National Marine Mammal Laboratory by Rolf
of their rounded, convex head and their short noses, the
Northern Fur Seal has been described as “bearlike.” A
sexually dimorphic species, the average male is up to four
times larger than the female, with a length of 5-7 feet and
weight of 400-600 pounds. The genders are also separated by
coloring; males are black or dark brown while females are a
lighter brown or grey. Northern Fur Seals have the longest
rear flippers of all eared seals, constituting for up to one
third of their body length. The front flippers, however, are
shorter, and naked from the wrist down. Their dense
under-fur on the rest of their bodies provides them with
warmth so they need not rely on blubber for insulation.
Feeding and Behavior
As the most pelagic pinniped, Northern
Fur Seals spend up to nine months of the year at sea, coming
onshore only for breeding. They reside mostly off the
continental shelf, 20-70 miles offshore, in deep waters,
concentrating in offshore islands and upwelling areas. These
seals are mostly solitary when at sea, but may form foraging
groups of 2-4, swimming at speeds up to 15 miles per hour.
Larger groups have been noted when food is abundant, but
this is rare. Northern Fur Seals typically feed in evening,
night, and early morning and have up to 70 species in their
diet; in California the dominant prey includes anchovy,
herring, squid, and rockfish.
Northern Fur Seals generally range from
Southern California to the Bering Sea, and across to central
Japan, but most of their breeding takes place in the
southern Bering Sea. The breeding season is April to
November, with a peak in late June. These seals are playful
and intelligent, but also very aggressive during breeding
season. Males defend group of 15-20 females with
vocalization, chest-butting, and charging. They fast during
breeding for an average of 40 days, losing up to 20% of
their body weight; their defenses rarely include fighting
because they need to preserve energy. Females nurse the pups
for about four months, leaving them gathered together on the
beach while out foraging.
Population Threats and Conservation
Due to mass hunting by European
sealers, the Northern Fur Seal population was taken from 2.5
million in 1787 to 300,000 in 1909. In 1911, however, the
Northern Pacific Fur Seal Convention was created between the
United States, Japan, and the United Kingdom, limiting
hunting to only adult males. The agreement was terminated
during WWII but reinstated in 1957, in which time the
population recovered to 1.5 million. With this recovery, an
annual harvest of females began, but was stopped in 1985
because of another large population decline. In addition to
hunting, El Niño Southern Oscillation (ENSO) events greatly
affect the population; 67-80% of the pups died in one colony
during the 1982 and 1998 events.
Sarah G., Joseph Mortenson, and Sophie Webb. "Northern Fur
Guide to Marine Mammals of the Pacific Coast: Baja,
California, Oregon, Washington, British Columbia.
Berkeley: University of
California, 2011. 442-54. Print.
Fur Sea (Callorhinus Ursinus)." NOAA
Fisheries Office of Protected Resources. N.p., 11 June
2013. Web. 07 Oct. 2013.