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Harbor Seal (Phoca vitulina richardi)
Haul-Out Impact on and Behavior in
the Rocky Midtidal Zone
Jean Boal
Boal
Seal Haul-Out Impact and Behavior
Introduction
The common harbor seal Phoca vitulina has been studied
both physiologically, and behaviorally in reference particu-
larly to fishing impact and mother-pup relations (Anderson,
1969: Ridgway, 1972: Wilson, 1974). However, little work
has been done on individual seal behavior with reference to
haul-out site, and on the impact of seal haul-out on the
intertidal forest community. This study on Phoca vitulina
richardi, the subspecies found on western North American coasts,
documents compositional and morphological changes in algae as
well as the differential animal populations found on haul-
out sites. A description of observed seal behaviors, par¬
ticularly as they relate to hauling out, is includéd.
Seals first began hauling out here at Hopkins Marine
Station Biological Preserve, Pacific Grove, California, only
about five to ten years ago (Abbott, 1979: Baldridge, 1979).
The local population appears to be stable (Harrold, 1977).
The area surrounding the point is urban; however, due to the
Preserve, island disturbance has been low.
Study Sites
Three principle and two auxiliary sites were used, all
within the Biological Preserve. All sites were chosen for
comparability of wave action, tidal height, and suitable rock
availability.
Boal
Seal Haul-Out Impact and Behavior
The first site, the southwest portion of a rocky island
(Seal Island) about 40 meters east of shore, is the haul-out
site of ten to fifty seals every low tide (see Fig. 1).
This part of the island is the most sheltered from wave action,
and the most heavily used by the seals.
The second site was located on the southwest of Bird Island.
It differed from Seal Island in having higher resident gull and
cormorant populations, slightly greater wave exposure, and less
easily accessible deep water suitable for escape (Loughlin,
1974) at low tide. The third study site chosen, a piece of
the main land facing Seal Island, was comparable to Seal Island
in all but its proximity to human activity and its absence of
bird inhabitation.
Finally, two auxiliary study sites were used, both on the
north side of Bird Island. Wave exposure was high here. One
site was accessible from the bay by deep nearby channels at
all tides; this area was used for haul-out by from zero to
eight seals (mean of three) at low tides. The other site,
located adjacently, was only reachable by shallow channels at
low tide. It was closer to the main land shore and no seals
hauled out at this location.
Behavioral observations were done primarily from the roof
of three-story building A (see Fig. 1), and also from points
B and C. In-water observations came from the coves off beaches
M and N. Forty hours of observations over forty-five days were
made.
Boal
Seal Haul-Out Impact and Behavior
Effects on Algae
In order to demonstrate possible differences in algal
species distribution, quadrates were placed in the study sites,
and the species under individual points were determined. Quad-
rate locations were randomly determined within axes parallel and
perpendicular to the coast. Individual points within the
quadrate were determined by random coordinates within a grid
system. Tidal heights from 15 to 190 cm. above MLL were in¬
cluded. A total of 180 points on 18 different rocks were deter-
mined for each of the three principle study sites, as well as
50 points on five rocks in each of the two auxiliary sites.
Although no significant differences were found in the three
areas due to the wide height range included, possible trends
in both Gigarina canaliculata and Rhodoglossum affine were
suggested (see Fig. 2).
Algal counts from the two auxiliary areas for these two species
were compared (see Fig. 3). G. canaliculata was found more
frequently on the haul-out sites as expected; however, R. affine
was found significantly less frequently. This suggests that
R. affine differences may not, in fact, be due to the hauling
out.
Per cent composition was then determined by ten 20 x 20
quadrates in each principle study area. Rocks heavily used by
seals were sampled on Seal Island, and rocks as similar as
possible in morphology and tidal height were chosen from Bird
Island and the Main Land. In this comparison, G. canaliculata
Boal
Seal Haul-Out Impact and Behavior
and R. affine cover on Seal Island was found to be significantly
higher on Seal Island (see Fig. 4).
In order to determine whether the observed differences were
due to general location differences, rock side algae composition
was studied. Four points on the north, the south, the east,
and the west sides of five rocks in each major area were counted
for algal species with use of a 20 x 20 quadrate. Quadrate loca¬
tion and point determination were done as on the algae rock top
study. No significant differences were found between Seal Island
and Bird Island or the Main Land (see Fig. 3).
Comparisons by height of the four principle alga, Endocladia
muricata, G. canaliculata, Gigartina papillata, and R. affine
showed range variations only in R. affine, which was found from
50-155 cm. above MLL on Seal Island, and from 45-130 and 80-130
cm. above MLL on the Main Land and Bird Island, respectively.
More study is required to determine if the difference is actually
attributable to the seals.
Preliminary viewing had suggested possible morphological
changes in Seal Island G. canaliculata. Five rock tops in each
area were sampled for frond height and branching studies. Five
fronds from dispersed holdfasts on the rock tops were chosen.
Holdfasts were chosen to be representative of G. canaliculata
on that rock, but frond selection was blind. In addition, one
holdfast determined by coin toss location was picked and brought
into the laboratory. Holdfast fronds were spread out and random
counts determined two additional fronds which were measured for
Boal
Seal Haul-Out Impact and Behavior
height (see Fig. 5). In the 25 sample study, significantly
smaller plants were found on Seal Island. In the 10 frond sample,
differences were not significant.
The twenty-five fronds per area collected above were meas¬
ured for branching. A frond was considered to start from the
holdfast itself and branches over 2 mm. in length were counted.
The Seal Island fronds were not significantly less branched,
but a trend for furthur study is suggested.
Six holdfasts from three rocks in each major area were coded
and three people not knowing the coding ranked the samples by
color. All Seal Island samples were universally ranked as
darker in color than all other samples.
Finally, observations had indicated Phyllospadix was torn
on Seal Island, so ten 20 x 20 cm. quadrates were placed on rocks
predominantly covered by Phyllospadix, and visible roots counted
(see Fig. 3). Clearly more were found on the Seal Island rocks
than in the other two study areas.
Effects on Animals
For determination of faunal differences, 20 x 20 quadrates
were randomly placed in the study sites and all animals easily
visible to the unaided eye were counted. For rock top versus
side comparisons, 50 cm. transects lines were run down the north,
south, east, and west sides of the rock from the quadrate, and
animals within 5 cm. of the lines also counted. Significant
differneces in numbers of Littorina scutulata and Tegula fune-
Boal
Seal Haul-Out Impact and Behavior
bralis were found on the rock tops, but not on the rock sides
(see Fig. 6).
Animals too small to be counted with the unaided eye were
counted by bringing 18 random 2 x 2 cm. algae samples from each
major site into the laboratory. Sample locations were determined
by random coordinates beneath the 40 x 40 cm. quadrates used in
algal studies. Barleeia haliotiphila, Lasea cistula, and Tri-
colia pulloides were all found in far greater numbers on haul¬
out sites, and amphipods were found significantly less frequently
(see Figs. 9 and8). (Amphipods were not counted on the auxil¬
iary sites).
Bacterial Differences
Bacteria on G. canaliculata was cultured on standard nutrient
agar medium (Difco) to determine if different bacterial composi¬
tion might be a factor in the greater small animal populations of
Seal Island. A total of fifteen 1.5 cm. high, comparable fronds
from five different rocks were taken from each principle study
area. One side of each frond was placed in contact with the agar
surfact, and then removed. The reverse side of the frond was
then touched to the agar surface of a second plate. The plates
were left under continuous florescent light for three days,
after which bacteria colonies were counted and described (see
Table 1). Total bacterial counts were not significantly differ¬
ent between Seal Island and the Main Land. However, if the
Boal
Seal Haul-Out Impact and Behavior
ubiquitous "white blobs" are excluded, the remaining bacterial
counts are quite different. Bacteria distribution is likely too
highly variable for this small sampling to be conclusive.
Discussion
That the algal and snail differences of Seal Island were
only found on rock tops, and that the differences were also found
in the auxiliary sites, clearly indicates that harbor seals have
a definate impact on the midtidal biota where they haul out. This
impact can be expected to fall into three categories: mechanical,
chemical, and the resultant environmental. The action of crawling
out and sliding in may cause structural stress to algae, includ¬
ing the tearing noted in Phyllospadix root counts. Less tightly
attached animals are probably getting knocked off, as the low
L. scutulata and T. funebralis numbers suggest. In addition,
200 - 100 lbs. of seal resting, on average, 10 hours a day
(Loughlin, 1974) on the rocks may be related to the smaller G. can¬
aliculata plants, and may be squashing animal life such as amphi¬
pods.
Chemically, on two instances feces were found on the rocks,
and on one, some liquid discharge was found pooled in a rock
crevice. This must also be affecting the plant and smaller
animal life, even though the rocks are washed off by each high
tide.
Less quantifiable stress factors include decreased sunlight
Boal
Seal Haul-Out Impact and Behavior
and warm, humid conditions maintained on the rocks during the
time the rocks are normally the most exposed. Qualitative
(tactile comparison) observations of rocks just vacated support
this stress hypothesis. Possibly, the higher range of R. affine
may be due to this seal-incubation phenomenon.
The possibility that seals may occationally feed in the mid-
tidal area places them in the position of top carnivore of the mid¬
tidal community. A comparison of fish found in seal stomachs
(Bigg, 1969 and Newby, 1969-71) and those found in the Preserve
intertidal (Nichols, 1979) suggest cabezon and sculpins as pos¬
sible prey. But, although as many as 32 seals have been sighted
in the area at high tide, a more usual number would be two to
four, and only upon disturbance were more than ten seals seen in
the water at a time. If the seals are feeding at this time, this
surely would affect the fishes and hence the community as a whole.
Thus, it is clear that at and near the harbor seals' hauling
out site, the seals have a definite and important impact on
the midtidal forest community. This should not be overlooked
in future studies of the midtidal region.
Seal Behavior
The harbor seal population at Seal Island ranged form seven
to fifty, with a mean of 31, at low tide during full daylight.
Observations were made for a total of about 40 hours in 45 days,
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10
Seal Haul-Out Impact and Behavior
over a period of six weeks (April to June). Although too few
counts were made to show significance, trends show a possibility
of more seals hauling out in sun than in rain, and more at nega¬
tive tides than positive low tides (see Table 2). In general, at
high tide from one up to six seals cound be seen in the water
around and between points A and D (see Fig. 1). These most often
were smaller seals.
Because the haul-out site was so close to and in full view of
the shore, and because of the smallness of the population, indi¬
viduals were able to be distinguished. Eleven different indivi-
duals, relatively easy to site, were observed for rock preference
and individual behavior. (For aide in future studies a sample
score sheet for seal identification has been included. See Table
3). Rock preference was definately shown by the individuals
followed. At least five different individuals were found to be
returning consistantly to one to six particular rocks (some, more
than 95% of observation sightings). With only one exception
every identifiable seal seemed to have a preferred social set¬
ting: either in the thick of the crowd (there was generally a
crowd of 10 + seals in the most sheltered part of the island for
that tide), on the fringes of the crowd, or off by itself.
Certain types of rocks appeared to be preferred. They were
low, had flat top surfaces, were well sheltered from waves, and
were near escape channels. In times of crowding, conflicts
errupted over choice sites. Snorting, snarling, and head-thrusts
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Seal Haul-Out Impact and Behavior
(Bishop, 1968, as cited in Loughlin, 1974) were all observed.
In addition, the seals displayed a tapping of the front flippers
on the other seal. Both seals might continue this tapping at
eachother for 5-10 minutes or more. Finally, if one seal did not
move over sufficiently, the larger seal would push the smaller
seal off the rock. This pushing was observed on at least eight
separate occasions, the small seal losing in every case. Con¬
flicts were observed greater than thirty times, and snarling and
flipper-taps included in approximately 90% of the displays.
Smaller seals were noted for choosing rocks for consistant
hauling out that were not preferred sites. These were largely
high rocks (bare or partly bare of algae), and in some cases were
pointed or steeply sloped. This choice is understandable in
light of the observed large seals' dominence of preferred rock¬
types.
Using size as an indication of age, the population of Seal
Island is young. Large seals accountfor from O to 7 of the
hauled out seals sighted, 7 to 20 were quite small relative to
these, and remaining 20-, medium sized. Behavior differences were
noted between large seals and others. In case of disturbance, the
smaller were quicker to look around. The larger seals never tol-
erated a close human approach and were never observed to swim up
and watch people on the shore or follow the small boats departing
from the beaches, as were smaller seals. It is possible that
smaller seals are more accustomed to people and avoid them less,
which would help account for why this island population, so close
to Marine Station activity, is predominantly made up of small
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Seal Haul-Out Impact and Behavior
seals.
Play in the water off the beaches was observed about 60% of
observation days by at least one and up to nine seals at a time.
Water slapping was definately not correlated with warning, but was
displayed frequently by single seals. From observation to obser¬
vation time, consistent in-water individual seal identification
was not generally possible. However, in any given observation
period, seals were observed to slap the water with only the right
or the left flipper. This preliminary observation indicates
handedness, which although not mentioned in previous harbor seal
studies, has been a noted characteristic of other marine mammals.
Only one mother and pup were observed in the Preserve this
spring. The pup was the first ever sighted here. It may not have
been born here as it was only sighted beginning the last week of
May, and in the second week of observations, was not observed to
be permitted to nurse (although it was still quite small). This
lack of pupping here is probably due to the amount of human activ¬
ity nearby.
Two seals were recognizable in the water. A medium sized seal
and a small seal, they were sighted swimming together on more than
twenty different occasions throughout the study. This suggests
some lasting pair-bonding may occur, even at non-mating times of
the year.
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Seal Haul-Out Impact and Behavior
Summary and Conclusions
Seal impact on haul-out sites was evidenced by;
1. Greater G. canaliculata and R. affine cover.
2. Shorter and darker G. canaliculata plants.
3. Plant tearing shown by Phyllospadix root visibility.
4. Increased B. haliotiphila, L. cistula, and T. pulloides
populations.
5. Decreased amphipod populations.
6. Fewer L. scutulata and T. funebralis.
7. Possible alteration of bacterial composition.
Seal haul-out behavior noted include:
1. Low tide population of 7 to 52 with a mean of 31.
2. Possible preference to haul out under conditions of sun
and negative tides.
3. Preferred rocks low, sheltered, near deep water, inacces¬
sible to land animals, and with as little nearby human
activity as possible.
4. Particular rock preferences shown by individuals.
5. Rock conflicts characterized by snorting, snarling, head¬
thrusts, flipper tapping, and pushing, with larger
seals' success.
6. Sustained pair bonding outside of mating season.
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Seal Haul-Out Impact and Behavior
Acknowledgenents
My greatest thanks for the great help provided particularly
by Robin Burnett, and also by Alan Baldridge, Donald P. Abbott,
and Judson Vandevere.
References
Abbott, Donald P. 1979. Personal communication.
Anderson, Harald T., ed. 1969. The Biology of Marine Animals.
Academic Press, N.Y.
Baldridge, Alan. 1979. Personal communication.
Bishop, Richard H. 1968. Reproduction, age determination, and
behavior of the Harbor Seal, Phoca vitulina L., in the Gulf
of Alaska. M.S. thesis, Univ. of Alaska, College, Alaska.
121 p.
Cooper, John, and Mark Wieland; Anson Hines. 1977. Subtidal
Abalone Populations in an Area Inhabited by Sea Otters.
The Veliger, 20 (2): 164.
Harrold, C. 1977. Data on file at Hopkins Marine Station Library.
Loughlin, T. R. 1974. The Distribution and Ecology of the Harbor
Seal in Humbolt Bay, California. M.A. thesis, Humbolt State
University.
Newby, Terrell C. 1969-71. Pacific Harbor Seal. Canada Fisheries
Research Board Bulletin, Nos. 168-175.
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15
Seal Haul-Out Impact and Behavior
Nichols, Andrew. 1979. Predation by Tidepool and Nearshore Fishes
and its Impact on the Rocky Intertidal Zone Community. Biology
175H paper on file at Hopkins Marine Station Library.
Ridgway, Sam H., ed. 1972. Mammals of the Sea, Biology and Medi¬
cine. Charles C. Thomas, Publisher. Springfield, Il1.
Wilson, S. C. 1974. Eliciting Play: A Comparative Study. American
Zoologist, 14: 341-370.
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Seal Haul-Out Impact and Behavior
Figures
Fig. 1
Map of Hopkins Marine Station Biological Preserve
(Cooper, 1977). Principle study sites on Seal Island
(SI), Bird Island (BI), and the Main Land (ML), with
auxiliary stidy sites on Bird Island - North (BI-N).
Seal in-water behavior observed between points (B)
and (D). Observations from (A), (B), and (C).
Fig. 2
Plant composition counts for 180 random sites at Bird
Island, Main Land, and Seal Island study areas.
A - G. canaliculata and R. affine counts from Fig. 2.
Fig. 3
B - Haul-out and non-haul-out algal counts.
C - Algal counts for rock sides. Studentst test done
with data transformed to the.2 power. Significance
not found.
Fig. 4
Per cent cover of heavily used haul-out rocks (SI) and
rocks similar in tidal height and morphology (BI and ML)
show significant differences.
G. canaliculata frond height comparisons.
Fig.
Fig. 6
G. canaliculata frond branching measured.
Root visibility counts as an indication of plant tearing
Fig.
are higher on Seal Island.
A - Fewer snails are found on Seal Island when rock tops
Fig. 8
are studied, but no differences found on rock sides.
B - Tegula recounts on rock tops confirm absence seen in
(A).
0
Boal
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Seal Haul-Out Impact and Behavior
Fig.
More B. haliotiphila, L. cistula, T. pulloides and
fewer amphipods found on Seal Island rock tops.
Fig. 10 Fig. 9 conclusions supported at auxiliary study sites.
Table 1
Bacteria from G. canaliculata fronds from the three
principle study locations show significant differences,
Seal Island from Bird Island, and Seal Island from Main
Land, excluding "white blobs"wwhich are ubiquitous.
Table 2 Numbers of seals counted under various conditions.
No differences significant due to high variability and
few observations. Possible trends for future study
are suggested, however.
Table 3 Seal identification sample data sheet.
r
De
8
18 35. 9
g


pn


0
2
A
,

R

J
X
Hilden¬
brandia
Irradaea
Pelvetia
Petrocelis
Phyllo-
spadix
Pryanitis
Rhodo¬
glossum
affine
Lepto¬
rhynchos
No
Algae


4
a


8
NUMBER OF PLANTS
Cladophora
columbiana
Corallines
18
(articulated
Corallines
(crustose)
Endocladia
muricata
Gastroclonium
coulteri
Gelidium
Gigartina
canaliculata
Gigartina
papillata
Green
Algae
0
e
19
8 8 8

2

USE
BI
Zm
□SI
&a 10
1 NHO
30
20
10
20
10
G. CANALICULATA
26
16

R. AEEINE
21

ROCK TOPS

0
28

ROCK SIDES
20
40
5 20
10
G. CANALICULATA R. AEEINE
24
0 00
o1
15 14
0

BI
N= 10
BI +MLX SI
M
(= 4.8 § =7.96
I = 2.53 P ( .02
S1
21
BI
E
m
LS1
ML X SI
ML X SI

N = 25
- 6.58
001
- 5.11
.001
4.2
N = 10
I = 1.29
NS
= 0.07
NS
4.7
20
BI
M
51
7.2
4.0

N = 25
23
5
PHYLLOSPADIX ROOT COUNTS
ML
BI
SI
10
10
10
0.30 2.40
0.20
3.07
0.63
0.67
BIX SI
ML X SI
I=2.22
I - 2.11
P K.05
P(.05
24
A. N - 18
L SCUTULAIA
L FUNEBRALIS
LI SCUTULATA
Li FUNEBRALIS
B. N = 10
L EUNEBRALIS
SNAIL COUNTS
BL
ML
81
80
31
19
345
119
139
83
41
33
SI
118
RXC
IOP 6 = 20.12
P (.005
RXC
G = 0.1
SIDES
NS
25
—
R
S
hoн sооаноNI 1о aa
O
250
L
o10
210
42
19
..
LR
K
IRICOLIA
BARLEEIA LASEA
BIRD ISLAND - NORTH AUXILLARY SITES
RXC G = 129.82 P K .0
HAUL-OUT
NON-HAUL-OUT
8
27
e
WHITE BLOB
WHITE
WHITE RADIAL
YELLOW CLUMPS
YELLOW BLOB
PINK EGGS
CLEAR GRAINY
CLEAR EGGS
WHITE CLUMP
TOTALS
EXCLUDING WHITE
BLOBS
BI
6
0
22
BACTERIA
ML
43
2
0 0
78
20
SI
19
60
X(-9
P (.001
28
e
SEAL ISLAND
TOTAL
SUNNY
OVERCAST
RAINING
NEG. LOW TIDES
POS, LOW TIDES
BIRD ISLA
TOTAL
SEAL COUNTS
Hn
M
25
32.5
34.6
11
29.0
25.5
41.5
30.3
18
3.0
11
815
2.02
3.76
5.57
1.50
6.81
10.42
0.54
29