The study that Block and three other scientists are heading is called Tagging of Pacific Pelagics (TOPP), and the plan is to monitor a dozen animal species, including tuna, Humboldt squid, great white sharks and elephant seals. Some tagged creatures are likely to cross paths, the researchers say, possibly providing new insights into how the animals interact in the wild. One of the scientists, Daniel Costa of the University of California at Santa Cruz, mounts electronic sensors and transmitters onto elephant seals, which weigh up to 7,000 pounds, when they come ashore to breed. He says he looks forward to learning whether the seals’ travels overlap with tuna migration patterns. If so, that might hint at common feeding strategies that the two species were previously not known to share.
Though the marine census project doesn’t officially start until later this year, pilot studies have been under way for a couple of years. Besides Block’s tuna-tagging project in Monterey, another pilot study involves tagging squid in the Sea of Cortés. William Gilly, of Stanford’s Marine Station, has worked with fishermen in Mexico to see how willingly they would return a yellow plastic ring attached to squid they caught—a dry run before attaching electronic sensors to the animals. First, Gilly went out with the fishermen at night and, using handheld lines, caught squid, some weighing 50 pounds or more. The scientists put the plastic rings on nearly 1,000 animals and released them. Signs posted near fishing docks offered a $50 reward for each tag returned. Over a three-month period, about 80 tags were recovered. That pleased the scientists, who also were glad to learn where the squid were caught, hinting at winter migrations of squid in the Sea of Cortés.
“The census is an example of an old fashioned mentality in science,” Gilly says, meaning it addresses a basic curiosity. “We’re reopening the blinders, the way we used to look at the world, through wide exploration.” Block and others engaged in the census may shed light on the condition of some of the world’s fisheries, which are under great strain. People exploit just a few hundred fish species for food, and populations of those species have fallen precipitously, some as much as 90 percent. Some environmentalists and marine experts call the situation a crisis, but even people who dispute that view do not doubt that fishermen and fishing nations are working harder than ever for smaller catches.
Whether the fishing industry will make the best use of data collected by the sea searchers is open to question. Recent studies by Block and colleagues in the Atlantic have found that far more tuna than previously believed cross the ocean. The finding overturns a basic assumption held by not only biologists but also international policymakers, who set different fishing quotas for the eastern and western Atlantic. But it now appears that alleged overfishing in the eastern Atlantic and Mediterranean has reduced catches in the western Atlantic and North America, say some researchers, who are calling for lower fishing limits in the Atlantic. Block says she hopes that fisheries managers take steps to “make the changes necessary to ensure the future of the species.”
At the end of a long day for Block in Monterey, she was still wearing a wet suit. She climbed down into a tank at the tuna center with her graduate students and resumed showing them how to affix satellite sensors to a couple of the corralled fish. Even when she got out of the tank, Block continued coaching from a walkway above it. “Keep the fish under water,” she called, pacing back and forth. Below her, the captured bluefin were swimming round and round, never stopping, as relentless as the researcher herself.