81
Technical Report Series
Number 87-1
32
32
HARD CLAM
MERCENARIA MERCENARIA (LINNE'),
POPULATIONS OF COASTAL GEORGIA
Randal L. Walker
31
31
Georgia Marine Science Center
University System of Georgia
Skidaway Island, Georgia
81
Hard Clam, Mercenaria mercenaria (Linne'),
populations of coastal Georgia
Randal L . Walker
Marine Extension Service
University of Georgia
P. 0. Box 13687
Savannah, Georgia 31416-0687
The Technical Report Series of the Georgia Marine Science Center i s issued by
the Georgia Sea Grant College Program and the Marine Extension Service of the
University of Georgia on Skidaway Island (P. 0 . Box 13687, Savannah, Georgia
31416). It was established to provide dissemination of technical information
and progress reports resulting from marine studies and investigations mainly
by staff and faculty of the Unive rsity System of Georgia . In addition, it is
intended for the presentation of techniques and methods, reduced data, and
general information of int erest to industry, local, regional, and state
governments and the public. Information contained in these reports is in the
public domain. If this pre-publi ca tion copy is cited, it should be cited as
an unpublished manuscript. (Sea Grant College Program, Grant #04-7-15844126) .
1987.
Acknowledgements
I wish to thank Mr. John Veazey, Drs . Peter Heffernan and Stuart Stevens
for their help in col l ecting clams from the Christmas Creek area and Bruce and
Cathy Paulson for their he lp in col lec ting c lams at the Crooked River and
northern Cumberland Island Stations .
typing the ma nuscript .
I wish to thank Mr s. J eanette Haley for
I would especia l l y like to thank Dr s. E. Chin, J .
Crenshaw, J . Harding, P . Heffernan, and Stuart Stevens for rev iewing the
manuscript.
The work was supported by the Georgia Sea Grant Program unde r
grant number s NA80AA-D-00 09 1 and NA84AA-D-00072.
i
Abstract
The growth rate, density, age structure, size structure and commercial
size structure of 40 populations of the h ard clam, Mercenaria mercenaria
(Linne'), throughout the coastal waters of Georgia are described.
The hard
clam grows to a commercial size in 2 to 3 years t hroughout the coastal area of
Georgia except under extreme environmental conditions.
In non-fished or
unexploited clam populations, a wide range of clam sizes (up to 11 . 8 em) and
ages (up to 40 years) may occur.
The range of clam sizes and a ges, however ,
narrows in the presence of fishing pressures.
Keywords:
aquaculture, bivalve, clam, coast , estuary, fishery, mollusc,
re cruitment, resource, saltmarsh, s tock, s urv ey
ii
List of Figures
Figure
1.
Map of Wassaw Sound showing collection sites of hard clam,
Hercenaria mercenaria, populations.
Figure
2.
Map of St. Catherines Sound and the Crooked River area showing
collection s ites of hard clams, Hercenaria mercenaria,
populati ons.
Figure
3.
Map of Sapelo Sound showing collection sites of hard clam,
Hercenaria mercenaria, populations .
Figure
4.
Map of Christmas Creek and Cumberland Island showing
co llection sites of hard clam, Hercenaria merc enaria ,
populat ions.
Figures
5 -17 .
Growth rate (mean ± standard deviation), age structure and
size structure of populations of hard clams, Hercenaria
mercenaria, from Wassaw Sound.
Figures 18-20.
Growth rate (mean± standard deviation), age st ructure and
size structure of populations of hard clams , Hercenaria
mercenari a, from St . Cathe rines Sound .
Figures 21-35 .
Growth rate (mean± standard deviat ion) , age structure and
size structure of populations of hard c lams, Hercenaria
mercenaria, from Sape l o Sound.
Figure s 36-42 .
Growth ra te (mean± standard deviation), age structure and
si ze structure of populations of hard clams, Herc enaria
mer c enaria, from Chr istmas Creek .
Fi gur e
43.
Growth rate (mean± standard deviation), age s t ructu re and
s i ze structure of populations of hard c lams , Herc enaria
mercenaria, from Cumberland Island .
iii
Figure
44.
Growth rate (mean± standard deviation), age structure and
size structure of populations of hard clams, Hercenaria
mercenaria, from Crooked River.
Figure
45.
Hard clam, Hercenaria mercenaria, age structure in areas not
fished, lightly fished and heavily fished.
Figures 46-47.
Commercial size grouping of hard clams, Hercenaria mercenaria,
for each c l am population sampled in Wassaw Sound.
Figure
48.
Commercial size grouping of hard clams, Hercenaria mercenaria,
for each clam population sampled in St. Cather ines Sound ,
Cumberland Island and Crooked River .
Figures 49-50.
Commercial size grouping of hard c lams, Hercenaria mercenaria,
for each clam population sampled in Sapelo Sound.
Figure
51.
Commercial size grouping of hard clams, Hercenaria mercenaria,
for each clam population sampled in Christmas Creek, Little
Cumberland and Cumberland Islands.
Figure
52.
Overall percentages of commercial grouping of hard clams,
Hercenaria mercenaria, from all populations in coastal
Georgia.
Percentage of c ommercial grouping of clams i n non-
fished, lightly fished and heavi ly fished clam populations.
iv
List of Tables
Table 1.
Hard clam, Herc enaria mercenaria , production in pounds of meat
landed from 1882 to 1986 in Georgia.
Table 2.
Habitat type, substrate type, mean density of clams, Hercenaria
mercenaria ±standard deviation per m2 , and relative commercial
harvesting pressure per stat ion.
Table 3.
Hard clam, Hercenaria mercenaria, densities reported for natural
clam populations.
v
Table of Con tents
Acknowledgements . ............. ........ .... . ...... . . . .. . .. . ............ i
Abstract ... .. .. . .. . . .. ..... .... . . . ... . .... ......... . .. ...... ...... . . . ii
List of Figures .. .. ... . ........... . .... . .. . .. .. ... . .. . ....... . .. . .. . i ii
Lis t of Tables . ... . . ....... . . .... ... . . .. ..... . .. ............... . ...... v
I nt roduction .. . .... ........ . ........ . ... .. ......... . ... ... ....... ..... 1
Methodology ..... . .. . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... 3
Re s ult s ........ . . .. . .......... . ....... .. . . .......... . .... ............. 4
Discussion ... .. ................ .. ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5
Conclusions . .... . .. ....... .... . ........ . ...... .. . . . .. . ............. .. 1 3
References ... .. .... ... ... ........... .. ........ ... ........ . .. . ....... . 14
Figures 1- 5 2 .... ... .. . .... ..... .... .. .. ... . ...... . ... . .. . . .......... . 19
Appendix .. .... . .. ..... . . .... .... . . . . ......... .. ..... .. . .... .. .... . ... 72
vi
Introduction
The hard clam, Hercenaria mercenaria (Linne'), fishery in the State of
Georgia dates back to 1880 with peak landings of clams occurring in 1908
(Table 1).
Since the 1930's, clam landings have been sporadic or virtually
non-existent in Georgia.
However, with the increase in consumer demand for
clams and the decline in clam landings in traditional northern U.S. clamming
areas due to pollution and overharvesting (Nat ional Marine Fisheries Serv ice ,
1977), there has been an increasing interest in Georgia clamming among local
as well as out-of -state fishermen.
This, coupled with the mariculture
potential of hard clam, Hercenaria mercenaria, (Walker , 1983; Walker, 1984a;
1984b), has led to a re-emergence of the fishery in Georgia with steady
landings reported since 1981.
Although the coastal waters of Georgia contain unexploited populations
of hard clams (Godwin, 1967, 1968;
Walker et al. , 1980;
Walker and Tenore ,
1984; Walker and Rawson, 1985), most of these populations occur in small areas
and are difficult to locate and harvest.
They are, however, indicat i ve of the
existence of extensive pollution-free marshes suitable for shellf i sh
production and culture.
Hard clams grow year round in southeastern U. S .
waters (Eldridge et al., 1979; Walker, 1984a), and clam densities above 25m- 2
are common in Georgia (Walker and Tenore, 1984).
Densities up to 101m- 2 h av e
been observed in intertidal regions of small creeks, headwaters of major
creeks, and in shel l deposits associated with oyster bars (Walker et al.,
1980; Walker and Tenore, 1984; Walke r and Rawson, 1985).
At present, the majority of Georgia clams represent natural unexploited
populations.
As fishing pressures increase, they wi ll undergo dramatic
c hanges in population dynamics.
Therefore, in the interest of future
1
Table l .
Hard clam, Hercenaria mercenaria, production in pounds of meat
landed from 1882 to 1985 in Georgia. Data from Department of
Natural Resources (1979-1986) and Lyles (1964-1978).
1880
24,000
1957
0
1887
0
1958
1,000
1888
0
1959
0
1889
3,000
1960
0
1890
4 , 000
1961
0
1897
3,000
1962
0
1902
10,000
1963
0
1908
43,000
1964
0
1965
0
1966
0
1918
1923
7 , 000
0
1927
1,000
1967
0
1928
1,000
1968
0
1929
2,000
1969
1,000
1930
2,000
1970
17,000
1931
1,000
1971
0
1932
1,000
1972
0
1935
0
1973
6,000
1936
0
1974
0
1937
0
1975
0
1938
0
1976
1939
0
1977
0
1940
0
1978
0
1945
0
1979
0
1950
0
1980
0
1951
0
1981
5,855
1952
0
1982
9, 725
1953
0
1983
3,482
1954
0
1984
3,474
1955
0
1985
6,966
1956
0
1986*
2,655
*Partial Landings from January to March, 1986
2
10,885
comparisons , it is important at this time to obtain base l ine studies on the
various disturbed and undisturbed clam populations in Georgia.
The purpose of this study is to assess the status of c lam populations in
the coastal waters of Georgia.
It describes distribution, densities, growth
rates, popula t i on age structure, population size structure and commercial size
structure for unharvested versus harvested clam populations in the coastal
waters of Georgia.
Methodology
Clams were col lec ted from 40 populations of coastal Georgia ( 1 3 from
Wassaw Sound , 15 from Harris Neck, 1 from Crooked River , 1 from Cumberland
Island, 7 from Christmas Creek, and 3 from Ossabaw Island) by taking three
0.44 m2 quadrat samples per site .
A 66 x 66 em square PVC frame was randomly
thrown on the creek bottom and clams were dug by hand, placed in field
samp ling bags and marked as to locality.
Clams were returned to t h e
laboratory, where they were counted, measured for she ll length ( longest
possible measurement, i.e., anterior-posterior), and aged by shell sectioning
techniques (see Rhoads and Lutz, 1 980; Rhoads and Pannella, 1970).
Growth
curves for each c lam were constructed by back-plotting shell length to each
summer annual ring increment.
Clams at each station were categorized according to the following
commercial size groups:
juveniles, <38 mm; pre-legal littlenecks, 38 to
44.4 mm; litt lenecks, 44.4 to 67.0 mm; cherrystones, 68 to 77 mm; and chowders
> 78 mm in shell lengths.
This classification scheme is similar to Godwin's
( 1967) scheme except that his littleneck s ize class (38 to 68 mm) was divided
3
into legal littlenecks, those >44.4 mm and pre-legal littlenecks , those <44.4
mm (Walker 1984b).
Results
The growth rates of the various clam populations are given in Figures 544.
In 95% of populations sampled, the mean time for clams within a
population to reach marketable size (44.4 mm in shell length or 25.4 mm in
shell width) is 2 to 3 years,while individual clams obtain this size in 2 to 7
years.
The exceptions to this are Sapelo Sound Station number 9 and
Cumberland Island Station number 1 in which 5 and 4 years of growth were
required before commercial size was obtained (Figures 30 and 45 respectively).
Population shell size and age structure are given in Figures 5-44.
Clams were aged to 40 years with an overall mean age of 10.8 years.
Overall,
clams less than 10 years accounted for 60% of the harvested animals, whereas
clams 11 to 20, 21 to 30 and those greater than 30 years old accounted for
25% , 13% and 2% respectively .
of older clams was reduced.
As clam populations were fished,
the percentage
Conversely, the percentage of juveniles increased
as fishing pressure increased (Figure 45).
Most populations appear to be
healthy as exhibited by the presence of younger individuals.
Christmas Creek
Station number 4 (Figure 41) is the major exception in that within this dense
population, only two individual clams were less than 10 years old.
In
essence, there has been virtually no recruitment to this population in 12
years.
Wassaw Sound Station number 3 had only 3 individuals less than ten
years of age, with the majority of the clams being over 20 years of age
(Figure 7).
In terms of shell lengths, clams were sized to 11.83 em with an
overall mean shell length of 7.21 ± 1.12 S.D. em.
4
In terms of commercial size grouping (Figures 46-51), juveniles
accounted for 3% of the overall population with pre-littlenecks, littlenecks,
cherrystones, and chowders accounting for 4%, 32%, 28% and 33% respectively
(Figure 52).
Chowders dominated in 40% of t h e populations with cherrystones
and littlenecks dominating at 38% and 22% of the clam populations respectively
(Figure 52).
In terms of effects of fishing pressure on clam populations,
chowders dominated in non-fished stations (N=27) with decreasing percentages
in areas lightly fished (N=l l) to lesser percentages in intensely fished areas
(N=2).
The percentage of littlenecks increases with increase in fishing
pressure (Figure 52).
Mean clam densities ranged from less than 1 to 151 clams per square
meter (Table 2), whereas individual samples ranged from 0 to 216 clams per
square meter.
Overall average density of the 40 clam populations sampled was
22 clams per square meter.
Large differences in clam numbers per sample per
station were observed.
Discussion
The results of this study show that the growth rate of the various clam
populations in coa stal Georgia result in a marketable product in 2 to 3 years.
These findings agree with those growth rates observed in other naturally
occurring c lam populations in Georgia (Walker, 1984b, Quitmyer et al., 1985;
Walker and Stevens, in press) .
Furthermore, they agree with growth rates
obtained from hatchery-rear ed c lam seed in Georgia (Wa lker, 1 984a, b), in
South Carolina ( Eldridge et al., 1976, 1979) and in Florida (Menzel, 1964).
Of t he 40 clam populations , only Cumberland Island Station number 1 and
Sapelo Sound Stat ion number 9 required over three years of growth to obtain a
5
Table 2.
Habitat type, substrate type, mean density of clams, Hercenaria mercenaria
standard deviation per m2 . and relative commercial harveting pres sure per station.
Substrate
Type
Mean Den~ity
per rn
Commercial
Harvesting
Intertidal Flat
Intertidal Flat
Creek
Feeder Creek
Feeder Creek
Feeder Creek
Feeder Creek
Feeder Creek
Feeder Creek
Feeder Creek
Creek
Creek
Creek
Shell/ Sand
Shell/Sand
Mud
Shell/Mud
Shell/Mud
Shell/Mud
Shell/Mud
Shell/Mud
Shel l / Mud
Sand/Shell
Shell
Shell/ Sand
Shell/Mud
8.8 ± 7.7
20.3 ± 8.9
13.5 ± 18.4
3.0 ± 1.5
47.3 ± 30.9
<l
3.2 ± 4.5
18 .0 ± 8.9
6.8 ± 4. 1
36.0 ± 45 . 0
14. 0 ± 10.2
10 . 0 ± 8.0
12.8 ± 15 .2
Intense
I ntens.e
None
None
Light
None
None
None
None
Light
Light
None
None
Major Creek
Major Creek
Sound - Intertidal Flat
Shell/Mud
Mud
Shell/ Sand
10.1 ±
ll . 5 ±
2. 1 ±
5.6
8.3
1.6
Light
Light
Light
Feeder Creek
Creek
Creek
Creek
Creek
Feeder Creek
Feeder Creek
Feeder Creek
Intertidal Flat
Intertidal Flat
Creek
Feeder Creek
Feeder Creek
Creek
Cree k
Shell/Mud
Shell/Mud
Shell/ Mud
Shell/ Mud
Shell/ Mud
Shell/Mud
Shell/ Mud
Shell/Mud
Shell
Shell/Mud
Shell/ Mud
Shell/Mud
Shell/Mud
Shell/ Mud
Shell / Mud
4.0 ±
<l
10.1 ±
3.0 ±
23.0 ±
8.1 ±
7 .0 ±
50.0 ±
21.0 ±
20.0 ±
46.6 ±
11. 0 ±
6.1 ±
4.2 ±
5.3 ±
3.5
None
Light
Light
None
None
None
None
None
None
None
None
None
None
Light
Light
Rive r
Sand
Area/Station
t-lassaw Sound
1
2
3
4
5
6
7
8
9
10
ll
12
13
St . Catherines Sound
1
2
3
Sapelo Sound
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Crooked River
1
Habitat
Type
<1
5. 7
1.4
14 . 1
6.7
4.8
21.3
8.9
16.1
25.7
10.8
5.8
2.6
3.3
Light
Table 2. (Cont' d).
Habitat
Area/ Station
Substrate
Type
Type
Mean Den ~ity
per m
Commerc i al
Harvesting
Christmas Creek
Feeder
Feeder
Feeder
Feeder
Feeder
Feeder
Feeder
1
2
3
4
5
6
7
Cumberland Island
1
*
**
Shell/ Mud
She ll/ Mud
Shell
Mud/Shell
Shell to Mud*
Shell/Mud
Shell/Mud
Creek
Creek
Creek
Creek
Creek
Creek
Creek
I ntertida l Flat
Sand/Gr as s
34.1
6. 1
73 . 5
151.0
85.7
14.3
67.7
10
±
±
±
±
±
±
±
19.6
3.9
27.2
10. 2
92.6
7.7
52.1
None
None
None
None
None
None
None
to 15**
None
Creek bottom had only small a rea of shell; most of c reek bot tom was mud . High density of
clams (9 5 per sample ) occurred i n shell bottom; whereas, 4 and 14 clams occurred per
sample in mud .
Estimated.
These animals were collected while a ccompany ing commercial clammers.
the 1817 clams harvested , 66 we re juveniles, 2 pre-l itt lenecks, 1741
litt1enecks, 6 cherr ystones and 1 chowde r.
7
Out of
mean marketable size.
In the Sapelo Sound Station, clams occur on top of an
oyster wrack well above the mean low water mark .
Clams here occur in a dense
substrate of dead oyster shells and are estimated to be above the mean low
water within the intertidal zone for 6 hours per tidal cycle.
At the
Cumberland Island Station, clams occur in a substrate of sand and Spartina
alterniflora short form roots.
Clams here are estimated to be uncovered
approximately 8 hours per tidal cycle and may be harvested by hand at a mean
high tide (mean tidal amphitude in Georgia is 2.1 m, Johnson et al . , 1974).
It is interesting to note that clams at Cumberland Island Stati o n 1 required 4
years versus 5 years at the Sapelo Sound Station to obtain commercial size.
One can hypothesize that substrate (i.e., clams growing in dense shell
substrate) inhibits clam growth more than increased exposure time.
For
instance, in Sapelo Sound Stations 9 and 10, the two populations occur with in
12 meters of each other.
Station 10 occurs on the same oyster wrack , but
clams here occur in a shelly mud substrate and are estimated to be exposed for
2 1/2 hours per tidal cycle.
Ye t c lams at Station 10 grew almost twice as
fast as those at Station 9 with only an l /2 hour greater exposure time.
Furthermore at clam populations in Beach Creek (St. Catherines Stations 1 and
2), both populations occur within approximately 4 meter s of each other .
Clams
at Station 1 occur in a shelly-sand substrate at the mean low water mark,
whereas those at Station 2 occur in mud up on the creek b a nk and are estimated
to be uncovered by the tide for approximately 6 hours per cycle.
Yet c lams at
Station 2 have a higher mean size per year than those at Station 1.
Thus it
appears that substrate in certain cases may be more inhibitory to clam growth
than exposure time .
8
The life span of the hard clam, Hercenari a mercenaria, is estimated to
be 40 years (Hopkins, 1930; Comfort , 1957).
Clams were aged to 40 years in
this study, to 34 years in c l am popul ations in t h e vicinity of Little Tybee
I sland (Walker, l984b), and to 25 years at King ' s Bay, Georgia (Quitmyer et
al., 1985).
I n oth er studies of hard clam populat i ons , c l ams were aged to 29
years at Cape Lookout, North Carolina (Peterson et al., 1983), to 32 years at
Co r e Sound, North Carol i na (Peterson et al .. 1985), to 20 years in Virginia
( Haven and Loesch, 1 9 7 3), to 15 years in F ishers Is l and, Ne w York ( Ma l inowski ,
1985). and t o 8 to 9 years in Barnegat Bay, New Je r sey (Kennish, 1978).
The
s ou t hern hard clam, Hercenaria campechiensis was aged to 22 years i n Boca
Ciega Bay, Florida (Saloman and Tay l or, 1969).
The clam populat i ons of coas t al Georgia consi st mostl y of chowders.
This is in agreement wi th the r esults of a c l a m re sour ce sur vey of Wassaw
Sound (Walke r et al., 1 980) and the State (Godwin, 1968 ; Walker and Rawson,
198 5).
The results differ from a c l a m resource survey in South Caro lina where
lit t l e n ecks were found to dominate (Anderson et al., 1978).
The difference in
findi ngs between states c an he ex plaine d by the p r esence and absence o f a
viable clam fishery.
In South Carolina, a viab l e f ish ery exis t s and the
large r and older c l a ms have probably been f i shed out over time.
Reductions o f
larger size and age c l asses of clams due to fishi n g pressure c an be seen in
t his s tudy (Figures 45 and 53).
In non - fished area s , chowders dominate.
In
heavily-fished areas, t h e percentages of c h owders and cherrystones decrease
and the percentages of smaller clams and littlenecks increase.
Th e low
percentage of juvenile clams in our study c an be attributed to sampling error.
Clams were collected by h a nd , whi c h is often an i neffective method of
collecting sma ll e r individua l s.
9
Theoretically, during the incipient stages of fishing, older and larger
clams are caught first .
With time and according to the level of harvesting
pressure, smaller, younger clams come to dominate.
the New York area.
This has been observed in
In heavil y fished areas of Great South Bay, c lams were
found to be under four years of age (i.e . , age that c lams are mar ketable
size), whereas in areas that are closed to fishing,
the populations contain
older and larger clams with few juveniles or littlenec ks (Greene, 1978).
In
Barnegat Bay, New Jersey, no clams were found under 9 years of age (Kenni s h,
1980) and Peterson ec al ., (1985) attribute this absence of older clams to
fishing pressure.
In the clam populations of coastal Georgia, mean clam densities ranged
from 0 to 151 adult clams per square meter.
These densities agree with
densities reported in other clam resource surveys in Georgia (Godwin 1967,
1968 ; Walker et al., 1980; Walker and Rawson, 1985) .
Rep orted clam densitie s
from other areas throughout the United States are given in Tabl e 3.
In
Georgia, clams frequently occur in dense numbers, however, the overall area of
the bed is u sua lly small.
For i nstance, in Was saw Sound, Georgia, a clam
population with a mean of 50 clams per square meter covered an area of
approximately 90m 2 .
In this population, the mean density was reduced to 20
c lams per square meter after 3 days of illegal harvesting (Walker, 1984b) .
The clam populations · of coastal Georgia are representative of harvest e d
and unharvested populations.
In unharvested populations in Georgia, chowders
generally dominate (Godwin, 1968; Walker et al., 1980; Walker and Rawson,
1985) and the population is comprised of older individuals (Walker, 1984b;
Walker and Stevens, in press).
MacKenzie (1979) describes unharvested clam
populations as those which exhibit sparse and sporadic setting, declining
10
Table 3 .
Hard c l am, Mercenaria mercenaria, densities
reported for natu ral c lam popul ations .
Reference
Location
Maquoit Bay, ME
Barnstable Harbor, MA
Narragansett Bay, RI
Greenwich Bay, RI
Greenwich Bay, RI
Long Island Sound, CT
Northport Bay, NY
Great South Bay, NY
Islip, NY
Open Areas
Closed Areas
Patchogue Bay, NY
East Patchogue Bay, NY
Patchogue Bay, NY
Barret Beach, NY
East Islip, NY
Goose Creek, NY
Raritan Bay, NJ
Raritan Bay, NJ
Little Egg Harbor, NJ
Chinocoteague Bay, MD
Poquoson Flats, VA
Johnson Creek, NC
Back Sound, .NC
Santee River, SC
North Inlet, SC
Coastal Georgia
Christmas Creek, GA
Wassaw Sound, GA
Coastal Georgia
Colorado Lagoon, CA
*860
1
4
2 to 12
215
0.9
6.5
18.4
16
30
81
16
50
16
11
10
14
5 to 11
34
1
5
6.4
2 to 10
18 to 24
6
0 . 1 to 21
151
0 to 100
0 to 91
556
Dow and Wal l ace, 1951
Sanders et al . , 1962
Russell, 1972
Stickney and Stringer, 1957
Stringer, 195 5
MacKenzie, 1977
MacKenzie, 1977
MacKenzie, 1977
Buckner, 1979
Greene, 1978
Greene, 1978
Greene, 1978
Greene, 1978
Greene, 1978
Kaplan et al., 1975
MacKenzie, 1977
Campbell, 1965
Carriker, 1961
Wells, 1957
Loesch and Haven, 1973
Peterson et al . , 1983
Peterson et al., 1984
Rhodes et al., 1977
Dame, 1979
Godwin, 1968
This Study
Walker et al., 1980
Walker and Rawson, 1985
Crane et al . , 1975
Southampton Waters,
Great Britain
6
to 8
Ansell, 1963
Southampton Waters,
Great Britain
0.3
to 12.3
Hibbert, 1976
*This popul.1tion was undergoing heavy mortality due to overcrowding.
11
setting densities of spat, increased predation of juveniles, and
comprised mostly of older clams.
populations
Malinowski (1985) concludes that even in
populations with low rates of annual recruitment (due to sporadic s e tting
and/or to predation) into the adult age classes, the population wil l
ultimately result in dens e assemblages of c lams.
From the data pre sente d in
this study, Malinowski's characteriz ation of old populations is more
applicable to Georgia populations than MacKe nzie's.
Sporadic and low setting
densities are the rule in Georgia (personal observation) regardless of whether
the population is being harvested or not.
Recruitment is a gradual event in
Georgia with spawning possibly occurring over most of the year (Pline, 1984).
Gonadal studies in Georgia show that spawning oc c urs over a 10-month period
(Pline, 1984), but peaks in fall and spring.
of any major sets occurring in Georgia.
This may account for the absence
Thus it appears that in Georgia, a
relatively few individuals recruit to the population each year resulting in
dense numbers of older clams over time.
Beal (1983) hypothesized that dense assemblages of neighboring large
clams (80 m- 2 ) may protect smaller clams from predation.
observed clam populations that were without juveniles.
Kennish (1978)
He hypothesizes that
this indicated an inv erse association between adults and juveniles .
He
further states that adult populations may preclude successful settlement of
young clams because of competition for food.
Therefore successful recruitment
of Hercenaria mercenaria may be regulated by a density-dependent factor, i.e. ,
when density of adults is high, juveniles are forced to settle unoccupied
areas (Kennish, 1978).
Unfortunately, Kennish (1978) gave no density
estimates, and his population was comprised of individuals less that 9 years
old.
If one looks at the four most dense populations in the Christmas Creek
12
2
area (Stations 3, 4, 5 and 7, with 74, 151, 86 and 68 clams m- respectively),
only Population 4 would support Kennish's conclusions that dense adult
populations preclude successful recruitment.
In Population 4, only 1.5% of
the clams are less than 12 years old, which suggests that adults preclude
recruitment.
Yet in Populations 3, 5 and 7, there are clams in nearly all
year classes, indicating there has been recruitment every year for the last 10
years into each of these populations.
The majority of the populations would
support Beal's hypothesis that dense assemblages of large clams protect
smaller clams.
Populations 3, 5 and 7 are approximately equivalent to his
experimental density of 80m- 2 , whereas Population 4 is almost twice that
density.
It is possible that both investigators are correct, but that the
density of adult clams needed to preclude successful recruitment is much
greater than that envisioned by Kennish .
Conclusions
The hard clam grows to a commercial size in 2 to 3 years throughout the
coastal area of Georgia, except under extreme environmental conditions.
In
n on-fished or unexploited clam populations, a wide range of clam ages (up to
40 years) and c lam sizes (up to 11 . 8 em) may occur, however, in lightly fish e d
to heavily fished populations, the range of sizes and ages is narrowed.
range decreases with increased fishing pressure.
It is hoped that the data
provided in thi s report will provide bas e line information for future
comparisons to determine the impact of a viable fishery upon presently
unexploited hard clam populations.
13
The
References
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vi + l7p + 15p. Appendix III.
Ansell, A.D. 1963.
44:396-397.
Venus mercenaria (L.) in Southampton wa t er.
Eco l ogy
Beal, B.F. 1983. Effects of environment, intraspecifi c density, predat ion by
snapping shrimp and other consumers on the popula tion in biology of
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Univer sity of North Carolina at Chapel Hill, Chapel Hill, North
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Campbe ll , R. 1965. A report on the economical ly impor tant shellfish
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Crane, J.M ., Jr., L .G. Allen and C. Eisemann. 1975. Growth rate,
distribution, and population density of the northern quahog, Hercenaria
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Calif. Fish and Game 61:82 - 94 .
Dame, R. F. 1979 . The abundance, diversity and biomass of macrobenthos on
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75-A through 85-A. Department of Natural Resour ces, Coastal Resources
Division, Data Management Section, Brunswick, Georgia .
Dow, R.L. and D.E. Wallace . 1951. A method of reducing winter mortalities of
Venus mercenaria in Maine waters . Dept. Sea Shore Fi sh., Augusta,
Maine , Res. Bull. 4, 3lp.
14
Eldridge, P.J., W. Waltz, R.C. Gracy and H.H. Hunt. 1976. Growth and
mortality rates of hatchery seed clams, Nercenaria mercenaria, in
protected trays in waters of South Carolina . Proc. Natl. Shellfish.
Assoc. 66:13-20.
Eldridge, P.J., A.G . Eversole and J.M. Whetstone. 19 79 . Comparative survival
and growth rates of hard c lams, Nercenaria mercenaria, planted in trays
subtidal ly and intertidally at varying densities in a South Carolina
Estuary. Proc. Natl . Shellfish. Assoc. 69:30-39.
Godwin, W.F. 1967. A preliminary survey of a potential hard clam fishery.
Georgia Game and Fish Comm. Contribu tion Series No. 1, Brunswick,
Georgia. 23 pp.
Godwin, W.F. 1968. The distribution and density of the hard clam, Nercenaria
mercenaria, on the Georgia coast. Georgia Game and Fish Commiss ion,
Series No. 10, Brunswick, Georgia. 30 pp.
Greene, G.T. 1978. Population structure, growth and mortality of hard clams
at selected lcoations in Great South Bay, New York. Master Thesis,
State University of New York at Stoney Brook, Stoney Brook, New York .
199 pp.
Haven, D.S. and J.G. Loesch . 1973 . Summary, conc lusions and recommendati ons
based on an investigation into commercial aspects of the hard clam
fishery and development of commercial gear for the harvest of molluscs.
Final Report for PL 88 -3 09, Project 3- 124- R, Va . Instit. Mar. Sci .
Gloucester Point, VA. 108 pp.
Hibbert, C.J . 1976. Biomass and production of a bivalve community on an
intertidal mud-fl at. J. Exp . Mar . Biol . Ecol. 25:249 - 261.
Hopkins, H.S. 1930. Age differences and the res piration in muscle tissues of
mollusks. Journ. Exper. Zool. 52:209-239.
Johnson, A.S., H.O. Hilles tad , S.F. Shanholtzer, and G.F. Shanholtzer. 1974.
An Ecologica l Survey of the Coastal Region of Georgia. National Park
Service Scientific Monograph Series. Number 3. 233 pp.
Kaplan, E.H., J.R. Welker, M.G. Kraus and S. McCourt. 1975. Some factors
affecting the colonization of a dredged channel. Mar. Biol. 32:193- 204.
Kennish, M.J. 1978. Effects of thermal di scharges on mortality of Nercenaria
mercenaria in Barne gat Bay, New Jersey . Environ . Geol. 2:223-254.
Kenni sh, M.J. 1 980. Shell microgrowth analysis. Nercenaria mercenaria as a
type example for research in population dynamics . p. 255-294. In D.C.
Rhoads and R.A. Lutz (editors), Skeletal growth of aquatic organisms.
p2 55 - 294. Plenum Press, NY . 750 pp.
15
Loesch, J.F . and D. Haven. 1973. Estimated growth functions and size-age
relationships of the hard clam, Hercenaria mercenaria, in the New York
River, Virginia. The Veliger 16:76-81.
Lyles, C.H. 1956 through 1976 . Statistical Digest No. 50 through No. 70.
Fishery statistics of the United States. Fish and Wildlife Service,
Bureau of Commercial Fisheries. Washington, DC.
MacKenzie, C.L., Jr. 1977. Predation on hard clam (Hercenaria mercenaria)
populations. Trans. Am. Fish. Soc. 106:530-537.
MacKenzie, C.L., Jr. 1979.
Fish. Rev. 41:10-22.
Management for increasing clam abundance.
Mar.
Malinowski, S . M. 1985. The population ecology of the hard clam, Hercenaria
mercenaria, in Eastern Long Island Sound. Ph.D. Dissertation,
University of Connecticut, Groton, Connecticut. 112 pp.
Menzel, R.W . 1964. Seasonal growth of northern and southern quahog,
Hercenaria mercenaria and H. ca111pechiensis, and their hybrids in
Florida. Proc. Natl. Shellfish. Assoc. 53:111-119.
National Marine Fisheries Service . 1977. The molluscan shellfish industries
and water quality:' Problems and opportunities. U.S. Dept . of Commerce,
NOAA, Natl. Mar. Fish. Ser., Off. Fish. Devel . , Supt. Docs . , Washington,
DC. v + 46 pp.
Peterson, C.H., P.B. Duncan, H.C. Summerson and G.W. Safrit, Jr. 1983. A
mark-recapture test of annual periodicity of internal growth band
deposition in shells of hard clams, Hercenaria mercenaria, from a
population along the southeastern United States. Fish. Bull. 81:765779.
Peterson, C.H., H.C. Summerson and P.B. Duncan. 1984. The influence of
seagrass cover on population structure and individual growth rate of a
suspension feeding bivalve, Hercenaria mercenaria. J. Mar. Res. 42:123138.
Peterson, C.H., P.B. Duncan, H.C. Summerson and B.F . Beal. 1985. Annual band
deposition within shells of the hard clam, Hercenaria mercenaria:
consistency across habitat near Cape Lookout, North Carolina . Fish.
Bull. 83:671-677.
Pline, M.J. 1984. Reproductive cycle and low salinity stress in adult
Hercenaria mercenaria L . of Wassaw Sound, Georgia. Masters Thesis,
School of Applied Biology, Georgia Institute of Technology, Atlanta,
Georgia. 74 pp.
16
Quitmyer, I.R., H.S. Hale and D.S. Jones. 1985. Paleoseasonality
determination based on incremental shell growth in the hard clam,
Hercenaria mercenaria, and its implications for the analysis of three
southeast Georgia coastal shell middens. Southeastern Archaeology
4:27-40.
Rhoads, D.C. and G. Panella. 1970. The use of molluscan shell growth
patterns in ecology and paleoecology. Lethaia 3(3):143-161.
Rhoads, D.C . and R.A. Lutz. 1980. Skeletal growth of aquatic organisms:
biological records of environmental change. New York, Plenum Press.
750 pp.
Rhodes, R.J., W.J. Keith, P.J. Eldridge and V.G. Burrell, Jr. 1977. An
empirical evaluation of the Lesile-Delury method applied to estimating
hard clam, Hercenaria mercenaria abundance in the Santee River estuary,
South Carolina. Proc. Natl. Shellfish. Assoc. 67:44-52.
Russell, H.J . , Jr . 1972. Use of a commercial dredge to estimate a hard shell
clam population by stratified random sampling. J. Fish Res. Bd. Canada
29:1731-1735.
Saloman, C.H . and J.L. Taylor. 1969.
quahogs from a Florida estuary .
Age and growth of large southern
Proc. Natl . Shellfish . Assoc. 59:46-51.
Sanders, H.L., E.M. Goudsmit, E.L. Mills and G.E. Hampson. 1962. A study of
the intertidal fauna of Barnstable Harbor, Massachusetts. Limnol.
Oceanogr . 7:63 - 79 .
Stickney, A.P. and L.D. Stringer. 1957 . A study of the invertebrate bottom
fauna of Gre enwich Bay, Rhode Island. Ecology 38:111-121.
Stringer, L.D. 1955. Greenwich Bay hard clam productivity studies.
Wildl. Serv., Clam Invest. Conf. Clam. Res. 5:1-9.
US Fish
Walker, R.L. 1984a. Effect s of densi ty and sampling time on the growth of
the hard clam, Hercenaria mercenaria, planted in predator-free cages in
coastal Georgia. The Nautilus 98:114-119.
Walker, R.L. 1984b. Population dynamics of the hard clam, Hercenaria
mercenaria (Linne'), and its relation to the Georgia hard clam fishery.
Masters Thesis, School of Applied Biology, Georgia Institute of
Technology, Atlanta, Georgia. 121 pp.
Walker, R.L.
1983.
Feasibility of mariculture of the hard clam, Hercenaria
Journal
Shellfish Research 3:169-174.
mercenaria (Linne'), and clam predators in coastal Georgia.
Walker, R.L . and M. V. Rawson. 1985. Subtidal hard clam, Hercenaria
me rcenaria (Linne) res ourc es in coastal Georgia. Georgia Marine
Center, Tech. Rept. 85 -1. 164 pp.
17
Scienc~
Walker, R.L. and K.R. Tenore. 1984. The distribution and production of the
hard clam, Mercenaria mercenaria, in Wassaw Sound, Georgia. Estuaries
7: 19-27.
Walker, R.L., M.A. Fleetwood, and K.R. Tenore . 1980. The distribution of the
h a rd clam, Mercenaria mercenaria (Linne'), and clam predators in Wassaw
Sound, Georgia. Georgia Marine Sci. Center, Tech. Rept . 80-8, 59 pp.
Walker, R.L. and S.A. Stevens.
Hard clam , Mercenaria mercenaria (Linne'),
Resources of Christmas Creek, Little Cumberland and Cumberland Island .
Georgia Dept. Natl. Res. Contrib. Series. No. 41.
(In Pre ss).
Wells, H . W. 1957. Abundance of the hard c lam , Mercenaria mercenaria, in
relation to environmental factors.
Ecology 38:123-128.
18
FIGURES 1 - 52
19
N
0
_,,
,_......,.
t!
.l
.:::o:'r-'"'~·
~:·/:·•:'
.l
•:I";: ,:.{
.
;ui:~r: ~f>\i :·
......
____.. ,, •
,,·;~~~..
\.~_{
Wosscw
Sound
0
Kilometers
2
Ossabaw Island
St. Catherines Sound
v
c
•
v
c
•
•
-;:
.a
e
:2
u
St. Catherlnee
Sound
Crooked River
STUDY
AREAS
21
"--
~
Sapelo Sound
22
STUDY
AREA
Little C"mberland leland
Station 1
,'::·:
_
__ :;- :··:)/!~C~
}~~(:\f~~l~
-: ..
'::' ~-. ~- . . ·..:
'
:
~-.
:
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Cumberland leland
:- ··
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.;··:.·~. ·. ~
~ .: ~ .
.....
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.'
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- •.1 .'··
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: =··;.:;::'
.
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.. ~-: ~~- :~. ':·· ,: ..
. .... --:· .·
.,~: :
..
·.··:
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.··
·.: .· . ;.·."' ·
~- .·. ·, . .: ~
·..-.· : ........ .' .... .
.:·!. .:>·:
__. . .-
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'
..··. ;.•. ~. .
":",:
.•·
....··
.
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·:-· ..
..·. ·_:
. ...
: .:
~.: ~-:::'·
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'
.....
:
,;.·
..
·.·-· .
. -.- _.....
~
·.. .
-~·
,.
23
..
Wassaw Sound
Cabbage Island
Clam Station 1
8
6
.......
0>
c
4
Q)
Q)
I
2
£
(f)
123456789
.28
.24
Clam age (summers)
.20
. 16
. 12
n
mean 4.0 ± 2.3yeara
median 4.0 years
.08
.04
-
.20
.......
. 16
Q)
>
ct1
Q)
a:
= 24
1 2 3 4 5 6 7 8 9
Clam age (summers)
n = 24
mean 4 .98 ± 1.40cm
median 5.14cm
. 12
.08
.04
0 .25
2.25 4 .25 6 .25 8.25 10.25
Class midpoint (em)
24
Wassaw Sound
Cabbage Island
Clam station 2
,--...
E
8
(.)
6
4
Q.)
.c.
(f)
I
2
1
2 3
4
5 6
7 8
9 10
Clam age (summers)
.28
>-
.20
(.)
c
Q.)
n
. 12
mean 3 .96 ± l.89years
4.0years
::::J
cr
Q.)
~
.04
Q.)
-
1
>
ro
Q.)
= 100
2 3
4
5
6
7
8 9 10
Clam age (summers)
. 18
a:
n
.12
= 100
mean 5.43 ± l.57cm
median 5 .66cm
.04
0 .25
2.25 4.25 6.25 8.25 10. 25
Cla ss midpoint (em)
25
Wassaw Sound
Cabbage Island
Clam station 3
10
r-"'1
E
(.)
1....-1
8
-
6
I I I I I II
.c
0>
c
II
(l)
(l)
.c
4
I
(./)
2
1 2 3
4 5 6
7 8 9 10
n=37
mean 25.3±8.9years
median 25years
Clam age (summers)
.08
.06
.04
.02
4
(l)
a:
. 18
. 12
.06
ro
(l)
12
16
20
24
28
32
36
40
Clam age (summers)
.30
.24
>
8
0.25
n:37
mean 9 .89± 1 .09cm
median 1 0 . 18cm
2 .25 4.25 6.25 8 .25 10.2 5 12.25
Class midpoint (em)
26
Wassaw Sound
Wassaw Island
Clam station 4
,...--..
u
8
7
..r::
........
6
E
II
'--'
CJ)
5
Q)
4
c
Q)
..r::
(f)
II I II·
I
I
3
2
1
1 2 3
5 6
7 8 9 10
Clam age(summers)
.32 ..28
.24
4
,-..
f-
n=l 6
mea n 12.7±4.lyears
med ian 13years
f-
.20
r-
. 16
. 12
.08
.04
r-
~
2
ro
Q)
a:
r
r-
4 6 8 1 0 12 14 16 18 20 2 2 24
Clam age(summers)
Q)
>
I-
.28
n :16
.24
.20
.16
.1 2
.08
mean 8.01 ±L58cm
median 7 .93cm
.04
0.25
2.25 4 .25
6 .25 8.25 10.25
Class midpoint(cm)
27
Wassaw Sound
W ass a w Island
Clam station 5
,--..
E
(.)
"--'
..c
........
9
8
0>
6
(l)
5
c
Q)
..c
(/)
3
1
>c
Q)
:::>
II
4
2
u
I I I III
7
I
n=95
mean 6. 7 ±6 .2years
median 4.0years
. 16
. 12
.08
.04
cr
Q)
2 4 6 8101 2 14161820222426283032
>
.1 4
.12
Q)
.10
Q)
-"'
0:
Clam age (summers)
n=94
mean 6 . 12±1.57cm
median 6.24cm
.08
.06
.04
.02
0.25
2.25 4 .25 6 .25 8 .25 10.2 5
Class midpoint(cm)
28
Wassaw Sound
Wassaw Island
Cia m station 6
,--..
E
(.)
8
7
'--"
6
0')
5
(l)
4
Q)
3
2
..c
........
c:
..c
(f)
I I
•
• •
7 8
9 10
I
I
I
I
I
1
1
.20
.16
g
~
.04
~
cr
1
<J.)
~
>
........
ro
Q)
a:
n= 11
mean 9 .2±3.9yea rs
median 9.0years
~
. 12 .-.08 r-
<J.)
4 5 6
Clam age(summers)
,...
>-
-
2 3
~
2 3
6
4 5
7 8 9 1011 12131415 16
Clam age(summers)
.36
.32 r.28
.24
.2 0.16
. 12
.08
-
t-
n = 11
mean 6 .69 ± 1.09cm
median 6 .86cm
f-
-
t-
.04 rI
0. 2 5
2.25
I
I
I
4.25 6 .25 8.25
Cla ss midpoint(cm)
29
I
Wassaw Sound
Wassaw Island
Clam station 7
8
7
6
5
l
4
Q)
£
(f)
3
I
2
1
l
2 3
4
5 6 7 8 9 10
Clam age(summers)
.32
.28
.24
.20
-
-
......__
I
Q)
1
-ro
£
2
3 4
I
...-
1
I
1
j_
.---
I
i
I
j_
1
56 7 8 910111213141516
Clam age(summers)
(1)
>
n=7
mean 8.1 ±4.2year s
median 7 .0years
~
.16
>- .12
()
cQ) .08
:::J
.04
cr
~
r--
.24
.20
.16
.12
n=45
mean 7 .40±0.76cm
median 7.34cm
.08
.04
0.25
2.25 4 .25 6.25
8.25 10.25
Class midpoint(cm)
30
Wassaw Sound
Wassaw Island
Clam station 8
I IIIIII
II
I
Q)
...c
(f)
1 2
3
4 5
6
7 8
9 10
Clam age(summers)
. 16
. 12
6
.08
~
.04
~
n=90
mean 1 0.0±3.90years
median ll..Oyears
~~~~~~~~~~~~~~~~~~~--
cr
1
Q)
-
.40
>
.......
.36
2 3
4
5
6
7
8
9 10 11121314 15 16
Clam age(summers)
Q)
ro
.32
Q)
.28
a:
. 24
.20
. 16
n=90
mean 7 . 11±0.76cm
median 7.llcm
. 12
.08
.04
0.25
2.25
4.25 6.25 8.25 10.25
Class midpoint(cm)
31
Wassaw Sound
Skidaway Island
Clam station 9
r--..
E
(.)
1.....-J
...c
......
CJ)
c
Q)
5
I
4
3
2
I
1
1 2 3
4 5 6
7 8
9 10
Clam a.ge(summers)
>(.)
c
Q)
:::J
.24
.20
. 16
.12
n=47
mean 14.1±5.0years
median l4 .0years
.08
.04
0"
Q)
2
Clam age(summers)
Q)
>
......
cu
£
4 6 81012141618202224262830
.28
.24
.20
. 16
n=47
mean 8.24±0.83cm
median 8 . 11 em
. 12
.08
.04
0.25
2.25 4.25 6 .25 8.25 10.25
Class midpoint(cm)
32
Wassaw Sound
Little Tybee Island
Clam station 10
,--.,
E
(.)
'---'
-c
...c
0'>
CD
CD
8
7
6
5
4
3
I
...c
U)
1
I
I
IIIIIII
1 2 3 4
5 6 7 8
9 10
Clam age(summers)
n=216
mean 6.5 ±4.8years
median S.Oyears
.12
>.
0
.08
CD
.04
c
::J
cr
CD
I....
Q)
>
+--'
ro
Q)
0:
.16
.12
n=215
mean 6.44 ±1.23cm
6.66cm
0.25
2.25
4.25 6.25 8.25 10.2 5
Class midpoint(cm)
33
Wassaw Sound
Little Tybee Island
Clam station 11
9
r-"\
E
(.)
'--'
-
.c
0)
c
Q)
Q)
.c
(/)
8
7
6
5
4
3
2
1
III
III
I
II
I
1 2 3 4 5 6 78
9 10
Clam age(summers)
.36
.32
.28
.2 4
.2 0
>(.)
c
Q)
:J
(]'
Q)
-
.16
. 12
.08
.04
1
Q)
>
ro
Q)
a:
n=lOO
mean 4.4±2 .5years
median 4.0years
2
3
4
5
6
7
8
Clam age(summers)
.20
.16
.12
n=lOO
mean 6.35 ±1 .36cm
median 6 .27cm
.08
.04
0.25
9 10 11 12 13 14
2 .25
4.25 6.25
8 .25 10.25
Class midpoint(cm)
34
Wassaw Sound
Little Tybee Island
Clam station 12
r--.
E
()
-
"--'
..c
Ol
c
Q)
10
9
8
7
6
5
I
4
3
I
2
1
1 2
3
4
5 6
7 8
9 10
Clam age(summers)
.16
n=68
. 12
mean 11.6 ±5.9years
median 9 .0years
.08
.04
Q)
>
....-
"'
Q)
a:
2
4
6
81012141618202224
Clam age (summers)
.24
n=68
.2 0
mean 8.29±0.99cm
median 8 .25cm
. 16
. 12
.08
.04
0 .25
2 .2 5
4.25 6 .25
8.25 10.25
Class midpoint(cm)
35
Wassaw Sound
Little Tybee Island
Clam station 13
I
1 2
Clam
>.
.16
.12
.08
3 4
5 6
7 8
9 10
age(summers) n = 3 9
mean 13.7±6.9years
median 14.0years
u
c
Q)
~
cr
-
.32
_..
.24
.20
.16
Q)
~
Q)
>
ro
Q)
0:
n=39
mean 8 .54±1.05cm
median 8.30cm
. 12
.08
.04
0 .25
2 .25 4.25 6 .25 8.25 10.25
Class midpoint(cm)
36
St. Catherines Sound
10
Station 1
Q
-
e
7
-
8
e
4
E
(.)
II
~
'&
c
6
I
..J
--
3
UJ
2
!
I
2
3
II I I I
...
6
8
7
8
I
8
10
Clam age (summers)
.30
N: 64
>o.
c
(,)
.20
•cr
. 10
Median • years
:1
...
•
~
..••
~
4
"i
a:
6
II
10
12
14
16
18
20
Clam age (summers)
.40
N: 5 ..
Mean 6 .88
.20
Median
3 .25
4 .2 5
5.25
6.25
7 .25
Class midpoint (em)
37
~1 . 16
5.e.-
em
em
9 .25
St. Catherines Sound
JO
Station 2
II
E
8
-'&
7
!-
4
u
.c
c
•
...1
0
e
a
2
I
I
IIlIII
I
5
2
I
3
4
e
6
1
1
•
10
Clam •ge (summers)
.30
N: 63
.20
Median 7 years
>-
u
c
•::::.
....•..
-••>
'i
.10
0'
2
3
•
5
e
7
I
8
10
11
Clam •ge (aummera)
~
a:
.40
N: 63
Mean 7 .10 t.O.II em
.20
Median 7.11 em
3.25
4 .25
6.26
• . 26
7.26
Claaa midpoint (em)
38
1 .25
12
13
St. Catherines Sound
10
St~tloi
8
-....,
a
E
(,)
7
s:.
•
c
6
-'i
4
3
f/)
2
CD
..J
iJf
II
I
I1
~
Clam age (summers)
N: 11
...
to-
. 18
Median 20 years
>c .oe
.,
- hll~
-
...
(,)
P""
:I
•cr...
...•>
II
'i
.
Mean 20 3 + 6 9 years
II
...
P""
""'
,._
••
16
111
20
22
2•
26
28
JQ
32
Clam age (summers)
.40
N: 11
a:
Meen 8.82 ! 0.73 em
.20
Median 10.14
7.26
9.25
10.25
Class midpoint (em)
39
~m
Sapelo Sound
10
Station 1
8
-E
u
~
a
e
'&
e
6
-•
,
3
II
_,• ..
~
I I I I JI I
7
I
2
1
2
3
4
15
8
7
8
g
10
Clam age (summers)
N: 18
.20
,...
u
c
•
•-..
.10
:I
17
.-•.
2
4
I
>
.!
•
I
.40
•a• (summers)
10
Clam
U
14
11
11
10
22
24
II
N: 18
g:
Mean 7.18 t0.87 c111
.20
...dian 7.48 em
3.25
4.25
6.25
8.25
7.25
Class midpoint (em)
40
8.25
8.25
21
30
»
3 . 25
•. 25
6 .25
8.25
7.25
Class midpoint (em)
41
8 .25
Sapelo Sound
10
Station 3
8
-- •
E
7
~
8
~
5
u
II
~
•
•
-'i
3
U>
2
..J
~
l
IfI
I I I
I
8
1
e
8
10
Clam age (summers)
.20
N: 32
Mean 10.2 ! 8.7 yeara
>-
u
.12
Median 7 yeara
c
•
..••...
-•>
;:::,
0'
.04
Clam age (summers}
~
'i
a:
,40
N : 32
Mean 8 .84 .t 1.60 em
.20
Median 7. 18 em
3 .25
4.25
6 . 25
•• 26
7.25
Class midpoint (em}
42
1.26
• . 26
Sapelo Sound
Station 4
8
-E
-'6
.. "'
e
u
.1:
c
-'i
IIIIII
7
e
II
6
...J
.1:
0
I1
3
2
2
3
Clam age (summers)
. 12
N: 28
Mean 18.1
.08
~
10.0 yeara
Median 16 y ears
~
u
r::
•
•04
~
cr
•...
~
•>
;;
•
'i
m:
' 2
4
a
I
10
12
14
IIi
18
20
22
24
21
21l
30
Clam age (summers)
.40
N: 20
Mean 7.44 :!: 1.1 2 e m
..20
...dian 7.45 em
2 .25
3 . 26
4 .26
~ .25
8 .25
Class mldpiont. (em)
43
7 .25
1 . 25
1 .25
32
34
36
Sapelo Sound
10
Station 5
8
-•
-...
E
7
.&.
e
u
g)
c
6
..I
4
=
.!
3
•
fJ)
I
I
2
2
3
4
5
8
7
8
8
10
Clam age (summers)
N: 60
.20
Mean 8.8 :!: 7.0 years
Median 5 years
.10
...•
-•
2
4
I
10
12
14
111
U
20
22
24
211
211
JO
Clam age (•ummers)
~
Ill
S
.40
N: 50
lr
Mean 8.88 t. 1.54 01n
.20
Median 7.00 em
2.25
6.26
8.26
Class midpoint (em)
44
7.25
1.25
1.215
10.215
Sapelo Sound
Station 6
-E
8
u
"i
~
0
7
3
2
I
2
3
4
6
7
8
8
8
10
Clam age (summers)
. 12
N: 40
Mean 14.8
.08
t
8 .3 years
~
(J
c
•
-•...
.0-4
:I
0'
..-..
•
4
~
•
I
I
10
12
14
11
18
Clam age (summers)
.so
N: 40
u:
Mean 7. 57 t 1. 12 em
.to
Median 7.85 em
.10
2.25
3 .25
-4.25
6 .25
8 .25
Class midpoint (em)
45
22
24
u
ze
30
Sapelo Sound
10
Station 7
8
-E
-...
u
~
c0)
•
8
1
8
15
..J
•
•
3
=
~
(I)
2
I
1
2
II
3
I 1I I I I
15
•
8
7
8
8
10
Clam age (summers)
N: 21
-
Mean 18.8 !. 10.8 yeara
~
Median 18 yeara
...
.08
~
~
12
,.
~
~
~
.o~
......_ ...~c(J
..-••
a
•
,.
11
ao
22
a•
Clam age (summers)
~
•
a
.40
N: 21
IE:
....n 7.24 t 0 .82 em
Median 7.32 em
3.215
~.26
15.25
1 . 215
7 .26
Class midpoint (em)
46
8.26
1.25
,....
~
Sapelo Sound
10
Station 8
0
E
u
8
-
e
~
0)
6
..J
4
cG)
--
3
tn
2
G)
I I I I III 1
7
I
I
~
2
3
4
6
1
8
0
8
10
Clam age (summers)
.30
N: 85
M ea n 4 .0
.2 0
Median 3 y e ars
>o
u
c
G)
± 4 .0 years
. 10
::;,
0'
e
~
•
2
0
e
>
-
•
10
12
14
Clam age (summers)
~
ca
•
..20
N: 8 5
G)
a:
Mean 5. 85
. 10
± 1.44 em
Median 6 . 12 em
1.25
2 .25
8 .25
4 .2 5
6 .25
8 . 25
Class midpoint (em)
47
7. 25
8 .25
1/.z::::::=
27
Sapelo Sound
10
-E
u
-.,
.c
0)
c
-•
..J
.c
0
Station 9
e
8
7
8
6
..
3
2
I
I
II
2
3
IIII
4
5
e
I I
e
1
e
10
Clam age (summers)
.20
N: 29
Mean
18.1 !. 11.1 years
no
-•
-
2
4
>
.!!
• ..a
Clam age (summera)
a:
N: 31
Mean 5 .70! 0 .56 em
.20
Median 5 .86 em
1.26
2.25
3 . 26
4.25
5.26
Class midpoint (em)
48
8 .26
7. 25
Sapelo Sound
Station 10
-
E
u
•
•
3
2
I
1
2
3
4
6
6
8
7
10
8
Clam age (summers)
.so
N : 43
.20
I!Aean 3.2 ! 1.2 year&
~
Median 3 yeau;
u
cG)
. 10
:II
CT
--...
...
G)
2
G)
6
3
>
a:
ca
6
7
8
8
10
Clam age (summers)
.40
G)
N: 43
Mean 5.6 1 ! 0 .71 em
.20
Median 5 .52 em
2.25
3.25
4.2 5
6 .25
8.25
Class midpoint (em)
49
7.25
8.25
N: 19
Mean 13 . 3 t. 7.0
Median 12
.,
.-.
2
I
years
..
6
II
J
s
8
10
11
Clam age (summers)
>
ID
3
yean
..La-.--.-7...Q.OO
.40
'i
N : 19
a:
Mean 7.74! 1. 06 em
.20
Median 8.08 em
4 .25
6 .26
8.26
7.25
Class midpoint (em)
50
8.25
8.25
10.2 5
3
2
-4
6
ti
7
8
8
10
Clam age (summers)
.26
N : 22
Mean 8 .80 ! 6.0 yean
.15
Median 7 year6
22 23
Clam age (summers)
.40
N : 22
.20
Mean 7 . 61 t. 0 . 72 em
Median 7 . 60 em
4. 25
5.25
6 . 25
7.25
8.25
Class midpoint (em)
51
9.25
10. 25
Sapelo Sound
JO
-
-E
u
s;
Station 13
e
8
7
II
6
0)
c
G)
6
I
...I
=Cl) "
3
s;
0
2
1I I
II
I
2
3
"
6
6
7
8
8
10
Clam age (summers)
.24
. 16
N: 27
>u
c
•
Mean 4.4 1 2.2 ye an
.08
:J
D'
CD
.......
Q)
-.>,
-.;
u:
Clam age (summers)
.20
N: 27
Mea n 6 . 49 :t 1 .65 em
.12
Median 6 . 34 em
.04
3.2 5
4.26
6.25
6 . 26
7 . 26
Class midpoint (em)
52
8.26
8.2 5
2
3
..
5
6
7
•
8
10
Clam age (summer&)
. 12
N: 38
Mean 12.8
.08
~
8 . 7 yaara
Median 11 yaara
e
Q)
...
·-cu>
-a:
•
10
12
14
t6
••
ao
z2
24
2"
Clam age (summers)
.40
Q)
N: 38
.20
Mea n 7 . 38 .t 0.78 em
Median
3 . 25
7 . 35 em
4.25
6.2 5
6 . 25
7 . 25
Class midpoint (em)
53
8 . 26
8 . 25
211
JO
Sapelo Sound
10
E
u
-...,
.1:
.,c
-.,
0)
Station 15
8
lIIIII
7
I
6
I
6
.J
.1:
I
8
~
I
3
0
2
1
•
3
2
7
8
l!i
•
10
8
Clam age (summers)
.12
H: 43
Mean 10.5 1 5. 7 year a
.08
>c
u
.,.•cr
::l
-
2
• •
4
10
t2
14
,.
"
20
22
24
Clam age (summers)
.40
N : 43
Mean 7 .21 11.12 em
.20
Median 7. 62 em
2.26
3 . 25
4 . 25
5 .25
6 . 25
Class midpoint (em)
54
7 . 25
8.26
8 . 26
Christmas Creek
Station 1
10
........
8
E
u
........
.c
...,
e
I
II
II
I
1
7
e
0)
cQ)
5
..J
..
Q)
3
(/)
2
.c
1
I
I
3
•
5
'
7
8
•
10
Clam age (summers)
H : 46
. 24
.20
M e an
.1e
Medl en
8.4 ± 6 . 8 y ear s
6 y ea r s
. 12
. 08
. 04
•
8
I
10
Clam
•
20
12
,.
H: 4 5
Mean
. 10
•a• (aummera)
8 . 8 6 ± 1. 04 em
M e d i a n 8 . 8 2 em
3.25
55
16
18
20
22
2•
26
Christmas Creek
to
.........
E
(.)
.........
Station 2
8
I
1
•
-
G)
.J::.
U)
3
2
I
1
J
4
5
fi
1.
'~
Clam age (summers)
.2.
N: 8
~
Mean 12. t :t 3.0 yeara
.20
~
Medi an 12 year•
(.) .te
c:
Q)
g.
......-
~
. t2
. 01
4D .o•
.t:
•
6
~
......
...
. 40
•
. 30
.!!
Q::
•
10
12
14
7.26
8.25
Clam ege (aummera)
16
N: 8
Wean 7 .e&
~
0.1 c:m
. 20
.10
4 .26
5 . 26
l
1 .25
I
'&. 25
·c lass midpoint (em)
56
Christmas Creek
10
.......
0
..
a
E
CJ
.__..
.c
0)
c
CD
..J
-.c-
Station 3
I I I I II I
7
e
II
6
..
CD
3
(/)
2
1
1
2
3
4
6
e
1
e
o
10
Clam age (summers)
N: 85
.10
~
()
c:
Mean
. 08
17.1 ~
8.2 yean
Median 18 year a
. 08
CD
5
CD
.::
.o2
2
CD
::...
.....
.....
.!!
. 40
N: 86
CD
ct:
•
Mean 7.80 ~ 1.07 em
.20
Median 7 .ee em
3 . 25
4 . 25
6 . 26
G.26
7.25
8 . 25
Class midpoint (em)
57
• . 26
6 .26
8.215
7.26
8 . 26
1 .26
·c lass midpoint (em)
58
Christmas Creek
10
..-..
Station 5
8
E
8
0
........
...en
I I 11I I I I
7
.1:.
e
c
6
CD
~
-
I
"
CD
3
.1:.
0
2
I
~
2
"
&
e
7
a
•
10
\;l•m age (aummera)
. 12
N: 100
.10
Mean 1 1. 7 .!: 7.1 yea rs
Median 1 1 years
~--------------------------~»0
4
6
•
10
12
14
16
18
10
22
24
26
Clam age (summers)
"
40
.30
. 20
N : 100
Mean 7 . 07 + 0 . 84 e m
M edle n 7.22 em
.1 0
4.2 5
6.2 5
6 .2 5
7.2 5
8 . 25
9 . 25
Class midpoint (em)
59
10 .25
35
Christmas Creek
10
.-.
E
(.)
.........
...
,c
0)
c
G)
-J
,c
G)
0
Station 6
8
e
7
8
11
6
"
3
2
Jill Ill
I
3
2
4
6
8
7
8
~
8
Clam age (aummersJ
.30
N: 32
~
(,)
c:
::s
•
.::•
•:..
.....
.....
.!!
•
0'
Mean 8 .0 :!: 0 . 4 yean
.20
Median 4 .0 years
.10
a
i:;
4
5
I
1
I
I
tO
lam age (aummera)
11
12
13
.<40
N: 32
Mean 8.4 7 ! 0.83 em
Q:
.20
Median 8 . 44 em
4.25
6.25
e .H
7 .26
e . 25
e.26
Class midpoint (em)
60
,.1rQ
Christmas Creek
Station 7
10
8
..-..
E
(.)
......
.r:.
..,
C)
c
Q)
_J
-
e
7
e
4
3
Q)
.r:.
I
6
2
0
II
1I I l I I
I
3
2
4
6
fl
7
8
8
}0
Clam age (summers
.1 2
N: 8 9
~ . 10
(.)
c::
Q)
. 08
~
.0 6
Cl)
.0 4
tt
.::
CD
....
·-.-
Mean 18 .5! 8 .2 y e ara
Median 20 yea rs
.0 2
~
•
•Clam
10
12
1.
HI
18
20
22
age (summers)
qJ
CD
a:
.4 0
N: 89
Mean 8 . 3 4 ! 1.03 em
.20
Median 8.4 7 em
4 .2 5
5 . 25
6 . 26
7 .25
8 .25
Class midpiont
61
8 .25
z•
~
Cumberland Island
10
Station 1
8
-
8
7
E
(,)
e
~
'&
c
6
•
-•
I
"
-J
3
~
U)
2
I
I
I
l
III
I1
1
2
3
4
6
8
7
8
8
10
Clam age (summers)
.20
H: 35
Mean 8.9 :!. 4.4 years
:1111\10
Co)
Median 15 yeera
c
•5
•.
-•,..
--...
a:•
• .20
2
12
13
14
1S
N: 35
Mean 6.84 ! 1.22 em
. 10
2.25
9 .25
4.25
Class midpoint (em)
62
16
Crooked River
10
St~ioi 1I
8
-
8
E
7
.c
Q
cG)
-'
6
-(.)
-.c.,
0
l5
4
I
3
2
l
II
3
2
III
4
6
6
7
8
8
10
Clam age (summers)
. 16
. 14
.12
N: 68
. 10
Mean 13. 9 ~ 4.8 years
.08
Median 14 years
.06
.04
.02
-.!•>
-.,
6
II
12
tO
14
16
18
20
!2
24
26
Clam age (summers)
.40
«
N: 58
.20
Mean 8.94 •. 0 .77 em
Median 8.99 em
5 . 25
6.25
7.25
Class midpoint (em)
fi3
28
1. 00
Overall
.eo
.eo
... o
I
.20
I
1.00
Non-fished areas
.eo
>u
c
.,
.,...c::r
•...->
.,•
a:
~
~
.eo
·"O
.20
1 .00
Lightly-fished areas
.eo
.eo
...o
.20
1
1.00
Heavily-fished areas
.eo
.eo
. .. 0
. 20
c 10
10 to 20 20 to 30
,. 30
Age In Years
64
65
Wassaw Sound
1.00
.eo
Station 7
Station 8
N:45
N: 90
.80
I
.40
.20
1
Station 9
Station 10
N:47
N: 215
1.00
~
0
c:
Q)
==
c:r
Cl)
::
.eo
. 60
.20
Q)
:a.
._
....
.!!
Q)
a:
1
. 40
I
I
Station 11
Station 12
N: 100
N: 68
1.00
.80
.80
.40
.20
r
Station 13
1.00
N: 39
.80
.60
..-o
. 20
c...
c
<
I
...
~
0
-• '
..• •- •,..
•
:•.
•
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•,..
n
•
66
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:7
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:;)
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n
!.
0
::>
••
0
:7
0
lE
D.
•...
Ill
I
St. Catherines Sound
Beach Creek
St. Catherine& Sound
1.00
Station 3
.80
N: 11
. 60
.40
.20
Cumberland Island
1.00
.80
Crooked River
Station 1
Station 2
N: 35
N: 58
.60
.40
.20
l
L.
"l:l
Cll
CD
l
c
<
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a>
(D
r
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n
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~
Sapelo Sound
Julienton River
1.00
. 80
Station 1
Station 2
N: 13
N: 32
.60
I
.40
. 20
I
1. 00
.80
Station 3
Station 4
N: 29
N: 50
Station 5
Station 6
N: 18
N: 40
.60
. 40
. 20
1.00
..I
I
1.00
. 80
Station 7
Station 8
N: 21
N: 85
. ISO
.40
.2 0
c..
c:
c
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0
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Sapelo Sound
Sapelo Sound
1. 00
. 80
Station 9
Station 10
N: 43
N: 31
. 60
. 40
. 20
I
Barbour Island River
1.00
. 60
Station 11
Station 12
N: 19
N: 22
. 60
. 40
.20L . c : : : ! : : = : = . . . _ j
1.0 0
.8 0
Station 13
Station 14
N: 27
N: 38
.60
.4 0
.20
I
I
1.00
Station 15
.eo
N:
43
. 60
.4 0
.20
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c:
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Christmas Creek
1 .0 0
.8 0
Station 1
Station 2
N: 45
N: 8
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,20
I
1.00
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Q)
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&~
.2 0
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Station 3
Station 4
N: 95
N: 133
I
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:a.
;:
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a:
1. 00
. 80
Station 5
Station 6
N: 100
N: 32
. 80
I
. 40
. 20
I
J
1. 0 0
.80
I
Station 7
Station 1-7
N: 89
N: 502
.60
.4 0
.20
I
...
b
~
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<
CD
c:
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i'
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Overall
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c
Cl)
. 60
. 40
.20
~
tT
...
-...
Cl)
Cl)
·...>C'O
-
1 .00
Lightly-fished areas
Heavily-fished areas
. 80
Cl)
a:
. 60
.4 0
. 20
1
~
c:
<
CD
--·
::J
Gl
(I)
...
-- ..."C
r-
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CD
CD
I
CD
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CD
0
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0
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0
71:'
(I)
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0
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0
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c:
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CD
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CD
c.
(I)
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l
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c.
...CD
Cl)
APPENDIX
72
Mean shell lengt:h in mm of the hard clam, Hercenaria mercenaria, per year
band per area.
Appendix I.
Year Band
5
6
7
8
55.3
58. 8
67.1
65.1
62.0
50.9
57. 1
60 . 0
65 .7
61.0
64.0
66.1
64 . 8
58 . 9
64.8
72.7
70.7
65.6
56.1
61.2
64 .3
70.5
65.1
69.9
71.6
70.1
62.3
70. 5
76 .9
73.9
68.2
61. 3
64 . 4
67.1
74 . 0
67.0
73.7
75.4
73.9
62.6
75.2
80.7
74.2
71.6
66.0
67.2
69.2
76.3
69.8
76.8
78.6
78.3
65 .2
75.9
83 . 8
76.8
74.1
68.1
73.3
70.4
77.2
71.7
79.7
79.5
79.1
48 .7
53.0
52.5
54.7
61.6
60.8
61.1
67.0
67.5
65.6
70.7
73.4
70.5
73.6
77.1
42.1
41.7
38.9
37.2
39.8
41.6
39.6
46.9
26.9
44.9
45.6
47.6
44.3
41.4
47. 2
52 .7
53 . 8
53.3
48.6
53.4
54.9
49.1
57.8
35.9
53 .0
54.8
59.3
56.7
52.3
56.5
60.6
62.0
61.2
56.8
60.7
61.8
55.3
61.7
42 . 1
59.1
61.5
65.9
65.6
59.3
62 . 8
65.0
69.0
66.5
62.5
66 .2
66.4
59.6
65.0
46 . 6
59 .1
66.4
69.5
73.9
64.1
67.2
65 . 1
72 .l
70.2
66.2
66.4
69.4
62.8
68 . 4
50. 1
23.5
26.5
24.5
27. 1
26.6
24 . 7
26.4
41.5
42 . 2
41.9
44. 1
42.4
42.9
44.5
53.4
54.5
54 . 2
55.3
54.3
53 .3
56.3
60.8
62.3
61.0
6 2.8
60.8
59.6
67.0
Cumberl and Island
16. 5
1
26.0
38.3
Crooked Ri ver
1
40 . 1
53.2
1
2
3
29.7
22.0
25.0
25.0
22.8
25.5
23.4
24.3
23.9
21.3
21.5
24.3
25.8
41.8
38.2
42.5
42.9
41.1
36.2
39.4
39.9
42.0
40.2
41.3
42.1
43.2
46.3
50.4
57.3
56.4
53.9
46.1
49.6
53.2
57.2
53.4
55.3
57.3
56.5
St. . Cat.herines Sound
21.2
1
2
23.9
3
23.0
36. 1
40.0
36.9
27.0
21.1
23.2
25.5
24. 7
25.6
25.5
29.0
16.8
26.2
31.6
28.5
30 . 5
25.9
33.0
Wassaw Sound
Population l
2
3
4
5
6
7
8
9
10
ll
12
13
4
9
10
70.5
85.7
82.1
74.3
68.7
88.2
79.8
75.6
69.8
71.4
79.0
73.2
83.6
80.8
81. 7
72.6
79 .9
73. 1
85.9
83.0
8.16
72.6
74 .8
78.7
75.4
75.0
81.6
73 .0
77.9
83.8
66.9
75.7
73 .7
68.1
68.4
72.3
64.7
69.1
50.4
68.4
76 . 0
76. 1
70.8
70.1
73.1
66.2
70 .0
52 . 5
69 .8
78.3
78.3
72 . 9
71.9
74.8
67 . 1
69.3
53.1
71. 1
80.4
78 .7
74.3
74 . 7
76.0
68.6
70 .6
54.0
69.6
73.0
80.7
67 .7
70 . 4
72.1
74.8
83.4
70.9
72.6
73.6
75 .6
8 9.9
72 . 2
74 .7
75.8
77 .5
92 .5
73.7
76.6
76.8
76.8
74 . 9
80.8
65.1
6 7 .0
65.5
6 7. 3
64.5
60. 7
71.9
68.3
69.6
68 .5
70. 9
66.0
64.0
75 . 3
71.2
71.7
70. 8
73.2
67.9
67.1
77.3
73.0
73.5
71.5
75.0
66.8
69.5
79 . 4
73. 9
74.2
73 .3
76.2
69. 8
71.4
80.8
73 . 4
76.4
74. 7
76 . 9
70 . 9
72 .2
82 . 0
47.3
53 .5
56. 8
59 .7
62 . 0
62.0
64 .8
64.1
70.5
76. 2
79.7
82 . 2
83.7
85.1
Sapelo Sound
l
2
3
4
5
6
7
8
9
10
ll
12
13
14
15
Chri st:mas Creek
1
2
3
4
5
6
7
24.9
73
UPD 8328{10-87