Warm Water Kills Seals

A warmer ocean is bad news for elephant seals, scientists said yesterday.

Elephant seals aren't the only ones that suffer. Sea lions and fur seals that must stay near their young are forced to feed in shallow waters. When the ocean warms, their prey migrate to cooler areas, depleting local food resources and causing pups to starve.

Elephant seals, like the healthy one above that is basking in the sun, generally feed in deep waters anyway and were thought to be less affected by ocean temperature changes.

Yet the new study found warmer waters are related to a 28 percent decrease in the weight of elephant seal pups that are nursing. This decreases their survival rate.

Here's what scientists think happens: Because their prey has migrated to colder waters, female elephant seals have to swim farther to find food, spending 36 percent more time foraging. So they are thinner while pregnant and then have less nourishment to give the pups.

The study looked at generally warm water temperatures off central California over the past three decades, as well as shorter-term fluctuations caused by El Nino cycles. The weights of 2,750 elephant seal pups were monitored from 1975 to 2004.

An abrupt change to cooler temperatures in the region, starting in 2000, corresponded to increased average body weight for the pups.

The research, led by Burney Le Boeuf and David Crocker from the University of California in Santa Cruz, is detailed in the journal BMC Biology.

-- LiveScience Staff

Credit: U.S. Fish and Wildlife Service.