Northern Fur Seal Born on the Farallones: Recent Returns
|On Southeast Farallon Island in the fall, one never knows what the next day will bring - even miserable, windy, foggy days, such as 28 August 1996. That was the day we discovered a northern fur seal pup, with several adults and subadults, on remote West End. This represents the first confirmed breeding of this species at the Farallones since at least the mid-1800s. It is even possible that this is the first breeding ever documented for this species here, as the fur seals that were extirpated from the island in the early part of the 19th century have never been conclusively identified (more on this below).||
In a group of northern fur seals, an adult male's call alerted biologists to the likely presence of a female with a pup nearby.
During the week leading up to August 28th, I had received a call from Marge Kohler, the
manager of the Farallon Islands National Wildlife Refuge, giving us permission to visit the
Indian Head area at West End, to attempt recovery of a satellite transmitter from a northern
elephant seal. A valuable device, the transmitter held data that were well worth trying to
recover about an individual marine mammal's travels. It was still transmitting from a
stationary location but only at low tides, suggesting that it had fallen off the seal in the
intertidal zone. PRBO biologists on the Southeast Farallon normally do not visit this area of
West End between March and November, leaving it completely to the nesting seabirds in
spring and the roosting Brown Pelicans in fall. In late August, though, there is a small
window of time between these two Farallon events, which we took advantage of to search
for the transmitter.
On the 28th, there was a good low tide in the late afternoon. Ed Ueber, Jan Roletto, and Natalie Cosentino of the Gulf of the Farallones National Marine Sanctuary were on the island to conduct on-going monitoring of the Farallon intertidal ecology. With as little disturbance to the wildlife as possible, the four of us headed across Jordan Channel toward Indian Head. There were numerous California sea lions in the area, including a record count of eleven pups frolicking in the intertidal pools. While searching for the transmitter we couldn't avoid flushing a few sea lions into the water but made sure to do this slowly, so as not to panic them.
A group of sea lions proceeding down to the water's edge from Mirounga Valley, above Indian Head, contained two or three northern fur seals. One of the male fur seals stopped and began to give an unusual machine-gun-like clicking call. Ed first spotted the tiny pup behind this male, and Jan (who has worked in fur seal breeding colonies) remarked that the clicking call is often given by males when in the vicinity of newborn pups - not so much to protect the pups as to attract their mothers returning from sea. At this point we were convinced we had a Farallon-born pup! Fur seals give birth in June and July.
The next day I returned to Indian Head alone, to survey the area without disturbing any animals. There were nine northern fur seals in Mirounga Valley: one group consisting of an adult male, an adult female lying next to the pup, and two subadult females; another group, about 50 meters away, consisting of an adult male and another subadult that had a pink tag; and two additional immature animals lying amongst a pod of about 100 sea lions. The animals had doubtless been there all summer, in an area that is out of view from the eastern portion of the island where we live and work.
Brief History of a Decline
When American and Russian sealers first plundered the northern California coast, in the early 1800s, a substantial fur seal population was breeding on the Farallones. Despite the removal of over 150,000 pelts from the island between 1810 and 1817, not a single scientific specimen was secured. Disintegrating bones found buried on the island over a century later were thought to be of the northern fur seal (Callorhinus ursinus) but possibly could have been from the Guadalupe fur seal (Arctocephalus townsendi), which breeds to the south. For all we know, more than one species may have been involved at the Farallones in the past. Northern fur seals were known to breed only on the Pribilof Islands in Alaska until the 1950's, when a colony formed on San Miguel Island off southern California. The San Miguel colony is the origin of the subadult seen at Indian Head, an animal that was tagged there as a pup in 1993.
Could we be witnessing the start of something significant? A 25-year-old entry in PRBO's Farallon Island journal, dated 20 January 1972, states: "Four elephant seals. Two immature animals and a cow and calf. This is the first calf born on this island in recent times." We all know what arose from that small start - a substantial breeding colony that has reached 300-400 pups per year during the past decade, perhaps matching populations of the pre- sealing era. Should a colony of northern fur seals become established on the Farallones and approach its former numbers, there will be significant consequences for the island's ecology. Especially affected might be the seabirds that nest on the flat portions of the island, including Brandt's Cormorants, Western Gulls, and Cassin's Auklets. Real estate on this tiny island is a very precious commodity. Whatever happens, PRBO biologists will be standing by as always, eager to document the long- and short-term changes in the natural history of the Farallones.
By the way, we never did find the satellite transmitter.