMALES ONLY
1 of fish classified as belonging to the:
Season & Location
of sample
southern Georges Bank and
Gulf of Maine and
Southern New England northern Georges Bank
Middle Atlantic
Sample
Group
Group
size
Summer
Gulf of Maine and
northern Georges Bank
southern Georges Bank and
Southern New England Middle Atlantic
80.4
19.6
51
22.2
77.8
81
72.9
27.1
70
26.8
73.2
71
76.0
24.0
121
24.3
75.7
152
Autumn
Gulf of Maine and
northern Georgea Bank
southern Georgea Bank and
Southern New England Middle Atlantic
Combined Summer/Autumn
Gulf of Maine and
northern Georgea Bank
southern Georges Bank and
Southern New England Middle Atlantic
121
analysis was able to detect the presence of statistically
separable groups in the study area during the spawning
season, complete reproductive isolation of the spawning
groups was not demonstrated. However, the higher
percentage of correctly classified individuals obtained
from an analysis of the spawners and postspawners did
demonstrate a division of the silver hake population into
separate spawning groups.
122
DISCUSSION AND CONCLUSIONS
Seasonal distribution patterns of silver hake as
indicated from bottom trawl survey and commercial fishery
catch data suggest a separation of fish into northern and
southern contingents. Major concentrations were found on
the northern portion of Georges Bank and in the Gulf of
Maine, and a virtually continuous distribution existed
along the continental slope between the Hudson Canyon and
southern Georges Bank. Anderson (1974) suggested the
possibility that silver hake could be divided into
"stocks" reflecting this pattern. Nichy (1969) also
indicated that silver hake could be separated into two
groups based on the otolith structure of young fish, with
the shoal portion of Georges Bank representing the
division between the groups. The results of the analysis
of morphometric characters of silver hake collected in
1978-1979 between the Gulf of Maine and Cape Hatteras
support the conclusions of Nichy (1969) and Anderson
(1974). Two other studies also support the conclusion that
two stocks of silver hake occupy the continental shelf
waters. Conover et al. (1961), while concluding that there
were two stocks, placed the division line between the
stocks in the Nantucket Shoals area. However, had the
sample coverage by Conover et al. (1961) been more
extensive and included samples from the southern part of
Georges Bank, the decision as to the location of the
123
boundary may have been somewhat different. Further
evidence in support of a twostock population of silver
hake was given by Schenk (1981). The results of her
biochemical analysis of tissue samples indicated
significant differences in the enzyme systems of spawning
silver hake collected from the two areas. No stock
boundary line was drawn based upon the results of the
biochemical analysis due to the limited sample
distribution.
The discriininant analysis performed in this study was
able to define significantly different groups inhabiting
the study area. However, the analysis did not show any
clearcut separation between the two groups as indicated by
the percentages of correctly classified fish in each of
the seasons analyzed. An average of 66.5% of the fish
collected from either group during any season were
classified as belonging to that group. This suggested that
some fish inhabiting the waters of southern Georges Bank
and the southern New England - Middle Atlantic area may
migrate north onto the northern portion of the Bank or
into the Gulf of Maine, and fish inhabiting the northern
areas may migrate south. This is generally consistent with
the patterns indicated from bottom trawl survey catch data
and appears reasonable given the wide tolerances with
respect to temperature and depth demonstrated by silver
hake. The results of the discriminant analysis showed
124
mixing during all seasons however.
Reproductive isolation of the silver hake stocks was
demonstrated through the discriminant analysis performed
on data collected from spawning and post-spawning
individuals. The percentage of correctly classified
individuals, which averaged 77.9%, was substantially
higher during the spawning season than during the
remainder of the year. This indicated that, while the
analysis was unable to completely separate the groups
during the spawning season (if, in fact, there is complete
reproductive isolation), it did demonstrate a significant
amount of separation during that time.
The results of the analyses indicated that, while
there did appear to be intermixture, there were enough
individuals from each of the groups present during each
season to produce functions that showed significant
differences between the groups. Although some evidence of
the degree of intermixture between the groups was obtained
through the calculated percentages of correctly classified
individuals during each season, it was not possible to
determine the actual degree of intermixture with the
methods and data used in this study. There are several
factors that may have contributed to the levels of
correctly classified individuals. One factor may have been
an inherent weakness in the ability of the morphometric
characteristics to separate between the groups, tested by
125
the calculation of Wilks lambda (Klecka 1975) (Table 5).
The values of Wilks lambda suggested that, while
significantly different groups could be identified, the
percentages of correctly classified individuals in each of
the groups would not be high. A second factor contributing
to the levels of correctly classified individuals may have
been the period from which the data set was collected. The
data from only one year (summer 1978 - spring 1979) may
not adequately account for the natural variations in the
population. Estimated biomass levels during 1978-1979 were
among the lowest since 1955 (average about 192,000 mt)
compared to the 1955-1960 average of 439,800 mt (Almeida
and Anderson 1981). The silver hake in the population at
the time of this study may have been undergoing
a
compensatory growth phase or may have deviated from their
normal migration patterns in response to the sharp
decreases in population biomass during this period. Data
from several periods would be required to examine this
possibility.
From the examination of international catch
statistics and total stock biomass (age 1+) from virtual
population analysis (Almeida and Anderson 1981, and
unpublished NEFC data)
,
there are further indications
that silver hake inhabiting the northern edge of Georges
Bank (statistical areas 521-526) and the Gulf of Maine
(areas 511-515) may, in fact, belong to the same stock.
126
Prior to the introduction of the distant-water-fleet,
total stock biomass and catch in the Gulf of Maine were
both relatively stable at levels averaging approximately
194,000 nit and 30,000 nit, respectively, during 1955-1961
(Figure 54). During this same period, catches from Georges
Bank and southern New England - Middle Atlantic waters
(areas 537-539 and 600+) were also stable, averaging about
19,000 mt and 15,000 nit, respectively (Table 12). However,
at this time, stock biomass in the Georges Bank and
southern New England groups was increasing sharply due to
above-average recruitment (when compared to other years in
the time series) in the early 1960s, primarily 1961-1963.
As catch and stock biomass on Georges Bank peaked and then
declined dramatically in the middle-to-late 1960s due to
recruitment overfishing, stock biomass and recruitment in
the Gulf of Maine fell precipitously, while the decline in
reported catches was much more gradual (Figure 54). The
sharp decline in stock biomass and very slow recovery in
this area also indicated that recruitment overfishing was
taking place. Anderson (1975) estimated that, in some
years, significant amounts of juvenile silver hake were
caught and discarded by the small mesh Northern shrimp
(Pandalus borealis) fishery in the coastal waters of the
Gulf of Maine. However, the impact of this unreported
discard was probably not sufficient to cause the dramatic
decline in stock biomass in the Gulf of Maine prior to
1970. It may, however, have contributed to the slow
Tabi. 12. Total international catch (.t) of silver hake off the northeast coast of the United States
during 1955-1982.
Distant Water Fleet
USA
DWF
USSR
Gulf of George.
Bank
Maine
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
33,833
21,448
36,980
35,522
34,750
23,628
26,576
26,253
22,978
31,722
22,649
21,495
14,653
24,706
14,632
11,384
8,263
5,570
8,347
4,635
8,042
9,760
8,728
6,220
2,635
3,812
3,787
3,236
19,595
20,729
25,856
14,498
15,899
22,070
14,468
16,339
14,007
5,522
8.208
12,713
12,300
6,451
1,654
4,238
3,069
879
5,698
2,283
4,588
3,793
3,749
6,394
893
1,166
1,150
1,819
SNEMA
15,155
16,349
18,790
14,699
18,800
9,952
12,896
14,568
20,117
28,477
23,715
11,205
9,671
9,295
8,238
6,955
5,681
6,322
6,944
8,275
8,475
11,217
13,400
13,446
15,296
13,488
13,201
13,569
Total
68,583
58,526
81,626
64,719
69,449
55,650
53,940
57,160
57,102
65,721
54,572
45,413
36,624
40,452
24,524
22,577
17,013
12,771
20,989
15,193
21,105
24,770
25,877
26,060
18,824
18,466
18,138
18,624
Gulf of Georges
Bank
Maine
-
-
-
3,660
-
-
-
53
1,081
549
578
1,099
2
-
-
SNEMA
-
-
41,900
4,191
103,697
164,763
19,434
230,666 68,493
88,086 126,211
47,367 41,264
30,977
28,951
16,752 58,691
20,667
12,271
68,673 22,861
76,633 29,493
56,509
59,017
51,228
64,081
58,607 33,436
42,016 16,442
40,514 14,480
3,607
10,764
1,022
3,888
498
339
104
973
2,703
2,293
B
Total
-
-
41,900
111,548
184,197
299,159
214,297
88,631
59,928
75,443
32,938
91,587
107,207
116,075
115,887
93,142
58,458
54,996
14,371
4,910
1,471
3,042
2,397
Total
68,583
58,526
81,626
64,719
69,449
55,650
53,940
99,060
168,650
249,918
353,731
259,710
125,255
100,380
99,967
55,515
108,600
119,978
137,064
131,080
114,247
83,228
80,873
40,431
23,734
19,937
21,180
21,021
of
Total
-
-
42.3
66.1
73.7
84.6
82.5
70.7
58.6
74.0
57.7
81.6
84.9
82.8
86.0
77.8
64.6
65.7
33.3
13.0
-
-
B
of
Total
-
42.3
66.1
73.7
84.6
82.5
70.8
59.7
75.5
59.3
84.3
89.4
84.7
88.4
81.5
70.2
68.0
35.5
20.7
7.4
14.4
11.4
I-
128
GULF OF MANE
Stock Blomoss
O__(a9e1+)
ltindings
'
GEORGES BANK
/
I
I
v
Stock Biomass
(agel+)
s
I
/
I
.'
*___/
/
/
- -
Landings
-
StEMA
I'
F
'
I
S
I
I
t
I
I
Stock Blames:
(ogel+)
I'
S.
S.
'
I
S.
I
S.,
I
S.
S.-
- - - -
5557596163656769 717 757779
81 83
Year
Figure 54. Stock bloinass and total international catch of
silver hake off the northeast coast of the U.S.
(Almeida and Anderson 1981).
129
recovery of the fishery in the early 1970s.
A portion of the silver hake catches reported from
Georges Bank (ICNAFINAFO Subdivision 5Ze (Figure 4))
belong to a northern Georges Bank - Gulf of Maine stock,
and previous assessments have not accounted for this
possibility. Catches from the Georges Bank area for both
the U.S. and distant-water-fleets prior to 1977 are listed
by statistical area in Table 13. During 1962-1976, 94% of
the U.S. catch from Georges Bank was taken from the
northern portion of the Bank (areas 521-523) (Figure 55).
Catches ranged from 869 mt to 16,174 mt and averaged about
6,600 nit annually. Distant-water-fleet catches were
assigned to statistical areas based on the monthly
percentage of vessel activity in each of the areas
estimated from U.S. Coast Guard overflight data.
Approximately 29% of the annual distant-water-fleet catch
from Georges Bank was taken from the northern part of the
Bank (Figure 56), with catches ranging between 6,900 mt
and 57,200 nit and averaging 21,209 nit annually.
The addition of the U.S. and distant-water-fleet
catch from statistical areas 521-523 to the total Gulf of
Maine catch would, in every year during 1962-1975 except
two, at least double the removals from the stock
inhabiting the region. Additional analyses, beyond the
scope of this thesis, are required to develop new
abundance indices from commercial fishery catch/effort and
130
Tabi. 13. Total imt.rnatioaal catch (at) from th. Georges Bank area during 1962-1962
by sampling area. (For locations of sampling area. Bee Figure 34.)
(+ indtcateø a catch of 1es than .5 mt).
Sampling Area
521
522
523
tT.,1..A
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1914
1975
1976
1977
1978
1979
1980
1981
1982
11,336
7,530
5,294
6,633
10,583
11,769
5,977
1,274
216
612
476
2,981
454
1,197
2,475
$19
588
269
788
316
215
524
525
-
+
3
200
166
1,399
6
-
l
+
190
3
1
+
-
-
1
1
+
148
413
126
213
1,198
44
25
5
7
1,085
581
48
21
1,408
726
-
2,538
1,702
346
2,669
1,772
3,302
1,246
3,195
5,534
34
7
464
277
331
392
5
3
21
+
1
-
1
47
12
58
68
32
2
4
1
2
3
t
1
+
.
267
98
4
6
6
9
6
17
274
168
126
22
7
165
582
1
-
10
-
Total
1
from
521-523
16,339
14,007
5,522
8,208
12,713
12,300
6,451
1,651
4,238
3,069
879
5,698
2,283
4,588
3,793
3,749
6,394
893
1,166
1,150
1,819
99.0
95.8
99.6
82.8
94.2
96.2
95.6
77.8
90.6
94.3
99.0
99.2
99.4
98.6
98.2
99.1
99.9
87.3
78.7
54.7
18.1
41,900
103,697
164,763
230,666
88,086
47,367
28,951
16,752
20,667
68,674
76,633
56,509
64,081
58,607
42,016
40,514
3,607
1,022
498
339
82.3
32.7
34.7
6.8
16.2
14.5
36.3
47.7
59.5
37.1
23.2
31.2
20.7
46.9
from
524-526
1
C
4,835
5,890
67
526
-
64
43
225
121
209
1.0
4.2
.4
17.2
5.8
3.8
4.4
22.2
9.4
5.7
1.0
.8
.6
1.4
1.8
.9
.1
12.7
21.3
45.3
21.9
Distant Water Fleet
1962
1963
1964
196$
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
426
3,283
751
1,821
499
-
1,343
1,576
86
2,239
2,021
3,102
4,401
12,001
19,673
17,036
25,000
13,537
10,229
3,609
7,035
6,086
10,170
17,231
12,267
6,551
3,503
11,030
44
-
68
-
16,477
13,546
31,489
435
3,511
3,273
2,128
328
2,049
5,983
3,471
7,969
5,359
4,463
1,207
-
-
-
5,324
20,647
13,778
32,219
22,430
6,774
649
3,248
1,089
11,435
29,050
2,092
9.229
3,659
10,314
-
-
49,185
86,206
120,024
32,773
15,491
11,348
670
1,209
24,623
13,274
15,629
18,945
17,110
24,611
(-)'
(_)1
(-)'
-
-'
-
(-)
(_)1
-
7,539
62,630
18,644
18,220
6,448
4,844
6,064
7,162
16,550
21,166
22,644
10,344
5,772
40,514
3,607
1,022
498
339
104
104
3.1
-
-
12.7
67.3
65.3
93.2
83.8
85.5
63.7
52.3
40.5
62.9
76.8
68.8
79.3
53.1
96.9
100.0
100,0
100.0
100.0
100.0
100.0
'Distant water fleet catch taken in Foreign Fishing Area #5 not reported by statistical
area; some catches were likely made in area 525.
131
100
'I
'1
50
'I
A.
521
1.
.,
Figure 55. DistrIbution of U.S. catch on Georges Bank by
statistical area for 1962-1982.
50
C
II
25
A.
526
Figure 56. Distribution of distant water fleet catch on
Georges Bank by statistical area for 1962-1976.
132
research vessel bottom trawl survey data and to complete a
revised virtual population analysis, in order to evaluate
the relative effect on stock trends of including the
northern part of Georges Bank with the Gulf of Maine.
In summary, the results of the analyses of research
vessel bottom trawl survey catch data, commercial fishery
catch data, and morphometric data collected during
research vessel bottom trawl surveys indicate that silver
hake inhabiting the continental shelf waters off the
northeast coast of the United States are separated into
two stocks, one comprised of fish from northern Georges
Bank and the Gulf of Maine and another with fish from
southern Georges Bank south to Cape Hatteras. For
assessment purposes, the northern stock of silver hake
should include statistical areas 511-515 and 521-523,
while the southern stock should include statistical areas
524-526, 537-539 and 600+. This division of the silver
hake resource represents the same boundaries as proposed
by Anderson (1974) (Figure 2).
133
LITERATURE CITED
Almeida, F.P., and E.D. Anderson. 1981. Status of the silver
hake resource off the northeast coast of the United
States - 1981. NMFS, NEFC, Woods Hole Lab. Ref. No.
81-36. 67p.
Amos, M.H., R.E. Anas, and R.E. Pearson. 1963. Use of a
discriminant function in the morphological separation
of Asian and North American races of pink salmon,
Oncorhynchus gorbuseha (Walbaum). [at. North Pac. Fish.
Comm. Bull. 11:73-100.
Anas, R.E., and S. Mural. 1969. Use of scale characters and
a discriminant function for classifying sockeye salmon
(Oncorhynchus nerka) by continent of origin. mt. North
Pacif. Fish. Comm. Bull. 26:157-192.
Anderson, E.D. 1974. Comments on the delineation of red and
silver hake stocks in ICNAF Subarea 5 and Statistical
Area 6. mt. Comm. Northw. Atlant. Fish. Res. Doc.
74/100, Serial No. 3336. 8p.
Anderson, E.D. 1975. Assessment of the ICNAF Division 5Y
silver hake stock. mt. Comm. Northw. Atlant. Fish.,
Res. Doc. No. 75/62, Serial No. 3544. 18p.
Anderson, E.D., and G.D. Marchesseault. 1980. Definition of
management units. NOAA Tech. Mem. NMFS-F/NEC-3. lip.
Anderson, E.D., F.E. Lux, and F.P. Almeida. 1980. The silver
hake stocks and fishery off the northeastern United
States. Mar. Fish. Rev. 42(i):12-20.
Anonymous, 1964. Soviet Research Report, 1963. mt. Comm.
Northw. Atlant. Fish. Doc. No. 59. Serial No. 1355.
25p. (mimea).
Azarovitz, T.R. 1981. A brief historical review of the Woods
Hole Laboratory trawl survey time series, p. 62-67 In:
W.G. Doubleday and D. Rivard [eds.] Bottom trawl
surveys. Can. Spec. Publ. Fish. Aquat. Sci. 58.
Berrien, P. 1983. Silver hake, Merliccius bilinearis, egg
census and adult population estimate for 1979 in waters
off eastern United States. ICES C.M. 1983/G:46. l7p.
Bigelow, H.B., and W.C. Schroeder. 1953. Fishes of the Gulf
of Maine. U.S. Fish. Bull. 53(74):1-577.
134
Bliss C.I. 1970. Statistics in biology. Vol.2. McGraw-Hill
Co., New York. 639p.
K.G. Konstantinov, and A.S. Noskov. 1965.
U.S.S.R. Research Report, 1964. mt. Comm. Northw.
Atlant. Fish. Res. Doc. No. 18. Serial NO. 1502. lip.
Bogdanov, A.S.
,
(mimeo).
Bowman, R.E., and W.L. Michaels. 1982. Food of seventeen
species of northwest Atlantic fish: Part I, Examination
of predator length and geographic area. NMFS, NEFC,
Woods Hole Lab Ref. Doc. No. 82-l6.88p.
Booke, H.E. 1981. The conundrum of the stock concept - are
nature and nurture definable in fishery science? Can.
J. Fish. Aquat. Sd. 38:1479-1480.
Burns, T.S., R. Schultz, and B.E. Brown. 1983. The
commercial catch sampling program in the northeastern
United States, p. 82-95. In W.G. Doubleday and D.
Rivard [eds.], Sampling commercial catches of marine
fish and invertebrates. Can. Spec. Publ. Fish. Aquat.
Sci. 66.
Butman, B., J. Loder, and R. Beardsley. 1984. Mean
circulation. In R.H. Backus [ed.], Georges Bank. M.I.T.
Press. (in press).
Carson, R.L. 1943. Food from the sea - fish and shellfish of
New England. Fish and Wildi. Serv. Cons. Bull. No. 33.
74p.
Colton, J.B., and R.R. Byron. 1977. Gulf of Maine - Georges
Bank ichthyoplankton collected on ICNAF larval herring
surveys September 1971 - February 1975. NOAA Tech.
Rept., NMFS SSRF-717. 3.5p.
Colton, J.B., Jr., and J.M. St. Onge. 1974. Distribution of
fish eggs and larvae in continental shelf waters, Nova
Scotia to Long Island. Amer. Geog. Soc., Ser. Atlas
Mar. Environ. Folio 23, 2p + 11 plates.
Conover, J.T., R.L. Fritz, and M. Viera. 1961. A
morphometric study of silver hake. U.S. Fish. Wildi.
Serv., Spec. Sci. Rept. Fish. 368. i.3p.
Cook, R.C., and G.E. Lord. 1978. Identification of stocks of
Bristol Bay sockeye salmon, Oncorhynchus nerka, by
evaluating scale patterns with a polynomial
discriminant method. U.S. Fish. Bull. 76(2)415:423.
135
Dixon, W.J., M.B. Brown, L. Engelman, J.W. Frane, M.A. Hill,
R.I. Jennrich, and J.D. Toporek [eds.]. 1981. BMDP
Statistical Software-1981, Univ. Calf. Press, Los
Angeles, 726 p.
Doubleday, W.G., and R.G. Halliday. 1975. An analysis of the
silver hake fishery on the Scotian Shelf. mt. Comm.
Northw. Atlant. Fish., Ann. Mtg. Res. Doe 104, Ser. No.
3597 (mimeo).
Edwards, R.L. 1965. Relation of temperature to fish
abundance and distribution in the southern New England
area. mt. Comm. Northw. Atlant. Fish. Spec. Publ. No.
6: 95-1 10.
1968. Fishery resources of th north Atlantic area. In
D. Gilbert (ed.), The future of the fishing industry of
the United States. Univ. Wash. Publ. Fish., New Ser. 4.
p. 52-60.
Edwards, R.L., R. Livingstone, and P.E. Hamer. 1962. Winter
water temperatures and an annotated list of fishes Nantucket Shoals to Cape Hatteras. U.S. Fish and Wildl.
Serv. Spec. Sd. Rept. Fish. No. 397. 31 p.
Ehrich, S.
and V. Rempe. 1980. Morphometric discrimination
between hake populations (Osteichthyes, Gadeiformes,
Gen. Merluccius) from the northeast Pacific by use of
size-independent discriminant analysis. Mitteilungen,
Bundesforschungsanstalt fur Fischerei, Institut Fur
Seefischerei, Hamburg. No. 31. 5Op.
,
Everhart, W.H., and W.D. Youngs. 1981. Principles of fishery
science. 2nd edition. Cornell Univ. Press. 349p.
Fahay, M.P. 1974. Occurrence of silver hake, Merluccius
bilinearis, eggs and larvae along the Middle Atlantic
continental shelf during 1966. U.S. Fish. Bull.
72:813-834.
Fisher, R.A. 1936. The use of multiple measurements in
taxonomic problems. An. Eugen. 7(2):179-188.
Fritz, R.L. 1959. Hake tagging in Europe and the U.S.,
1931-1958. J. Cons. mt. Explor. Mer., 24(3):480485.
1962. Silver hake. U.S. Fish. Wildi. Serv. Fish.
Leaflet No. 538. 7p.
1963. An analysis of silver hake tag returns. mt.
Comm. Northw. Atlant. Fish., Spec. Publ. 4:214-215.
136
Fukuhara, F.M., S. Mural, J.J. Lalonne, and A. Srlbhibhadh.
1962. Continental origin of red salmon as determined
from morphological characters. Jut. North Pacif. Fish.
Comm. Bull. 8:15-109.
Grosslein, M.D. 1974. Bottom trawl survey methods of the
Northeast Fisheries Center, Woods Hole, MA, USA. Jut.
Comm. Northw. Atlant. Fish. Res. Doe. No. 74/96. Ser.
No. 3332 (mimeo), 27 p.
Hill D.R. 1959. Some uses of statistical analysis on
classifying races of American shad (Alosa sapidissima).
U.S. Fish. Bull. 59:269-286.
Hubbs, C.L. and, K.F. Lagler. 1947. Fishes of the Great
Lakes region. Bull. Cranbrook Inst. Sd., No. 26, 186p.
Kendall, A.W.,Jr., and N.A. Naplln. 1981. Diel-depth
distribution of summer ichthyoplankton in the Middle
Atlantic Bight. U.S. Fish. Bull. 79:705-726.
Klecka, W.R. 1975. Discriminant analysis. In Nie, N.H., C.H.
Hull, J.G. Jenkins, K. Steinbrenner, and D.H. Bent.
SPSS, Statistical Package for the Social Sciences, 2nd
ed. McGraw Hill. p434-467.
Konstantinov, K.G., and A.S. Noskov. 1966. U.S.S.R. Research
Report, 1965. mt. Comm Northw. Atlant. Fish. Res. Doc.
66/39. Serial No. 1656. 26p. (mlmeo).
1967. U.S.S.R. Research Report, 1966. Jut.
Comm Northw. Atlant. Fish. Res. Doc. 67/21. Serial No.
1821. l7p. (mimeo).
1968. U.S.S.R. Research Report, 1967. mt.
Comm Northw. Atlant. Fish. Res. Doe. 68/15. Serial No.
1996. 34p. (mimeo).
1969. U.S.S.R. Research Report, 1968. mt.
Comm Northw. Atlant. Fish. Res. Doc. 69/17. Serial No.
2224. 29p. (mimeo).
1970. U.S.S.R. Research Report, 1969. mt.
Comm Northw. Atlant. Fish. Res. Doe. 70/20. Serial No.
2385. 4Op. (mimeo).
1971. U.S.S.R. Research Report, 1970. Jut.
Comm Northw. Atlant. Fish. Res. Doe. 71/53. Serial No.
2603. 32p. (mimeo).
1972. U.S.S.R. Research Report, 1971. mt.
137
Comm Northw. Atlant. Fish. Res. Doe. 72/42. Serial No.
2819. 29p. (mimeo).
1973. U.S.S.R. Research Report, 1972. mt.
Comm Northt. Atlant. Fish. Summ. Doe. 73/22. Serial No.
3018. 14p. (mimeo).
1974. U.S.S.R. Research Report, 1973. mt.
Comm Northw. Atlant. Fish. Summ. Doe. 74/26. Serial No.
3286. 32p. (mimeo).
1975. U.S.S.R. Research Report, 1974. mt.
Comm Northw. Atlant. Fish. Summ. Doe. 75/30. Serial No.
3546. 34p. (mimeo).
1976. U.S.S.R. Research Report, 1975. mt.
Comm Northw. Atlant. Fish. Summ. Doe. 76/VI/20. Serial
No. 3844. 3/ep. (mimeo).
Kuntz, A., and L. Radcliffe. 1917. Notes on the embryology
and larval development of twelve teleostean fishes.
Bull. U.S. Fish. 35:87-134.
Lachenbruk, P.A. 1975. Discriminant analysis. Hadner, N.Y.
ix+1 28p.
Langton R.W., and R.E. Bowman. 1977. An abridged account of
predator-prey interactions for some northwest Atlantic
species of fish and squid. NMFS, NEFC Woods Hole Lab.
Ref. Doe. No. 77-17. 22p.
Lear, W.H., and E.J. Sandeman. 1974. Use of scale characters
and a discriminant function for identifying continental
origin of Atlantic salmon. mt. Comm. Northw. Atlant.
Fish. Res. Doc. 74/40. Serial No. 3226. l2p.
Mahalanobis, P.C. 1936. On the generalized distances in
statistics. Proc. Nat. Inst. Sd., India. 2(1):49-55.
Marak, R.R., and J.B. Cotton, Jr. 1961. Distribution of fish
eggs and larvae, temperature, and salinity in the
Georges Bank - Gulf of Maine area, 1953. U.S. Fish.
Rept. Fish. 398, 6lp.
Wildl. Serv., Spec. Sc
Marak, R.R., J.B. Cotton, and D.B. Foster. 1962a.
Distribution of fish eggs and larvae, temperature and
salinity in the Georges Bank - Gulf of Maine area,
1955. U.S. Fish. Wildi. Serv., Spec. Sd. Rept. Fish.
411, 66p.
1962b. Distribution of fish eggs and
138
larvae, temperature and salinity in the Georges Bank
Gulf of Maine area, 1956. U.S. Fish. Wildi. Serv.,
Spec. Sd. Rept. Fish. 412, 95p.
-
Messieh, S.N. 1975. Delineating spring and autumn herring
populations in the southern Gulf of St. Lawrence by
discriminant function analysis. J. Fish. Res. Bd. Can.
32: 471-477.
Nichy, F.E. 1969. Growth patterns on otoliths from young
silver hake, Merluccius bilinearis, (Mitchell). mt.
Comm. Northw. Atlant. Fish., Res. Bull. 6:107-117.
Noskov, A.S. 1970. Results of tagging silver hake
(Merluccius bilinearis) on Georges Bank in 1964. In
A.S. Noskov (ed.), Commercial fisheries research in the
west Atlantic (Ocean conditions, stocks and
distribution of commercial fish in areas of Nova Scotia
and Geoges Bank in 1962-1966), p. 160-164. Trans. Vol.
27, Kaliningrad. (translated from Russian).
Noskov, A.S., G.P. Zakharov, and I.N. Sidorenko. 1963.
U.S.S.R. Research Report, 1962. Soviet fishery
investigations in the ICNAF area in 1962. mt. Comm.
Northw. Atlant. Fish. Doe. No. 54. Serial No. 1125.
23p. (mimeo).
Noskov, A.S., V.1. Rikhter, and V.A. Isakov. 1976. A brief
description of the Soviet herring, mackerel, silver
hake and red hake fisheries in ECNAF Subarea 5 and
Statistical Area 6. mt. Comm. Northw. Atlant. Fish.
Res. Doe. 76/XII/167. Serial No. 4063. 5p. (mimeo).
Parsons, L.S. 1972. Use of meristic characters and a
discriininant function for classifying spring- and
autumn-spawning Atlantic herring. mt. Comm. Northv.
Atlant. Fish. Res. Bull. 9:5-9.
Pearson, R.E. 1964. Use of discriminant function to classify
North American and Asian pink salmon, Oncorhynchus
gorbuscha (Walbaum), collected in 1959. mt. North
Pacif. Fish. Comm. Bull. 14:67-90.
Pimental, R.A. 1979. Morphometrics. Kendall/Hunt Publishing
Co., Dubuque, Iowa. 276p.
Rao, R.C. 1952. Advanced statistical methods biometric
research. John Wiley and Sons, Inc., New York. 39Op.
Reyment, R.A. 1966. Homogeneity of covariance matrices in
relation to generalized distances and discriminant
139
functions. Computer Contrib. State Geol. Surv. Kansas.
7 : 5-9.
Rounsefell, G.A. 1975. Ecology, utilization and management
of marine fisheries. C.V. Mosby, Co., St. Louis. 516p.
Sarnits, A.A., and V.1. Sauskan. 1966. Hydrographic
conditions and distribution of silver hake (Merluccius
bilinearis (Mitchell) on Georges Bank and off Nova
Scotia in 1964. mt. Comm. Northw. Atlant. Fish. Res.
Doc. 66/Si, Serial No. 1660, 8p (mimeo).
Sauskan, V.A. 1964. Results of Soviet observations on the
distribution of silver hake in the areas of Georges
Bank (5Z) and Nova Scotia (4W) in 1962-63. mt. Comm.
Northw. Atlant. Fish. Res. Doc. No. 61, 8 p.
Sauskan, V.1., and V.P. Serebryakov. 1968. Reproduction and
development of the silver hake, Merluccius bilinearis
(Mitchell). Vopr. Ikhtiol. 8(3):398-414.
Schaefer, R.H. 1960. A study of the growth and feeding
habits of the whiting or silver hake, Merluccius
bilinearis, (Mitchell) of the New York Bight. N.Y. Fish
Game J. 7(2):85-98.
Schenk, R. 1981. Population identification of silver hake
(Merluccius bilinearis ) using isoelectric focusing.
NMFS, NEFC Woods Hole Lab. Ref. No. 81-44, 3lp.
Scott, J.S. 1982. Depth, temperature and salinity
preferences of common fishes of the Scotian Shelf. J.
Northw. Ati. Fish. Sci. 3:29-39.
Sharp, J.C., K.W. Able, W.C. Leggett, and J.E. Carscadden.
1978. Utility of meristic and morphometric characters
for Identification of capelin (Mallotus villosus)
stocks in Canadian Atlantic waters. J. Fish. Res. Bd.
Canada 35:124-130.
Silverman, M.J. 1982. The distribution and abundance of
silver hake, Merluccius bilinearis, larvae off
northeastern United States, 1977-1980. ICES, C.M.
1982/G:58. 16p.
Vinogradov, V.1. 1972. Studies of the food habits of silver
and red hake in the northwest Atlantic area, 1965-1967.
mt. Comm. Northw. Atlant. Fish. Res. Bull. 9:41-50.
Wilk, S.J., W.G. Smith, D.E. Ralph, and J. Sibunka. 1980.
Population structure of summer flounder between New
140
York and Florida based on linear discriniinant analysis.
Tran. Amer. Fish. Soc. 109:265-271.
Wilson, R.C. 1953. Tuna marking, a progress report. Calif.
Fish Caine 39:429-442.
APPENDIX
141
Appendix I
Algorithm utilized to remove the effect of
correlation between morphometric characters and fork
length (as used by Ehrich and Rempe (1980)).
The auxiliary variable for each character is calculated
as:
a(j) = Syz(j) / Sxz.
m
n(k)
[x(k,i) - x(k)]
Sxz
* [z(k,i) - z(k)], and
k=1 1=1
m
n(k)
[y(j,k,1) - y(j,k,i)] * [z(k,i) - z(k)]
Syz(j)
k=1 1=1
where there are:
N samples numbered k(k1,2,3...,M),
N(K) individuals in the k-th sample,
j characters.
and:
z(k,i) = 1/ age of the i-th individual in the k-th
sample,
x(k,i) = ln(fork length) of the i-tb individual in
the k-th sample,
y(j,k,i) = ln(character j) of the i-th individual in
the k-tb sample.
Each character was then adjusted to a standard reference
length.
This length was chosen to be the mean overall
length of each sex, 282 mm for males and 309 mm for
Therefore adjusted, unbiased characters, y,
females.
were calculated for males as:
y(j,k,i) = a(j) * ln(282) + [y(j,k,i) - {a(j) *
and for females as:
y(j,k,i) = a(j) * ln(309) + [y(j,k,i) - [a(j)
* x(k,i)]J.