BULLETIN No. 146
Comparative feeding habits of the
FUI S''II. S.,I LiDn
lind H,IlbDUI S .,II
)
on the British Columbia coast
D.J. Spalding
Fisheries Research Board of Canada, Ottawa, 1964
COMPARATIVE FEEDING HABITS OF THE
FUR SEAL, SEA LION, AND HARBOUR SEAL
ON THE BRITISH COLUMBIA COAST
Editor:
. J. C . STEVENSON
Associate Editor:
E. G. BLIGH
Fisheries Research Board of Canada
Sir Charles Tupper Building
Ottawa, Ontario, Canada
Bulletin No. 146
Comparative Feeding Habits of the
Fur Seal, Sea Lion, and
Harhour Seal
on the British Columhia Coast
by
D. J.
Spalding
Fisheries Research Board of Canada
Biological Station, Nanaimo, B.C.
THE FISHERIES RESEARCH BOARD OF CANADA
under the control of
The Honourable the Minister of Fisheries
OTTAWA,1964
95250-1�
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19M
IV
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print
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v
Contents
ABSTRACT, ix
INTRODUCTION, 1
HISTORICAL REVIEW OF PINNIPED
COLUMBIA WATERS, 1
FOOD
STUDIES
IN
METHODS AND MATERIALS, 2
GENERAL HABITAT DESCRIPTION, 11
DISTRIBUTION, NUMBERS, AND MIGRATORY BEHAVIOUR, 12
FEEDING HABITS, 14
EFFECT OF SEAL AND SEA LION PREDATION UPON BRITISH
COLUMBIA'S COMMERCIAL FISHERY, 33
ACKNOWLEDGMENTS, 44
REFERENCES, 45
ApPENDIX 1, 48
ApPENDIX 2, 51
VI!
BRITISH
ABSTRACT
The stomach contents from 2 1 1 3 fur seals, 393 sea lions, and 1 2 6 harbour
seal s formed the basis for studying the effect of pinniped predation u pon
commercially val uable fish stocks of the B ritish Columbia coast. All samples
were grouped as to season and area of collection , and comparative seasonal
feeding habits are discussed. The effect of the reproductive period upon
feeding habits was examined. There is l ittle evidence regarding fur seal feedi n g
habits on t h e rookeries except f o r conflicting observations m a d e on harem
bulls ; the majority of the sea lion rookery population fasts for a few days o n l y ,
d u r i n g pupping ; harbour seals on t h e Skeena River appear to f a s t f o r a t
least part o f J u ne. There is no evidence o f i nterspeci fi c competition between
the three species studied on the British Colu mbia coast. Sea lions and harbour
seals each year eat an estimated amount of sal mon equivalent to about 2.5%
of the annual commercial salmon catch and a n amount of herring equivalent
to about 4% of the annual commercial herring catch. Predation a t this level
is believed to be of negligible importa nce i n the reduction of existing sal mon
and herring stocks. I nsufficient data from waters greater than 3 5 miles from
shore preclude a n assessment of fur seal predation u pon ocean sal mon.
lX
95250-2
INTRODUCTION
The predatory activities of several members of the order Pinnipedia provoke
heated arguments whenever inshore fisheries are carried out near seal or sea lion
populations. On the one hand co mmercial fishermen advocate stringent control,
and in some instances complete eradication, of all pinnipeds whose depredations
may affect fish catches. "The only good seal (or sea lion) is a dead one" is a
favourite expression. On the other hand many naturalists and seal lovers vigor­
ously oppose such control measures. Control is often synonymous with "slaugh­
ter" and "extinction" to some members of the latter group.
Three pinnipeds, the northern fur seal (Callorhinus ursil1us), the northern
sea lion (Eumetopias Jubata), and the harbour seal (Phoca vitul1:na), are found in
British Columbia's coastal waters where commercial fishing is carried out. This
study is an attempt to describe the seasonal feeding habits of these three pinnipeds
with particular reference to the commercially valuable fish species in their diet.
HISTORICAL REVIEW OF P IN N IPED FOOD STUDIES IN
BRITISH COLUMBIA WATERS
Food items have been described either by common names or by both
common and scientific names in the studies reviewed. For the sake of consistency
common names have been used in this study. Appendix 1 includes scientific and
common names of all food items referred to .
FUR SEALS
Fur seals have been studied extensively in both the eastern and western
Pacific. l\Jost collections have been mad e under the terms of two international
programs of investigations : (a) In 1952 a 1-year program was undertaken by
Japan, the United States, and Canada to study the distribution, migration, and
food habits of the fur seal; (b) In 1957 representatives from Russia, Japan,
United States, and Cana da signed an "Interim Convention on Conservation of
the North Pacific Fur Seals" . ThIS convention, effective for 6 years, was designed
to investigate the numbers, migration, wintering areas, feeding habits, and the
effect of seals upon commercial fish stocks and fishing gear.
Fur seal stomachs from British Columbia were first examined in 1933 and
1935 (Clemens and Wilby, 1933; Clemens et al., MS, 1936). These early studies
attempted to assess the role of fur seals in the economy of the ocean off the
Canadian Pacific coast. In the 593 stomachs examined, herring formed 84% by
volume of the contents and was obviously important in the diet of seals off
southern Vancouver Island.
1
95250-2�
Between 1935 and 1958 no fur seal stomachs from British Columbia were
examined. During the second (1957) international investigation (mentioned
above) Canada agreed to collect between 500 and 750 seals each year in the
northeast Pacific. Collecting began in 1958 and during the 4 years from 1958 to
1961, 1520 stomachs were examined from British Columbia coastal waters. I II
order to fulfil Canada's quota commitments an additional 500 seals have been
collected during the 4 years in Washington or Alaskan waters. Collections will
be continued at least until 1964.
SE A LI ONS
Sea lions were first studied in British Columbia during 1913 (:'\ewcombe
and :"Jewcombe, 1914) and again during 1915 (::\ewcombe et al., 1918). Although
few stomachs were examined many fishermen and fishing company officials were
interviewed. In two areas, the mouth of Rivers Inlet and in Barkley Soun d , sea
lions, when present in large numbers, evidently adversely affected the fishin g
industry. Little research was done between 1916 and 1956, when an investigation
vvas initiated by the Fisheries Research Board of Canada to gather information
on the general biology of sea lions. Three hundred and seventy-four stomachs
have been collected since 1956. Pike (1958), reporting on 81 stomachs collected
during the early part of this latter program, tentatively concluded that com­
mercially valuable fishes did not play as important a role in the sea lion diet as
was often claimed.
HARBOUR SEALS
Fisher (1952) was the first to investigate the life history of the harbour seal,
its distribution, numbers, and food habits, particularly in the Skeena River
area. Emphasis was placed on the role of salmon in the diet. Herring, salmon, and
rockfish contributed 68% by volume to the contents of 2 7 stomachs. ".'\lthough
Fisher realized his study was not exhaustive, he concluded that harbour seal
predation upon Skeena River salmon warranted some control. On his recommen­
dation the Department of Fisheries of Canada undertook a control program on
the Skeena River . Forty-five stomachs were examinee! during June of 1948 and
1949 by control officials. Fifty-four additional stomachs have been collected
since 1958, when I Joined the �\Iarine :\[ammal Investigation of the Fisheries
Research Board of Canada.
:VIETHODS A�D l\L.'\TERI ALS
SPECIMEN COLLECTION
Table I indicates Ilumbers of specimens collected throughout the year. The
fur seals were mainly females, although both sexes were represented approxi­
mately equally in the h arbour seal and sea lion samples.
2
TABLE 1. :\I onthly collections of harbour sea l , fur sea l , and sea lion stomachs.
I
:\Ionth of collection
'
No. specimens collected
Harbour
L s.:.�
, _______________________
J a nuary . .
February.
March . .
April. .
May, '
J u ne, '
J u ly, . . , '
A,ugust,
September .
October. , .
:'-Jovember,
December . , .
1
2
3
1
1
47
9
16
19
20
6
'
,
Totals,
�
Fur
__
�.:�
17
68
308
861
741
118
I,
I
1
I
1-2 -- 21
-
I
Sea
___
�io�_
5
�1
,
14
4
70
143
81
10
49
3
14
393
FUR SEAL
From 1958 to 1961, Canadian research vessels collected 1520 fur seal stomachs
between 48°00' and 55°00'N latitude during the months of January to June,
inclusive. Only 25 were collected more than 35 miles from the British Columbia
coast. Specimens were collected pelagically, while either wintering in British
Columbia waters, or on their northward migration to the breeding grounds in
the Bering Sea.
Quota commitments centered most hunting effort in areas of seal concen­
n-ations. Large numbers of seals were collected between Cape Flattery and the
northern tip of Vancouver Island. A small wintering population of adults in
Hecate Strait was also sampled.
Hunting, when weather permitted, was carried out as follows. The vessel
left harbour each morning and ran out 25-40 miles from shore, collecting all seals
possible. During the afternoon the vessel returned to the coast, which was
reached by nightfall. In this way the collecting vessel moved up and down the
coast, searching for seal concentrations. Occasionally one or more nights were
spent offshore, particularly if the weather was favourable.
.5:eals were sighted from the bridge of the vessel (Fig. 1) and were killed by
shotguns loaded with S.S.C. shot, or a 3 0. 06 rifle. Fortunately, dead fur seals
do not sink rapidly and only about 6% were lost due to sinking. Records included
time, date, and location of capture, sex and breeding condition, and feeding
behaviour. Stomachs were removed, injected with 10% formalin, placed in
cotton sacks, and stored in wooden barrels containing 10% formalin. The pres­
ence or absence of food in the stomach was noted in the laboratory and if the
3
"'"
FIG. 1. M. V.
Pacii
f c Ocean, used extensively for collecting fur seals, harbour seals, and sea lions.
FIGo 20 Analysis of stomach contents: top: (M�erlucci1ts jJ}'oductus) examples
from skeleton collection ; centre: (Sebastodes maliger); bottom: weighing fur seal
stomach contentso
5
stomach was not empty the following data were recorded: weight of contents i n
grams (Fig. 2), volume b y displacement (cc), food species, and numbers of
individuals present.
SEA LIONS
:Vlost specimens were collected by Fisheries Research Board of Canad a
personnel, although Department of Fisheries officials saved or reported o n
several stomachs. I n addition, I accompanied a commercial expedition for five
weeks during the spring of 1959 collecting sea lions for mink food; 115 stomachs
were examined .
Sea lions were collected mainly on their rookeries or haul-out rocks (Fig. 3) ;
collecting at sea was seldom successful as the animals were elusive and sank
rapidly when killed . Rifles were used exclusively to collect specimens. Data
collected were similar to those collected for fur seals, except that volume by
displacement was not recorded for th e contents of some stomachs examined in
the field.
HARBOUR SEALS
The urgency of fur seal and sea lion
research" and few specimens are available.
Pender Harbour, working in conjunction
very kindly saved a substantial sample of
Charlotte Islands during the fall of 1961.
studies has restricted harbour seal
Messrs D. and W. Mc�aughton of
with the Department of Fisheries,
29 stomachs collected in the Queen
FIG. 3. Collecting sea lions, Scott I sla nds, 1 959.
6
Harbour seals , which sink almost immediately upon being killed , were
collected mainly while swimming in shallow water. Toward the end of the col­
lecting period , however, it was found that a good marksman in a fast boat
could kill and collect seals before they sank. Data recorded for harbour seals were
similar to those recorded for sea lions.
ANALYSIS OF STOMACH C ONTENTS
An examination of stomach contents is the favoured method for the in­
vestigation of pinniped feeding habits. Scats and spewings have been noted
occasionally (Scheffer and Slipp, 1944; Scheffer, 1950; Wilke and Kenyon,
1952, 1954), but they are seldom found . M ost food items are consumed under
water and sight observations are few (Scheffer, 1950) . Hynes (1950), outlining
the several possible methods of analysing fish stomach contents , also reviewed
the methods for analysing pinniped stomach contents. The carnivorous feeding
habits of most fish and pinnipeds lead to similar problems in assessing stomach
contents . These several methods are discussed below.
DEGREE OF FULLNESS
An arbitrary estimate of the fullness of the stomach has been used to demon­
strate seasonal variations in food intake.
N UMBERS OF INDIVIDUALS
Total numbers of individuals of each food item are tabulated and may be
expressed as a percentage of the number of all food organisms found in the sample.
D OMINANT ITElIIS
The number of stomachs in which each food item occurs as the dominant
food stuff is expressed as percentage frequency of occurrence.
POINTS
Food items in each stomach are listed as common, frequent, etc., on the
basis of rough counts or judgments made by eye, and each category is then allotted
a number of points. All points gained by each food item are summed and per­
centage calculations are carried out using these points .
VOLUME ,\ND WEIGHTS
This method, and the following one, have been the customary techniques
for handling pinniped stomach contents . The weight of each food item in each
stomach is calculated in either of two ways : (a) the items in each stomach are
separated and weighed; or (b) an estimation by eye is made of the percentage
contribution of each item to the contents of each stomach; this percentage is
then applied to the known weight of the contents of the stomach to esti mate
the weight of the individual item. The weight of each respective food item in
the sample is then summed and may be expressed as a percentage of the total
contents examined. Volume analyses are carried out in a similar fashion to that
95250-3
7
described for the weight analyses, except that volume by displacement i s mea­
sured, rather than weight. Stomach content percentages in both international
fur seal programs have been calculated on a per cent by volume basis (Taylor e t
al. , 1955; Anon., I\1S, 1961).
The weight method of analysis has been modified (Ricker, 1937; Bogorov,
1934) by multiplying the n umbers of organisms of each item in the stomach by
the known mean live weight of that item. This gives a weight of each kind of food
eaten, rather than a weight of each item of food in the stomach at the time the
predator was killed.
A third modification of the volume or weight method has been to sum the
percentages each item contributes to each stomach.
J'\ UMBER OF OCCURRENCES
The number of stomachs in which each food item occurs is tabulated;
these occurrences of individual items may be summed and expressed as per­
cen tages of the total occurrences of all food items.
COMPARISON OF THE VOLUl\!E OR �WEIGHT AND THE NUl\!BER OF OCCUR­
RENCES ANALYSES
Two methods, numher of occurrences and the volume or ''v"eight method, were
considered for this study. Ricker' s ( 1937) modifications of the weight analysis
give the most accurate analysis if (a) numbers of individuals of each item can be
determined, and (b) if prey sizes can be estimated accurately. The numbers of
individuals can be counted, but size of prey is extremely difficult to estimate in
pinniped stomach contents. Only rarely does one find, as in Fig. 4, a stomach in
which lengths or weights of the prey can be taken directly . Large fish are swal­
lowed piecemeal, and a s will be pointed out later, heads may be discarded.
Estimates of length, therefore, can only be made from the broken remains of
vertebral columns. Finally, estimates of squid and octopus weights from beak
size are only just now receiving attention (Clarke, 1962 a, b); at present, there is
no information relating beak size to body weight of the squid and octopus
species found in pinniped stomachs collected from British Columbia waters.
For these reasons the analysis must either be based on the actual volume or
weight of the stomach contents, or a frequency of occurrence of the individual
items.
Hynes (1950) has shown that any of the commonly accepted methods of
assessing the composition of an animal' s diet will give much the same results,
if the data are scaJed down to percentages, and if large samples are used. This
point, with one exception, is illustrated ill Fig. 5, which shows the 1958 to 1961
fur seal sample (volume data from Pike et al., 1958, 1959, 1960, 1961). The one
major exception, squid, contributes only 4. 7 % by volume but 2 2 .3% by occur­
rence to the sample. Squid remains, usually consisting of beaks and eye lenses,
differ markedly from fish remains, whi ch usually include more flesh. Octopus flesh
was rarely found in sea lion stomachs. The Jack of cephalopod flesh indicates that
8
FIG. 4. Sma l l black cod found in fur seal stomach.
either squid and octopus are preyed upon earlier in the morning than fish, or
their flesh is digested more rapidly th an fish flesh. Regardless of h ow the dis­
crepancies between these two calculations are explained, I believe the h igher
percentage, based on occurrence, is the more meaningful calculation.
A volumetric or weight analysis of a small sample is particularly susceptible
to faulty interpretation. As shown later, sea lions and fur seals feed mainly during
the early morning. Thus, stomachs collected in the morning are full while those
collected towards nightfall are empty. The contents from one stomach collected
at daybreak will outweigh the contents from many stomachs collected later in
the day, an d the item or items in the former stomach will have an exaggerated
importance in a per cent by weight analysis.
However, percentages based on frequency occurrence calculations avoid
such errors. Each item encountered in a stomach is given one point, regardless
of th e weight of that item in the stomach.
The occurrence method will produce erroneous results when the predator
shows a consistent selection of one food item. Ricker (1937), examining the food
preferences of young sockeye salmon in the laboratory, found that two equ ally
abundant food items were eaten, but one item was consistently taken more often
than the other. A frequency of occurrence analysis would have exaggerated the
importance of that item taken ill lesser amounts.
95250-3�
9
40
o Per
ce:".'�
by vo:ur.;e
30
20
10
�
�
0
�
!
H
-"
>>
0
"'
�
FIG. 5 .
Comparison of analyses of contents from 869 fur seal stomachs
( 1 9 5 8- 1 9 6 1 data), based on per cen t by occurrence and per cent by vol u m e.
However, there is no evidence to indicate a consistent selection of one food
item by either fur seals, sea lions, or harbour seals. Taylor ct al. ( 1955) concluded
that fur seals were non-selective in their feeding habits, a nd tended to prey on
that item which was easiest to catch at the moment. The following two obser­
vations support this conclusion for all three species studied: (a) each predator
usually restricted itself to one prey item per feeding period (77% of fur seals
stomachs with food contained only one item; comparable figures for sea lion and
harbour seals were 78% and 7 6%, respectively), and (b) in the total of 33
identified food items only four (lamprey, sea perch, cabezon, and skate) had not
at one time or another been the sale item ill a stomach. Thus, seals and sea lions
all the British Columbia coast prey mainly on one item per feeding period, and
have a wide range of possible food items to choose from.
Abundance of prey may in fluence the prcdator in its choice of food. Pikc
ct al. ( 1961) reported that a mid-water trawl, fishing at 2 8-36 fathoms, caught
anchovy and culachon in approximately equal a mounts, plus a few herring; the
stomach contents of a fur seal collected at the same time and in the same location,
consisted of 50% eulachon and 50% anchovy, thc two most abundant species
in the area.
To summarize, under the circumstanccs described above per cent frequcncy
of occurrence will give approximately the same results as pcr cent by volume (or
weight) in a large sample, but a more realistic and unbiased interpretation of a
small sample.
Pcr cent frequency of occurrence calculations have been carried out as
follows: the number of times a given item occurred has been expressed as
a percentage of the total number of occurrences of identifiable food items 111
10
the sample. An example from Table VII will clarify this: 92 stomachs with
food were collected from sea lion breeding colonies during the summer. In this
sample, 14 different items were encountered 8 5 times; rockfish, occurring 11
times (i.e. in 11 stomachs) contributed 12.9% to the total diet in that area at
tha t time of year.
IDENTIFICATION OF STOMACH CONTENTS
A fish skeleton collection was started during the early winter of 195 8 and
specimens were added when necessary. Frozen or salted specimens were gently
boiled, the flesh removed, and all bones saved. An attempt was made to keep the
skull and vertebral column intact as it was found the vertebrae and vertebral
column were the most useful aids in identifying stomach contents (Fig. 2).
Total vertebral counts, relative positions of first haemal arch and spines, and
modifications of parapophyses and zygapophyses were particularly useful in the
identification of fish species.
Fish identification was aided by the following publications: Chapman, 1941 ,
1944; Clemens and Wilby, 1961; Clothier, 1950; Gregory, 1933; Hart and Mc­
Hugh, 1944; Sunde and Lindsey, 19 5 8. Scientific nomenclature and system of
classification follows Clemens and Wilby (1961).
I did not succeed in satisfactorily identifying all squid and octopus remains,
which usually consisted of beaks only. Identification of whole squids was facili­
tated by reference to Berry (1912). One sample was sent to the United States
Fish and Wildlife Service in Seattle , Washington , for identification.
GENERAL HABITAT DESCRIPTION
A description of the several habitats frequented by fur seals. sea lions, and
harbour seals is included to help understand the differences and similarities in
food habits.
Rugged promontories, peninsulas, and islands break up the British Columbia
coastal waters into numerous straits , gulfs , bays , and inlets of varying shapes
and depths , and have resulted in a coastline of an estimated 1 6 , 900 miles (ScageI,
1961). In addition, there are many rivers emptying into the sea , creating estuarine
conditions. These environments may be roughly divided into four categories,
the first two of which have already been described (Cowan and Guiguet, 195 6):
(1) pelagic waters biotic area-waters outside any protection from land and open
to the full force of all oceanographic and meteorological changes; (2) coast waters
biotic area-bodies of water lying behind, and protected by, islands , points, or
reefs; (3) estuaries-river mouths where a mixing of salt and fresh water occurs;
(4) fresh water-coastal rivers and lakes connected to the marine environment
by large rivers.
Table II outlines the distribution of pinnipeds on this coast in relation to the
above four environments.
11
TABLE II. Coastal habitats and pinn iped distribu tion,
��------ ---,------�-------
----,---,,-----�-----�---
Pelagic waters biotic area,
Coast waters biotic area .
Estuaries . .
Fresh water ..
.
.
.
.
.
.
.
.
.
.
.
��-
I
Habitat
Seal or sea lions presen t
'-- ---,---- --------
,
�
'
I
�
-��---"---.------------'--------
. 1 F llr sea l 't i'I
Harbour seal"
, , "
Fur seal
, ,. I Fur seal I Harbour seal"
Harbour seal
.
,
�
<
. .. '1
"I ndicates area of greatest preference.
'
I
Sea I'wn
Sea l �on'"
Sea lIon
-�---
Fur seals are seldom found within 5 miles from the coast; in comparison, sea
lions and harbour seals are rarely found further than 5 miles from shore.
DI STRI BUTI ON, NUMBERS, AI\D l\II GRATORY BEHAV I OU R
FuR
SEALS
The fur seal migration is one of the best docunwnted migrations of marine
mammals (Jordan , 1899; Kenyon and \,\filke, 1953; Taylor et aT., 1955), The
mature cows leave the Pribilof Islands during late October and I';ovember.
:\Iany move as far south as southern California in the eastern Pacific, and southern
Japan in the western Pacific. During the spring they return to the Pribilofs,
arriving in June and July, having covered a distance of up to 6000 miles each year
on their round trip, Most adult males remain in the Bering Sea and northern
Gulf of Alaska throughout the year.
From publish ed life tables (Abegglen ct al., :\IS, 1960) the Pribilof seal
herd consists of approximately 1,250, 000 females anel 400, 000 males one to four
years of age. Therefore, approximately 1,650,000 fur seals move south each fall
from the Bering Sea into the Korth Pacific. Some of these, perhaps a relatively
large percentage, \vinter in waters within 150 miles off either the American or
Asian land masses,
Seal concentrations in the eastern Pacific froIll southern California to the
Bering Sea h ave been studied by United States and Canadian investigators.
Investigations have shown older females move farther south , and that few 1-,
2- , and 3-year-old males or females travel south of vVashington. Relatively high
concentrations of seals in these age groups are found in British Columbia coastal
waters, Yearlings first appear in December ane! hv January may be found ill
Hecate Strait, Queen Charlotte Sound, and the inside channels and inlets of
northern British Columbia. Most yearlings remain in these waters until the end
of April, and some stragglers may still be found during June and July,
South of British Columbia, particularly off California, there are heavy
concentrations of mature females which first appear in December (Taylor et aT.,
1955; Anon. , :\IS, 1961).
12
During the spring most seals begin their return to the Pribilof Islands.
l'v[any yearlings, h owever, and some 2- and 3-year-olds remain at sea the entire
year. The northward-moving h erd of adult cows first appears off southern
Vancouver Island during late }\'Iarch; the greatest numbers of these seals are
encountered between the middle of April and the middle of �Vlay, passing by in a
series of waves, the h eaviest concentrations being found from 5 to 35 miles from
shore.
Sufficient information is not available to estimate accurately the numbers of
seals migrating through or wintering in British Columbia coastal waters.
SEA L IONS
The sea lion migrations are no t fully understood at present, although it is
known that much of the population undergoes a seasonal movement. In contrast
to the fur seals, where the longest migration is undertaken by the females and
young males, many sea lion cows with pups remain near the rookeries throughout
the entire year; males one year and older move from the exposed rookeries into
the inlets or to rocks closer to more sheltered bodies of water. Barren cows and
impregnated cows which h ave lost their pups on the rookeries may also move
inshore with the males.
vVinter counts indicate that over h alf the breeding population gradually
leaves the rookeries following pupping and breeding. A population of 1600 animals
on th e Scott Islands during September 1960 had dwindled to only 700 (mostly cows
and pups) by January 1961; 200 animals on Cape St. James in April 1962 h ad
increased to 600 by :\[ay 31, 1962.
A census in 1956 indicated 11, 000- 12, 000 sea lions (±5%) on the British
Columbia coast (Pike and �\ faxwell, 1958). During 1959 and 1960 the Department
of Fisheries reduced these numbers by sending out several h unting parties and
by encouraging killing for mink or pet food. A census taken during th e summer
of 1961 (Fisheries Research Board of Canada, unpublished data) indicated there
,vere approximately 1500 pups and 4500 adults resident in British Columbia
waters. During the sum mer months approximately 70% of the 1956-57 popu­
lation, or 3100 adults, were found to be concentrated on the two rookeries of
Cape St. James and the Scott Islands ( Pike and �\r axwell. 19.18).
HARBOUR SEALS
This species is regarded as non-migratory in the sense of a seasonal exodus
and return of all or a large part of the population into or out of the population
area. However, Fisher (1952) noticed a movement up the Skeena River following
salmon, and bounty h unters have noticed that many seals h erd together in small
groups during the early summer. Future studies will determine the extent of
harbour seal movements, but present information indicates no migration com­
parable to that of either the fur seal or the sea lion.
A harbour seal census has never been conducted along the British Columbia
coast. However, obervations made on field trips since 1 9 5 8 suggest that during
the fall and winter, when these animals are widely dispersed, there may be as
many as one seal per mile of shoreline, or 17,000 seals. Two bounty hunters,
the McNaughton brothers, have estimated that there are approximately 20,00 0
harbour seals on this coast.
FEEDING HABITS
COMPARATIVE FEEDING BEHAVIOUR
CAPTURE OF PREY
Most fur seal food consists of small schooling fishes or squids which are
eaten beneath the surface (Fig. 4). Except for very small items, such as lantern­
fish, the prey is usually swallowed head first. Seals have been observed eating
salmon and rockfish at the surface on four occasions, and on one occasion a fish
believed to be a cod. Larger fish such as salmon, cod, and rockfish are brought to
the surface, reduced to pieces by violent shaking, and swallowed piecemeal.
Fur seals waste little of their prey when feeding. Fish flesh unaccompanied
by bones has been observed only twice during the examination of 2000 stomachs.
However, heads of rockfish may sometimes be discarded; 18 out of 2 8 freshly
eaten rockfish ( 6 5 %) lacked heads.
Euphausiids are frequently encountered in fur seal stomachs containing
herring or rockfish remains. Data comparing frequency of occurrence of euphau­
siids and the stage of digestion of fish remains in the seal stomach indicate that
these invertebrates are found only when the contents of the fish stomach are
exposed by the digestive juices of the seal stomach. Such euphausiids had been
eaten by fish which in turn were preyed upon by seals.
Sea lions eat small fish such as herring under water. Larger prey are brought
to the surface and reduced to small pieces by violent shaking. On eight occ asions
sea lions have been observed feeding at the surface on lingcod, rockfish, salmon,
and halibut. Sleptsov (195 0) observed a sea lion surfacing with an octopus in
its jaws.
An adult harbour seal was observed eating a large sculpin or rockfish at the
surface on one occasion, and Fisher (1952) observed harbour seals feeding on
salmon in the Skeena River. Small schooling fish, such as herring and eulachon,
are probably eaten below the surface, while larger prey are consumed at the
surface.
Table III lists the maximum numbers of fish encountered in the stomachs of
the three pinnipeds.
FEEDING IN RELATION TO HOURS AFTER SUNRISE
Both fur seals and sea lions have less food in their stomachs as the day
progresses (Fig. 6 and 7). Figure 6 illustrates two samples of fur seal stomachs,
one from the Gulf of Alaska and one from British Columbia, relating mean
14
/
TABLE III.
Maxim u m n umbers of certain food items found in individual
stomachs of fur seals, sea lions, and harbour seals.
Maxim u m n u mbers of items found
i n individual stomachs
Food item
Fur
seals
.
... ..
...
244
Squid . .. .. .... . . .. . ........ . ... .. ...
Dogfish ... . . . . . . . . . . . . . .... . .. . . . . . ..
Herring .. ......... . . .. . .. . . ........ . .
Salmon . .
. ...
Eulachon . . .. . . . . . . . . . . . . . . ... ..... . .
Hake
Whiting ... . .. . . . ... .. . . . . . . . . . . . . . . .
Sablefish ... . .. . ...... . . ... . .... . .. . ..
Rockfish ...... ... . . . .... . . . . ... . . ....
.
. . . .
, . ... . . , .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
�
1000
600
if
o
0/
.
.
0�0�
0,0
/
'"
o
British
11
22
15
7
$)
18
2
148
7
1 54
18
19
.
/'0"
Harbour
seals
7
34
15
o
.
400
.
Sea
lions
100
0-0
!V
80
60
Columbia
1958-1961
",0
(1962 stomachs)
40
0/
20
2000
ti'I600
Portlock BanK,
Gulf of Alaska
June
10-25,
1962
(222 stomachs)
1200
800
....
Mean volume
G-0
%
empty stomachs
400
o
2
4
6
8
10
Hours after
12
14
16
18
sunrise
FIG. 6. Fur seal stomach content (volume) and per cent empty
stomachs in relation to number' of hours after sunrise.
95250-4
15
1750
100
1500
80
60
40
20
1·5
3·5
5·5
7·5 9·5 11·5 13·5 15·5 17'5
!-lours
after sUfJrise
FIG. 7. Me�n stomach content (volume) and per cent empty
stomachs of 269 sea l ions in relation to n umber of hou rs after sunrise.
stomach content (volume) and hours after sunrise. The Alaska sample sh ows
clearly that feeding begins late in the evening and reaches a peak some tim e
during the h ours o f darkness. All stomachs contained food early in th e morning
but by 11 hr after sunrise all stomachs were empty The British Columbia sample
illustrates the same type of feeding behaviour, and shows a corresponding in­
crease in the percentage of empty stomachs as the clay progresses. Sea lion
stomach contents show a similar decrease from a mean of 1732 cc at 1. 5 hI' after
sunrise to only 2 cc at 15. 5 h r after sunrise (Fig. 7); a corresponding increase in
empty stomachs is also ind icated.
In contrast to fur seals and sea lions, the harbour seal sample of SO stomachs
indicates daylight feedin g (Fig. 8). Samples were not collected during the hours
of darkness and conclusions cannot be reached regarding feeding h abits of harbour
seals during this time; feeding may or may not occur.
DAILY FOOD CONsm1PTION
Quantitative estimates about th e effect of pinniped predation UPOl! com­
mercially valuable fish stocks are dependent upon some knowledge of daily
food reljuirements. Table IV indicates that pinniped food requirements range
from 2% to 11 % of body weight, with an average daily food intake of 6% of
16
12.00
1000
800
o
o
2.
4
6
8
10
12.
Hours after sunrise
FIG. 8. Mean stomach contents ( volume ) in relation to
nu mber of hours after sunrise in a sample of 50 harbour
seals.
TABLE J\". Daily food consumption of pinnipeds as reported in the literature, plus the maxi mum
weights of stomach contents from individual animals collected i n the field .
· ='__�
-_c==--c.c···=-=
.____
Species of seal
); orthern fur seal
,\u thority
SchelTer ( 1 95 8 )
A n o n . ( 1 96 2 )
Serge a 11 t ( 1 962)
Observed max-imum:
I
Bod\­
weigl1 t
(lb)
Food
i n take
(lb/day)
66
65
4
4
106
11
7
6
5
10
I
Daily food intake as
a percentage of body
weight
); orthern sea lion
SchelIer ( 1 95 8 )
Observed maximum:
600
490
1 500
14
19
35
2
4
2
Harbour seal
H avinga ( 1 93 3 )
Scheffer ( 1 95 8 )
Observed maximum:
66
70
62
3
4
7
5
6
11
--_._---
M ean:
--- -----------
17
95250-H
6
the animal's body weight. Refinement of these data to allow for growth, preg­
nancy, lactation or activity is impossible; detailed studies of the nutritional
requirements of pinnipeds have not been undertaken.
COMPARISON OF FOOD ITEMS EATEN
Food items identified in the stomachs of each of the three pinniped species
under investigation have been summarized in Fig. 1 1, regardless of date or
location of collection. Items which occurred only once in the sample are not
included. This Figure has been arranged to point out similariti es and differences
which exist between each of the predators studied. Food items common to all
three pinnipeds are shown first and items common to two or only one, follow.
The factors which prevent extensive intermingling of the northern fur seal,
sea lion, and the harbour seal do not appear to restrict movements of their prey.
Ten of the 2 1 food items in Fig. 9 (squid, clupeids, salmon, rockfish, cod, hake,
flatfish, greenling, lamprey, and smelts) are common to all three pinnipeds;
combined they contribute over 50% to the diet of each predator. The differences
50
40
30
Fur seals
20
10
Harbour seals
w
�0�
G
::1
�
0-
'"
c
0
S
�
m
<f)
�-tj
�
Ii! 8 �
'"
-0
�
..,
m
�
u.
'"
�
i7 �
0� k �
0
�
..,
it
k m �
'" -' '" 8
w
�
.:;;
�
...
�
�
�
"'
<f)
.�
k
"'
<f)
�
u
C
."!
-0
C
�
<f)
�
�
...
'"
�
�
�
!l! 8 -;J
if)
..,
-"
u
�
3
'"
�
�..,
'"
>-
�
{j
c
«
>k
:>
�
'"
FIG. 9. Stomach contents of fur seals, sea lions, and harbour seals
collected along the coast of British Columbia.
18
which do exist, however, may be explained largely by differences in distribution
of each group of predators. :\Iost fur seals are offshore and their diet consists
largely of small fish and squid schooling at the surface. Sea lions and harbour
seals are inshore; bottom fish and octopus are more important in their diet.
The high percentage of salmon in the harbour seal sample is due to 29 stomachs
collected in the vicinity of salmon spawning creeks during September and October
1961; this is not representative of the actual role of salmon in the year-round diet
of these seals.
UNUSUAL STOMACH CONTENTS
Small pebbles, sand, bits of wood or bark, kelp, and small clam shells have
occasionally been found in stomachs of each of the three groups studied. It is
believed these are ingested accidentally. However, smooth stones of varying
shapes from �. to 3 inches across, are found so frequently in sea lion stomachs
that some functional explanation is indicated. One to ten stones weighing up to
4 lb were found in one-third of all sea lion stomachs examined.
Several suggestions have been presented in an attempt to explain the presence
of stones in pinniped stomachs: (a) stones are taken accidentally when sea
lions prey on octopuses which have stones grasped in their tentacles (Sleptsov,
1950); (b) they add bulk to the stomach during periods of fasting (Howell, 1930;
Laws, 1956); (c) they aid in diving (Murray and Renard in Emery, 1941;
Hamilton. 1933); (d) they macerate stomach parasites (Hamilton, 1933); (e)
they aid in the physical breakdown of food in the stomach (Mathews, 1929).
Two observations do not support the theory that stones are ingested acci­
dentally with octopus remains: (a) stones were found in the stomach of a 6-month­
old nursing sea lion; apparently even young animals are capable of picking up
and swallowing such objects; (b) stones are not found in the stomachs of harbour
seals which frequently prey upon octopuses. Although Laws (1956) presentee!
convincing evidence to support his theory that stones ade! bulk to the stomachs
of fasting elephant seals, his theory does not apply to the stones founcl in northern
sea lion stomachs. These are found throughout the year and ill the stomachs of
lactating cows, when nutritional requirements are high.
l\Jathews' (1929) theory that stones aid in the breakdown of food is supportecl
by evidence from the northern sea lion. The sea lion's teeth, particularly the post
canines, are designee! for grasping and tearing rather than grinding (Fig. 10);
thus, food is swallowed in pieces. Since much of the sea lion's food consists of
large, heavily-boned species the grinding activity of stones in the stomach would
be of great assistance in the physical maceration of flesh, bones, and octopus
beaks. Observations of captive animals have shown that such stones are easily
regurgitated, and this occurs after the digestion of food (Emery, 1941). Stones
similar to those found in sea lion stomachs are also found on sea lion haul-out
rocks.
l\Iost of the fur seals' food, and probably that of the harbour seal, is smaller
fish or squid; an additional grinding mechanism in the stomach is not needed.
19
'-----'
FIG. 1 0.
1 inch
Top: 3- to 4-month-old male sea lion skull; Bottom: 1 5-mo nth-old
female sea lion sku ll (d
deciduous teeth).
=
COMPARATIVE SEASONAL FEEDING HABITS
Differences in feeding habits of these three pinnipeds are evident, relating to
time of year and also to area. Accordingly, the samples have been grouped as to
season and area of collection. The feeding habits of fur seals during January,
February, March, April, and May are described in detail (Table V); whenever
possible, comparisons have been made with the feeding habits of sea lions and
harbour seals (Table VI).
Following the northward migration of fur seals, only sea lions and harbour
seals remain along the British Columbia coast. The samples from these two
species have been divided into "summer breeding" and "summer non-breeding"
categories for sea lions, and a "summer" sample for harbour seals. Samples from
September 16 to December 15 have been combined.
The British Columbia coast has been divided into four main areas (Fig. 11)
as an aid in describing feeding habits. This Figure also shows the major sea lion
and harbour seal localities mentioned in the text. Area I extends from 48°00'N
to 51°00'N along the west coast of Vancouver Island; area II includes waters off
20
TARLE V. Fur seal stomach contents by month and area.
Month
Jan.
February
March
Area
IV
III
III
Stomachs with food:
Stomachs empty:
8
9
17
Totals:
-- - -
1
1
22
19
41
-- --
Species
Fb
--
LaZiga ap ....
G. magister.
N
......
Unid. Squid.
Lamprey...
Ratfish...
Herring...
Shad....
Clupeids.
Anchovy.
Salmon.
Eulachon.
Capelin.
Smelt....
Saury..
Hake...
Whiting.
Cads...............
King-of -the-salmond.
Flatfish...
Greenling.
Pomfretd .....
Squaretaild . ........... , .
Sablefish.
Rockfish...
Stickleback.
Sandlance..
Birds......
Misc;d" ,., ..
Unid. Fishd.
Totals: .......
F
F
-- --
6
4
IV
-- ------
15
II
69
118
-
-- --
20
16
April
IV
--------
46
39
--- -----
334
495
- - ----
-----
------
--_._-
-- ------- -
-----
-- -----
------
26
F
187
F
<;{)c
%
85
F
--- - -- --- --
--
--
3
3.4
3
19
3
21.9
24
2
27.6
2.3
3
6
2
3.4
6.9
2.3
3
1
36
F
6.2
4
12.5
8
25.0
3.4
3.1
1.2
1.2
21.9
3.1
2.3
28
11
%
----
58.3
22.9
4
8.3
2
I
4.2
2.1
829
%
F
--
4
6
II
I
2
1
1
9
I
I
4
22
9
14
16
87
4.6
6.9
12.6
2.1
I
2
3
----
100.0
---
32
3.1
I
1
4
--- - -
99.9
48
2.1
----
100.0
oper cent frequency of occurrence.
dN ot used in calculations.
--
9
16
25
6
I
7
--
--
F
F
-----
324
413
---_._--
737
- - - ----
%
F
-- --
----
180
19
44.8
4.7
6
4
14
30
1
6
6
1.0
3.5
7.5
0.2
1.5
1.5
5
0.2
0.2
--
403
2
4.5
7.0
6.2
4.5
0.5
4
---- - -
�\
'/
1QO.I
--
2
I
3
--
F
---
----
43
53
------
96
- --- - --
F
%
II
III
IV
3
I
1
I
_
1
11
--
7
44
1
1
188
3
4
13.1
0.2
0.2
56.0
0.9
1.2
34
5
10.1
1.5
1
7
4
3
0.2
2.1
1.2
0.9
9
7
16
1F
-- -- - --- --
4
--
2
1
4
3
1
I
12
7
2
7
1
8
93
0.2
1.2
0.9
0.2
0.2
3.6
2.1
0.6
2.1
0.2
--
339
-
---
100.1
- ---
-- --
- - --
-F
2
9
7
1.8
1.8
46
41
39
26
9
51.9
2
4
5
3.7
7.4
9.3
54
F
5.6
28
- - --
2.112
-
F
1.8
11.1
3
912
_���
13
28
158
6
6
443
24
5
9
59
48
I
10
15
12
16
6
6
3
Totals
-- - - - ---
1.5
2
18
28
25
18
2
9
60
-
I
June
IV
0.5
10.9
0.2
-One empty stomach collected in area IV during May not included.
bFrequency of occurrence.
--
44
I
0.5
0.2
21.9
IV
- --- --
3.1
3
May
III
9
I
I
5.6
-- --
100.0
4
14-
I I I
1 1 1
-2-
-1- -1-.036
TABLE V I . Harbour seal and sea lion stomach contents. by month and area.
Harbour seals
Sea lions
\\.Tintt"[ -SIJring
Month:
Area :
Stomachs with food:
Stomachs emptv :
T ot c:!l s
N
N
:
14
Feb.
Mar.
Apr.
IV
IV
IV
F
F"
·4
F
J an .
Feb.
Mar.
Apr.
I
May
May 1 5Sept . 1 5
Bre('ding
colonies
1'\onbreeding
colonies
l-'�n Li[e
coast
IV
IV
IV
IV
1
IV
IV
IV
35
22
3S
17
26
48
38
6
247
F
2
3
36
5
1
1
12
Fall
Sept. 1 6 ·
Dec. 1 5
Sept. 1 6Dec. 1 5
<J2
F
Summer
May 1 5Sept . 1 5
1 55
14
\Vinter
May 1 5 Sept . l S
3
2
o
14
Species
Shrimp .
Clamshell .
Octopus
Squid .
Lamprey .
Skate .
Ratfish .
Dogfish .
Herring .
Salmon .
Eulachon .
Smelt .
Hake .
Graycod . .
Whiting.
Halibut .
Flatfish .
Seapereh .
Mackerelj aek.
Sablefish .
Lingcod .
Greenling .
Rockfish .
Cabezon . .
Sandlance .
Sea bird
Milk .
Kel p {' . . . . . .
\ T n i rlent i fied ('
Total s :
--- I
Fall
Summer
5
1
6
57
j{) h
2
3
42
5
1
F
4
S
4
.9 ,
.2
.4
9
2
. 1
,
1
1
o
o
0
1
F
D'
52
%
1
1
2.4
12 . 2
4.9
1
3
4.9
4.9
1
3
1
4
74
3
Sir!
F
F
2
2
2
7
.4
.4
.4
. 1
2
7
2
9
.
.
.
.
D'
F
F
2
8
1
2
4
1
4
5
44
%
6
25
3
6
D'
2.2
15 . 2
17.4
5
8
.2
.5
9
16.
%
.5
14
10.8
30 . 4
.2
3
2.4
21 .9
2.4
9.8
8
19 . 0
1
2.4
3
3
2.
7 . 1
I
4
1
7 . 1
2 . 4
3.2
3.2
2.4
11
21.9
8.7
2.2
22 . 6
16 . 7
4.9
I>
17
-
aFrequcncy of occurrence.
bPer cent frequency of occurrence.
C7\Tot used in calculations.
I
1
4.9
25
11
1-
4
85
99 . 9
4
1
4
42
I
3.2
9.5
6
19
1
99 . 9
o
--. -'------'-.
33
1 1 00 . 0
46
1 00 . 1
55
�
\
I
54
53
t
+
BRITISH
COLUMBIA
i
r
ARE A
:rr
·
5 1 ---,
5 0· -�-
_ �i_ _ _ �___
AREA
_�-----rr133r---�13�2--�1*31--�130�--�h---�--�12�7---'�26�--�'��5�--�
- I
j-- ��
,
CAPE FLATTERY
4 8'
FIG. 1 1 . Collecting areas on the B ritish Colnmbia coast (area IV incl udes all protected
i nlets and channelsl .
the west coast of the Queen Charlotte Islands ; area III includes Hecate Strait,
Queen Charlotte Strait, and D ixon Entrance; and area IV includes all protected
channels and inlets of the British Columbia coast.
References to numbers of stomachs in the following account refer to numbers
of stomachs with food only.
WINTER-SPRING
January. Fur seals first appear in January and are to be found in Hecate
Strait, Queen Charlotte Sound, and some of the northern i nlets. These are mostly
23
young males and females, but some adult cows are also seen at this time. Eight
fur seal stomachs were collected during January in Knight Inlet and Queen
Charlotte Strait. Squid and small sablefish were the most important food
species identified.
l\ I ale sea lions, plus a few non-lactating cows and immature females, are to
be found on haul -out rocks adjacent to the coast, or in more protected waters
following herring; most cows with pups are on the rookeries. No sea lion stomachs
were collected during this month.
Harbour seals may be found anywhere along the coast. One harbour seal,
collected in Knight Inlet during January, had been feeding on eulachon.
February . Distribution of all species is quite similar to that during January,
although more young fur seals are evident in all northern areas and some adult
and young fur seals may also be found off the west coast of Vancouver Island.
Stomach contents from 22 fur seals collected in Hecate Strait indicate that
herring was the primary item in the diet while whiting and squid were of secondary
importance. Fur seals from inside waters were feeding mainly on small sablefish,
ratfish and squid; these three species formed over half the diet.
Three sea lions, collected from Barkley Sound and Saanich Inlet, had been
feeding on whiting, herring, and dogfish.
One harbour seal collected in Barkley Sound during February had been
feeding on hake.
l11a rch . By late \ I arch the young fur seals begin to leave the protected
coastal waters, and the number of adult fur seals appearing off Vancouver Island
increases. One hundred and thirty-five fur seal stomachs containing food were
collected during �\ I arch in areas I, III and IV. Twenty stomachs from Hecate
Strait indicated that herring was the preferred fish, but squid, ,"hiting, and
small sablefish were also important. A sample of 69 stomachs from area I indi­
cated that herring and squid were the two most important items contributing
50% to the diet. Fur seals from inside waters, predominantly yearlings collected
in Knight Inlet, were preying heavily upon the squid, Gonatus mag1·ster.
Quantitative data on the movement of sea lions in Barkley Sound indicate
that sea lions reach their maximum numbers in March, presumably following
the herring which are abundant in inshore waters at that time. Sea lions move into
Knight Inlet during March and April. Nine sea lion stomachs were collected in
Knight Inlet and Queen Charlotte Strait during March. Whiting, herring, and
rockfish occurred seven times in a total of 11 occurrences.
The two harbour seals collected in Knight Inlet during l\Iarch had been feed­
ing on eulachon.
A p n·Z. During April the main northward-migrating fur seal herd has reached
southern British Columbia waters and most of the young fur seals have moved
out of the sheltered inside waters. Three hundred and forty-nine fur seal stomachs
were collected in areasJ , III and IV. Herring predominated in the nine stomachs
24
collected in Hecate Strait. A large sample of 334 stomachs from southern Van­
couver I sland indicated that herring was again the most important food species,
but squid, shad, stickleback, eulachon, and rockfish were also taken frequently.
Squid predominated in stomachs of six young animals collected from area I V .
Sea lions which, prior t o April, had scattered throughout many of the inlets
and inside passages probably begin their migration back to the rookeries by the
end of April. Two sea lion stomachs were collected during April in Barkley
Sound and Knight I nlet; the former had been feeding on rockfish, octopus, and
skate, while the latter had been feeding on eulachon.
One harbour seal collected off Maude I sland, Strait of Georgia, in April had
been feeding on herring.
May. During the early part of May, virtually all fur seals have left Hecate
Strait and area I V waters, while fur seals of all ages are abundant off Vancouver
I sland. By the end of May the adults have passed into Alaskan waters. Three
hundred and twenty-six fur seal stomachs from areas I, I I I and I V contained
food during M ay. A large sample of 324 stomachs collected in area I indicated
that herring again comprised over half the food. Salmon assumed its greatest
importance during May in the fur seal diet in this area when it contributed 10. 1 %
to the total intake of food. King-of-the-salmon, pomfret, and squaretail were
encountered in one stomach collected 200 miles southwest of Estevan Point,
Vancouver I sland.
No sea lion and harbour seal specimens were collected in early May, and
those sampled after May 15 have been placed in the appropriate "summer"
category below.
SUMMER
During June there are still a few late migrant fur seals off British Columbia
which are mostly young animals. Forty-seven seals from the west coast of
Vancouver I sland had been feeding on herring, hake, cod, and squid. Onl y nine fur
seal stomachs have been collected from waters west of the Queen Charlotte
I slands. These seals, collected during June between 100- 150 miles offsh ore,
were feeding mainly on an unidentified squid (9 out of a total of 14 occurrences),
although saury, ratfish, whiting, and lamprey remains were also id entified. One of
these nine stomachs, collected at 54°2 1'N- 136°24'W, contained lamprey, whiting,
and ratfish, which is typical of an inshore stomach. A mistake may have been
made in positioning this seal; if this was the case squid has an even greater
importance in this sample than is shown in Table V.
By late May and early June 70% of the sea lion population has congregated
on the rookeries of Cape St. James and the Scott I slands, for pupping and breed­
ing. Octopus, forming nearly half of the contents examined, is by far the most
important food, although rockfish, dogfish, and salmon are also preyed upon
quite heavily . S.ix yearling stomachs contained milk. The sample from n o n ­
breeding or haul-out rocks indicates that octopus is o f less importance than on
the rookeries and that whiting and rockfish are the two maj or food items.
25
During June, according to D. l\Ic]'\aughton (personal communication),
many harbour seals congregate into small herds in isolated areas along the coast
and remain together until the end of the summer when pupping occurs. However,
in some areas (e. g. the Skeena River) seal herds break up following the pupping
period and the animals move either down or up river by the end of June (Fisher,
1952). Twenty-six stomachs were available for the summer months, collected
mostly from the Fraser and Skeena Rivers. In this sample, octopus, rockfish,
salmon, and herring are the most important food items.
FALL
There are no fur seal stomachs available for the 4 months from September to
December. This species is rarely found in British Columbia waters until January
C\;I anzer and Cowan, 1956).
During the early fall many sea lions begin to leave the breeding rocks and
scatter along the coastline. :\ I ales, and females without pups, probably move
south from the Scott Islands towards Vancouver Island or towards the mainland
inlets. Sea lions on Cape St. James probably move northwards up both the east
and west coasts of the Queen Charlotte Islands, or across Hecate Strait to the
mainland. The sample of 35 stomachs from Scott Islands, Cape St. James, and
inside waters of }\I oresby Island, Skedans, and Isnor Rocks indicates that at
this time of year rockfish and hake are the most important food species. Salmon
is the third most prevalent food and is taken largely by sea lions which have
moved into the inlets and creek mouths where salmon are readily available. Five
mackereljack, totalling 18 pounds, were identified in one stomach collected
from the Scott Islands during September 1961. This species is fairly common
during the summer months in waters off the British Columbia coast (Clemens
and \Vilby, 1961). Milk was identified from four 14- to I S - month-old animals
collected during the fall.
During the early fall the small herds of harbour seals apparently break up
and all members disperse. It is believed these movements are relatively limited
although they have not been studied closely. The 44 stomachs available for this
period are predominantly from the Queen Charlotte Islands, collected when
salmon were moving into the streams to spawn; collections were also made on
the Scott Islands and in the Gulf of Georgia. Salmon was the most important food
item (mostly chum and pink salmon) contributin g 30. 4% to the diet (Table V I) .
Octopus and squid were frequently eaten.
SUMMARY
The seasonal food habits of these three pinnipeds may be summarized as fol­
lows :
Herring is the most im portant food of fur seals during all mOll ths off Vancou­
ver Island and in Hecate Strait, but squid are also taken frequently. Salmon
assumes importance only during l\J ay off Vancouver Isl;;md. Seals in inside waters
feed mainly on squid, ratfish, and sablefish.
26
Rockfish is one of the main food items for all sea lions at all times of the
year. In addition to rockfish , h erring is important during the winter; octopus,
dogfish, and salmon are taken frequently by breeding animals, while non-breeding
animals feed heavily on whiting during the summer. Rockfish , salmon, whiting,
and h ake are important food items during the fall.
Meagre sampling of harbour seals during the winter gave little indi­
cation of the main food items during that season, but eulachon may be
important, particularly in the inlets. Summer sampling, mostly on the Skeena
and Fraser Rivers, indicated that octopus, rockfish , and salmon were the impor­
tant food items. During the fall, salmon constitutes nearly one-third of the
food eaten.
PREDATOR-PREY SIZE RELATIONSHIPS
Prey size may have an important bearing upon the fish species preferred by
predators and two aspects of this problem have been investigated : (a) different
feeding habits between sea lions and fur seals produced by interspecific size
differences; (b) an increase in prey size with the increasing age (and size) of fur
seals.
TABLE VI I . Comparison of large and small food items eaten by fur seals and sea lions. Frequency
expressed as a percentage of total occu rrences of all food items from Tables V and V I .
Size
range
(inches)
Prey (l arge)
-----------------------
Salmon . . .
Rockfish . . . . . . . . . . .
Cod . . . . . .
Dogfish . . . .
Hake . . . . . .
Halibut
.
. . . . .
Lingcod . . . . . . .
. . . . . . . . .
. . .
Mackereljack . . .
. . . . .
_
.
.
_
.
.
.
.
.
.
.
1 2- 1 8
1 2- 1 8
.
Sea lions
Fa
Fur seal s
Fa
------� ------ -�-----
7-3 6
8- 1 4
6- 1 4
1 2-3 6
6- 1 4
.
Predators
10
30
20
13
11
1
2
1
59
41
22
12
----- ----.--
Subtotal : . . . . . . . . . . . . . . . . . .
. . . . .
Total occu rre nces (all spec ies) : . . . . . . . .
Percen tage : . . . . . . . .
. . . . . . .
.
.
.
. . .
.
Prey (small )
---- ---- ----------_·_---_·------
Clupeids . . . . . . . .
Smelt . . . . . . . . . .
Sablefish (sma] ] ) .
Stickleback . . . . .
Sandlance . . . . . .
.
.
.
.
.
.
.
.
.
.
. . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . . .
. .
. . . . . . . . . . .
_
88
203
43 . 4
. . .
. . .
.
. . .
. . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. . . . . . . . .
. . . . . . . . .
.
. . . . . . . .
. .
.
.
.
.
.
Subtotal : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Total occurrences (all species) : . . . . . . . . . . . . . . . .
Percentage : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
aFrequency of occurrence.
27
1 ------
4-9
4-7
7-1 1
2-3
4-7
1 34
1036
11.9
- -- -- - ------
18
1
3
22
203
10 . 8
481
59
46
39
26
651
1 03 6
62 . 8
i NTERSPECIFIC DIFFERENCES
Table VII compares the importance of large and small food items in the
diet of fur seals and sea lions. The mean fur seal weight was only 29. 1 kg with a
range of 5.9-63.5 kg, while the mean female sea lion weight was 17 7 kg with a
range of 58-265 kg. Although no mature bull sea lion weights were taken, some
bulls weigh 900 kg (Cowan and Guiguet, 1956). Professional butchers have esti­
mated that large bulls taken for mink food weigh 680 kg (1500 Ib).
Table VII illustrates the importance of small schooling fishes in the fur
seal diet : 63% compared to 11% in the sea lion diet. In comparison, the larger
prey species, such as salmon, rockfish, dogfish, cod, hake, halibut, and lingcod
comprise 43% of th e sea lions ' food but only 12% of the fur seals ' food.
INTRASPECIFIC DIFFERENCES (FUR SEALS)
Table VIII and Fig. 12 summarize the available data on fur seal food pref­
erences according to age. Unidentified contents and species which occurred
only rarely have not been included.
\Vith increasing age, and thus size of predator, fish of larger size (salmon,
cod, hake, rockfish, and shad) become increasingly important. A. rise occurs
from 3% frequency of occurrence in the i -year age group to 38% and 37 % in the
9- 10 and 10 + age groups, respectively. vVith increasing age of fur seals , foods
other than those larger species mentioned above become less important.
TABLE VI I I . Analysis of 699 fur seal stomachs conta i ning food showing selective feedi n g behaviour
accord i n R to age . ( Data from presen t i nvestigation only . )
Age (years) o f f u r seal
Food i tems (size in brackets)
Clupeidsa and smelt
(4 - 9 i nches)
Totals
I
P
-- Sal mon , cod , rockfish , hake ' l F
and shad
i "-c
( 7 -36 i n c h es)
-_. _- "" --_._----_. _ ..
77
�-; ' i 3 7 . 0
, -- -
- I-F';e
-
1
i
-
-
7
3 .4
--
39
44 . 3
45
50 . 0
38
52 . 0
1- 2
i 25
15
16 . 7
2.7
28 . 4
1
16
1
15
13
14 . 8
42 . 8
21 .9
16. 7
- - -- ! -l js j1 21 . 5 1
stickleback , F i 3S I 1 7
'1;
16 . 8
23 . 3 1 16 . 7
Squid
Sablehsh , samy ,
and sandlance
(2- 1 1 i nC'hes)
- -- ;;
��
To l
-
-
Total with food :
Total empty :
I
_
__
1
-1-
tI96-1261
18
36 . 0
28
30 . 1
19
38 . 0
1
18 9
F 208
'?, ' 1 00 . 0
3S
37 6
I
_
_
_
15
16. 1
1 98I
--- ------ ._----------
aClupeids do not i nclude shad.
bFrequency of occurrence.
cper cent frequency of occurrence.
28
I
I
!
49
41 . 5
30]
44
37 . 3
140
1-81 6 --0 : -13
11 .0
15
16 . 1
_. _ .
_. .
90
88
73
93
1 00 . 0 ) 00 . 0 : 1 00 . 0 1 00 . 0
-- ----- " --------1
90
79
77
115
1 40
80
75
1
1
1 69
.
5
10 . 0
12
I 10 . 2
110
720
699
777
/
50
--e- - .
/
/
/
/
'./
I '.
\
\
40
30
\
"
. . . l.,: . .
"<
"
�
20
e- . -e
. ....... .
. '-.: ..
�
.
.
10
0
I
2.
3-4
..
- . • - . -: ,.., . . ··-:- · _ · - · Il _
.
.
.
•.. . .
5-6
7- 8
..
9-10
.•
:J
10+
(Years ) o f
FIG. 1 2 . Analysis of 699 fur seal stomachs containing food , showing selective
food preference according to age.
These comparisons show that predator size has a direct bearing upon prey
size. Large fur seal s prey on larger food items than small fur seals; sea lions
prey on larger food items than the smaller fur seals.
FEEDING HABITS AND REPRODUCTION
Pinniped food habits during the pupping and breedin g season were examined
primarily to determine the period of reduced food intake.
FUR SEALS
Available data indicate that food intake by the males is reduced during the
breeding season. Abegglen et al. ( :\I S, 1 958) report that " only 27 stomachs
contained food among the thousands of empty ones in the St. Paul Island fur
seal harvest". Bartholomew and Hoel (1953) con cluded that harem masters did
not feed for the 2 months of June and July while they maintained their territories.
However, Russian investigators (Anon. , l\ I S , 1961) h ave shown that h arem
bulls on the Commander and Robben Islands remain on their territories for
less than 1 month at any one time, and that vacancies on the rookeries are
filled by reserve bulls.
The cows come ashore, and within 3 days give birth to their pups (Bartholo­
mew and Hoel, 1953). Within 4-7 days after parturition, copulation takes place;
the cow then goes to sea either on the same day or the day following that on
which copulation occurred, leaving her pup on the rookery. Her first stay away
from the rookery lasts approximately 6 days. She returns for 1-2 days and then
re-enters the sea for an average of 8 days; each successive trip to sea becomes
longer. The pups first venture into the water in August (Baker, 1957) and from
29
August until October or ::\ovember, when abandoned by the cows, they gradually
learn to feed for themselves. Fur seal pups have tripled their birth weight by
October.
The lack of food in waters adjacent to the rookeries may provide an ex­
planation for the lengthy trips of post-partum females. Dragging operations
(Wilke and Kenyon, 1954) and pelagic stomach samples indicate that only a
limited food supply is available within a radius of 30 miles of the Pribilof Islands.
Eighty-five per cent of the stomachs collected within this 30-mile radius are
empty (Niggol et al. , _vr s , 1960). These authors suggest that the 1.5-2 million
seals in this area during the 6 mOll ths from June to N ovember have reduced the
available food, particularly bottom fish. Salmon migrate past the Pribilof
Islands but are seldom taken by fur seals (\Vilke and Kenyon, 1954) Chapman
( 1961) has suggested that the lack of food in this area may explai n the heavy
mortality of fur seal pups.
SEA LIONS
Pupping begins during the last week in M ay and is finished by the end of
June (Pike and M axwell, 1958; personal observations made during 1959).
Information on the feeding habits of male and female sea lions in the pupping
and breeding season is given by a series of samples collected from M ay to
September. Table IX compares the percentage of empty stomachs to those
with food during this period. Normally about 60% of the sea lions collected
during daylight hours contain food.
TABLE I X . Changes in n umbers and percentage of stomachs with food and of empty stomachs
throughout the pupping and breeding season i n 2 2 8 male and female sea lion s tomachs. Pups not
included. ( Da ta from present i nvestigations o n ly . )
Femalc
Male
� - -----,,---_.-
Food
E m pty
Food
Empty
---" ---
May 2 2-2 9
Rookeries
Fa
14
(58 . 3)
10
(4 1 . 7 )
13
(4 1 . 9)
18
(58 . 1 )
J u ne 5- 1 8
Rookeries
J u ly 3-22
Rookeries
F
16
( 76 . 1 )
5
( 2 3 . 9)
15
(2 7 . 2 )
40
(12 . 8)
F
2
7
12
(57 . 1 )
9
(42 . 9 )
September 2 1 -30
Rookeries
F
2
0
16
(64 . 0)
9
(36 . 0)
May 2 1 -August 1 7
Non-breeding
F
15
(60 . 0)
10
(40 . 0)
11
(73 . 3 )
4
(26 . 7)
------
----
(7 h
Ie
C;"
/0
-- - -
r:,
/0
(1;'
/c
01
/0
aFrequency of occurrence.
bPer cent frequency of occurrence.
30
During the last week in May, males have taken up territories but are
feeding fairly regularly as 5 8 % of stomachs contain food. The females, which
have just started to pup, show the first signs of a decrease in food intake, with
only 42 % of stomachs containing food.
The next period of observations, June 5-18, is during the peak of the pupping
period and presumably there is little breeding activity on the part of the males.
This sample of 21 males indicates an increase in feeding. Female food intake is
at a minimum, with only 27 % of female stomachs containing food. The probable
explanation for the high percentage of empty female stomachs at this time is
that cows are remaining with their newborn pups.
The first 3 weeks in July indicate a complete reversal of the June situation.
Feeding appears to be at a minimum in the male population, but is nearly
normal for the females. Although the male sample is small I believe the high
frequency of empty stomachs (7 out of 9 examined) accurately reflects the
fact that many males are busy maintaining territories and breeding. The cows
have finished pupping, lactation is well in progress and normal feeding has been
re-established (57% of stomachs with food). Although no detailed study of sea
lion breeding behaviour comparable to Bartholomew and Hoel's (195 3 ) fur seal
study is available, it is probable that sea lion cows, in contrast to the fur seal
cows, do not leave their pups for extended periods of time. Food is abundant
in the immediate vicinity of the sea lion rookeries and the cows' feeding
trips are probably only of a few hours duration.
The sample collected during late September is predominantly of females.
By this time nearly all the bulls and many cows without pups have departed
for more protected waters, leaving the lactating cows and pups on the rookeries.
Feeding by the adult cows is probably at a maximum, with 65 % of stomachs
containing food. Pups have more than doubled their birth weight and must make
heavy nutritional demands on the cows.
It is not known when lactation ceases. However, observations of females
that are suckling animals 12 and 15 months old indicate that up to 2 5 % of the
yearlings are not completely weaned. In some instances a yearling sea lion will
be nursing, and supplementing this milk diet with fish, e.g. on July 6, 1959, a
yearling sea lion was collected with milk and a ratfish in its stomach.
HARBOUR SEALS
During the actual pupping period food intake is at a minimum. Only five
stomachs contained food in 45 collected on the Skeena River during the peak
of the pupping period. How long this period of fast continues is not definitely
known, but in the case of the Skeena River population probably only until the
adults move down river. From Fisher's (1952) study it is evident that by August,
harbour seal pups, born in June, are feeding on their own. These observations
are strengthened by those of D. McNaughton (personal communication) who
has observed that the first pups are born during the last week of May and
pupping reaches a peak about the middle of June. This is comparable to the
31
sea lion pupping behaviour. However, M r M cN aughton noted that, in contrast
to sea lion pups, the harbour seal pups are quite capable of looking after them ­
selves within one month of birth, and at this early age are abandoned by the
cows.
INTERSPECIFIC COMPETITION
The term competition as used here refers to an interspecific interaction which
adversely affects the growth and survival of individuals of one species by another
dominant or more successful species (Odum, 1960) .
During February and M arch of m ost years, yearling fur seals congregate
towards the head of Knight I n let. which is 4 miles wide. During M arch 1961
there were approximately 100 fur seals in m id channel at a distance greater than
1 mile from either shore and 2 miles from the estuary of the Kleena Kleen River
at the head of the Inlet. When this area was sampled, only four fur seals had ven­
tured inshore in the direction of the estuary. These four had been feeding ex­
clusively on eulachon . Sixty seals collected in the m iddle of the inlet had been
feeding on squid.
During this same period approximately 30 sea lions in groups of 4-10 were
ranging up and down the shore, m oving occasionally into the m iddle of the inlet
or the estuary of the river. One sea lion collected had been feeding on dogfish
and whiting. (Another sea lion stom ach collected and examined by Departmen t
of Fisheries officials during April 1960 in Knight Inlet, contained eulach on.)
Twenty-five harbour seals were found during March 1961 in the estuary
of the Kleena Kleen River ; some solitary individuals were observed along the
shore of the inlet, maintaining a stationary position, close to the beach. Two
harbour seals from the river estuary had been feeding on eulachon.
Therefore, harbour seals plus the few fur seals which had moved into the
Kleena Kleen estuary were feeding on eulachon . The m aj ority of the fur seals
were feeding on squid, while the one sea lion collected had been feeding o n
dogfish and whiting .
During February 1958 the three pin nipeds were found together in Barkley
Sound ; distribution there was similar to that observed in Knight Inlet. The fur
seals were greater than one m ile from shore ; sea lions and harbour seals were
both close to shore although the sea lions were usually actively swim m ing, i n
contrast t o the more sedentary harbour seals. A t this time there were approx­
imately 25 fur seals, 300 sea lions, and an unknown number of harbour seals
in the area. Stomach contents indicated that fur seals (four stom achs with food)
were feeding on herring, ratfish, hake, and smelts, while sea lions (two stomachs)
were feeding on herring and whiting ; one harbour seal had been feeding on hake.
Although both fur seals and sea lions were feeding on herring, the sm all numbers
of fur seals in the area, and the large numbers of herring in B arkley Sound at
that time of year, indicated that any active competition between these two species
was unlikely, particularly when their relative distributions are considered .
32
Sea lions are rarely found offshore in the vicinity of fur seals, and when
located are difficult to kill. H owever, on M ay 2 1, 1961, a young sea lion was
collected 10 miles off Tofino (west coast of Vancouver Island) in 30 fathoms of
water. This animal, killed in waters where fur seals were feeding predominantly
on herring (75% by volume), had been feeding on lingcod and on unidentified
flatfish. Fur seal stomachs occasionally contain flatfish, but lingcod have never
been identified in stomachs collected in British Columbia waters.
On Triangle Island a small population of 25 harbour seals lives near 500-600
sea lions. The sea lions haul out on small rocks situated a few yards to one mile
off Triangle Island, while harbour seals haul out on the beaches of the main
island and spend considerable time in protected pools behind the outer reefs
(Fig. 13). Occasionally harbour seals have been seen outside the surf, near a
sea lion rock or a group of swimming sea lions, but no animosity has been observed
between the two species. Two harbour seals collected had fed on lingcod and
small sablefish, neither of which has been identified in an examination of 35 sea
lion stomachs with food from Triangle Island.
Thus, interspecific competition appears to be negligible in British Colum bia
waters even though it is known that in several instances the same species of fish
may be preyed upon by each of the three pinnipeds. In the relatively few areas
where the three predators (or only two of them) occur together, intermingling
is rare. \Vhen stomach contents indicate that the same food species is being
preyed upon by two (or the three) predators in the same area and at the same
time, the numbers of predators are so few, and the prey species is so abundant,
that competition is unlikely.
\Vhere larger populations are concerned, however, com petition may exist .
Intermingling of adult fur seals, sea lions, and harbour seals was observed during
June 1962 on the Portlock Bank, Gulf of Alaska, 30-40 miles from shore. \il/hether
or not active competition for food occurred was not determined as only fur seals
were collected. They were feeding exclusively on sandlance. Sea lions were
observed at the surface eating rockfish twice and salm on once.
EFFECT OF SEAL AN D SEA LION P REDATJ O)J
UPON BRITISH COLUM BIA'S COM MERC IAL FISHERY
Two problems must be faced when considering pinniped predation U P O Il
the commercial fishery : (a) the effect of seal and sea lion predation upon fish
stocks, and (b) the effect that this predation has upon fishing gear. This study
has attempted to investigate the former. The second problem requires investi­
gation in the form of questionnaires and interviews with fishermen. The Depart­
ment of Fisheries of Canada is at present undertaking such a program .
FUR SEALS
Species of greater or lesser economic importance make up a large part of
the fur seal diet in British Columbia waters. Over the past 4 years they have
totalled 65% of the contents examined, and include herring, salmon, hake, cod,
33
FIG. 1 3 . Triangle I sland :
in far right background ;
Top: harbour seal habitat behind breakers-a sea lion rock
Botlom: sea lion rock with Triangle Island in background.
34
sablefish, rockfish, and flatfish. However, only predation upon herring, salmon,
and some of the species exploited by the trawl fishery can be regarded as poten­
tiall y serious, as it is these groups of fish which at present are being heavily
exploited by man. N o concern is expressed regarding predation upon other
commercially valuable fishes since they are either fished spasmodically or taken
in very small quantities by fur seals.
As it is at present impossible to estimate the numbers of fur seals migrating
past the British Columbia coast, the amount of herring and salmon eaten by
this predator cannot be calculated.
H ERRING
Herring are the 111 0st favoured fish species taken by fur seals in British
Columbia waters, and contribute 43% to the total diet (Fig. 9).
The northward migration of fur seals off the west coast of Vancouver
I sland coincides with the offshore movement of herring out of Barkley and
Clayoquot Sounds after spawning which reaches a peak during mid M arch. An
index of the size of the adult herring population is computed on the basis of
"miles of spawn" deposited (Outram, 1961). I ndices of abundance for 1958,
1959, 1960, and 1961 have been compared with the percentage frequency occur­
rence of herring found in stomachs col lected in waters between Barkley and
Clayoquot Sounds (Fig. 14). The sharp decrease in the size of the herring spawn­
ing population (as exhibited by the "miles of spawn" index) from 1958 to 1959,
followed by a levell ing off from 1959 to 1960 and an increase in 1961, appears to
be fairly wel l duplicated in the presence of herring in seal stomachs. Thus, the
magnitude of fur seal predation upon herring is apparently related to the
abundance of spawning herring.
SALMON
Salmon have occurred only 59 times (5.8% frequency of occurrence) in a
total of 2 113 stomachs examined. Fur seals do not appear to show a preference
for salmon and they may, in fact, prefer smaller fish such as herring, when the
two types of prey are available. The only indication of salmon availability is the
presence of the troll ing fleet off southern Vancouver Island; seals collected in
the vicinity of trollers presumably have had an opportunity to prey upon salmon.
During 1960, in nine stomachs containing food col lected in the vicinity of the
trolling fleet on La Perouse Bank, none contained salmon . H erring was the
predominant food species . In 1959, six stomachs containing herring were collected
in an area where salmon were reported as plentiful by trollers. Du ring the 1961
fur seal col lecting program there was an apparent increase of small coho off
Barldey and Clayoquot Sounds, as reported by commercial trollers. However,
seal stomachs were empty when col lected in the vicinity of trollers. Despite
these negative results the overall occurrence of salmon in stomachs increased
during 1961 (over 1960), which probably reflected an increased a bundance of
small salmon.
35
18
90
0----0
0- - -<)
80
F::CE: � c e r : c y
16
70
1
4
o
>
60
\
�
\
50
\
\
/
\
/
\
\
/
/
/
\
\
\
8
\
\
(y �
1 960
1 959
1 9 58
10
/
\
\
40
/
1961
year
FIG . 1 4. Per cent frequency o f occu rrence o f herring i n 1 3 9 f u r sea]
stomachs off southern Vancouver I sland and m iles of herring spawn
in Barkley and Clayoq uot Sounds.
There is n o correlation between frequency of occurrence of salmon in seal
stomachs and th e com mercial catch of spring and coho salmon in the areas
under study .
Studies i n both the western and eastern Pacific have concluded that fur
seals do little damage to commercially valuable fishes, including salmon (Taylor
et al., 1955 ; Niggol et al., MS, 1960 ; Fiscus et at., MS, 1961).
TRA WL-C\ UGHT
FISH
The migratory path of many fur seals passes across m ost of the trcnvl
fishing banks, and several fish species identified in seal stom al'hs are also exploited
by this fishery.
During February and March, from 1959 to 1962 inclusive, fur seals were
hunted in the vicinity of the \iVhite Rock trawling ground in northern Hecate
Strait. A total of 38 stomachs with food was collected during these 4 years.
Catch statistics for the 2 months under consideration, totalled for 3 years, have
been compared with seal stomach contents (Fig. 15). These com m ercial e1 ata
include not only fooel fish, but also fish species caught for mink or pet fooel , anel
are therefore representative of bottom fish available on the grounds.
36
There is little relationship between the two sets of statistics illustrated ill
Fig. 15. Commercial grey cod are large mature fish caught between 45 and 63
fathoms, which may be too deep for fur seals (Kenyon, 1951). Whiting, although
apparently not too abundant, are second in importance to herring in the fur seal
d iet. There are virtually no sablefish of commercial size in this area, but small
sablefish do show in som e of the trawl catches ; these smaller fish are taken by
seals.
80
70
0
E
60
0
Fer
s e a
1
0
>
"
.0
�
c
0
�
50
40
30
20
10
80
.�
0
70
�
60
0
Co
2
50
u
40
C
"
J
"
c
CO,
30
20
1 0
-;i
.g
�
co
0
g;
�
�
w
�
�
�
en 0
a>
5
H
H
$
0:
co
8
;;H
'0
a>
c
�
.c
'"
u
0
0
-0
0
"
-;i
�
�
�
""
0
0
u
a>
C
-'
�
�
0
0
cr
.�
0
FIG. 15. Fur seal stomach contents collected frolll \\,hite Rocks
lishing grou nds, and trawl tishery catch statistics for 1 95 9- 1 9 6 1 from
the same area .
Studies conducted by the Fisheries Research Board of Canada have shown
that sablefish, whiting, and herring frequently school together. On herring
fishing grounds the only two species present in large numbers, other than herring.
were small sablefish (9-14 inches) and small whiting (11- 14 inches). Exploratory
fishing with mid-water trawls in Saanich Inlet indicated that herring and small
whiting (12 inches) were well off the bottom (Barraclough and Herlinveaux, M S,
1961). This suggests that small whiting and sablefish rise off the bottom and in
some cases mingle with the herring schools ; commercially valuable grey cod and
flatfish remain on the bottom, and are seldom preyed upon by fur seals.
37
SEA LIONS
Commercially valuable fish contributed 5 2. 5 % to the total sea lion sample.
These include herring, salmon, hake , grey cod , whiting, flatfish , halibut, sablefish ,
l ingcod , and rockfish. Several of these fish species are not fully utilized by man
and only the herring, salmon , and halibut fishery will be d iscussed in detail .
H ERRING
Compared to fur seals, sea l ions do not rely so much upon herring as a food ;
approximately 10% of the sea l ion diet is herring, compared to 43 % for fur seals
(Fig. 9). Nevertheless, in certain localities sea lions prey extensively upon herring
during the winter months. Fishermen frequently observe sea lions swimming
close to , or in, their herring seines.
As mentioned earlier, herring migrate into B arkley Sound during the l ate
wi nter months to spawn. Each winter, sea l ions are also found in these waters,
remaining until April . A total of 30 stomachs has been examined from the
Barkley Sound area since 1914. Herring, which occurred 16 times in a total of 29
identifiable food items, was the most important food item (Table X). However,
the relatively high number of octopus and rockfish remains indicates that herring
were not the exclusive diet of sea l ions, even in areas of herring abundance .
TABLE X. Contents of 2 3 sea l i o n stomachs from B arkley Sound : 1 4 collected
i n December 1 9 1 5 (Newcombe et al. , 1 9 1 8) ; 9 collected during the present
i nvestigation.
Species
Herring . .
Rockfish . . . . . . . . .
Octopus . .
Skate . . .
Lingcod . . .
.
Flatfish . .
.
.
Whiting . . . . . . . . .
�u� . . . . . . . . . . . . . . . . .
Dogfish . . .
. .
Frequency
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. . . .
. . .
. . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. .
.
. .
.
.
.
.
.
.
.
.
.
.
.
. . . . . .
. .
.
.
.
.
.
Tota l . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
Percentage
frequency
16
3
3
1
1
2
1
1
1
55 . 1
10 . 3
10.3
3.5
3.5
6.8
3.5
3.5
3.5
29
1 00 . 0
SALMON
The overall percentage contribution of salmon to both the fur seal and sea
lion diet is quite similar : 5.6% for sea l ions and 5.8% for fur seals (Fig. 9) .
However, predation by fur seals begins when salmon are still offshore�during
March , April , and May in waters examined. Sea l ion predation begins in June,
and continues during July and August (Table X I). Following the summer
breeding activity most male sea lions and females without pups leave the rookeries
and move to haul-out rocks closer to the mainland , or. i nto the i nlets. During this
time there is a further predation upon salmon .
38
TABLE XL Con tents from S2 sea lion stomachs from the Scott I slands and adjace n t waters.
(Data from presen t i nvestigations only.)
Stomach contents (frequency of occurre nce)
M o n th
0:
o
6
JJ
'';::
:.a
B
u
o
�.�
:\II a y .
10
J u ne . .
16
July . .
bIJ
0:
if)
5-
4
�
_+ ___ : __
.---- 1
_ _ ____ _ ___
i
I
5
--
22
17
"
2
August .
September.
6
7
20
Sea lions on the Scott Island rookery, at the north end of Vancouver Island,
are advantageously situated to prey upon the la rge salmon runs moving toward
the spawning rivers on the mainland. During the years under study this popu­
lation has varied from 1700 to 1100 adults per breeding season. From a total of
63 occurrences of identifiable food remains, only four (6%) were salmon (Table
X I), but this figure may be low. There was virtually no predation upon salmon
in this area during M ay, June, and September, but salmon occurred in three of
the four stomachs collected during July and August. Commercial catches of
sockeye, coho, and pink salmon in the Department of Fisheries statistical area
(which includes the Scott Islands) reach a peak during July and August, indica­
ting that the main salmon runs pass these rookeries during the m onths when
there are very few data on sea lion feeding habits.
Although no direct evidence is available regarding the effect of sea li ons
on these salmon run s, Fig. 16 compares the salmon catch with the reduction
of the Scott Island sea lion population since 1956 . The reduction in sea lions has
not resulted in a corresponding increase in the commercial salmon catch.
Salmon predation by the Cape St. James sea lions during the summer
months of June, July, and August may not be as serious as around the Scott
Islands. Du ring July, the only month when salmon were encountered in stomachs
from Cape St. James, these species were found once in a total of 10 identifiable
food occurrences.
Following the gradual breakup of the breeding population, which begins
dnring August and early September, some sea lions follow and prey upon salmon in
the coastal inlets. Stomachs from three fema le sea lions, collected at the mouth of
K!inkwoi Bay in the Queen Charlotte Islands in October 1960 contained remains
39
of pink and chum salmon. These three were pregnant and had therefore moved
from a breeding rookery (probably Cape St. James) some time during the late
summer.
35
0
3
r
I
3500
3000
20
1 0
....
- -
.
-------
1954
1955
S e a :" i o r . .:J op u L , t i o r .
S a ';'::: o r . c a t c h
1956
1957
1 9 58
1959
1960
196 1
FIG. 1 6. Salmon catches (all species) and the decreasing sea lion
population i ll the fisheries s tatistical area which includes the Scott
I slands, in the period 1 954 to 1 9 6 1 .
HALIBUT
During this investigation, practically no data have been collected O il the
predation of sea lions on halibut. H alibut was identified once in a stomach
collected on the west coast of the Queen Charlotte T slands and a sea lion was
observed eating a halibut at the surface in northern Hecate Strait on M arch 6 ,
1959.
HARBOUR SK\LS
Fish of commercial value comprise about 54% of the harbour seal diet
(Fig. 9). Havinga (1933) estimated that commercially valuable fish comprised
75% of the harbour seal diet in Dutch waters. In British Columbia these include
herring, salmon, eulachon, hake, whiting, flatfish, sablefish, and lingcod. Concern
is directed mainly towards the possible effect of harbour seal predation upo n
herring and salmon.
40
HERRING
This species is eaten frequently by harbour seals, but the present study
may not show its true importance. The sample indicates only a 12 % contribution
to the total diet (Fig. 9), but herring have been found in stomachs collected
during April, July, September and N ovember-essentially throughout the entire
year. There are few, if any, complaints from the fishing industry regarding
harbour seal predation upon herring.
SALMON
Harbour seal predation upon salmon may be extensive at certain times of
the year. Salmon contributed approximately 30% to the contents of a sample
collected for the m ost part near salmon spawning streams during the fall ;
sam pling indicates that salmon are also eaten during the summ er months,
particularly June. Imler and Sarber (1947) estimated that harbour seals in the
Copper River delta (Alaska) destroyed an amount of salmon equivalent to
2-3% of that area' s total annual salmon catch. Fisher (1952), discussing the
relative importance of salmon in the harbour seal diet on the Skeena River cal­
culated, from a sample of five fishermen, that monetary losses from seal-damaged
chinook salmon represented approximately 7 % of the total value of the catch.
Fisher also recorded two observations of food other than salmon in the
stomachs of seals collected in areas of salmon abundance.
During the present investigation a harbour seal collected in Luxanna B ay,
Queen Charlotte Islands, was feeding on herring while pink salmon were moving
into a creek at the head of the Bay. At the same time three seals were killed in H owe
Bay, approximately 10 miles away, where there was no salmon spawning creek ;
these stomachs contained rockfish, octopus, and greenling. Thus, there was no
obvious movement of seals following the salmon (or herring) which were present
in Luxanna Bay. This type of behaviour was also evident in Barkley Sound in
1958. One harbour seal collected had eaten hake, although spawning herring
were in the area.
These observations on food other than salmon or herring in harbour seal
stomachs have been recorded not to m inimize the possible seriousness of seal
predation, but to illustrate the necessity for accurate figures on numbers of
seals preying on com mercially valuable fish.
CONCLUSIONS
Fur seals, sea lions, and harbour seals eat fish of com mercial importance,
especially herring and salmon. H erring is the most important food for the
migrating fur seal herd moving up the British Columbia coast, and for the
wintering animals ; it is preyed upon from January to June. H arbour seals also
feed on herring and will take this fish whenever it is available. In contrast, sea
l ions feed upon herring m ainly during the winter m onths. The total tonnage of
41
herring eaten annually by sea lions and harbour seals has been estimated at
7 2 50 (2400- 13, 250) tons, or 4% ( 1. 0-6. 2 %) of the average annual commercial
catch of 2 00, 000 tons (Appendix 2).
Herring are subjected to intense predation throughout their entire life
cycle by many fish, birds, and mammals. Total mortality of mature and maturing
fish is up to 8 0%, of which an average of 50-60% results from natural mortality
from age 5 to 12 years (F. H . C. Taylor, personal communication). Sea lion and
harbour seal predation, accounting for an estimated 4 % of the average annual
catch, is not therefore a serious factor in herring mortality.
Salmon also are taken by these three predators. M igrating fur seals occasion ­
ally take salmon, usually small fish, o ff the west coast o f Vancouver Island, as
salmon are moving towards coastal waters. Fur seal predation upon salmon
cannot be evaluated until tl1e numbers of seals preying upon these species can be
estimated. Harbour seals prey upon salmon, particularly during the fall when
the salmon are moving into the rivers. However, harbour seals do not always
make a special effort to congregate in areas of salmon abundance, and when
salmon are available do not restrict their diet exclusively to salmon . Salmon
form up to 3 0% of the diet of seals collected in the mouths of salmon streams.
Sea lions prey upon salmon during the summer months as the salmon
migrate past the rookeries. In addition, sea lions probably follow the salmon into
bays and river mouths, and prey upon them there.
The total amount of salmon eaten by sea lions and harbour seals is estimated
to be 4 . 0 (1. 2-7. 1) million Ib annually, which is approximately 2 . 5% (0. 8-4. 7 %)
of the average 148 million Ib an nual commercial catch (Appendix 2).
Salmon mortality rates are high both in fresh water and the ocean . I\eave
(1953) estimated that freshwater survival of pink and chum salmon varies
between 1 and 24% ; ocean survival was assumed to average approximately 5 %
for each species. Ricker (1962) estimated average total losses o f sockeye i n the
ocean to vary from 64 to 95%. Fishing mortality of return ing adult salmon
ranges from 50 to 80%, depending upon t he species (Shepard and Stevenson ,
1956) . The present study indicates that sea lions and harbour seals take an
amount equal to about 2 . 5% of the fishing mortality.
Parker (1962) has estimated, on a theoretical basis, that although a coastal
natural mortality factor could be calculated for adult migrant salmon, such
m ortality ,,"as slight and \;vas of negligible influence on the total mortality. The
present study supports these theoretical conclusions.
I ,,"ish to emphasize that knowled ge concerning the effect of pinnipeds,
particularly fur seals, upon salmon is far from complete. Although the coastal
zone has been stud ied, it is difficult to estimate numbers of migrating fur seals
in this area. In addition, virtually nothing is known about the feeding habits
of adult fur seals which must winter in, and migrate over, much of the mid­
::\ orth Pacific Ocean. These seals are usually scattered and difficult to hun t ;
as a result very few have been collected farther than 2 00 miles from shore durin g
42
the present pelagic fur seal program. During June 1962, however, a Canadian
vessel collected 3 7 seals in the middle of the Gulf of Alaska. Salmon occurred in
10 of the 2 6 stomachs with food. No conclusions can be d rawn from such a small
sample.
In summary, each year sea lions and harbour seals consume an estimated
amount of salmon equivalent to 2 .5% of the annual commercial salmon catch
and an estimated amount of herring equivalent to 4% of the annual commercial
herring catch. Predation at this level is not believed to be a serious factor in
either salmon or herring mortality. No conclusions can be reached on the effect
of fur seal predation on salmon until more information is obtained on the extent
of this predation on the high seas.
43
ACKNO\VLEDGMENTS
Material for this study was obtained as part of a larger investigation on
pinniped s conducted by the Marine Mammal Investigation of the Fisheri es
Research Board of Canada's Biological Station in r\anaimo, B. C. I wish to extend
my thanks to Dr A.\V. H . N eedler, Director of the l\anaimo Biological Station
during the time this study was carried out, for his assistance and encouragement.
This paper was originally submitted as a thesis in partial fulfilment of the
requirements for an M.A. degree in Zoology at the University of British Columbia.
It has been slightly modified for the present publication. Drs Ian McT. Cowan,
W. S. Hoar, N . J. Wilimovsky, J. Bendell, and D. Chitty of the University of
British Columbia, and Messrs F. C. Withler, G. C. Pike, and R. LeBrasseur of
the Biological Station, read this paper in draft form and m ade m any helpful
suggestions. Drs M. P. Shepard and F. H . C. Taylor assisted in the assessment
of the effect of pinniped predation upon salmon and herring stocks.
The collecting of seals and sea lions is difficult, often unpleasant, and
occasionally dangerous. The co-operation of those mentioned below has greatly
increased the number of specimens available for this study : Mr R. Kelly and
crew of the Pacific Ocean; Messrs T. and A. Boroevich and crew of the St. JosePh;
lVIr D. Berven and crew of the T. �v. Islander; Messrs \V. and D. Secord; Messrs
D. and \V . :;\!I cNaughton of Pender Harbour; Messrs 1 . B. MacAskie, T. Bin­
nersle�y , \V . Pinckard and F. Velsen of the Biological Station. The Department
of Fisheries has co-operated in the collection of specimens whenever possible.
I also wish to extend my thanks to lVIr C. Morley for his excellent photo­
graphs, and to Mr MacAskie for his skull drawings.
44
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OUTRAM ,
Xanaimo, Circular, General Series, N o . 6 0 , 1 7 pp.
PARKER, R. R . 1 96 2 . Estimations of mortality ra tes for Pacific salmon (Oncorhynchus) . J. F i s h .
Res. Bd. Canada , 1 9 (4) : 5 6 1 -5 8 9 .
PIKE, G. C. 1 95 8 . Food o f t h e northern s e a lion. F i s h . R e s . Bd. Canada , P a c i fi c Prog. Rept. , N o .
1 1 2 , pp. 1 8 -2 0 .
P I K E , G. c . , AND B . E . MAXWELL. 1 95 8 . T h e abu ndance and distribu tion of t h e northern s e a l ion
(Eumetopias jubata) on the coast of British Columbia. J. Fish. Res. B d . Canada , 1 5 ( 1 ) : 5 - 1 7 .
PIKE , G . c . , D . J . S PA L D I N G , I . B . M ACASKIE AND A. CRAIG. 1 95 9 . Report o n Canadian pelagic
fur seal research in 1 95 9 . Fish . Res. B d . Canada , M S Rept. ( B iol . ) , No. 629.
1 960. Report on Canadian pelagic fur seal research i n 1 960. Fish. Res. Bd. Canada ,
MS Rept. (Biol . ) , No. 700.
46
1 96 1 . Report on Canadian pelagic fur seal research in 1 9 6 1 . Fish. Res. B d . Canada,
M S Rept. (Biol . ) , No. 7 1 9 .
D . J . SPALDING, I . B . MACASKIE AND F. J . VEL SE N . M S , 1 95 8 . Report o n Canadian
pelagic fur seal research i n 1 95 8 . Fish. Res. Bd. Canada, M S Rept. BioI. Sta. , No. 736.
PIKE , G . c . ,
W. E . 1 93 7 . The food and food supply of sockeye salmon (0.
B ritish Columbia. J. BioI. Bd. Canada , 3: 450-468.
RICKER,
nerka) i n Cultus Lake,
1 96 2 . Comparison of ocean growth and mortality of sockeye salmon during their last
two years. J . Fish. Res. B d . Canada , 1 9 (4) : 5 3 1 -560.
R. F . 1 96 1 . Marine plant resources of B ritish Columbia. Bull. Fish. Res. Bd. Canada ,
No. 1 2 7 , 39 pp.
SCAGEL ,
V. B. 1 950. The food of the Alaska fur sea l . Trans. 1 5 th N . Amer. Wild. Conf . , pp.
4 1 0-42 1 .
SCHEFFE R ,
V . B . , AND J . W . SLI PP. 1 944. The harbour seal i n Washington State. Amer. M idI .
Nat. , 32 : 3 73-4 1 6 .
SCHEFF E R ,
M . P. , A N D J . C. STEVE NSON. 1 95 6 . Abundance, distribution and commercial exploitation
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SHE PARD ,
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47
APPEN DIX 1
Scientific and common names of food items mentioned in text.
Invertebrates :
P. M OLLUSCA
C. PELECYPODA
C. C EPHALOPODA
S. Order OCTOPOD.c\
S. Order DECAPOD.c\
shell fish
octopus
squid
Loligo opalescens
Gonatus magister
P. ARTH ROPODA
C. C RUSTACEA
O. D ECAPODA
crayfish , lobster, shrimp, crab
CARIDAE
Pandalus platyceros
Vertebrates :
C. CHON DRICHTHYES
Family PETROMYZONTID.\E
Pacific l amprey
Entosphenus tridentatus
Famil y SQUALIDAE
Squalus suckleyi
dogfish
skate
Family RAJIDAE
Family CHIMAElUDAE
IIydrolagus colliei
ratfish
C. OSTEICHTHYES
Family CLUPEIDAE
herrings (cl upeids)
Pacific herring
shad
anchovy
northern anchovy
salmon
pink salmon
coho salmon
chum salmon
sockeye salmon
chinook salmon
steel head
Clupea pallasii
A losa sapidissima
Family ENGRAULIDAE
Engraulis mordax
Family SALMONIDAE
Oncorhynchus gorbuscha
O. h�utch
O. keta
O. nerka
O . tshawytscha
Salmo gairdneri
48
smelts
capelin
eulachon
lantern fish
Family OSM EIUDAE
Mallotus villosus
Thaleichthys pacificus
Famil y M YCTOPHIDAE
Family SCOMBERESOCIDAE
Pacific saury
Cololabis sa ira
Family M ERLUCCIIDAE
Pacific hake
cods
whiting (walleye pollock)
Pacific cod
Pacific tomcod
Merluccius productus
Family GADIDAE
Theragra chalcogrammus
Gadus macrocephalus
Microgadus proximus
Family TRACHYPTERIDAE
Trachypterus rexsalmonorum
Family PLEURONECTIDAE
A theresthes stomias
Hippoglossus stenolepis
Lepidopsetta bilineata
Parophrys vetulus
Platichthys stellatus
Family EM BIOTOCIDAE
Damalichthys vacca
king-of-the-salmon
flatfish , flounder
arrowtooth flounder
Pacific halibut
rock sole
lemon sole
starry flounder
sea perches
silver perch
Family B RAMIDAE
pomfret
Erama raii
Family CARANGIDAE
mackerelj ack
Trachurus symmetricus
Family TETRAGONURIDAE
squaretail
Tetragonurus cuvieri
Family ANOPLOPOMATIDAE
sablefish
A noplopoma fimbria
Family H EXAGRAMMID.�E
Hexagrammos sp.
greenling
lingcod
Ophiodon elongatus
rockfish
Family SCORPAENIDAE
Sebastodes sp.
S. ruberrimus
red snapper
Family COTTIDAE
Scorpaenichthys marmoratus
cabezon
Family GASTEROSTEOIDEA
threespine stickleback
Gasterosteus aculeatus
Family AMMODYTES
sandlance (launce)
A mmodytes hexapterus
49
Class AVES
Ptychoramphus aleuticus
Brachyramphus marmoratus
Synthliboramphus antiquus
50
Cassin' s auklet
marbled murrelet
ancient murrelet
APPEN DIX 2
A quantitative estimate of the effect of sea lions and harbour seals
on the British Columbia salmon and herring fisheries.
Estimates of the amount of salmon and herring eaten by pinnipeds must be
based on the following information :
(a) Daily food intake of predator . This ranges from 2 to 1 1 % of the body
weight, with a mean of 6% (Table IV). All calculations are based on 6% of the
body weight with the possible range included in brackets.
(b) Numbers of predators and duration of predation . The highest estimate of
a population size has been used. Period of predation is based on how long the
predator population was in the vicinity of its prey.
(c) Per cent contribution of each prey to total food intake . This has been
calculated on a percentage frequency of occurrence basis, and has been taken
from Tables V and VI and Fig. 9.
The calculations have been carried out by multiplying the daily food intake
(estimated from mean body weight) by the number of predators, by the number
of days of feeding, by the per cent contribution of the particular food item.
The following calculations are based on data which are often incomplete;
further studies may alter these estimates.
SEA LIONS
The mean female sea lion weight is 17 7 kg (450 lb) ; a representative sample
of males has not been weighed. H owever, as large adult males frequently weigh
1500 lb, the mean female weight has been doubled to arrive at a mean body weight
of 900 lb for the total population.
HERRING
The population of 4500 animals (excluding pups) will require an estimated
8 7 . 5 (29. 2-160.4) million lb of food annually. H erring, formin g 10 % of this
(Fig. 9), will contribute 4650 (1550-8500) tons.
SALMON
Salmon contribute 8% to the food intake of 3100 sea lions on the rookeries
from May 15 to September 15 (Table V I). During these 4 months an estimated
20.4 (6.8-37.4) million lb of food are required ; salmon would contribute 1. 6
(0.5-3.0) million lb. During the early fall approximately one-half, or 1500 sea
lions, leave the rookeries and move inshore to join the non-breeding element of
the population. Therefore, salmon forms 10% of the diet of approximately 3000
51
sea lions during October and N ovember when the late salmon runs are still
available. During these 2 months 3 000 sea l ions require 9 . 7 (3 . 2- 1 7 . 8 ) million Ib
of food and salmon would constitute 1 . 0 ( 0 . 3- 1 . 8 ) million lb.
Combining these two estimates of summer and fall consumption of salmon
by sea lions gives a figure of 2 . 6 ( 0 . 8-4. 8 ) million lb.
H,\RBOUR SEALS
The mean body weight of 23 harbour seals was 1 00 lb.
HERRING
The estimated 2 0 , 000 harbour seals annually require 43 . 2 ( 1 4.4-7 9 . 2 )
million Ib of food. Herring forming 1 2 % o f this would contribute 2 600 ( 850-4 7 5 0 )
tons annuall)·.
SALMON
The numbers of harbour seals preying on salmon may be estimated by
calculating the average number of seals per salmon spawning stream and multi­
plying this by the total numbers of such rivers and streams on the coast.
There are approximately 900 salmon spawning creeks entering salt water or
lakes accessible to seals , excluding the Skeena River system (Department of
Fisheries files). An average of 5- 1 0 harbour seals per creek is estimated from my
own observations, plus those of fisheries officers and others working on salmon
stream s. If 1 0 seals per creek is taken as a maximum, 9000 seals may be regarded
as potential predators upon sal111 0 n in the 900 streams mentioned above. Fisher
( 1 95 2 ) estimated there were 400 seals in the lower Skeena River, plus "several
hundred" upriver. For the purpose of these calculations a total population of
1 000 seals in the Skeena River system has been estimated. An average predation
period of 70 days was calculated from the seasonal duration of salmon runs in
37 streams chosen at random (Department of Fisheries files). Runs of salmon of
all species lasted an average of 70 d ays in each stream.
Therefore, 1 0 , 000 seals would require 4 . 2 ( 1 .4- 7 . 7 ) million lb of food for
70 days . Salmon forming 3 0 % of this would constitute 1 . 3 ( 0 . 4-2 . 3 ) million lb.
\Vhen these estimates are combined sea lions and harbour seals eat an
estimated 7 2 5 0 (2 400-1 3 , 2 5 0 ) tons of herring and 4.0 ( 1 . 2-7 . 1 ) million lb of
salmon annually. The average annual herring catch is 200, 000 tons (Outram,
1 96 1 ) , and pinniped predation, therefore, may account for an amount equivalent
to 4% ( 1 . 0-6 . 2 %) of the annual catch. The average annual salmon catch is
1 48 million lb and pinniped predation may account for an amount equivalent
to 2 . 5 % (0. 8-4. 7 % ) of the annual commercial catch.
52