scholarly journals First-Year Survival of Northern Fur Seals (Callorhinus ursinus) Can Be Explained by Pollock (Gadus chalcogrammus) Catches in the Eastern Bering Sea

2021 ◽  
Vol 9 (9) ◽  
pp. 975
Author(s):  
Jeffrey W. Short ◽  
Harold J. Geiger ◽  
Lowell W. Fritz ◽  
Jonathan J. Warrenchuk
Keyword(s):  
Bering Sea ◽  
First Year ◽  
Callorhinus Ursinus ◽  
Population Declines ◽  
Fishing Activity ◽  
Eastern Bering Sea ◽  
Fur Seals ◽  
Fur Seal ◽  
Seal Population ◽  
Pribilof Islands

The Pribilof northern fur seal (Callorhinus ursinus) herd in the eastern Bering Sea has declined by ~70% since the 1970s, for elusive reasons. Competition for pollock (Gadus chalcogramma) with the commercial fishery has been suspected as a contributing factor, but no correlative relationship between fishing activity and fur seal population declines has heretofore been demonstrated. Here, we present evidence for a moderately strong inverse relationship between fishery catches of pollock and first-year survival of fur seals, based on three different approaches to evaluation. We suspect this relationship results from the dependence of lactating female fur seals on locating dense and extensive schools of pollock near the Pribilof Islands to efficiently provide nutrition for their pups, because the pollock fishery also targets these same schools, and when fished, the remnants of these schools are fragmented and dispersed, making them more difficult for fur seals to locate and exploit. Inadequately fed pups are less likely to survive their initial independent residence at sea as they migrate south from the Pribilof Islands in the fall. Our results imply that pollock catches above ~1,000,000 t within ~300 km of the Pribilof Islands may continue to suppress first-year survival of Pribilof fur seals below the estimated equilibrium survival value of 0.50, leading to continued decline of the population.

Pup Production Following Harvest of Female Northern Fur Seals

1981 ◽  
Vol 38 (1) ◽  
pp. 84-90 ◽  
Author(s):  
Anne E. York ◽  
James R. Hartley
Keyword(s):  
Cohort Analysis ◽  
Survival Rates ◽  
Callorhinus Ursinus ◽  
Northern Fur Seal ◽  
Fur Seals ◽  
Fur Seal ◽  
Seal Population ◽  
Northern Fur Seals ◽  
Early Survival ◽  
The Difference

Female northern fur seals (Callorhinus ursinus) were harvested commercially from 1956 to 1968 and pelagic collections were taken for research purposes from 1958 to 1974. Early survival rates (birth to age 2) for males increased from an average of 0.32 before the harvest to 0.38 afterwards. Numbers of female pups whose births were precluded by the harvest are estimated for the years 1956–79; these account for about 70% of the difference between the numbers of pups actually born and the level of pup births before 1956. Estimates of the increased numbers of pups due to the increase in the early survival rates are presented for the years 1958–74.Key words: northern fur seal, population dynamics, female harvest, cohort analysis, St. Paul Island

Growth of a fur seal population

1977 ◽  
Vol 279 (963) ◽  
pp. 67-79 ◽  
Keyword(s):  
Age Groups ◽  
Population Increase ◽  
South Shetland Islands ◽  
First Year ◽  
South Georgia ◽  
Fur Seals ◽  
Fur Seal ◽  
Younger Age ◽  
Seal Population ◽  
Incipient Colonies

The Antarctic fur seal Arctocephalus gazella is a polygynous Otarid in which a single pup is produced annually by cows over the age of 2 years. Following exploitation to the verge of extinction, a small breeding colony was discovered at Bird Island, South Georgia, in the 1930s. Up to 10000 pups a year were produced in the early 1960s and by 1975 the figure had reached an estimated 90000. The rapid population increase has resulted in the colonization of extensive breeding areas on the adjacent mainland of South Georgia with incipient colonies springing up on more distant parts of the island, and also in the South Sandwich, South Orkney and South Shetland Islands. Age determinations from the teeth of 195 breeding cows reveal a low mean age, early first breeding and a predominance of the younger age groups relative to the age structure of a stable population of northern fur seals Callorhinus ursinus . Annual adult cow survival is estimated at 89.8%, while that of first-year animals is about 64.5%. A decline in the rate of population increase is forecast within ten years and an outline for investigating the most likely factors influencing such a change is suggested.

The Food of Fur Seals in the Eastern Bering Sea

1957 ◽  
Vol 21 (2) ◽  
pp. 237 ◽  
Author(s):  
Ford Wilke ◽  
Karl W. Kenyon
Keyword(s):  
Bering Sea ◽  
Eastern Bering Sea ◽  
Fur Seals

At-sea behavior of juvenile male northern fur seals (Callorhinus ursinus)

2004 ◽  
Vol 82 (10) ◽  
pp. 1621-1637 ◽  
Author(s):  
J T Sterling ◽  
R R Ream
Keyword(s):  
Body Mass ◽  
Mass Gain ◽  
Callorhinus Ursinus ◽  
Juvenile Male ◽  
Deep Waters ◽  
Fur Seals ◽  
Straight Line ◽  
Northern Fur Seals ◽  
Straight Line Distance ◽  
Pribilof Islands

The at-sea behavior of juvenile male northern fur seals, Callorhinus ursinus (L., 1758), captured at two haul-out sites on St. Paul Island, Alaska, during the 1999 and 2000 breeding seasons (July–September) was studied. To compare at-sea locations, dive behavior, and changes in body mass, 31 juveniles between the estimated ages of 3–6 years were captured, instrumented, and released. Individuals behaved like central-place foragers by making trips to sea and returning to the Pribilof Islands. Trip durations ranged between 8.74 and 29.81 d, whereas distances from departure site ranged between 171.27 and 680.68 km (maximum straight-line distance). Differences in maximum straight-line distance traveled and trip duration were not observed when comparing years or departure site. Diving tended to reflect patterns associated with different bathymetric domains; shallow nighttime diving was common in ~3000 m deep waters, whereas deeper diving was generally observed in <200 m deep waters. Proportion of body mass gained over a single trip to sea averaged 27.8% (range 3%–65%, n = 19). Mass gain was similar between individuals that dove in shallow waters (over the continental shelf; 10.9 ± 1.8 kg (mean ± 1 SE), n = 11) versus individuals that dove in pelagic waters (8.5 ± 1.0 kg, n = 8). These results demonstrate that the at-sea behavior of juvenile males can extend farther from the Pribilof Islands when compared with previous reports of parturient female at-sea behavior, thus revealing important variation within this species.

A painter in the Bering Sea: Henry Wood Elliott and the northern fur seal

Polar Record ◽  
2013 ◽  
Vol 50 (3) ◽  
pp. 311-318
Author(s):  
Robert McCracken Peck
Keyword(s):  
Abundant Species ◽  
Historical Record ◽  
Fur Seals ◽  
Commercial Harvest ◽  
Dramatic Decline ◽  
Fur Seal ◽  
Pribilof Islands ◽  
Breeding Seasons ◽  
The U.S

ABSTRACTHenry Wood Elliott (1846–1930), a U.S. Treasury official assigned to monitor the harvest of northern fur seals on the Pribilof Islands in the 1870s, became a self-taught expert on, and defender of, the species. His careful documentation of the seals’ breeding behaviour, and of their commercial harvest, complemented by hundreds of detailed and evocative watercolours, provides a unique record of this once abundant species and the lucrative industry that revolved around it. Elliott's outspoken lobbying on behalf of the seals’ protection is often credited with saving the species from extinction. His paintings of the seals, the seal harvest, and life on the Pribilof Islands in the second half of the nineteenth century constitute an unmatched historical record of this remote region.Elliott was able to witness two full breeding seasons (and harvesting) of the fur seals during his initial stay on the Pribilofs from April 1872 to October 1873. He returned to the islands to conduct a follow-up census of the seals, on behalf of the U.S. Government, in the summer of 1874. He traveled there unofficially and at his own expense in 1876. His fourth trip to the Pribilofs was in the spring of 1890 (again on behalf of the U.S. Department of the Treasury), in response to news of a dramatic decline of the seal populations. In April, 1891, because of his public revelation of mismanagement of the fur seal harvest, Elliott was fired by the Treasury. He continued his tireless lobbying on behalf of the fur seals as a private citizen for the rest of his life. He visited the Pribilofs for the last time on behalf of the House Committee on Expenditures in the Department of Commerce and Labor in the summer of 1913. Born in Cleveland Ohio on November 13, 1846, Elliott died in Seattle Washington on May 25, 1930.

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