Fish Know No National Boundaries
We have fairly solid fisheries management in U.S. waters, but what happens when a subadult thresher shark passes over the border into Mexico, or a blue shark heads out into waters crisscrossed by longlines--or simply into international waters, and into the hands of fishers interested only in their dorsal fins? Dan Cartamil, also a doctoral student at Scripps, is interested in this area where biology, politics, economics, and conservation intersect.

He is looking at how artisanal fisheries affect elasmobranch (sharks and their ray and skate cousins) populations in Baja California. "We’re starting to understand [these animals’] movements in U.S. waters, but we don’t know anything about their habits in Mexico or [commercial uses] in Mexico," he said. The study involves a detailed survey of traditional, small-scale fisheries from the U.S. border to the Vizcaíno Peninsula, halfway down the Pacific coast of Baja. "We visit every single camp at various times of the year to determine what the fishing effort is there, what the target species are, how many fishermen are at the camp, and what kind of gear they use," he explained. "Once you know that, though, it doesn’t tell you much about what they’re doing with the catch." So he’s chosen two camps to focus on, going once a month and spending five days. "We’re on the beach the entire day when the boats come in, and we collect data on every animal that comes in--what species they are, what sex they are, how they were caught."

Some 30 species of sharks and rays are taken in the study area, and all except two species are being used (because they’re too small and don’t have any market value). "The catches are being correlated. The basic idea is to get some biological information of the species being caught. If, for example, you’re getting a lot of juveniles of one species, that indicates that the area is a nursery for these animals. If you’re only getting males at one part of the year and females at another part, that tells you about sexual segregation of these animals."

The study also involves looking at the animals’ market value; where they end up--whether in local cooking pots or in markets in Ensenada; and what the impact of the fishing enterprise is on the local economy. "The economic part is more complicated, so we’re going to be teaming up with people who specialize in that," Cartamil said. In particular, he points to a working group of Mexican and American fisheries biologists and managers that has come together to address issues of conservation, known as the Southern California Bight Elasmobranch Consortium (www.sharkbight.com, site now under construction).

Threats to Sharks
Research like Cartamil’s will add to our knowledge of sharks and shark fisheries, but will it be enough, and come in time to prevent decimation of these populations? Cartamil’s doctoral adviser, Jeff Graham, points to three factors that are working against sharks, especially outside U.S. waters, where fishing regulations lack teeth. The first is sharks’ natural history--their story from birth to death, including how they find food and where and when they bear their young. The fact that as a group they reproduce late in life and have relatively few offspring is especially critical. "They simply don’t have the reproductive potential to recover from overwhelming mortalities," Graham said.

The second is commercial fishing--not for sharks necessarily, but in other fisheries in which sharks are bycatch. Graham pointed to the gillnet as being particularly harmful; he called it "the scourge of fishing" because it kills everything that blunders into it. Off California, beyond the three-mile limit, drift gillnets are used in the swordfish fishery. Bycatch includes mako and thresher sharks, which are taken to market, and blue sharks, which are not. "Every time a drift gillnet is set, which usually means every night" during the season, said Graham, "eight blue sharks are killed."