The “Beautiful-Nosed Sea Bears”: Catching Up with a Colony in Recovery
November 17, 2015
A recent post to Los Farallones gave us an update on the changing status of Zalophus (i.e., California Sea Lion) on and around Southeast Farallon Island and greater California. But how about the Northern Fur Seal (Callorhinus ursinus)? Extirpated from the island in the mid-19th century, how is their population faring today, especially in light of El Niño and a changing climate? Let’s take a closer look.
The Northern Fur Seal (Callorhinus ursinus) is thought to have been the most abundant pinniped on Southeast Farallon Island (SEFI) historically. Our knowledge of their historic abundance is deduced from the simultaneously awe-inspiring and tragic firsthand accounts of early New England merchants who scoured the northern Pacific Coast of North America. Barred from trade with the West Indies by the British Empire, these merchants instead established a lucrative trade route linking New England with the northwest Pacific Coast and by extension to the Chinese market. The dense pelts of sea otters and fur seals became the primary medium of exchange.
Commercially, there was a trade-off between these two marine mammals. Sea otter pelts, more prized overall, could command nearly 20 times the price of a fur seal skin but required a great deal more labor, time and skill to harvest. Fur seal skins, on the other hand, sold for no more than $2.50 a piece but could be readily harvested in huge numbers at colonies like the one on SEFI. The economy of scale that was achieved on SEFI in the first two decades of the 19th century was enormous. In the words of William Dane Phelps, a sea captain from Boston:
“Judging from the number of parties known to have been left on [SEFI], within the last three years [circa 1812] by Boston ships…it will be safe to state that 150,000 fur seal skins were taken from there during that time.”
The colony was soon extirpated. There are no known records of fur seals from SEFI from the mid-19th century through the mid-20th century.
Point Blue Arrives on SEFI
Point Blue began year-round monitoring of SEFI’s avifauna in 1968 and weekly surveys of all pinnipeds hauled out on SEFI began a couple of years later. In 1970, biologists recorded observing one fur seal. Only one. Another lone individual was recorded in 1974. From there, numbers creeped slowly up through the 1990’s. Between 1974 and 1995, 181 individuals were recorded. The precise location where fur seals ultimately re-colonized the Farallones is on West End Island (WEI), which is separated from SEFI by a small channel. Because only a small portion of WEI is visible from SEFI, and access is restricted in the summer to avoid disturbance to breeding seabirds, monitoring the growth of this colony has been difficult. Starting in the late 1980’s, annual surveys to WEI were conducted in late summer for the primary purpose of tracking the fur seal colony’s growth, and then starting in 2006, bi-monthly pinniped surveys were conducted.
It wasn’t until 1996 that pups (between 1 and 4 per year for the five years following 1996) were first observed at Indian Head on WEI, a telltale sign of breeding. Some of the mature fur seals showing up at Indian Head around this time bore tags tracing their lineage to the colony on San Miguel Island, a colony that wasn’t discovered until as late as 1968. Thus, it is generally believed that, after a 150-year absence, fur seals of the San Miguel stock officially re-colonized SEFI in or around 1996.
This is what Indian Head looked like in 2014:
The tan-colored animals in this shot are sea lions, both California and Steller. All of the smaller, darker individuals onshore, as well as the majority of seals that are seen floating offshore, are Northern Fur Seals.
In 2015, there were 362 total pups observed, continuing the exponential trajectory of growth colony-wide. This is great news! An adult female and her pup are pictured here. Notice the tag on the adult’s left pectoral flipper.
But what does El Niño and a changing climate spell for this recovering fur seal population? Will there be enough food in our over-fished oceans to sustain their exponential growth? And how will the re-introduction of a top predator into the SEFI ecosystem be felt ecologically? Not surprisingly, there are no simple answers to these questions.
What we do know is that warming ocean temperatures brought to the California coast as part of El Niño–Southern Oscillation (ENSO) events can spell trouble for fur seals. From 67 to 80 percent of the pups born at the San Miguel Island colony died before weaning during the 1982 and 1998 ENSO events, and the population did not recover for several years after the 1982 event.
Sea surface temperature anomalies for the North Pacific Ocean on August 30, 2015. Image generated by the National Weather Service Environmental Modeling Center. On SEFI, there was a pattern of increased arrivals during years preceding major El Nino events (1982–1983, 1992–1993, 1997–1998) followed by decreased arrivals and/or breeding activity during and after these events.
For now, the fur seal colony on SEFI is centered around Indian Head Beach on WEI, a relatively small slice on that island. Every year the colony has been expanding and filling that small area of WEI. If the growth rate continues exponentially we can expect to see fur seals begin breeding on other parts of the island, where they haven’t bred for over 150 years. If this expansion continues onto the Marine Terrace on SEFI, their presence will certainly disrupt the burrowing seabirds that nest there as they trample their burrows. Also of interest will be whether the more aggressive fur seals continue pushing the larger, yet more passive California sea lions away from their haul out and breeding sites.
Fur seals have come a long way back from the days of the California “fur rush.” But they still have a long way to go to establish a population that resembles anything close to historic levels. Globally they remain a vulnerable species, as listed by the IUCN. Here’s hoping that fur seals can continue to thrive in the face of an uncertain future!
Look! An upcoming media spot! National Geographic will be releasing a video feature on the recovery of the Northern Fur Seal colony on the Farallons. Stay tuned.
Posted by Oliver James, Fall Intern