Oregon Coast Scientists: Sharks May Be Killing Endangered Sea Lions

Published 11/02/2014

(Newport, Oregon) – A new study out of Newport's Hatfield Marine Science Center and Oregon State University in Corvallis finds that one species of shark may gobbling up and endangered species of sea lion. Pacific sleeper sharks are slow-moving and bulky, but the study says they seem to be preying on Stellar sea lions in the Gulf of Alaska. (Above: sea lions near Florence).

The study was conducted by Markus Horning of the Marine Mammal Institute at OSU and the Hatfield (on the central Oregon coast), along with Jo-Ann Mellish of the Alaska SeaLife Center. Over the last decade, the team implanted a special kind of transmitter into the abdomens of young sea lions, which later float to the surface after the creature dies. These archival tags record data on temperature, light and other properties during the sea lions’ lives.

Out of 36 juvenile Steller sea lions implanted, 17 have died so far. Fifteen transmitters sent data indicating the sea lions had been killed by predation.

This is judged to be remarkable because evidence pointed to the sleeper shark, which so far has been known to mostly consume smaller fish.

Thousands of sleeper sharks are caught in nets by fishermen each year, and that could be helping to cut down the number of stellar sea lions eaten by the sharks. However, groundfish harvests in the Gulf of Alaska have been limited in order to preserve the food source for the endangered species.

“If sleeper sharks are involved in predation, it creates something of a dilemma,” said Horning. “By limiting fishing, however, you may be reducing the bycatch that helps keep a possible limit on a potential predator of the sea lions. The implication could be profound, and the net effect of such management actions could be the opposite of what was intended.”

Other studies have found remains of Steller sea lions and other marine mammals in the stomachs of sleeper sharks, but those could have been the result of scavenging instead of predation, Horning pointed out.

The western distinct population of Steller sea lions has declined to about 20 percent of the levels they were at prior to 1975.

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