Arctocephalus townsendi
Written off as extinct, twice, and rebuilt from fourteen animals hiding in a cave.
Commercial sealers worked Isla Guadalupe, off the Pacific coast of Baja California, hard through the 1700s and 1800s. In 1892 the naturalist Charles Townsend, whose name the species now carries, found seven animals on the island. Seven. Hunting continued anyway.
A small group was found again in 1926. By 1928 those animals had been killed, two males had been captured and sold to the San Diego Zoo, and the species was written off as extinct for the second time. For the next twenty six years there was exactly one unconfirmed sighting.
It is worth pausing on what "extinct" meant here, because nobody was lying. The island had been searched. The animals genuinely were not on the beaches where they had always been. What nobody realised was that the survivors had changed their behaviour, moving into sea caves and shaded overhangs at the base of Guadalupe's cliffs, where a boat passing offshore would see nothing at all.
Every seal has hair. Fur seals have two kinds, and that is the whole reason this species was hunted to seven animals while the sea lions sharing the same coastline were largely ignored. Under each stiff guard hair sit 35 to 40 fine underfur hairs, growing from separate follicles that funnel up through one opening in the skin. Shave off the guard hairs and what remains is a pelt of extraordinary quality. Sea lions do not have that layer, so nobody wanted them.
For the seal, the underfur is a permanent air mattress. The outer coat wets through on a dive, but a film of trapped air stays against the skin and does the insulating that blubber does in other animals. The trade off is that the coat has to stay clean and working, which is why oil is far deadlier to a fur seal than to a walrus.
The rest of the body reads as classic eared seal. Narrow ear flaps stand out clearly on the sides of the head. The broad fore flippers do the swimming, flapped like wings, with a fringe of hair running past the wrist in a distinct V onto the top of the flipper, which is a real field mark. The hind flippers swing forward under the body, which is how an animal that looks clumsy on sand gets itself up onto a cave ledge above the waterline.
Recovery from a bottleneck that tight is not guaranteed. A population squeezed down to a handful loses most of its genetic variety, and inbred populations often fail even after the original threat is gone. This one did not.
In 1975 the Mexican government declared Isla Guadalupe a pinniped sanctuary, and full legal protection followed. Pup counts have been tracked ever since. Between 1984 and 2013 the population grew at an average of 5.9 percent a year, roughly a doubling every twelve years. Garcia-Aguilar and colleagues estimated 34,187 animals for 2013, with a minimum of 31,019, and NOAA currently works with a minimum abundance near 31,000.
The legal picture is deliberately more cautious than the numbers. The IUCN downlisted the species to Least Concern in an assessment published in 2015, but under United States law it is still Threatened under the Endangered Species Act and depleted under the Marine Mammal Protection Act.
Away from the breeding beaches this is an unusually solitary eared seal, and it feeds at night on squid and small schooling fish such as mackerel, sardine and lanternfish. The dives are shallow by seal standards, averaging about 20 m with a maximum near 75 m, because the prey comes up to meet it. Squid and lanternfish rise toward the surface once it is dark.
It rests at sea in a posture that looks alarming the first time you see it. NOAA describes animals floating with the head submerged and the hind flippers sticking up out of the water. From a passing boat, a sleeping Guadalupe fur seal looks like a dead one.
Satellite tagging since 2016 has put GPS dive recorders on 60 juveniles, 50 adult females and 78 weaned pups. The tracks show animals that avoid the shallow continental shelf almost entirely, staying over deep water but generally within 800 km of the mainland coast.
Between 2015 and 2021 NOAA declared an Unusual Mortality Event for this species along the coasts of California, Oregon and Washington. A total of 715 Guadalupe fur seals were found stranded on the United States west coast during that period, most of them weaned pups and yearlings, most of them malnourished and emaciated. The cause was ocean temperature. Those years include the marine heatwave nicknamed the Warm Water Blob, a strong El Niño, and several further heatwaves. Warm surface water suppresses upwelling, the plankton fails, the small fish and squid thin out, and the animals least able to cope are the ones that have just been weaned and are finding their own food for the first time.
Almost every Guadalupe fur seal alive descends from that one cave, and almost every one still breeds on that one island. A species concentrated in a single place is exposed in a way that raw population numbers hide. A serious oil spill, a new disease, or a local shift in the ocean could hit all of it at once. That is why the recolonisation of the San Benito Archipelago, absent for over a century, matters more than its small numbers suggest, and why the handful of animals now breeding on San Miguel Island in California count as insurance.
One last change: this animal used to be filed as a subspecies of the Juan Fernández fur seal. Genome sequencing published by Lopes and colleagues in 2021 put the split between them at roughly 600,000 years, as old as splits between other undisputed species, and it is now recognised as a full species in its own right.
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