Stranded Fur Seals: Mass Death Leads NOAA to Declare 'Unusual Mortality Event'

Along California's coast, an increasing number of endangered Guadalupe fur seals have died after stranding themselves on shore. Since January, almost 80 dead fur seals have been found in the area, leading the National Oceanic and Atmospheric Administration (NOAA) to declare an "Unusual Mortality Event" (UME).

In the wake of this UME, researchers have turned to ocean-warming trends to better understand why the animals are traveling outside their natural habitats.

Guadalupe fur seals breed almost entirely on Guadalupe Island off the coast of Baja California, Mexico, an island that is more than 600 miles from where they stranded themselves, according to the NOAA.

"We think that warm water conditions have really changed the range of quite a few of the forage fish species that the fur seals would be going after," Toby Garfield, an official with NOAA's Southwest Fisheries Science Center, said in a statement.

Of the 80 Guadalupe sea lions stranded so far this year, 42 were found dead, Justin Viezbicke, a NOAA coordinator in Long Beach, said. This is a significant increase from the 10 that were recorded from 2009 to 2014. And this year, many of the stranded fur seals were pups.

So what exactly does it mean when the NOAA declares an Unusual Mortality Event (UME)?

Under the Marine Mammal Protection Act, a UME is defined as a significant die-off that requires an immediate response, according to the NOAA. There are seven criteria that a large-scale die-off must meet to be considered unusual. For this event, three of the seven criteria were met: There was an increased mortality rate compared to previous records, the animals exhibited abnormal characteristics when found, and the fur seals are already considered endangered.

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