Sea otters falling prey to great white sharks
Pacific Southwest Region USFWS/Flickr (CC BY 2.0)

Sea otters falling prey to great white sharks

The death rate of California sea otters (Enhydra lutris nereis) from great white shark attacks has risen dramatically in the last decade, researchers report  online today in Marine Mammal Science. By analyzing annual records from the U.S. Geological Survey going back to 1985, they found the percentage of dead otters with evidence of shark bites tripled from 19% in 1990 to 61% in 2013. The death rates started rapidly accelerating in 2003, and the pace is still on the rise today. Researchers say the trend is a bit mysterious, as great whites aren’t thought to hunt otters, preferring fatty seals and sea lions. It could be that the sharks are simply sampling the otters. But even though the great whites don’t swallow, the “investigatory bites” are still fatal, often by causing infections. Why are these shark-related deaths on the rise? One theory is that legal protections have boosted shark populations around the places where otters live. Whatever the reason, the death rate is high enough that it may be hampering recovery of the sea otter population in California, which remains a fraction of its historic size.