Otarie a fourrure

The population history for Northern Fur Seals throughout the North Pacific and Bering Seas has been tied to the harvest of seals for their pelts (Kuzin 1999, NMFS 2007). Between the mid 1700s and early 1800s, Russian sealers used Aleut labour to harvest an average of 100,000 Fur Seals, mostly pups, annually in Alaskan waters (Roppel 1984). The commercial harvest of Fur Seals on the Pribilof Islands continued with periodic modifications to the sex/age classes of focus until and after the United States purchase of Alaska in 1867. In the late 1800s and early 1900s commercial harvests on land and pelagic sealing continued unregulated until the Fur Seal act of 1911 was signed by Japan, Russia, Great Britain (for Canada) and the United States. This treaty prohibited pelagic sealing and reduced the take on land which at its peak in 1868 had harvested 240,000 seals in a single year (Roppel and Davey 1965, NMFS 2007).

In the early 1900s the Pribilof stock continued to grow in abundance despite commercial harvest. Between 40,000 and 126,000 seals were harvested each year during 1943-1968 (NMFS 2007). A new harvest regime was followed in the early 1960s which allowed for annual harvests of approximately 300,000 adult females and 30,000-96,000 subadult males (York and Hartley 1981). The population did not increase as anticipated after this new regime and ultimately commercial harvest of Fur Seals was terminated on St. George Island in 1973 and on St. Paul Island in 1983. Subsistence harvest of subadult males has continued on both islands since that time (NMFS 2007). In 2014, subsistence harvest rules were changed to allow the annual take of up to 150 male pups on St. George Island during a new autumn harvest season. This harvest occurred for the first time in the autumn of 2014.

Contrasting to the Northern Fur Seal abundance trend on the Pribilof Islands is Bogoslof Island, a small volcanic island in the eastern Aleutian Islands of Alaska. Northern Fur Seals were first reported on Bogoslof in 1976 with the first breeding seals noted in 1980 (Lloyd et al. 1981, Loughlin and Miller 1989). Subsequent surveys revealed an exponential growth rate during the 1990s and early 2000s with the estimated number of pups increasing at a rate of 48.5% annually between the time pups were first observed in 1980 and 2005. This rate then dropped to approximately 10% annually between 2005-2011, the last time the island was surveyed. Such a dramatic growth rate can only be explained by a combination of recruitment and immigration from other sites (Ream et al. 1999). Recent studies suggest that the recent slowing in growth rate coupled with increases in foraging trip duration and distance may represent a typical density dependent response to a limited resource (Kuhn et al. 2014). The Northern Fur Seal population on Bogoslof has increased to the point that it is the second largest Northern Fur Seal rookery in the United States, surpassing St. George Island. This growth has served to ameliorate the overall decline of the population.

Northern Fur Seal rookeries in Russia have not been counted since 2006-2009 depending on the site. However, basic trends until that time are documented. Overharvesting in the 19th century eradicated the population on the Kuril Islands where Northern Fur Seals were considered extinct until the mid 1950s. Pup production grew rapidly on the Kurils during 1962-1977 (19.9% annual increase). The population stabilized around 1978 and trend became slightly negative (-0.8%) during 1978-1988. Pup production in the Kuril Islands has increased 82.4% since 1988 (+3.8% annually) and is now comparable to the Tuleny (Robben) Island population. During the last count in 2006, approximately 27,090 pups were counted. Total abundance of Fur Seals in the Kuril Islands currently exceeds 100,000 individuals (Kuzin 1999).

In 1999, A. Kuzin published a detailed description of the biology and history of Northern Fur Seals in Russia with special emphasis on Tuleny Island. He reported that the population at Tuleny at the time of its discovery in 1852 was approximately 120,000. Subsequent unregulated harvest reduced the population to as low as a few thousand animals in the late 1890s. Tuleny Island then underwent a series of population highs and low during various periods of harvest. The maximum population was approximately 180,000 individuals in the late 1960s (Kuzin 1999). The most recent estimate was 140,000 individuals including 42,200 pups in 2009 (Kuzin 2010).

The San Miguel stock of Northern Fur Seals breeds primarily on San Miguel Island, California, at the southern extent of the breeding range. This population has increased or been stable since its discovery in 1968 (Caretta et al. 2013). The trend in pup births includes a steady increase followed by a sharp decline that has been shown to be directly tied to El Niño events; pup production in 1997-1998 declined 81% due to the redistribution of prey caused by the event. Overwinter satellite telemetry studies have shown that Northern Fur Seals from all of the US breeding sites use similar foraging grounds along the west coast of Southeast Alaska, British Columbia, Washington and Oregon (Lea et al. 2009, Ream et al. 2005, Sterling and Ream 2004). The overlap is not limited to foraging habitat as genetic studies indicate that there is very little differentiation between animals throughout the range (Dickerson et al. 2010).

Population estimates for Northern Fur Seals are generally derived by multiplying pup counts by a correction factor of 4.4747 to include all non-pups. A global abundance estimate was generated from the most recently available count and estimate data for all subpopulations in the range using the agTrend model (Johnson and Fritz 2014). The 2014 estimate for localities other than the Pribilofs is a projected number based on the trends at each site. The modelled population estimate used all of the data available since 1966 to project the estimates reported above. The most recent actual count and estimated numbers used in the model are shown below.

Pribilof Islands, 2014

St. Paul Island: 91,737 pups x 4.4747 = 410,496 (Towell et al. 2014)

St. George Island: 18,937 pups x 4.474 = 84,737 (Towell et al. 2014)

Sea Lion Rock: 5,250 pups x 4.4747 = 23,492 (Towell et al. 2014)

Commander Islands, 2006: 59,805 x 4.4747 = 267,609 (Burkanov and Calkins 2007)

Tuleny Island, 2009: 42,200 x 4.4747 = 188,832 (Kuzin 2010)

Kuril Islands, 2006: 25,164 pups x 4.4747 = 112,601(Burkanov et al. 2007)

Bogoslof Island, 2011: 22,905 pups x 4.4747 = 102,493 (Towell et al. 2012)

San Miguel Island, 2014 (not including Castle Rock): 2,327 x 4.4747 = 10,412 (A. Orr, NMFS pers. comm.)

Farallon Islands, 2014: 656 pups x 4.4747 = 2,935 (R. Berger, Point Blue Conservation Science pers. comm.)

The global population of Northern Fur Seals is estimated to be approximately 1.29 million in 2014, a decline of approximately 658,000 since 1976. Note that this number is different than the sum of abundances given above because most were projected forward to 2014 in the model. Using the agTrend model to project the population reduction at all sites over the past three generations (1972-2014) gives an estimated reduction of 30.1% (95% CI -47.1% to 14.5%). Annual abundance estimates for the entire range do not exist as there are no consistent monitoring strategies in place. Although abundance is declining, the overall decline is not proportional across all sites. The greatest decreases are occurring in the Pribilof Islands, while populations in the Kuril Islands and Tuleny Island in Russia, and on Bogoslof Island in Alaska have increased.

The decline described above understates the total reduction of the Northern Fur Seal population in historic times. It is estimated that the population numbered up to 2.5 million animals in the 1950s, and it may have been considerably larger than that when there were many more active rookeries before the onset of human exploitation.

To date the only population viability analysis conducted for Northern Fur Seals was described in a report from the Canadian Science Advisory Secretariat, Department of Fisheries and Oceans, Canada (Olesiuk 2012). This analysis concluded that all subpopulations are presently secure with little risk (0.00%-0.42%) of extirpation within the next century.