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Figure 1. Steller sea lion rookeries and haulouts
along the coast of Asia.
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by Vladimir N. Burkanov
Scientists from the United States, Japan, and Russia conducted Steller
sea lion (Eumetopias jubatus) research in remote and hard to access areas
of the Russian Far East aboard the Russian fish cargo vessel MTR Bolsheretsky
from 23 June through 22 July 2001. Forty-six of 59 sea lion rookeries and
haul-out sites were surveyed. A total of 4,897 Steller sea lions age 1+
years old and 1,896 pups were counted on all rookeries in the Kuril Islands;
1,509 non-pups and 952 pups were counted on Iony Island, and 119 non-pups
were counted along the southeastern coast of the Kamchatka Peninsula.
Two hundred fifty-seven branded or flipper-tagged animals from previous
years were resighted; 480 scat samples were collected throughout the surveyed
sites; blood samples were taken from 335 pups (50-60 samples per rookery),
and 129 skin punches from the rear flippers of these pups were taken for
nuclear DNA analysis; 619 pups were branded, and of these, 572 were simultaneously
tagged with paired plastic tags. All the data collected during this expedition
are being analyzed. A full report will be prepared after all analyses
are completed.
Introduction
Steller sea lions are widely distributed along the Asian coast, from the
China coastline to the Bering Strait. However, the major breeding areas
are located on the Kuril Islands (Figure 1 above), where up to 50 percent or more
of the total number of pups are born every year. The Kuril grouping of
Steller sea lions has always been the most abundant on the Asian coast.
The first reported abundance estimates of Steller sea lions at the Kuril
Islands were made by visual assessment from a captain of a hunting schooner,
(Snow 1902) According to him, at the end of the nineteenth century the
Steller sea lion population in the Kuril Islands was about 100,000 animals.
However, all the later data showed that his estimate was too high. The
first and most complete survey of the islands was carried out by a special
expedition of the Russian Academy of Sciences in 1955. The abundance of
Steller sea lions (1 year old and older) at that time was estimated at
15,000-17,000 animals throughout the Kuril Islands range. The first pup
counts at the Kuril Islands occurred in 1963. A total of almost 3,500
new-born pups were counted at all the rookery sites. These data are the
earliest figures on abundance of Steller sea lions in the Kuril population
that can be used for comparative analysis. Later counts of Steller sea
lions were carried out concurrently with surveys dedicated to research
on northern fur seals (Callorhinus ursinus) and sea otter (Enhydra
lutris).
These surveys were carried out somewhat later in the year than the optimal
period for counting Steller sea lions (late May to early June), and often
not all the sites were surveyed. Therefore, the acquired data are difficult
to analyze and required an estimation of data on sites that were not surveyed.
The most complete data are counts of pups and non-pup sea lions on major
rookery sites while data on haulouts are the most irregular (Figures 2-5).
The first data collected on the abundance of Steller sea lions on Iony
Island are attributed to the 1930s. At that time harvesting of Steller
sea lions was carried out on the island. During one of the first harvesting
voyages an accurate count of new-born pups took place. In 1933 at all
rookeries around the island 1,510 pups were counted. The abundance of
mature animals was estimated as 2,000-5,000. Later counts of Steller sea
lions on Iony Island took place in 1948, 1974, 1989, and 1997 (Figure 6).
In 1989 Russian and U.S scientists launched a program of marking Steller
sea lions to study migration and survival and to evaluate the extent of
isolation at individual rookeries. A total of 3,070 pups have been branded/tagged
over 10 years, and of these, 368 have been resighted. Movement patterns
determined from these studies show that Steller sea lions travel along
the Asian coastline, and animals born on the Kuril Islands have been resighted
from the Yellow Sea (China coast) to the Bering Sea (Karaginsky Gulf) (Figure 7).
In 2001 a group of scientists from Russia, Japan and the United States
(with financial support provided by the National Marine Mammal Laboratory,
Alaska Sealife Center, and Amway Nature Center, Japan) conducted observations
of Steller sea lions and collected biological data at most rookeries and
haul-out sites along the Kuril Islands and on Iony Island. Major tasks
were to conduct detailed counts of Steller sea lions for current abundance
estimates, search for tagged/branded animals, and measure and tag/brand
500 new-born pups at five major rookeries in the Kuril Islands and 150
pups on Iony Island. Additional tasks were to collect data on pup morphometry,
take blood samples to analyze pup health, and study the extent of isolation
of reproductive groupings by electrophoresis of serum and erythrocytes.
Skin samples also were collected to evaluate by nuclear DNA the extent
of isolation at rookeries.
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Figure 2. Non-pup counts of Steller sea lions on 16 trend sites
Figure 3. Non-pup counts of Steller sea lions on the five major
Figure 4. Non-pup counts of Steller sea lions on 11 trend
Figure 5. Pup counts of Steller sea lions on the five major
Figure 6. Steller sea lion counts on Iony Island, 1930-2001.
Figure 7. Movements of branded Steller sea lions born on the Kuril Islands in 1989-99.