Monitoring Thresher Shark Fishing in Ensenada

October 30, 2007

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

To gather the binational data needed to protect thresher sharks from overfishing, biologists recently established what amounts to a mini observer program for the drift gillnet thresher shark fishery in Ensenada, Mexico.

Thresher shark, so named for its sickle-like tail.

The observer program, a collaboration among UC San Diego researchers, Mexican researchers and Mexican fishermen, puts marine biology graduate students on local fishing vessels to record the number and weight of thresher sharks caught.

The observers, masters students in marine biology at CICESE University in Ensenada, also record where the fish were landed, the set-depth of the nets, net size and mesh size. Bycatch is also recorded.

Funding from the Ocean Protection Council and California Sea Grant will provide two years of support for about 30 to 50 percent observer coverage of the Ensenada fleet, which is the center of the drift gillnet fishery in northern Baja California. Like the fleet's counterpart in California, the Ensenada fleet targets swordfish and thresher shark. Like the California fleet, it has shrunk in recent years and is facing tighter regulatory action.

Sea Grant Trainee Dan Cartamil, who helped to organize the observer program with his thesis adviser and lead investigator on the grant, Jeffrey Graham, a research biologist at Scripps Institution of Oceanography, said the project was a first step toward the ultimate goal of having a binational management strategy for the thresher shark fishery.

“To do this, we have to get a handle on the magnitude of the Mexican fleet,” Cartamil, a doctoral student at Scripps, said. U.S. fisheries management plans do not take into account any landings in Mexico because they don't have the data. “This project will fill that gap.”

“We know that if their fishery is not sustainable, then ours probably is not,” said Santa-Barbara based gillnetter Gary Burke. “It's the same group of fish basically.”

Besides providing data to fisheries managers, California fishermen hope the observer program will also "level the playing field."

“We have had mandatory 25 percent observer coverage for 17 years,” Burke said. “We have pingers on our nets and submerge our nets to reduce interactions with sea turtles.” There are also seasonal and spatial closures and restrictions on net size. “We catch one sea turtle and they close the whole fishery.”

“We don’t play on a level playing field,” said Steve Fosmark, a drift gillnetter based in Morro Bay. “We are heavily regulated and they aren’t, but their catch still ends up in our markets.”