I
ABUNDANCE,MOVEMENTS,
MOVEMENTS, AND
AND FEEDING HABITS OF
ABUMANCE,
VITLILINA, AT
AT
SEALS,PHOCA
HARBOR SEALS,
PHOCA VITULINA,
AND TILLAMOOK BAYS, OREGON
NETARTS AND
-
ROBIN F.
F. BROWN
BROWN AND
AND BRUCE
BRUCE R.
ROBIN
R. MATh'
MATE'
(.Q
,-_
t
ABSTRACT
Patternsof
ofseasonal
seasonalabundance
abundanceof
ofharbor
harborseals
sealsatatNetarts
Netartsand
andTillamook
TillamookBays,
Bays,Oregon,
Oregon,were
were documented
documentedby
by
Patterns
recording numbers
numbers of
of seals hauling out on tidally exposed
at
recording
exposed sand flats in both bays. Harbor seal abundance at
pupping (May-June)
(May-June) and
and molting
molting (August)
(August) periods,
periods, while
while peak abundance
abundance atat
Tillamook Bay peaked during pupping
heta, to a
NetartsBay
Baycoincided
coincidedwith
with the
the annual
annual return
return(October-November)
(October-November)ofofchum
chumsalmon,
salmon,Oncorhynchus
Oncorhynchus keta,
Netarts
hatchery on Whiskey
losses of
Whiskey Creek.
Creek. Observations
Observations of seals
seals preying
preying on
on adult
adult salmon
salmon resulted
resulted in estimated losses
6.1, 7.2, and
and 1.5%
1.5% of the total chum
chu~ returns for 1978, 1979, and 1980, respectively, due
6.1,7.2,
due to
to seal
seal predation
predation in
in
the Whiskey Creek area. Other
Other prey
prey species
speciesof
of harbor
harborseals
sealsat
atNetarts
NetartsBay
Baywere
wereidentified
identifiedby
bythe
therecovery
recoveryof
of
the
hexapterus,
prey hard parts
parts from
from seal
seal feces collected on haul-out areas,
areas. The Pacific sand Iance,Amnodytes
Jance,Ammo dytes hexapterus.
prey item.
item. Ten
Ten species
species of
of flatfish
flatfish (Order
(Order Pleuronectiformes)
Pleuronectiformes) were
were idenidenwas the most frequently identified prey
tified as harbor
harbor seal
seal prey
prey with
with five
five species
species (Parophrys
(Parophrys uetulus,
uetulus, Glyptocephalus
Glyptocephalus zachirus,
sor·
rifled
zachirus, Citharichthys sorexilis) ranking
ranking among
among the
the seven most frequently occurring
LyopseUa exilis)
occurring food
food
didus,Microstomus pacific us, and Lyopsetta
didus,Microstonsuspacificus,
items. In general, benthic and
and epibenthic
epibenthic fish
fish appeared
appeared to be important
important in the harbor seal diet. Distributions.
Distributions,
abundances, and estimated sizes of identified prey species
indicated that harbor
harbor seals
seals had
had fed
fed both
both in
in
abundances,
species indicated
Netarts Bay
Bay and in the nearshore ocean. Movements of radio-tagged
Netarts
radio-tagged harbor seals
seals between
between Netarts Bay and
% of
. Tagged harbor
Tillamook Bay were
were common
common (45.4
(45.4%
oftagged
taggedseals
sealsmade
madeatatleast
least one
onemove
movebetween
betweenbays)
bays).Tagged
estuaries and
and one
one coastal
coastal haul-out
haul-out area, ranging from
seals
seals frequented at least four different estuaries
from 25
25 to
to 550
550 km
km
from the tagging area.
Pacific harbor
harbor seal,
seal, Phoca
Phoca vitulina
vitulina richardsi
richardsi
The Pacific
(Shaughnessy and Fay 1977), aa year-round
year-round resident
of Oregon,
Oregon, is
commonly found
along
is commonly
found in
in estuaries, along
shorelines, and on nearshore
nearshore rocky
rocky islets.
islets.
isolated shorelines,
Before protection
protection was afforded the harbor
harbor seal by the
Marine Mammal Protection
Act of 1972, a combinaProtection Act
State of
of Oregon
Oregon and
tion of bounties offered by the State
from commercial
commercial and sport
sport
traditional harassment from
fishermen kept
kept these
these animals
animals atatrelatively
relativelylow
low numnumbers in most
and rivers. During
During the
the years
years followfollowbers
most bays and
ing 1972, the
the numbers
numbers of harbor
harbor seals seen in many of
of
Oregon's
increase. At
Oregon's estuaries
estuaries began
began to
to increase.
At Netarts
Bay, where
of Fisheries
Fisheries and
and Wildlife
Wildlife
where the
the Department
Department of
at Oregon State University
University operated a hatchery
hatchery for
for
chum salmon, Oncorhynchus
Oncorhynchus keta,
keta, aa similar increase
increase
in harbor
harbor seal
seal abundance
abundancewas
was observed
observed(Lannan2).
(Lannan2 ) .
A
primary objective
hatchery program
program at
A primary
objective of
of the hatchery
Netarts
Baywas
was to
tore
build the
the vestigial
vestigial stock
stockof
of chum
Netarts Bay
rebuild
returnsannually
annuallyto
to Whiskey
Whiskey Creek
Creek (Lansalmon that
that returns
nan 1975). Each year, during the months of October
predation by
by harbor
harbor seals
seals on
on returnreturnand November, predation
ing adult chum salmon was
was observed
observed near the mouth
'School of Oceanography, Oregon State
State University,
University, Marine
Marine SciSciOR 97365.
97365.
ence Center, Newport, OR
'J.
ZJ,E.
E.Lannan,
Lannan,Department
Department of Fisheries
Fisheries and Wildlife, Oregon
Oregon State
State
Center, Newport,
Newport, OR
OR 97365,
97365, pers.
pers. comcom·
University, Marine Science Center,
April1977.
mun. April
1977.
accepted October
October 1982.
1982.
Manuscript accepted
VOL. 81,
FISHERY BULLETIN: VOL.
81, NO.2,
NO.2, 1983.
staff. Our
Our study
studyof
of harharof Whiskey Creek by hatchery
hatchery staff.
bor seals in this
this area
area was
wasinitiated
initiated to
to learn
learn how
howharbor
harbor
seals use Netarts Bay and its resources. The specific
objectives
1) document
document the
objectives of
of this
this study
study were
were to
to 1)
seasonal
(adults and
and
seasonal abundance
abundance of
of harbor
harbor seals
seals (adults
pups)
hauling out in Netarts Bay
Bay and
and in
in Tillamook
Tillamook
pups) hauling
estuaryalso
also used
usedby
by harbor
harborseals;
seals;2)
2)
Bay, the nearest
nearest estuary
examine possible
possible movements
movements of
of harbor
harbor seals
seals beexamine
tween
tween Netarts and Tillamook Bays;
Bays; 3)
3) estimate
estimate the
the
by harharlevel
chum salmon
salmon by
level of
of predation
predation on returning chum
bor seals near
near the
the hatchery;
hatchery; and
and 4)
4) identify
identify other
other food
bor
items of harbor seals using Netarts
Netarts Bay.
Bay.
STUDY AREA
AREA AND
AND METHODS
METHODS
Netarts and
and Tillamook
Tillamook Bays
located on the
the
Netarts
Bays are
are located
Oregon coast, 110 and 95
95 km
km south of
of the
northern Oregon
Columbia
seal
Columbia River,
River, respectively
respectively (Fig.
(Fig. 1).
1). Harbor seal
abundance in the bays
bays was
was monitored by
by recording
the number
number of
of animals
animals hauled out on sand
sand flats
flats exexduring low
low tides. All counts were made from
posed during
the shoreline using a 45X spotting scope. The numnumbers of harbor seals were recorded at
at aa minimum
minimum of
twice per month from May 1977 through November
1981
Bay and from
from June 1978
1978 through
through
1981 at Netarts Bay
November 1981 at Tillamook Bay.
Bay. A
Astudent's
student's t-test
was
differences in
in obobwas used
used to ascertain statistical differences
291
FISHERY BULLETIN: VOL. 81
81., NO.
NO.22
GRAYS
HARBOR
W
l.~ APA
WLLAPA
WASHINGTON
BAY
TILLAMOOK
z
<[
BAY
COLUMBIA
RIVER
ILl
u
0o
TILLAMOOK
T1LLAMOOK BAY..
NETARTS BAY
PORTLAND
TILLAMOOB
0
OREGON
OREGON
:-
-
WHALE
:.
NETARTS
NETARTS
COVE
YAQ4JINA
NEWPORT
BAY
0.8 U FISHERCES
RESEARCH STATIOW
(WHISKEY CREEK)
1
N
I
WINCHESTER
BAY . · ·•· •
BAY
--·' .
0
100
ioo
60
20
II
II
I
I
km
II
II
t
N
0o
I
5
I
I
I
I
I
km
II
FIGURE 1.Harbor
1.-Harbor
seal
study
area
Netartsand
andTillaniook
TillamookBays
Bayson
onthe
thenorthern
northernOregon
Oregoncoast.
coast.
seal
study
area
ofofNetarts
served abundances between years.
To examine movements,
movements, 12
12 harbor seals were capcaptured
in August and October
October 1978,
1978, using
using aa modified
modified
tured in
gill net (Brown
(Brown 1981),
1981), and tagged
tagged with
with numbered
numbered
gill
radio transmitters
transmitters (Telonics
(Telonics
plastic cattle tags and radio
3
Inc., Mesa, Ariz.
). The
Ariz.3).
Theplastic
plastic tags
tags were
were placed
placed in the
the
webbing of each hind flipper of all
all harbor seals, and
radio
were attached
anklet to aa hind
hind
radio tags
tags were
attached by
by an
an anidet
appendage of 11 seals.
appendage
seals. Each
Each transmitter
transmitter package (84
g) was
between148
148
g)
wasoperated
operated on a discrete
discrete frequency
frequency between
149 MHz,
MHz, allowing
allowing identification of
of individual
individual
and 149
animals. Movements
were
animals.
Movements of
of tagged
tagged harbor
harbor seals were
documented by identification of plastic tags
tags and by
radio signals
signals from
from seals
seals carrying
carrying
reception
reception of
of radio
transmitters. Radio
Radio signals
signals could be received
received only
only
animals were
were out
out of
of the
the water.
water.All
All haulwhen tagged animals
sites in
in Netarts
Netartsand
andTillamook
TillamookBays
Bayswere
werecheckcheckout sites
visually and
radio for
for tagged
tagged harbor
harbor seals
seals
ed visually
and by radio
'Reference
names does not
not imply
imply endorsement
endorsement by the
'Reference to trade names
Fisheries Service,
Service, NOAA.
NOAA.
National Marine Fisheries
292
during a minimum of seven low
during
lowtides
tides per
per month,
month, from
1979. An
An additional
additional 36
36
August 1978 through June 1979.
harbor seals were tagged
Netarts and
and
harbor
tagged and
andreleased
released at
atNetarts
Tillamook Bays in 1979,1980,
1979, 1980, and
and 1981.
1981. Movements
Movements
TillamookBays
harbor seals
seals were
were not monitored on
on a reguof these harbor
lar basis.
preying on chum
chum salmon
sahnon near the
the
Harbor seals preying
mouth of Whiskey
Whiskey Creek
Creek were
were observed
observed during
during
mouth
daylight hours from a 4 m
m high
highblind
blind using
using binoculars
binoculars
and a spotting scope. The observation area included
25m
the lower 25
m of the creek and a semicircular area
at the
the creek
creek mouth
mouth and
and extending
extending out
out onto
centered at
centered
at aa radius
radius of
of about
about200
200 m.
m. Whiskey
Whiskey Creek
Creek
the bay at
Netarts Bay
Bay in
in its
its shallow
shallow upper reaches so
so
enters Netarts
thatlow
low tides prevent
chum salmon from returning
that
prevent chum
returning to
hatchery. Only
Only when the rising tide has
has flooded
flooded
the hatchery.
can chum
chum salmon
sahnon approach
this area can
approach and
and enter the
creek. Harbor
seals use
use this
this area
areaonly
only when the tide
tide is
Harbor seals
high enough
enough to
to allow
them deepwater
high
allow them
deepwater access
access or
averaged over
2.5 h
averaged
over all
all observation
observation periods;
periods, about
about 2.5
after the
the peak
peakof
of each
each high
high tide.
tide.
before and after
.
ondMATE:
OF HARBOR
HARBOR SEALS
SEALS
BROWN and
MATE: ABUNDANCE, MOVEMENTS OF
The numbers
numbers of chum salmon taken
taken by
by harbor
harbor seals
in the Whiskey
Whiskey Creek area were estimated by
by mulmultiplying
tiplying observed
observed predation
predation rates
rates by
by the
the estimated
number
area. The
number of
of hours
hours that
that seals
seals fed
fed in
in this area.
observed
was the number of chum
chum
observed predation
predation rate
rate was
salmon seen taken by harbor seals per
per hour of observation.
vation. The
The number
number of hours
hours that
that harbor seals could
near Whiskey Creek was estimated
to be
be 55 h per
per
feed near
estimated to
high
high tide
tide over
over the
the total number of high
high tides during
each
impact on the chum
chum
each chum
chum salmon
salmon run.
run. The
The impact
salmon
seals
salmon return
return through
through predation
predation by harbor seals
as:
near Whiskey Creek was
was then calculated as:
Percent
of total
total salmon
salmon taken
taken by
by seals
seals =
Percent of
low abundance
winter and
and early
early
cycle of
cycle
of low
abundance in
in late winter
spring, an increase through late spring and summer
peak in
in late
late fall-early
fall-early winter,
winter, followed
followed by
by aa midmidto a peak
winter decline.
decline. With
exception of 1977,
1977, the
the
winter
With the
the exception
highest annual
annual counts
counts were
were made
made during
during the
the month
monthof
of
highest
November (Fig. 2).
2). Seasonal
Seasonal numbers
numbers of harbor
harbor seals
hauled out
out in Tillamook Bay showed a general trend
of peak abundance
abundance during
during the
the spring and summer
months with relatively
relatively lower
lowernumbers
numbers at
at other
other times
of the year (Fig.
(Fig. 3).
An increase in the use of Netarts
Netarts Bay haul-out areas
was
was observed
observed over
over the
the latter
latter part of the study period
estimated
taken by
estimated no.
no. of
of salmon
salmon taken
by seals
seals x
X 100
100
estimated no.
no. salmon
total no. salmon
taken at hatchery +
+ taken by seals
Other food items of harbor
harbor seals using Netarts
Netarts Bay
were
from
were identified
identified by
by prey
prey hard
hard parts recovered from
feces collected on haul-out areas. Harbor
seals were
were
Harbor seals
not purposely
purposely disturbed
disturbed to gather
gather feces.
feces. Samples
Samples
were collected
collected on
on an
anopportunistic
opportunistic basis when harbor
harbor
seals left the haul-out areas before the
the flooding
flooding tide
had covered them.
them. Fecal samples were
were frozen
frozen after
after
collection and later thawed and
and emulsified
emulsified in either
either a
5%
buffered Formalin
Formalin solution
solution or 70%
70% isopropyl
isopropyl
5% buffered
alcohol
alcohol for
for aa period
period of
of 24
24 h.
h. Prey
Prey hard
hard parts were
removed
removed and stored dry after samples were washed
mm sieve.
with water over a 0.5 mm
the size
size of
of fish taken by harbor seals,
To estimate the
otoliths removed from fecal samples were measured
otoliths
under aa dissecting
dissecting microscope
microscope with an ocular
ocular mimicrometer and,
and, when
crometer
when possible,
possible, compared
compared with
with the
of otoliths
otoliths from fish of
of known sizes. Data
on
lengths of
Data on
length of
of fish
fish were
were
otolith length versus standard length
gathered from available specimens in collections at
the School of Oceanography
Oceanography at Oregon State
State University. A simple
simple linear regression
regression was
was performed
sity.
performed on
these data. Standard
Standardbody
bodylengths
lengths(SL)
(SL) of
offish
fish conconwere estimated for 12 prey
sumed by harbor seals were
species. A subsample
subsample of 621 Pacific sand lance,Ammodytes hexapterus,
modytes
hexapterus, otoliths
(20.9%
otoliths (2
0.9% of
ofthe
thetotal
total numnumber recovered)
recovered) from
from 11
11 randomly
randomly selected
selected fecal
fecal
samples (29.7%
(29.7% of
samples that
that contained
contained
samples
of those
those samples
Pacific sand lance otoliths)
otoliths) was
wasmeasured
measured to estimate
estimate
the size range
range 6f
of this
this prey species.
(Fig.
(Fig. 2).
2).Numbers
Numbers of
of harbor
harbor seals
seals hauled out during
period of peak annual abundance (Septemberthe period
November) were
November)
were significantly
significantlygreater
greater inin the
the years
1980-81 than during
during 1978-79
1978-79 (P<0.05).
(P< 0.05) . Similarly,
Similarly,
1980-81
throughApril
April (annual
(annuallow
abundance)
from February
February through
low abundance)
a significantly
significantly greater
greater number
number of harbor
harbor seals hauled
during 1980-81
1980-81 than during
during 1978-79
1978-79 (P<0.05).
(P<0.05).
out during
There was
was no apparent
change in
in numbers
numbers of
of harbor
harbor
There
apparent change
seals
using Tillamook
Tillamook Bay
study period
period
seals using
Bay over
over the
the study
(Fig. 3).
3) .
InN
etarts and
and Tillamook
Tillamook Bays,
Bays, pupping
pupping began
began durdurIn
Netarts
first 22 wk
wkofMay
inthe
thefirst
first22wk
wk of
of
ing the
the first
of May and peaked
peaked in
June. Molting
Molting seals were first observed in late July
June.
the process
process was
was generally
generally complete
complete for
for all
all
and the
animals
animals by
by early
early September.
September. Percentages
Percentages of pups
of harbor
harbor seals hauled out in the study
among groups of
peak of the pupping
pupping periods
periods of
of 1978197 8area during the peak
81 ranged
ranged from
from 16.3
16.3 to 21.4%
21.4 % at Netarts Bay
Bay and
17.8 % at Tillamook Bay (Table 1).
1) . Pup
from 14.2 to 17.8%
counts
counts at
at Netarts
NetartsBay
Baywere
were made
made at
atclose
close range
range and
and itit
unlikely that any
any newborn
newborn pups
pups were
were missed.
missed.
is unlikely
However, counts made from aerial photographs
have
photographs have
shown that ground
ground censuses
censuses at
at Tillamook
Tillamook Bay
Bay ununshown
derestimated pup
abundance and
derestimated
pup abundance
and that actual
actual pup
pup
of the study
study area
area may
may have
have
percentages in this part of
closer to22.4%
22.4 %in
in 1980
1980 and
and 24.3%
24.3 % in 1981 (Jefbeen closerto
fries') . Similar
fries4).
Similarpercentages
percentages were
were reported
reported for harbor
British Columbia
Columbia (20.0%)
(20.0%) by
by Bigg
Bigg (1969),
(1969) , in
in
seals in British
northern
Sound (13.2
(13.2 to
to 19.4%)
19.4%) by
by CalamCalamnorthern Puget Sound
5
bokidis et al.,
al.,5 and in the Columbia
Columbia River and adja-
RESULTS AND
AND DISCUSSION
DISCUSSION
Seasonal Haul-Out
Haul-Out Patterns
Patterns
Examination
monthly counts
counts of harbor
harbor
Examination of
of mean
mean monthly
Netarts Bay
Bay revealed
revealed aa seasonal
seasonal
seals hauled out in Netarts
'S. J. Jeffries,
Jeffries, Washington
Washington State
State Department
Departmentof
ofGame,
Game, Marine
Marine
4S.
Mammal Project, 53 Portway
Portway St.,
St., Astoria, OR 97103,
97103, pers.
pers. commun.
August 1982.
' Calambokidis, J.,
J ., K.
K. Bowman,
Bowman, S. Carter, J.
J. Cubbage,
Cubbage, P.
P. Dawson,
'Calambokidis,
Skidmore, and B.
B. Taylor.
Taylor.
T. Fleischner,
Fleischner, J.
J . Schuett-Hames,
Schuett-Hames, J. Skidmore,
197 8. Chlorinated
Chlorinated hydrocarbon
hydrocarbon concenUations
concentrations and the
the ecology
ecology
1978.
293
F1SHERY
BULLETIN:VOL.
VOL.81.
81 , NO.2
FISHERY BULLETIN:
NO.2
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1977
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979
1980
1981
1981
FIGURE
FIGURE
34
66
89
78
F
32
26
41
41
94
M
M
32
23
69
95
A
26
30
74
74
06
106
M
47
41
41
45
64
100
00
J
54
70
46
,J
74
86
103
101
101
s
A
73
99
S
110
110
100
tOO
84
128
128
100
123
161
161
121
121
0
107
107
115
115
103
138
138
154
N
109
09
127
127
107
107
167
67
205
0
55
97
85
83
83
2.-Seasonalabundance
harborseals
sealsatatNetarts
Netarts
Bay,Oreg.,
Oreg.,shown
shownby
byaa plot
plotof
of monthly mean numbers
2.Seasonal abundance ofof
harbor
Bay,
numbers of
of seals
seals hauled
hauledout
outininthe
the
Listedatatbottom
bottomofoffigure
figureare
aremonthly
monthlymaximum
maximum numbers
numbersof
ofseals
sealsobserved
observedon
onhaul-out
haul-outareas.
areas.
bay. Listed
cent waters, including
including Netarts
Tillamook Bays
Netarts and Tillamook
~),
et a16
al. 6
-(-1.&'%),by
byEveritt
Everitt et
Seasonal
numbers of harbor
harbor seals
seals
Seasonal increases
increases in
in numbers
hauled
many areas are
are common
common during
during the
hauled out in many
pupping and molting
molting periods
periods (Johnson and Jeffries
1977;7 ; Everitt
1977
Everitt et
et aL
al. 1979;
1979; Johnson
Johnson and
and Johnson
Johnson
1979;8 ; Stewart
1979
Stewart 1981).
1981). Prior
Prior to
to giving
giving birth,
birth, female
female
harbor seals may seek out
out areas
areas preferred
preferred for parturition and nursing.
nursing. Roffe
Roffe (1981)
(1981) described
dedescribed the departure
harbor seals
seals from
from the
the Rogue
Rogue River
River
parture of harbor
by the end
end of
of April,
April, presumably
presumably to use sites more
and behavior of harbor
The Everand
harbor seals
seals in
inWashington
WashingtonState
Statewaters.
waters. The
WA 98505,
98505, 121 p.
green State College,
College, Olympia, WA
p.
~Eve.
'Eventt,
ritt,R.
R.D.,
D., R.
R. J.
J .Beach.
Beach, A.
A. C. Geiger, S.
S. JJ.. Jeffries,
Jeffries. and S.
D.
s. I).
Treacy,
l 9 1. Marine
Marine mammal-fisheries
mammal-fisheries interactions
CoTreacy, 1981.
interactions on
on the Columbia River
River and adjacent
adjacent waters,
waters, 1980.
1980. IFirsti
[First) Annual
Annual Report
Report
lumbia
Wash. State
Dep. Game
March 1,
March
1, 1980
1980 to
to October 31,
31, 1980.
1980. Waah.
State Dep.
Game to
to
Northwest and Alaska Fish. Cenl,
Nat!. Mar.
Mar. Mammal
Mammal Lab.,
Lab., Nati.
Nat!.
Cent, NatL
NOAA, Seattle,
WA 98115, 109 p.
Mar. Fish. Serv., NOAA.
Seattle, WA
L, and S.
S.J,J.
Jeffriea.1977.
1977. Population evaluation
evaluationof
M. L.,
. Jeffries.
of
''Johnson,
Johnson, M.
the harbor seal (Phoca
(Phoca L'dulina
richardi)
uitulina.richardt) in the waters of the
the State
State of
Washington.
Report to
to the
the U.S.
U.S. Marine
Marine Mammal
Mammal CornCom·
Washington. Contract Report
mission,
C., 27
Technleallnformation
miaeion,Washington,
Washington,D.
D.C.,
27 p.
p. National Technical
Information
294
86
108
08
JJ
61
61
TABLE I.-Maximum
pupcounts,
counts,number
number of
of nonnonTABLE
1.Maximum pup
pup animals present
present during counts, and number of
expressed as a percentage of the
pups expressed
the total number
1980, and
animals present for the 1978,
1978, 1979,
1979, 1980,
of animals
1981
1981 harbor
harbor seal
seal pupping
pupping seasons
seasons at
at Netarts
Netsrtu and
Tillamook Bays, Oreg.
yea,
Year
1978
Pups
Pups
Pups
Non-pups
Non-pops
Netarta
Netarts
Tillamook Bay
Bay
Tillamook
63
381
14.2%
14.2%
Pups/to1ai(X1
00)
Pups/total
(X100)
16
15
55
21.4%
214%
1979
1979
Pups
Non-pups
Non.pups
Pups/ totai(X100)
Pups/total
(X100)
9
36
20.0\1\
20.0%
58
334
14.8%
14.8%
1980
Pups
Non-pups
Pups/ totai(X1
00)
Pups/total
(X100)
16
80
16.7%
55
254
17.8%
17.8%
1981
Pups
Non-pups
Non.pups
Pups/ total (X100)
Pups/total
(Xl 00)
15
15
77
16.3%
70
330
17.5%
17.5%
Service, 5285 Port
Port Royal
Royal road,
road, Springfield,
Springfield,VA
VA 22151
221~ 1
'Johnson,
tJohnson, B. W., and P. A.
A. Johnson.
Johnson. 1979.
1979. Population peaks during the molt in harbor seals.
at the
the
tag
seals. In
In Abstracts
Abstracts from
from presentations at
Third Biennial
Biennial Conference
Conferenceof
ofthe
the Biology
Biology of Marine Mammals, OcThird
7-11, 1979, Seattle, Wash., p.
31.
tober 7-11,
p.31.
BROWN and MATE: ABUNDANCE.
ABUNDANCE , MOVEMENTS
OF HARBOR
HARBOR SEALS
SEALS
MOVEMENTS OF
I
I
I
I
I
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1-
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400
(/)
U)
-J
<(
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••
-
- - - · 1979
......·
········+
1980
-·-·-0
1981
100 -
-
I
J
1978
978
1979
1980
1980
1981
1981
273
183
183
246
F
200
195
195
307
I
M
304
138
138
325
I
A
285
260
359
I
392
392
312
312
330
I
I
I
J
A
s
444
353
314
314
456
262
262
375
375
437
289
386
310
310
353
394
390
485
434
414
I
I
J
M
0
273
273
191
191
316
316
236
N
260
255
250
220
D
229
207
196
198
FIGURE 3.-Seasonal
abundance
harbor
seals
Tillamook
Bay,Oreg.,
Oreg.,shown
shownbybyaaplot
plotofofmonthly
monthlymean
meannumbers
numbersof
ofseals
sealshauled
hauledout
outin
inthe
the
FIGURf
3.Seasonal abundance
ofof
harbor
seals
at at
Tillamook
Bay,
Listedatatbottom
bottomofoffigure
figureare
aremonthly
monthlymaximum
maximum numbers
numbers of
of seals
sealsobserved
observedon
onhaul-out
haul-outareas.
areas.
bay. Listed
desirable
young. Beach
desirable for
for birth and care of young.
Beach et
et aP
al.9
identified females
females with
Grays Harbor
identified
with neonates
neonates in Grays
Tillamook Bay, Oreg.,
Oreg.,
and WillapaBay,
Wilapa Bay, Wash., and in
inTillamookBay,
(Jeffries
footnote 4)
4) that were tagged as pregnant
(Jeffries footnote
pregnant
pups were
were obobfemales in the Columbia
Columbia River.
River. No pups
females
served in
in the Rogue
Rogue River
River and
and very
very few were seen in
served
the Columbia
Columbia River. Peaks
Peaks in seasonal
seasonal abundances
abundances of
harbor seals
seals during
during the
the winter
winter months
months have
have been
been obobharbor
served in the
the Rogue
Rogue (Roffe
(Roffe 1981)
1981) and
and Columbia
Columbia
served
10
Rivers (Everitt and Jeffries
Jeffries'°),
), although
although this
this pattern
pattern
been less
less commonly
commonly reported.
has been
Local changes in
in harbor
harbor seal abundance may occur
in
availability of food
food
in response to variations in the availability
1944; Fisher 1952;
1952; Graybil
Graybill
(Scheffer
(Scheffer and
and Stipp
Slipp 1944;
1981). Beach
(footnote 9)
the
1981).
Beach et al.
al. (footnote
9) suggested
suggested that the
•Beach,
., A.A.C.C.Geiger,
9Beach,R.
R.J.J.,
Geiger,S.S.J .J.Jeffries,
Jeifries,and
andS.S.D.
D.Treacy.
Treacy. 1982.
Marine mammal-fisheries
mammal-fisheries interactions
interactions on
on the Columbia River and
adjacent
Second Annual Report
November 1,1980
1, 1980 to
to
adjacent waters, 1981.
1981. Second
ReportNovember
November 1,
1981. Wash.
Wash. State
StateDep.
Dep.Game
Game to Northwest and Alas1,1981.
Alas.
ka Fish. Cent., NatI.
Nat!. Mar. Mammal
Mammal Lab.,
Lab., NatL
Nat!. Mar. Fish. Serv.,
NOAA,
NOAA, Seattle,
Seattle, WA
WA 98115.
98115. NWAFC Proc. Rep.
Rep. 82-04, 186
186 p.
p.
••Everitt,
1979. Marine
Marinemammal
mammalinvesinves·
'°Evetitt, R. D., and S. J. Jeffries. 1979.
tigations
in
Washington
State.
In
Abstracts
from
presentations
at
tigations in Washington State.
from
at
the Third
Third Biennial
Biennial Conference
Conferenceof
ofthe
the Biology
Biology of
of Marine Mammals,
p. 18.
18.
7-11 , 1979,
1979, Seattle,
Seattle, Wash.,
Wash., p.
October 7-11,
winter
seal abundance
abundance in
winter increase
increase in
in harbor
harbor seal
in the
Columbia River occurred in response to the presence
presence
Thaleichthys paci{icus
, inin the
of eulachon, Thaleichthys
pacificus,
the river
river at
that
At NetartsBay,
Bay, the
the late
late fall
fall return
return of chum
that time. AtNetarts
the only
only regular
regular occurrence
occurrence of
of aa
salmon constitutes the
species in
in the Bay (Lannan footnote
2) . The
salmonid species
footnote 2).
coincidence of
the
coincidence
of peak
peak harbor seal abundance and the
this highly
highly seasonal
chum salmon
salmon run suggests that
that this
food
food source
source may
may have
have influenced
influenced harbor seal abunbay.
dance in the bay.
At Tillamook
Tillamook Bay,
seal
Bay, seasonal
seasonal peaks
peaks in
in harbor seal
and salmonid
salmonid abundance
abundance did
did not
notcoincide.
coincide.
numbers and
of harbor seals declined
declined to
to low
low annual
The numbers of
September through
through December
December while
while
levels
from September
levels from
Salmo gairdneri;
gairdneri ; chinook
chinook salmon,
salmon, OnOnsteelhead, Salmo
corhynchus
kisutch;
corhynchus tshawytscha;
tshawytscha; coho
coho salmon,
salmon, 00.. kisutch;
and chum salmon were
were passing
passing through the estuary
(Heckeroth 11 ).High
High counts
counts of
of harbor
harbor seals during the
(Heckeroth").
however, coincide with peaks in annual
summer did, however,
abundancesof
ofnorthern
northernanchovy,
anchovy,Engraulis
Engraulism.ordax;
mordax;
abundances
Heckeroth, Oregon
Oregon Department
Department of
of Fish
Fish and
andWildlife,
Wildlife, 6617
6617
"D. Heckeroth,
Officers
Officers Row,
Row, Tillamook,
Tillamook,OR
OR 97141,
97141, pers.
pers. commun.
commun. September
1978.
295
BULLETIN: VOL.
VOL. 81,
FISHERY BULLETIN:
81, NO.2
NO.2
surf smelt,
smelt,Hypomesu_s
Hypomesus pretiosus;
pretiosus; shiner
perch,
shiner perch,
Cymatogaster
herring, Clupea
Clupea
Cymatogaster aggregata;
aggregata; Pacific
Pacific herring,
English sole,
Parophrys
harengus
harengus pallasi;
pallasi; and
and English
sole, Parophrys
uetulus,
(Forsberg et
etaL'2).
al.12). All five
vetulus, in
in Tillamook Bay (Forsberg
five
species were
were identified
identified as prey of harbor
harbor seals using
Netarts Bay
Bay (see
(see results
results of
of fecal
fecal analysis)
analysis) and have
have
Netarts
been commonly
commonly reported
reported as food
food of harbor seals in
other areas (Pitcher
(Pitcher 1980a;
1980a; Bowlby
Bowlby 1981;
1981; Graybill
Graybill
1981;
et aL
al.
1981; Calambokidis
Calambokidis et
et al.
al. footnote
footnote 5; Beach et
footnote 9).
The differences
differences in
in seasonal
seasonal abundances
abundances of
of harbor
harbor
Netarts and
and Tifiamook
Tillamook Bays may be in part
seals at Netarts
related to the quality of habitat
habitat available for
forpupping
pupping
and nursing.
nursing. As
As in
in other
other areas
areas (Johnson and Jeffries
footnote 7),
7), harbor
harbor seals
seals at Netarts and
and Tillamook
Tillamook
footnote
sites within
within each
each bay during
during
Bays use more haul-out sites
the pupping season than at other times of the year.
Females
tend to
to form
form smaller,
smaller, more
more
Females with
with pups
pups tend
isolated groups,
groups, usually
usually in
in the
the more
more remote
remote parts
parts of
the estuaries. Tillamook
Tillamook Bay,
Bay, because
because of
of its
its greater
greater
size and
and more
more varied
varied bottom
bottom topography,
topography, has aa larger
larger
number
number of small
small channels
channels in
inthe
the upper
upper portions of the
the
bay.
bay. These
These channels rarely carry boat traffic and so
offer access
access to
to aasubstantially
substantially greater
greater number of prepreferred haul-out areas for female-pup pairs.
about 220 kin
km south of
of the
the tagging
tagging site (Winchester
Bay; Fig.
Fig. 1).
1). Single
Singleflipper
flipper tags
tags from
from two
two harbor
harbor seals
were
commercial fishing
were recovered
recovered during commercial
fishing operaoperations at two locations.
locations. One
One tag
tag was
wasfound
foundentangled
entangled in
in
gill net
a set herring giU
net in
inHumboldt
Humboldt Bay, Calif., 550
550 km
south of Netarts
Netarts Bay, and another tag was recovered
in aa scallop
5 km north of the
scallop drag
drag fishing
fishing operation
operation 775
tagging site.
longSimilar evidence of haul-out site fidelity and longdistance movements in harbor seals has been reported for other areas. A newborn pup, flipper-tagged on
Tugidak Island, Alaska, was
km
was found
found 33 yr
yr later
later <5 km
from
tagging site
site (Divinyi
(Divinyi 1971).
1971). Bonner and
and
from the tagging
dispersal of 55
55
Witthames
Witthames (1974)
(1974)reported
reported the
the dispersal
flipper-tagged juveniles
juveniles from the Wash, East
East Anglia,
England,
England, and
and their
their subsequent recovery
recovery up
up to
to 250
250
km
tagging area. Pitcher and
and McAllister
McAllister
km from
from the tagging
(1981)
in Alaska
Alaska and
(1981) radio-tagged
radio-tagged 35
35 harbor seals in
while 8 animals
animals had used
used haul-out
haul-out
reported
reported that while
km from the tagging
tagging
areas, ranging from
194 km
from 24 to 194
site, 23 were found
found only
hauling area where
where
only at the hauling
they were
were captured.
Movements of
of Tagged
Tagged Harbor
Harbor Seals
Movements
Predation on chum salmon by harbor seals was not
often
bay. Harbor seals
often seen
seen in
in other parts of the bay.
clearly
clearly took
took advantage
advantage of the concentrations of fish
that occurred
occurred as chum
chum salmon
salmon funneled
funneled from
from the
wide
the narrow
narrow mouth
mouth of
of Whiskey
Whiskey
wide open
open bay into the
Creek. Harbor seals preying on chum salmon in
in this
this
area took
took an estimated
estimated6.1,7.2,
6.1, 7.2,and
and1.5%
1.5%of
of the
the 1978,
1978,
area
1979, and 1980 returns, respectively (Table 2). It is
to note
note that
thatwhile
while the
the average
average number
number of
of
important to
feeding in
high tide was
was
harbor seals feeding
in this area per high
similar
similar from
from year
year to
to year,
year, the
the percent loss of each
Between
1979, 5 of 11
11
Between August
August 1978
1978 and
and March
March 1979,
radio-tagged harbor seals (45.4%)
(45.4%) made
made at least one
from Netarts
Netarts Bay to Tillamook
move from
Tillamook Bay (a distance
by sea of about
about 25 km).
kin). Three
Three of the
the five
five harbor
harbor seals
least one trip from Netarts
Netarts Bay to Tillamook
made at least
visited both bays at least
least twice
Bay and back, and one visited
(Fig. 4).
4). The
The propensity for movement
(Fig.
movement seemed to
vary among
among individuals.
individuals. One
One harbor seal
seal (no.
(no. 900)
900)
vary
moved between Netarts
Netarts and Tillamook Bays
Bays at
at least
least
its release.
release.
three times
times during
during the
the first
first 19
19 dd following
following its
(no. 580)
580) was
was resighted more often
Another animal (no.
and more regularly (27
(27 times in 9 mo)
mo) than
than any
any other
other
seal, yet was
was always
always found
found at
at Netarts
Netarts Bay.
seal,
Bay. Harbor
seals carrying
plastic tags
tags have
have been
been identified
seals
carrying plastic
identified at
Netarts Bay
Bay up to 29
29 mo
mo after
after tagging.
tagging.
Long-range movements
movements of
of harbor
harbor seals tagged in
Long-range
1979, 1980,
1980, and
and 1981
one harbor seal that
1981 include
include one
that
traveled
traveled 75
75 km
km south
south (Whale
(Whale Cove; Fig.
Fig. 1)
1) and
and later
later
returned to
returned
to Netarts
NetartsBay,
Bay, and
and another
anotheranimal
animal that
thatwas
out among
among a large group of harbor
hauled out
found hauled
harbor seals
"Forsherg,
and S.
Klug. 1977.
"Forsberg, B.
B. D., J. A.
A. Johnson,
Johnson, and
S. M. Klug.
1977. Identi.
Identitication, distribution,
fication,
distribution, and
andnotes
notesof
offood
food habits
habitsof
offish and
and shellfish
shellfish in
Tillamook Bay,
Bay, Oregon.
Oregon. Federal Aid Progress Reports, Fisheries,
ContractNo.
OregonDeContract
No. 14.16-0001-5456RBS,
14-16-000 1-5456RBS, Research
Research Section, Oregon
Department
of Fish and Wildlife,
Wildlife, 117
partment of
117 p.
p.
296
Predation on
on Chum
Chum Salmon at
Predation
Whiskey Creek
TABLE 2.
2.Estimatedimpacts
impactsonon1978,
1978,1979,
1979,and
and1980
1980chum
chum
Estimated
salmon
Bay, Oreg.
Oreg. through
salmon returns
returns at Netarts Bay,
through predation by
by harbor
seals in the Whiskey
Whiskey Creek area.
area
ObservatiOn
(days)
Observation hours
hours'1 (days)
Mean estimated no. seals
feeding/high tide
feeding/hrah
No. salmon seen taken
seals
by seals
No. salmon
salmon trapped
trapped following
following
observat ion periods
penods
Observation
Total
Total no. salmon trapped
Observed
Observed predation
predation rate
(salmon/hour)
(salmon/hoar)
Estimated
hours asals
seals fed
Estimated no.
no hours
fed
area during ,un
run
in area
Estimated no. salmon taken
taken
by seala
byssals
Percent
Percent of
of total return
taken by
by seals
seals(95%
(9596CC.L.)
taken
L.)
1
Observation
'Observation
1978
1978
1979
1979
1980
1980
44{11)
44)11)
76.5(15)
78.5(15)
91.6(28)
91.61281
5.0
5.0
4.1
4 .1
5.4
5.4
22
22
12
12
24
432
1,774
1.774
242
539
3,015
4,972
4.972
0 .5
0.5
0 .2
0.2
230
210
115
115
42
6.1(±4.9)
6.1
(±4.91
7,2(±5.5)
7.2(±5.5)
0 .3
0.3
255
255
76.5
76.5
1.5(±0.9)
1.61±0,9)
periods averaged
averaged 44.1
. 1 and
.2 to
.3 h
in duration
duration,
periods
and ranged
ranged from
from 11.2
to 77.3
hin
lll0
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I
I
I
AUG
AUG
SEP
OCT
NOV
DEC
DEC
JAN
FEB
MAR
APR
APR
(14)
(14)
(II)
(II)
(26)
(26)
(18)
('8)
(10)
(10)
( 7)
(7)
(8)
(B)
(9)
(9)
(7)
(7)
11978
978
FIG
URE 4.-Summary
radiosignal
signal receptions
r~ e.• ption s and
and visual
visual sightings
sight in g~ of
2
FIGum
4.Summary ofofradio
of 112
MAY
(8 )
(8)
JUN
(9)
(9)
1979
date appears
appears at left margin).
harbor seals
captured , tagged,
tagged, and
Bay, Oreg.
(taggmg date
margin) .
harbor
seals captured,
and released
released at
at Netarts Bay,
Oreg. (tagging
identification of tagged seals
Open and closed boxes
boxes represent
represent identification
seals at
at Netarts and Tillamook Bays,
Bays, respectively,
respectively. Figures
Figures in
inparentheses
parentheses under months are resighting efforts in
in number of haul-out
(low tides) per month that
that were
were checked
checked for
for tagged
tagged seals.
sea ls.
periods (low
1-.:J
<:0
-1
FISHERY BULLETIN;
NO.22
BULLETIN: VOL. 81, NO.
declined as the
the number
number of
of returning
returning chum
chum
return declined
3.-Fish species
species identified
identified as
as harbor
harbor
TABLE 3.-Fish
salmon increased. The
The hydrography
hydrography of
of this
this area
area may
may
set an
an upper
upper boundary
boundary on
on predation
predationby
bylimiting
limiting the
the
set
number of harbor seals that
that can
can occupy the area and
number
amount of
of time
time during
during which
which feeding
feeding can
can occur.
occur.
the amount
These estimates assume that
that predation
predation rates
rates were
were
day and
and night
night high
high tides.
tides. Night
Night
equal during both day
feeding by
as comcomfeeding
by harbor seals
seals has been reported as
mon behavior
behavior in many
many areas (Scheffer
(Scheffer and Slipp
Slipp
mon
1944;
1964; Boulva
Boulva and McLaren
McLaren 1979;
1979;
1944; Spalding
Spalding 1964;
to
Roffe 1981). Generally, more chum salmon return
return to
Netarts Bay
Bay hatchery
hatchery on high
high tides at
at night,
night,
the Netarts
resulting in a potential
at this time.
resulting
potential for greater
greater losses at
However, as visual
seals may
may be
be
However,
visual predators, harbor seals
less
successful at
at capturing
capturingfree-swimming
free-swimming chum
chum
less successful
salmon at night.
night. In the unlikely
unlikely event
event that
that no predation occurred at night, the estimated
losses would be
estimated losses
half those
those presented
presented in Table 2. Unrecorded feeding
events within the
the observation area were believed to
seals usually
usually bring
bring large
large fish,
fish,
be few since harbor seals
salmon, to
once during
during
such as salmon,
to the surface at least once
consumption. The
predation estimates presented
presented
consumption.
The predation
overall impact on the
here may underestimate the overall
since any
any predation
predation on
on salmon
salmon occurring
occurring in
return, since
parts of
of the
the bay
bay was
was not considered.
other parts
identification of prey
seal prey by recovery and identification
parts (otoliths
(otoliths and
and teeth)
teeth) from
from seal
seal fecal
fecal
hard parts
collected at Netarts
Netarts Bay,
Bay, Oreg.
Oreg. Prey
Prey
samples collected
by frequency
frequency of
of occurrence
occurrencein
in
items are
are ranked
ranked by
items
samples that
that contained
contained identifiable
identifiable hard
hard
95 samples
parts.
parts.The
Theminimum
I,Ilinimumnumber
numberof
ofeach
each species
speciesreprep·
resentedininthe
theentire
entirecollection
collection is presented.
presented
resented
Other Harbor Seal Prey Items
parts (fish
(fish otoliths and teeth)
Identifiable prey hard parts
were found
(63.3%) of
fecal
were
found in 95 (63.3%)
of 150
150 harbor seal fecal
samples
Bay from
from May
May 1977
1977
samples collected
collected at Netarts Bay
through August
1979. Teeth
Teethfrom
from hagfish (Eptatretus
August1979.
sp.)
of the arrowarrowsp.) were
were present
present in six samples; teeth
teeth of
tooth flounder, Atheresthes
Atheresthes stomias,
stomias, were
were found in
three samples;
samples; and
and 3,800
3,800 fish
fish otoliths
otoliths were
were rerethree
covered from
of at
at
from 91
91 samples,
samples, representing a total of
species (Table
(Table 3).
3). Since
Since the
the
least 27 different prey species
majority of those samples
samples containing
containing identifiable
identifiable
majority
prey
(91.5%) were
were collected during the
prey hard parts (91.5%)
months of August,
August,September,
September, and October, some of
the species listed in Table 3 may be only
only seasonally
seasonally
important
important in the diet of harbor
harbor seals in this
this area.
area. The
The
presence or absence of chum
chum salmon
salmon otoliths
otoliths in
in the
the
harbor seal feces
feces could not
not be
be documented,
documented, since attempts to
to collect
collect samples
samples during the chum
chum salmon
salmon
unsuccessful. The 12 prey species for
returns were unsuccessful.
which
which size
sizewas
wasestimated
estimated ranged
ranged from
from 40
40 to
to 280
280 mm
mm
SL (Table 4).
Otoliths
Pacific sand
lance, found
found in 37
37
Otoliths of
of the
the Pacific
sand lance,
(38.9%)
containing identifiable
identifiable
(38.9%)of
ofthe
the 95
95 samples containing
hard parts, were the most
most common
common in the collection.
A
minimum of
1,503 Pacific
Pacific sand
sand lance
lance was
was
A minimum
of 1,503
represented,
with a mean number
number per
per sample
sample of 40.6
represented, with
(range
(range of
of 1-338
1-338 per
per sample).
sample). These fish may have
298
298
Frequency
~
Specie$
Speciec
Ammodytes/tesapterus
hexapterus
Ammodytes
Pt~rophtys vetulus
vetulus
Psrophrys
Glyptocephalus zachirus
ech,,us
G/yptoc.ephaius
Citharichthys so,didus
sordidus
Cit/,arichthps
Leptocottus ai'matus
armatus
Leptocotfus
M icrostomus pacificus
Mic,ostomus
Lyopsetttt coil/s
exms
Lyopsetta
C/upelt h. pa//asi
pallasi
Clupea
Atlosmerus e/oogatus
e/ongatvs
AI/osme,uo
No.
No.
%
\16
37
37
30
30
25
25
17
16
16
16
11
11
88
38.9
31.6
31
.6
26.3
17.9
16.9
16.9
11,6
11.6
8.4
8.4
1.4
7.4
6.3
6 .3
5 .3
5.3
5.3
5 .3
5.3
4.2
4 .2
4.2
4 .2
4.2
4 .2
4.2
4 .2
4.2
4 .2
3.2
3 .2
3.2
3.2
2.1
2 .1
2.1
2.1
2.1
2 .1
2.1
2. 1
1.0
1 .0
1.0
1.0
1.0
1.0
1.0
1.0
7
Eptarrerus up.
sp.
Epiatretus
6
Sebastes op.
sp.
Sebasies
Microgadus p,00imus
proximus
Microgadus
5
5
5
Cvmatogaster
Cyrnatogaster aggregata
Hexagrammos decagrammus
Hexagrammos
Thaleichthys pacificus
pacificus
Thaleichrhys
Anoplopoma fimbria
Anop/opoma
Citharichthys stigmaeus
C,tharichrhys
Isopsetta
/sopsetta iso/epic
isolepis
Hypomesus pretiosus
pretiosus
Hypoflesus
Atheresthes stomias
Atheresi/ies
Pl• tichthys ste/lotus
stellatus
Plapchthys
Eflgr8i'IiS
Engraulis mordao
mordax
Psettichthys melanostictus
Psettichthys
Embiotocld junenifes
juveniles
£mbiatocid
$almo gairdneri
Sa/,nogeirdne
$pirinchus star/cal
starksi
Spirinchus
M erluccius productus
Merluccius
Radulinus asprellus
IISprellus
Rods/mao
Unidentified osrnerid
osmerid
Unidentified embiotocid
Unidentified pleuronectid
pleuronectid
Total
To tal
4
4
4
4
4
3
3
2
2
2
22
1
1
1
1
I
1
I
Minimum
no
no. fish
fish
1.903
1.503
126
126
79
79
53
54
39
16
16
22
10
10
66
20
20
66
24
24
6
11
14
20
6
5
8
3
1
44
2
7
1
1
1
1
2
1
11
2,048
2.048
been taken by harbor seals within Netarts Bay. In a
the icthyofauna of Netarts
Netarts Bay,
Bay, the
the
limited survey of the
size range
range of Pacific
Pacific sand lance
lance found
found by
by Howe
Howe
size
(1980) (60-140 mm SL)
SL) was
was similar
similar to
to that
that taken
taken by
present study
study (80-130
(80-130 mm
mm SL).
SL).
harbor seals in the present
The Pacific sand lance has been frequently reported as prey of
of harbor
harbor seals
seals in
in the
the northeastern
northeastern Pacific
foot(Scheffer and Sperry 1931; Calambokidis et al. footnote 5; Pitcher
Pitcher 11980a),
980a),but
buthas
hasnot
notbeen
beenidentified
identified as
as
a numerically
Pacific sand
numerically important
important prey
prey species. Pacific
of 387
387 harbor
harbor
lance otoliths were found in only 2.6% of
seal fecal
fecal samples
samples collected in Washington
Washington (Beach et
et
al.
al. footnote
footnote 9)
9) and in just
just 4.0% of296
of 296 samples
samples collected in Oregon (Graybill
(Graybill1981).
1981).
Ten species
species of flatfishes
Ten
flatfishes (Order
(Order Pleuronectiformes)
Pleuronectiformes)
were identified
identified as food
food of
of harbor
harbor seals
seals hauling
hauling out
out in
in
were
Netarts Bay.
Bay. Of
Of these
thesespecies,
species,five
five(Parophiysuetu(Parophrysvetulus, Glyptocephalus
zachirus, Citharichthys
lus,
Glyptocephalus zachirus,
Citharichthys sordisordi, Microstomus pacific
pacificus
and Lyopsetta exilis)
exilis) were
dus ,Microstomus
us,,andLyopsetta
found in 11.6%
more of the samples. Engeach found
11.6% or more
lish sole otoliths were found in 30 (31.6%)
(31.6 %) of the 95
fecal samples and ranked second
fecal
second only
only to the
the Pacific
Pacific
BROWN and MATE: ABUNDANCE,
OF HARBOR SEALS
SEALS
ABUNDANCE, MOVEMENTS
MOVEMENTS OF
TABLE
sizesof
of12
12 harbor
harborseal
seal prey
prey species
species based
based on
on the
the relationship between
between otolith length
TABLE4.-Estimated
4.Estimated sizes
(OL)
length (SL) of collected fish specimens.
(OL) and
and standard
standard length
specimens. Also given are the coefficient of determination
determination (r')
and the sample
sample sizes
sizes of
of otolitbs
otoliths from both the
the collected
collected fish
fish specimens
specimens and
and the
the fecal
fecal samples.
samples.
Estimated
Estimated prey
prey size
size
No
from
No. otoliths
otoliths trans
Species
S pesos
hexapterus
Ammodytes heaapferus
Parophrys
Pa,'oph,ys vetulus
eetulus
Glyptocephalus
Glyptocepha/us zachirus
zach/,us
Citharichthys
Citharichthys sordidus
said/duo
Leptoconus
armatus
Leptocotws a,'ntafus
Microstomus
Mic,-ostomus pacificus
pacifecus
Lyopsetta
exilis
Lyopsetta ee/I/s
Microgadus
Microgadus proximus
proeenus
Cymatogaster
Cyi-natogaster aggregata
aggregate
Citharichthys
stigmaeus
Citharichthysscigmaeus
Isopsetta
lsopseaa isolepis
Psettichthys
Psettichthys melanostictus
melanostictus
Regression
Regression
eQuation
equation
SL
SL== 25.0(0L)
25 0(OL)+52.2
+522
SL
SL== 33.3(0L)-1
33 3(OL)-1 7 7
SL
SL== 50.0(0L)-51
50 0(OL)-51 00
SL
5
SL==50.0(0L)-53
500(014-535
SL
SL = 33.3(0L)-43
33.3(014-4377
SL== 50.0(0L)-31
50.0(014-31 00
SL
SL
SL = 50.0(0L)-15.0
50.0(014-15.0
SL
4
SL==20.0(0L)-28
200(014-284
SL
4
SL = 20.0(0L)-10
20.0(014-104
SL
= 33.3(014-11.1
33.3(0L)-11 7
SL=
SL
= 33.3(0L)53
SL=
33.3(014 5.3
SL
50.O(OL)-44.5
SI. = SO.O(OL)-44.5
sand lance
lance by
by frequency
frequency of
of occurrence.
occurrence. However,
However,
English
fewer fish
fish (a
English sole
sole otoliths
otoliths represented far fewer
minimum of only 126, with
with aa mean
mean number
number of 4.2 and
a range
range of 1-38
1~38 per sample)
sample) than
than did those of the
Pacific sand lance. This observation may reflect differing
(e.g., schooling behavior in the
fering prey densities (e.g.,
Pacific sand lance) or variation
variation in
in the
the passage
passage rates of
otoliths from
from different species.
English
seals using
using Netarts
English sole
sole taken
taken by
by harbor
harbor seals
Bay
about 90%
90%
Bay ranged
ranged from
from 40
40 to 240 mm SL, but about
were
mm SL.
SL. Since
Since English
English sole
sole (juve(juvewere under 100 mm
were common
niles) ranging from 39 to 120 mm SL
SLwere
common in
Netarts Bay (Howe
(Howe 1980)
few under 100
1980) and very few
mm SL
SL were
in the nearby
mm
were found
found in
nearby coastal
coastal ocean
ocean
(Demory 1971),
1971), itit isis likely
likelythat
that harbor
harbor seals
seals fed
fed on
(Demory
most of these fish within
within the bay.
bay. In contrast, Morejohn et
et al.'3
al. 13 found harbor
seals hauling
hauling out
outin
in E
Elkhorn
john
harbor seals
lkhorn
slough,
slough, Calif.,
Calif., had
had taken primarily larger (120-320
mm
mm SL)
SL) English sole
sole from
from over
over the
the oceanic shelves,
rathe.
smaller (20-140 mm SL)
ratherr than smaller
SL) sole
sole that were
widely
widely distributed throughout the
the slough.
slough.
Rex,
Rex, Dover,
Dover, and
imd slender
slendersole
sole(Glyptocephalus
(Glyptocephalus
exMicrostomus
zachirus, Micros
tomus pacificus,
pacificus, and Lyopsetta exilis), ranking
ilis),
ranking third,
third, sixth,
sixth, and seventh, respectively,
by
by frequency
frequency of
of occurrence
occurrence in
in the
the harbor seal fecal
fecal
samples (Table 3), were not found in Netarts
Bay by
by
Netarts Bay
Howe
Howe (1980).
(1980).Demory
Demory(1971)
(1971)found
foundsmall
small(:::;180
(180 mm
SL) rex,
10,
rex, Dover,
Dover, and
and slender
slender sole in
in no
noless
lessthan20,
than 20,10,
and 30 fathoms
These fish
and
fathoms of water,
water, respectively.
respectively. These
fish
species, and the few
few larger English sole, were most
species,
likely
Bay.
likely taken
taken by
by harbor
harbor seals
seals outside
outside of Netarts
Netarts Bay.
Demory (1971)
(1971) also
also found
found little
little separation
separation by depth
of
large and small
small flatfish
flatfish of the
the same
same species.
species.
of large
taken some
some larger
larger fish,
fish,
Although harbor
Although
harbor seals had taken
13
Morejohn, G.
G. V.,
V., J.
Hazvey, R.
R. C. Helm,
Helm, and J. L.
L. Cross.
Cross.
"Morejohn,
J. T. Harvey,
1979. Feeding
Feeding habits
habits of
of harbor
harbor seals,
seals, Phoca
Phoca uitulina,
vitulina, in
in Elkhorn
Elkhorn
1979.
Slough, Monterey
Bay, California.
Unpubl manuscr., 30
Oregon
MontereyBay,
California. UnpubL
30 p.
p. Oregon
Science Center, Newport,
Newport, OR
OR 97365.
97365.
State University,
University, Marine Science
,,r
0096
98
00 98
0096
96
0 .86
0,86
0
,96
0.96
094
0
94
0.96
0 98
0098
98
00.92
.92
096
0,96
00.94
,94
Collected
Collected
specimens
5
81
81
78
46
14
45
47
61
61
34
61
61
44
14
Fecal
Fesal
samples
samples
621
140
113
74
85
62
21
21
8
31
29
10
2
(S
L,mm)
(SLmm(
Range
flange
Mean
80.130
80·130
40·240
40-240
95
70
165
165
60
110
110
50·260
50280
40· 215
40-215
40·210
40-210
70·21 0
70-210
80-205
60·205
40·230
40-230
65·110
65110
50·100
50-100
70·260
70-260
100· 180
100-180
150
135
140
85
65
180
140
they may have selected primarily
primarily for
for rex, Dover, and
slender sole
sole under
under 200 mm SL.
Flatfishes
Flatfishes (Order Pleuronectiformes)
Pleuronectiformes) have
have been
been a
frequently
frequently reported prey of harbor seals (Imler and
1947; Morejohn
Morejohn eta!.
footnote 13;
13; Pitcher
Sarber 1947;
et al. footnote
1980a;
1980a; Bowlby
Bowlby 1981)
1981) and
and aa numerically
numerically important
group. Scheffer and Sperry (1931)
(1931) identified flatfish
group.
28.4 % of
79 harbor seal
seal stomachs
stomachs collected
collected in
in
in 28.4%
of 79
Washington.
Washington.Beach
Beachetet a!.
al. (footnote
(footnote 9)
9) reported
reported 9
species in
in 27.1%
27.1 % of 387 seal fecal
Pleuronectiforme species
samples collected
collected in
in the
the Columbia
Columbia River
River and
and
samples
southwesternWashington.
Washington.Gray
Graybill ((1981)
1981) identified
southwestern
identified
27 %of
ofall
all fish
fish
species, representing
representing27%
12 pleuronectid
pleuronectid species,
identified
296 seal
seal fecal
fecal samples
samples collected
collected in
identified in
in 296
southern Oregon.
Oregon.
There
There are
are limitations
limitationstotothe
theutility
utilityofoffeces
fecescolleccollecpartidentification
identification in
in the
the analysis
analysis
tion and prey hard part
of
feeding habits.
relative importance
importance of
of difdifof feeding
habits. The relative
ferent prey in the diet may be biased if the ratio be(i.e., otoliths and
tween consumption
consumption of
tween
of the
the head (i.e.,
teeth) and the body
body is
is not
not the
the same
same for
for all
all species.
species.
Some observations
heads of
of large
large
Some
observations suggest
suggest that the heads
fish, such
such as salmon, may not be consumed
often as
consumed as often
those
smaller ones
ones (Scheffer
(Scheffer and Slipp
Slipp 1944;
1944;
those of smaller
Boulva
McLaren 1979;
1979; Pitcher 1980b;
1980b; Roffe
Roffe
Boulva and
and McLaren
at Netarts
NetartsBay
Bay have
have occasionally
1981). Harbor
Harbor seals at
been
observed consuming
consuming heads
adult chum
chum
been observed
heads of
of adult
salmon (average weight 4.5 kg).
kg). Thus
Thus they
they are able to
swallow
swallowfish
fish of
of considerably
considerably larger
larger size
size than
than those
identified from the otolith collection.
collection. The
The magnitude
magnitude
not known.
known.
bias is
is not
of this potential bias
Ot her sources of bias in the relative importance of
Other
food items included variation in rates of
of
identified food
digestion or passage
passage through
through the
the gastrointestinal
gastrointestinal
digestion
of hard
hard parts
parts from
from different
different prey
prey species
species
tract of
1980b). Variation
Variation in
in the amount
amount of
oftime
be(Pitcher 1980b).
(Pitcher
time between seal feeding and hauling out may
may have
haveresulted
resulted
in the otoliths of some species being eliminated
eliminated in the
water. Prey items that lack
lack resistant
resistant hard
hard parts
partswill
will
water.
299
FISHERY
NO.22
FISHERYBULLETIN:
BULLETIN:VOL.
VOL.81,
81 , NO.
be identified.
identified. Even
Even in the
the presence
presence of
of such
such
not be
limitations, feces collection and
and prey hard part idencan provide useful
useful information
information on
on the
the prey
prey
tification can
species being
being used
used by
by seals
seals (Pitcher
(Pitcher1980b).
1980b).
SUMMARY AND
AND CONCLUSIONS
The seasonal abundance
abundance of
of harbor
harbor seals auling out
Tillamook Bay
during
in Tillamook
Bay displayed
displayed a general peak during
June, July,
July, and August, coincident with the
the pupping
pupping
These high
high counts
counts did
did not
not coincoinand molting periods. These
cide with
with the
the fall
fall peak
peak in
in salmonid
salmonid abundance
abundance in
in the
the
bay.
more important in
bay. Two
Two other
other factors
factors may
may be
be more
regulating seal abundance here:
here: 1)
1) High densities of
species, known
known to be
be seal
seal prey,
prey, ococmany smaller fish species,
months, and
and 2) Tillamook Bay
cur during the summer months,
Bay
provides the
preferred by
by seals
seals during
during the
provides
the habitat preferred
pupping season.
The peak in the seasonal abundance
abundance of harbor seals
Netarts Bay
Bay coincided
coincided with
with the return
return of
of chum
chum
at Netarts
salmon to the Whiskey
Whiskey Creek hatchery during
during the
salmon
months of October
October and
and November.
November. Conditions
Conditions for
for
successful predation
predation were ideal here: Shallow water,
water,
narrow channels, the
the concentrating
concentrating effect that
that occurs
and a general lack
as salmon funneled into the creek, and
of
disturbance to feeding
feeding harbor
harbor seals.
seals. Compared
Compared
of disturbance
with
fall, the lower
lower numbers
numbers of harbor
harbor seals
with the
the fall,
hauled
spring months
months may
may indicate
indicate
hauled out during the spring
that
Netarts Bay
Bay was
was not
not aahighly
highly preferred
preferred
that Netarts
pupping area.
The
estimated losses
Netarts Bay
aay chum
chum
The estimated
losses to
to the Netarts
salmon
salmon returns
returns through
through harbor
harbor seal
seal predation
predation at
(1.5-7 .2% per year) might have been
been
Whiskey Creek (1.5-7.2%
tolerated
returning chum salmon were
tolerated ifif numbers of returning
great enough to provide ample brood stock for future
future
(Lannan 14). However, while
while an attempt
was
releases (Lannan'4).
attempt was
being
build the
the stock,
stock, any
any loss
loss of eggs
eggs
being made
made to
to build
female spawners
spawners was
was conconthrough predation
predation on female
through
sidered serious.
Recovery and
and identification
identification of prey
prey hard
hard parts from
feces
feces indicated
indicated that
that while feeding in
in Netarts
Netarts Bay and
in
select fish
in coastal
coastal waters,
waters, harbor
harbor seals
seals appeared
appeared to select
species that were found near the bottom of the
the water
column.
seven top-ranking
top-ranking food
were
column. The
The seven
food items were
benthic or epibenthic
species, or,
or, as in the
epibenthic species,
the case of the
the
Pacific
least some
some time
time closely
closely
Pacific sand
sand lance,
lance, spent
spent at least
associated with the bottom
bottom (Howe
(Howe 1980).
As
As evidenced
evidenced by movements of tagged animals, interchange
terchange of harbor
harbor seals
seals between
between coastal
coastal estuaries
was
was common
commonand
andoccurred
occurred up
up to
to distances
distances of
of at
at least
least
••J.
E . Lannan,
Lannan,DepartmentofFisheries
and Wildlife,
Wildlife, Oregon State
"J. E.
Department of Fisheries and
State
University,
University, Marine
Marine Science
Science Center,
Center, Newport,
Newport, OR
OR 97365,
97365, pers.
pers.
commun.
commun. March 1980.
300
550 km.
km. Groups
Groups of
of harbor
harbor seals
seals hauling
hauling out
out in
in difdif550
isolated
ferent estuaries
estuaries apparently
apparently do
do not represent
ferent
represent isolated
stocks, but
but may instead
instead be
be part
partof
ofaa common
common populamovements of
of harbor
harbor seals
seals were
tion of animals. The movements
seemingly related
use of
of particular
particular areas
areas
seemingly
related to
to the use
by harbor
harbor seals
seals for
for feeding, for
specifically preferred
preferred by
birth and
and care
care of
ofyoung,
young, or
or for both.
birth
ACKNOWLEDGMENTS
to J.J. Harvey
Harvey for
for his invaluable
invaluable conWe are indebted
indebted to
of ideas
ideas and
andskills
skills during
duringplanning,
planning, field,
field,
tribution of
reporting stages
stages of
of this project; to J.
J . Lannan and
and reporting
the Department
Departmentof
of Fisheries
Fisheries and
and Wildlife
Wildlife at
at Oregon
Oregon
University for use of the Fisheries
Fisheries Research
Research
State University
Station atNetarts
at NetartsBay;
Bay;to
toJ.J .Fitch
Fitchfor
for identification
identification of
Station
to C.
C. Bond for identification of teeth of
otoliths and to
seal prey species; and
and to
to D. Herzing
Herzing and the
the many
many individuals
dividuals who
who donated
donated their time and energy in the
field. N.
N. Brown
Browntyped
typed drafts
drafts and the final manuscript.
manuscript.
We are
are grateful
grateful to
to B.
We
B.Antonelis,
Antonelis, R.
R. DeLong,
DeLong, D.
D.
J . Gilbert,
Gilbert, M.
M. Johnson,
Johnson, T.
T.Loughlin,
Loughlin, K.
K.
DeMaster, J.
Pitcher, and
and Washington
Washington Department
Department of
of Game
Game
Pitcher,
personnelfor
for critical
critical review
Marine Mammal Project
Marine
Project personnel
of manuscript
drafts. This
This work
work is a result of research
manuscript drafts.
research
sponsored
sponsored by the Oregon State University Sea Grant
College
by NOAA
NOAA Office
Office of Sea
College Program supported
supported by
of Commerce,
Commerce, under grant
grant
Grant, U.S.
U.S. Department
Department of
106.
NA79AA-D-00106.
no. NA79AA-D-00
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