ARCEPVES FISHERIES RESEARCW. BOARD OF CANADA
Translation Series N 2498 '
. Influence of thetrophic factor On thé population 'and distribution of the sea otter in the central and northern • Kurile Islands
bY M: Shitikov
Original. title: Vliyanié troficheskogo faktora na. chislennostli . raspredelenie. kalana na.srednikh .ostrovakh . ,• • . • . .« .
From: TrudY.Vsesoyuznoge-Nauchno-IssledovatelSkogo • • Instituta -Morskogo Rybnogo Khozyaistva Okéanografii '(VNIRO) Vol. 82 (proceedings of , the AllUniOn• Research institute of Marine ' Fisheries and Oceanography). Izvestdya 'Tikhookeanskogo. Nauchno-IsSledovatel. 'skogo instituta RYbnogo. , Khozyaistva d Okeanografii .(.TINRO) Vol.' 80 (Proceedings of the Pacific Scientific Research . - ' Institute of Marine Fisheries and ObéandgraPhy) . , 82 _& 80 '227-239,. 1971 • ''
Translated by the Translation'. •Eureau (IPST1 . Foredgn,4anguages Division. • Hi.'; Department-Of the.Secretary . of Stateof Canada' •
. Department of.' the Environment.-
Fisheries_ReSearch'Board 6f Canada ' 'ArctiC Biological:Statdon. *Ste. Annede Bellevue',
1973
22 :pages typescript .D--'PARTMENT OF THE SECRETARY OF STATE . SECRETARIAT WETAT FRR ;-1 TRANSLATION BUREAU . BUREAU DES TRADUCTIONS .
MULTILINGUAL SERVICES r" DIVISION DES SERVICE S CANAD A DIVISION MULTILINGUE S
TRANSLATED FROM - TRADUCTION D E INTO - EN Russian English
IAUTHOR - AUTEU R ~''A .M . Shitikov, TINR O
JITLE IN ENGLISH - TITRE ANGLAI S ~Influence of the Trophic Factor on the Population and Distribution of the Sea Otter in the Central and Northern Kurile-Islands .
TITLE IN FOREIGN LANGUAGE (TRANSLITERATE FOREIGN CHARACTERS) Ti TRE-EN LANGUE ~TRANG~RE (TRANSCRIRE EN CARACTERES ROMAINS ) Vliyanie troficheskogo,faktora na chislennost'i raspredelenie kalana na srednikh i severnykh-Kuril'shikh ostrovakh .
REFERENCE IN FOREIGN LANGUAGE (NAME OF BOOK OR PUBLICATION) IN FULL . TRANSLITERATE FOREIGN CHARACTERS . REFERENC -1 EN LANGUE ETRANGERE - (NOM DU LIVRE OU PUBLICATION) . AU COMPLET, TRANSCRIRE EN CARACTÈRES ROMAINS .
VNIRO,vol . 82/TINRO Vol-80
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227 _From: Trudy VNIRO, Vol. 82 and lzvestiya TINRO, Vol. 80, 1971, pp. 227-238. 599.742.4 INFLUENCE OF THE TROPHIC FACTOR ON THE POPULATION AND DISTRIBUTION OF THE SEA OTTER IN THE CENTRAL AND NORTHERN- KURILE ISLANDS
(Vliyanie troficheskogo faktora na chislennost' i • LINEDITZD na srednikh i severnykh raspredelenie kalana TRANSLATION Kuril'skikh ostrovakh) .Por inforrna'don only TRAID:XTKL)N NON REVISEE A. M. Shitikov, TINRO Infornlailon soulement
The sea otter (E nhy dr a lutr is L.) now occurs on almost all the
islands of the Great Kurile Ridge north of Kunashir and numbers 4,000-7
The question of the further growth of the population is controversial. 5,000.
A. N. Belkin (1966) and later S..K.Klumov (1968) estimated that the sea
otter population on the Kurile Islands should attain 7,000-10,000 by 1970;
Belkin considered the latter figure as the limit for the area. In his
opinion, the number on each island will increase due to both natural growth
and to animals' .corning in from other Islands, thus making it unnecessary
for more to be introduced by man. This view was shared by I. I. Barabash-
Nikiforov, S. V. Marakov and A. M. Nikolaev (1968). Klumov (1968), on the
other hand, thought that 10,000 is not the limit for the Kurile Islands.
‘.;305-43001 0-3 I This number will be made up mainly by the growing populations on the islands
of Urup and Paramushir, whi.c3.i is liable to cause an epizooty on these islands.
He suggests that more sea otters be brought in to increase their number on
the other islands.
Data of the latest counts show the sea otter population to _be growing very.
slowly, not yet having, reached 10,000. On some islands, the number of animals
has not been increasing for the last 10-15 years. Thus, 200 sea otters
inhabited Onekotan Island in, 1955 (Klumov, 1957), 139 in 1963 (Belkin, 1966), 69
in 1967 (Nikolaev, 1968), and 64 in 1970 (our data). No count has been made on
the islands of Urup, Shikotan, and Makanrushi since 1963, although the initial
populations there-were fairly large. 'The distribution by island has also changed
little since 1963, and about 70% of the entire population is still concentrated
on the shores of Urup and Paramushir islands. The sea otters flock together
mainly at the tips of the islands and on their eastern shores. In the central
and northern Kurile Islands, they have„appàrently settled in all the suitable
habitats. The creation of new habitats calls for a study to establish the
biotope required by the animal.
^ 228 Numerous observations have •now made it possible to identify the sea
otter's haunts. The first professional hunters had noticed that "kelp-rich rocky
promontories and reefs are favbrite hideouts of the beaver. .." and that .''beavers
keep mainly to the ends of thëislands and their Pacific sides". (Snow, 1902).
These habits have,s'till not changed. Barabash-Nikiforov, (1947), observes that
sea otters are attraeted.bÿ, steep or relativèly gently sloping, rocky shores, .. ;,^> _. ^ . . . - .. _ :. .. .. barrier reefs, little rocky islands, around which the Stirf consta.ntly breaks,
.and finally, clumps of kelp which for m a j'agged S trip "along the shore. According
to the presence of reefs and rocky islets in the offshore area of the sea, the
size of the seaweed fields, the nature of thé littoral and sublittoral, the depth
of the sea and the. distance from the extreMities Of the islands, Nikolaev (1963)
suggests a tentative classification of the Sea otter haunts into four categories:
excellent, good, fair, and poor. AmeriCan 'c-m5logiStà (Èyerdam, 1933; 1938;'
Williams, 1959, 1963; .Kenyon, 1965) alSO hotiCed the animal's predilection
. .for areas with rocky shores .and -abundant reefs ; tôéky islets and kelp.
Nevertheless, it is not enough tô know the ablotic Conditions of life in order
to be able to establish the catt8e8 that deterMine thé ntunber . and distribution
of the population, as theSe depend ôn the trôphic faetôt às well.
But the importance of this factor has not been Studied at all. With
• .reference to the Paramushir .population, the diStribution of the animals on
Paramushir Island and the eastern Shore Of Kamehatka has been• 'shown tà
depend on the abunda-nce ôf food iternS in the areaS where a certain trophic
group'of benthos developS: the iMmobile Seg-Eônophages. To study the
distribution of food items for the Sea ôtter on the other islands and to collect
data on its feeding habits, TINRO organized a series of expeditions in the
central.and northern Kurile Islands in 1969 and 1970. The investigation was
carried out by the trapping boat "Krylatka." A group of scuba divers
participated in the research cruiSeS.
The Urup, Chirpoi (Chernye.Uratya-),..Sinuskr an:kicha (Ushishir),
Paramushir,..Ilatua,:AntSiferov - and Psttàsov iSlands Were investigated. The areas of work are indicated on the figure.
Number and distribution of sea otters in the central and northern Kurile Islands: 1 — about 100 specimens; 2 — about 50 specimens; 3 — about 25 speci- mens; 4 — about 10 specimens.
In the study of macrobenthos of the Kurile Islands sublittoral, invertebrates and algae were counted by the method of hydrobiological sections of incomplete profile, the stations located at the depths of 5, 10, 15 and 20m. A: few stations were taken to a depth of 30-40m. The number of sea otters was determined, excrement was collected and analyzed, and the contents of stomachs and intestines were examined at the same time. In all, 1,429 excrements and the contents of 60 stomachs and intestines were investigated.
The frequency of occurrence of a food item and its predominance in the food . 5
(i. e. more than 50% of the overall volume of the excrément, by visual
assessment) were carefully studied. Whenever the excrement consisted of
equal parts of two or more kinds, preference was given to that which
contained less hard parts: the remains-of octopuses were given priority
over remains of-fish, fish to crab, crab to -sea urchin, and so on. Thus, whereas
the first index can serve as a qualitative characteristic of feeding, the
second one is quantitative. These.indexes were also used when.analyzing
the contents of stomachs and intestines. In this case, the predominant kind.
of food was determined not only by'visual assessment, but also by weighing.
229 The feeding habits of the sea otter on the Kurile Islands have.been little..
described in the.literature. K. Miyatake (1940) studied the suzniner diet;
after analyzing the contents of the stomachs of 332 sea otters, he came to
the conclusion that the main food items were Oc t o p u s d o f 1 e i n i, the
Sakhalin sea urchin Strongylocentrotus sachalinicus;thè mussel
Mytilus eduli.s, and the fish Hexagrammus otakii, Sebastichus
sp., and Cycloptericht-hys .ventric.osus. Unfortunately, the author
Aid not mention where the investigations were carried out. The feeding.of
the Kuriles sea otter was studied by Nikolaev (1963) on Urup Island, and by
Maminov and Shitikov (1969) on Paramushir Island. It was established that
here the animals feed on up to 40 species of marine .animals, the main items
being sea urchins, bivalve and armored mollusks, crustaceans.and fish.
. The material at our, disposal, prov'idés additional inforrn.ation. Let us take ,
island by island. 6
Urup Island. A breakdown of the sea otter's food is given in Tables " .
and 2 . '
230 TABLE 1 . , Items (in %) in the food of the sea otter along the Okhotsk and Pacific shores of Urup Island (from an analysis of 617 excrements )
March-April August- September
Okhotsk Pacific Okhotsk Pacific Food side side sid e side
2 2 1 2 I 2
Sea urchin 92 70 60 38 89 51 85 33 Vilazina 10 . 7 45 29 .4 15 5 78 46 M Yt~i I u s 15 1 31 6 'il None 3 1 None Chit~n 10 0 .6 4 0 .6 25 None None None Crab 60 1 0 42. 16 44 11 31 None Idothea 13 8 1 0 .6 I I 1 5 14 Amphipoda 10 . None 20 None None None None None Goose barnacle 0 4 0 .4 12 9 None None None None Fish 12 3 4 0 .5 46 3 0 5 4 7 Note : 1 - total incidence ; 2 - incidence as the predominant food .
TABLE 2 . Contents of the stomach and intestines of 19 sea otters on Urup Island (September)
Sea urchin ,Vilazina , Chiton Crab Idothe a Fish egg s .~Octopus , -Fish Seaâôhal fl-nettiations were noted in the amount and quality of the food • âñumed. In Winter, the food consists ma.inly of sea urchins, bivalve mollusks
Vernicosa,and the craboid Dermaturus mandtii. In
additiOn, Hothea ochotensis, Mytilus edulis and the chiton
TOM- ell a .Sp oCcur frequently. Along the Sea of Okhotsk shore of the •
ieand sea urchins predominate, while Vil a zina predominates along the
Pâé ifi c shore. Interestingly, \vhen stud.ying the feeding habits of the Urup
é:ea ôtter, NikôlaéV (1958,.. 1963) found no Vila z ina, but our observations
â1I(5W. that the aril Mal- feeds on this mollusk both along the Pacific and the
OkhôtSk ShOreS càf the island.
- Aldh.g. the Pa.éif ic shore, Vil a z ina predominates much more frequently,
• iftâ ëôï'i'..(5bC1ated by observations made by Sakhalinrybvod's..inspector
Sàenko,Whô reported that the - mollusk is found in large numbers in the
è31 excrements of the sea otter.along,both the Okhotsk and the Pacific littoral.
fl Sôniè place, n important role in the winter diet can also be played by
. êi'ila•tadea...ns,-aS had been indicated by Nikolaev (1958).
--rh -late A11----- early May, fish, mainly Cyc 1 o -p teri Cht hys ve ntr -
• d éS -tià, • appears in the food, its 'proportion reaching .32%.,in summer. This
•ià •suppléMénted In summer by the eggs of the fish-and of greenlings Of the
• fnily He-3.-agra.mmidae,- which.form one of the: main summer items for all
• age •groupà. eish eggs are .partid-ularly im.portant in the -diet of the young
fe:tha-1-eb.. The Sea.urchin is .fairly .significant in the summer :feeding of
"the Sea k-itteb,-hii-t ils proportion fluctuates considerably from one area of the
fibrand - -tà -ahô-th-er, s.a.mé applies to mollusks . 8
Chirpoi (Chernye Bratya) .Island. Table 3 gives an idea of feeding on
Chirpoi Island. Sea urchiris predominate; crustaceans come next, followed
by mollusks. There is a certain similarity with Urup - Island, but V i 1 a z i n a.
is absent.
TABLE 3. Breakdown of the winter food of the sea otter on Chirpoi Island (from an analysis of 308 excrements)
Incidence in the total number of excrements
Food total as predominant food
nurriber number
Sea urchin 279 90 248 80 Mytilus 33 11 9 3 Chiton 40 13 11 3.5 Dermaturus 69 22 21 6.5 Idothea 15 48 11 3.5 Goose barnacle 6 6 1 0.3.. Fish 26 8 7 2
Simushir Island. Forty excrements were collected in September 1970
from the Sea of Okhotsk shore of the island; the findings are given in
Table 4.
232 TABLE 4. Breakdown of the summer food of the sea otter on Simushir Island
'Incidençe in the total number of excr em_ents
Food total as predom nant food
number number . %
39 . 98 19. 47 1 4 10 None 13. .32.. None 9
Sea. urchins, octopus, fish and their young were found in the stomachs of
three sea otters taken in summer 1970.
The winter feeding of the Simushir sea otter can only be judged from the
stomachs and intestines of two animais caught in 1969 from the Pacific
littoral, \vhich were filled with the remains of sea urchins. Two samples of
excrement found on shore were also composed of sea urchin remains.
Thus, in spite of the scant data, a general picture can be traced of the
feeding habits of the Simushir sea otters. The main winter food item is •
.evidently the sea urchin, and mollusks of the genus T o ni c ell a also play
a certain role. This agrees wè.11 with the data on the distribution of the
forage reserves of the animals along the Simushir Island littoral. In summer,
feeding is more varied, including in addition fish, crabs and octopus which
come to the island's shores.
Onekotan. Island. Our data are very limited. An analysis of 18 samples of
excrement collected in late winter from Cape Subbotin showed them to consist
of remains of sea urchins (72%) and mussels (28%). Three stomachs examined
• in summer 1970 alsà contained remains of sea urchins (67%) and mussels (33%).
Thus, thèse two items probably represent the main food of sea otters on this
Paramushir Island. The nature of the winter feeding on the eastern shore
of the island can be sen from. Table 5. 10 TABLE 5. Breakdown of the winter food of sea otters on the1 ea.stern shore of Pararnushir Island (from an analysis of 164 excrements and the contents of five stomachs) Iticidence in the total number of exc rements (1) and stomachs (2)
Food total as predom inant food
1 2 2
Sea urchin 69 60 23 None Mytilus and Modiolus 64 80 50 80 T ell i n a 23 None 5 None Siliqu aria 6 None 4 None Crab 41 . 100 9 25 Fish 2 None None None Fish eggs None 15 None None
233 The winter feeding on the Sea of Okhotsk shore of the island is almost
unknown. Nine excrements found in the inlet Bukhta Maiora area consisted
of remains of sea urchin, with admixtures of xnussels. The composition of
the summer food indicates a greater importance of fish, fish eggs, and
octopus (Table 6).
TABLE 6. Results of an analysis of 55 excrements and of the contents of 11 stomachs and intestines of sea otters from the eastern shore of Para- mushir Island (August—September)
Incidence in the total number of excrements (1) and stomachs (2)
:Food total as predominant food
Sea urchin 22 55 Mytilus and Modiolus 34 - 36 18 Tellina 11 9 8 Unidentified mollusk 1.8 ■■■• Crab 46 Fish. . . 67 18 56 None Fish eggs None 86 None 55 Octopus '1 1 9 11 9 '.ec:m;^:;tzrtiw;,•r:a^:^;.:^t,x:i.t:v.z.en ^rs
1 l
These data indicate that the animal's feeding habits on Paramushir
ksland di£fer according to season and habitat. Bivalve mollusks (Mytilus
and M o d i o 1 u s), sea urchins and crabs predominate in winter in the foraging
grounds. The incidence of these invertebrates is roughly the same; but
their importance as food items depends on their abundance in the littoral
strip. The bivalve mollusks yield their largest biomass on the eastern and
southern shores of Paramushir Island. The sea urchin, although fairly frequent,
does not form great accumulations. Small accumulations of the crabs
Eri-macrus isenbeckii, Paralithodes brevipes and Derma-
tu r u s m a n d t i i are found in some areas àlong the eastern shore. On the
Sea of Okhotsk side the number of mollusks is small, but the sea urchin
forms considerable accumulations on sections with rocky and pebbly bottoms.
These fluctuations in the numbers of the main food items are reflected in
the sea otter's feeding.
in summer, fish and octopus approaching the island start to become
important in the diet. During the same period, the animals begin to eat fish
eggs in large quantities.
An analysis of the data on the sea otter's feeding on the different islands
reveals that only a few species of invertebrates and fish are of great
-importance.
There are insignificant variations in the qualitative composition of the
food from island to island. The quantitative composition displays sharper.
variations, depending mainly on the abundance of different items. Seasonal 12
234 variations in feeding are clearly pronounced throughout the Kurile Islands.
In winter, the food consists almost exclusively of sea urchins and mollusks,
while in summer it is supplemented with fish, fish eggs, crabs and octopus.
The sea otter obtains its food mainly from the shallow depths of the sub-
littoral and the lower horizon of the littoral. The greatest depth to which this
animal can dive is 50-60m according to Barabash-Nikiforov, Marakov and
. Nikolaev (1968), and 90m according to Lensink (1960). The present author
has encountered feeding sea otters down to a depth of 65m. A specimen
eating a large crab was seen from a ship at Cape Temnyi on Urup Island.
Judging by its size, it was an adult. Off Paramushir Island, sea otters were
frequently observed at depths of 50-55m. But only a few feed at such depths:
most of the animals usually feed in areas where the depth does not exceed
20m, especially in winter. Females with young all year round stay closer to
the shore than individual animals. Pups can.not fend for themselves before -•
the age of 3-4 months; to support themselves and the young, the females must
therefore stay around places of mass concentration of little mobile or immobile
food items (fish eggs, sea urchins), i. e., the littoral shallows. At the age of
6 months, the pups can catch their own sea urchins, fish eggs and mollusks,
but evidently not fish or octopus. In August 1969, a female with a pup were
seen feeding at Cape Zhdi on Urup Island. The female was found to spend an
average of one minute at a time under water in search of food; the pup,
whose Size indicated it to be of last year's brood, stayed only half a minute.
In 25 minutes, the female caught and ate four frogfish, while the pup caught none. 13
Single animals often gather in separate groups and lead a more mobile
life. Isolated groups of single sea otters were observed on Mednyi Island
by Barabash-Nikiforov and Marakov (Barabash-Nikiforov et al., 1968) and by
B. V. Khromovskikh (1968). The present author has seen groups of bachelors
on Pararnushir. Mature males often lead a vagrant life, roaming the island's
shores. They may eVen swim to other islands during their wanderings and
may cross the boundary of their range, as indicated by the capture of a
male near the Chukchi Peninsula (Zimushko et al., 1968). ,Their food in
summer includes octopus, fish and large crabs much more often than that
of females.
A peculiarity in the sea otter's feeding habits is the narrow specialization
in feeding on little mobile animals which form large accumulations; this has
a certain influence on the animal's distribution. Data on the distribution
(Belkin, 1966; Nikolaev, 1968) and on that of The basic food items in the
• central and northern Kurile Islands indicate that the sea otter's habitats
:coincide with areas of development of immobile sestonophages, as pointed
out earlie'r '(Maminov and Shitikov, 1969, 1970) for the Paratnushir and
Kamchatka population. Such areas include the littoral waters of almot all
- the Kuriles, except the regions with sandy bottoms, where conditions are
favorable for the development of other trophic groups of benthos (mobile and
little mobile sestonoPhages); no accumulations of the sea otter's food items were , 235 found in these zones of 'development of mobile sentonoplies, and- the animals
therefore avoid them. 1 4
Highly indicative in this respect is the sea otter's distribution on
Paramushir and Urup . The animal occurs only on the east and south coasts
of Paramu8hir but along the entire littoral of Urup . As reported earlier
(Maminov and Shitikov, 1970), the nonuniform distribution on Paramushir is
due to different habitat conditions . The eastern pebbly shore and rocky bottom of the Paramushir littoral promote the development of immobile
sestonophages, hence the accumulation of food items : bivalve mollusk s
(M y t i I u s and M o d i o 1 u s), sea urchins and crabs . On the west coast of
Paramushir, the zone of immobile sestonophages occupies just a small portion
of the littoral, while the zone of mobile and little mobile sestonophages pre-
dominates and here no food accumulations were found . On the Urup littoral,
With a rocky bottom, the zone of immobile sestonophages embraces portion s
of both the western and the eastern shore, which facilitates a uniform
distribution of sea otter Is food all -along -the island Is littoral . The zone of,
.little mobile sestonophages here'occupies only isolated portions with sandy
mainly at the apexes of bays and inlets .
Inside'the zone of inamobile'sestonophage's, the sea otter keepts to area s
of development of laminarlaceous biocenoses, which are widespread in the
littoral zone of -the Kurile Islands to a depth of 15-20M . In addition, o n
Paramushir, the animal occurs in the areas of development of the M o d i o I u s
,modiolus + Mytilu*s edulis .+ Spongla + Hydroidea bioceno-sis .,
The "s'e a otter-Is distribution both over the'islands and-within the limits o f
one island is thus mainly determined by .the distribution of its food items . 11^
Obviously, the number of animals on an island will depend on the abundance of
food there. Our investigations indicate, however, that their number depends
on other factors too. The greatest biomass of food items was found of.f Matua
Island (17,203 g/m2, maximum 32,000g /M2 ), and the lowest off Ürup (326 g fxriz).
The number of sea otters was and is, however, larger on Urup, and only
isolated individuals are ever found on Màtuà. Few sea otters live on the
Ushishir and Chernye Bratya islands as well, although the biomass of sea
urchins there is fairly high (5,754 and 2,476 g/m2, respectively), reaching
11,000 g/m2 in places. In some areas of the Okhotsk coast of Paramushir
the average sea urchin biomass is 6,622 g/m2, but the sea otters visit them
only during their, roamings along the island's littoral and never linger there.
On the other hand, the animal is constantly found on the Pacific coast of
P.aramus.hir, where it forms large groups, although the average .biomass of
-food items is lower there than,on -the Okhotsk coast.
An -investigation of the areas of .frequent occurrence revealed that a
distinctive feature is the consid'erable e.xtent of the shallow strip, when the
20-m isobath lies 2,000-2,500:in, the -5-m isobâth 100-200m, and the 10-rn
isobath 500-1,000m away from the shore.
Such areas are particularly numerous in the littoral strip of _`Ur.up and
along the east and south coasts of Paramushir. The littorals of other islands
`236 investigated (Simushir, Matua, Chirpoi (Chernye Bratya), Ushishir) and the
'western littoral of .Paranxushzr have nc tsignificant shallows. The,20-rri ^,iso-
bath lies 200-300 m and the 5-m isobath 20-30 m off the Si.musl1ir shore.
The -20-m isobath lie% .5-0-100:m off thë -shore of Matua and IJshishir and the
west coast of Paramushix;, cand the 5=ixi isobath rtins close along the shore. 16
This results in changes in the qualitative and quantitative composition of the invertebrates included in the laminariaceous biocenobes, some of which serye as food items for the sea otter; this, in turn, causes fluctuations in the animal's numbers. •
In view of the high food requirements of the sea otter (a quarter of its weight according to Reshetkin and Shidlovskaya, 1947; Kirkpatrik, Stullken and
Jones, 1955; Kenyon, 1959, 1963), many sea otters can occur on an island only if the food reserves .are plentiful in the littoral strip, and this depends not only on the magnitude of the food biomass per unit of area but also on thelforaging area..
For purposes of comparison, let us examine the distribution of the sea otter's food items off Maiva and Urup. •The 20-m isobath lies 20m off the
Matua shore; 1 m of coast thus provides 20m2 of feeding grounds. Since almost the only source of food on Matua is the sea urchin (the chiton reserves are insignificant), at an average biomass of 17kg/m2, the food reserves per meter of coast are 340 kg. The same 20-m isobath runs 2,000m off the
Urup coast and thus 1m of coast there provides 2,'Ù00 m 2 of feeding grounds.
The sea otter's main source of food here is the sea urchin, along with
Vil a z in a and craboids (chitons, Me s id othe a and some bivalves are not taken into account). At an average biomass of 0.09 kg/m2 for sea urchins,
0.2 kg/m2 for Vil a z in a and 0.02 kg/m2 for the craboids, the food reserves per meter of shore will amount to 660 kg. At the highest value 'Of food biorn.ass per unit of area, the sea otter's food reserves per meter of.shoreline can 17
attain 640 kg on Matua and 7, 800 kg on Urup.
Thus, the wider the shallow strip around an island, the better are the feeding
conditions for the sea otter and the larger their possible number. Not only
is the foraging area large off Urup and the east and south coast of Paramushir,
but also the choice is wider. Aside from the sea urchin, the littoral of these
islands harbors large accumulations of bivalve mollusks and Decapoda,
and therefore sea otters are abundant here.
In the littoral zones of other islands in the Kurile Ridge, sea otter
colonies are also found .in the shallôwest'areas. On Simushir., examples of
such areas are the northeastern, and northwestern littorals, on the Ushishir.:.
'Islands the northeastern littoral of Rypônkich Island and the southwestern
littoral of Yankich Island, and on Onekotan the southwestern littoral. Shallows
are most frequent around capes, extremities, and on the Pacific coasts of
the islands.
All these facts prove that, in spite of the existence of suitable habitats
for sea otters in most of the central and northern Kurile Islands, conditions
are far from being favorable for large numbers everywhere. Scattered
information on the size of the sea otter population on the Kurile Islands
indicate it to have been largest last century on Urup (Sergeev, 1947) and Iturup
237 (Slyunin, 1895; Snow, 1902). The Urup population has apparently never
-exceeded.2,600 specimens, even during the best years. During the last 7-8
years the number of :sea otters has been..about 2,000.- It may be inferred that
the Urup population probably does not exceed 2,000-2,600 specimens. Since
the number of animals is determined by _the size of the rocky shoals area,
L. e., the area of the feeding grounds, the density of sea ôtters per km2 of 18
feeding grounds is 4-4.5 specimens, at a length of the Urup shoreline of,
270 km and a width of the shallow strip of 2km. Assuming this density of
occurrence as normal for the entire Kurile Ridge, the possible number of sea
otters on the islands we investigated can be calculated as follows:
Urup 2,000-2,600 Simushir 96-110 Chernye Bratya 32-40 Ushishir 24-30 Param.ushir 1,480-1,700 Matua 6-10
At present, the number of sea otters on these islands is close to the
calplated. Since no data are available on the food resources of sea otters
on other Kurile Islands, we will not estimate the possible number of animals
along their shores. But in view of the fact that the number of sea otters on
the central and northern Kurile Islands has not been increasing over the last
few years, it may - also be assumed to be close to the limit.
On most isle.. nds, the sea otter has already occupied all the favorable
habitats. A small increase in population can be expected on Simushir,
Paramushir and Chernya Bratya, but that would hardly alter the overall picture.
We do not share the opinion of S.K.Klumov (1968) concerning the need for
sea otters to be introduced into the central and northern Kurile Islands. We
think that the prerequisite of wide rocky shallows where laminariaceous
biocenoses develop with the associated fauna of bottom invertebrates is one
of the main ecologiçal characteristics. At present . the sea otters have already
: populated all the littoral areas that meet this requirement in the central and
northern islands of the Kurile Ridge, and wherever.their number has not yet de •
19
reached the limit, it soon will. Nor do we consider Broughton Bay on
Simushir as suitable for sea otters to be kept in sémi-captivity. The food
reserves there, mainly sea iirchins, are concentrated on a narrow littoral
strip of 20-30m, which could hardly supply the needs of many animals.
Conclusions
The main part of the sea otter's food in the Kurile Islands consists of
little mobile forms of benthos (sea urchins, mollusks, decapods). In summer,
fish, fish eggs and octopus play an important role in the feeding.
2. • When foraging, sea otters can dive to depths of 65m, but most feed at
depths down to 20m. •
3. The animal's range in the central and northern Kurile Islands is
bordered by 'areas where a .certain trophic group of benthos develops:
immobile sestonophages. Within this zone, sea otters ca.n be found mainly in
areas of laminariaceous biocenoses, where their food items accumulate.
238 4. The number of sea otters on each island and along its littoral depends
-on the area of the rocky shallows, which form the feeding grounds. A rough 2 density of sea otters per km of feeding grounds would be 4-4.5 specimens.
.5. ,The num.ber of sea otters in the central and northern Kurile Islands is
• at present close to the upper limit. •
• 6. Artificial colonization of sea otters in the central and northern Kurile
•Islands is inadvisable. 20
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Barabash-Nikiforov,I.I., S.V.Marakov,and A.M.Nikolaev.
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Kh romo vs k ik h, B. V. Chisleimost' i ekologiya kalana na o. Mednom
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Klum 0V, S. K. Beregovye lezhbishcha kotikov i mesta obitaniya kalanov na
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• Klum o v, S. K. Iskusstvennoe rasselenie kalanov kak osnovnoi metod
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Biology of the Urup Sea Otter). - Soobshcheniya SakhKNII, No. 6. 19580
Ni k o 1 a e v, A. M. and V. A. S k a 1 k i n. : O pitanii kuril'skikh kalanov (The
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R e s h e t k i n, V.V. and N. K. S h i d l*o v s k a y a. Akklimatizatsiya morskoi
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'Moskva, Izdaterstvo Glavnogo upravleniya po zapovednikam. 1947,
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S1 yunin, N. V. Promyslovye bogatstva Kamchatki, Sakhalina, Komandorskikh
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Komandorski Islands). Sankt-Peterburg. 1895.
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Zimushk o, V. V., G. A. Fedosee v, and A. P. Shu s t o v. Kalan v Arktike
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Publications in Other Languages
Daugher ty, A. E. Marine Mammals of California. 1965.
Ey e r dm an, W. J. Sea Otters in the Aleutian Islands.— J. Mammal.,
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K e ny on, K. W. The Sea Otter. 1959.
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