Unusually Large Numbers Of Fur Seals Stranding On Californian Coast

The seals are mainly found on the island of Guadalupe, off the coast of Mexico. Alan Harper/Flickr CC BY-NC 2.0
Josh Davis 01 Oct 2015, 15:20

In a curious echo of the mass stranding of Californian sea lions along the west coast of the U.S., the National Oceanic and Atmosphere Administration (NOAA) has declared another “unusual mortality event,” except this time for the Guadalupe fur seal instead.

So far this year, around 80 of the pinnipeds have come ashore, many of them dead, and the rest weak and thin, thought to be due to a lack of food. This is eight times more than expected over an entire year. It is due to this shocking increase in strandings that the NOAA has declared this an unusual mortality event, a classification that frees up additional funding that can be used to study the animals and understand what exactly is going on.

Guadalupe fur seals, while not globally threatened, are considered endangered by the United States government because they are only found in small populations off the southern Californian coast. Brought to near extinction, by the late 19th century it is thought that only around a few dozen of the creatures survived the onslaught of commercial hunting. There are now more than 10,000, the vast majority of which live and breed on Guadalupe Island off the Baja California coast in Mexico.

While most of the seals breed around 965 kilometers (600 miles) from where they’re being washed up on the Californian coast, it is thought that they’ve been following the fish they feed on. The extra funding now available will be used to find out if the mass die-off is due to warming of the Pacific altering the movement patterns of the seals' food source, forcing them to swim further and further north in search of a meal.

For the past 18 months there has been an unusually large area of warm Pacific surface water off the west coast of America, believed to be caused by a high-pressure ridge in the northeast of the ocean. These weather events have previously been linked to the California sea lion die-offs, as well as starving seabirds found on the Oregon and Washington coasts. It’s thought that the warm Pacific water drives the fish further north, and out of reach of the seals, sea lions, and birds that depend on them for food.

All that can be currently done at the moment is to help those animals found alive, and wait it out until the high-pressure ridge moves or dissipates. In the meantime, we can study the outcomes of extreme weather events like this in the hope that we might be better prepared if such episodes happen again, as they are predicted to.    

Main image: Alan Harper/Flickr CC BY-NC 2.0

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