Swimming with giants
Have you talked to your shark today? Embedded computer chips keep track--and reveal much
Still, from very few measurements scientists learn a lot about pelagic life. Some tags show not only where an animal has been but also when it ate and, at least once, when it mated. Ambient sunlight measurements can fix longitude. And latitude can be derived from light and surface temperature readings. In the case of bluefin tuna, which have a body temperature warmer than surrounding waters, researchers can tell when a fish ate. Because the sardine the tuna munched is colder than the tuna, there's an ice cream effect: a dip in the tuna's body temperature that's followed by warming as it digests the meal.
Human ignorance of pelagic life remains immense, but the knowledge base is growing. Consider the bluefin tuna. For fishing, the Atlantic's population has been managed in east-west sectors, along an imaginary line. Scientists long suspected that boundary was arbitrary, and tagging proved them correct. "The fish don't turn around when they hit that line," says University of New Hampshire researcher Molly Lutcavage. "Bluefins are regularly crisscrossing the Atlantic. There may be one vast Atlantic stock."
Far-flung. Tagging has also revealed that bluefins are capable of traveling incredible distances. One peripatetic Pacific bluefin, tagged over four years, swam from the waters off Baja California to Japan and back again, logging around 18,000 nautical miles.
Another long-distance swimmer is the Atlantic leatherback turtle. From nesting beaches in French Guiana and Suriname, sea turtles have been tracked to such far-flung locales as the west coast of Africa and north beyond the Azores. At the same time, scientists are discovering that because the Atlantic turtles don't stick to narrow migration routes--instead dispersing widely over the Atlantic--it will be difficult to set aside no-fishing zones to protect them.
Emerging technologies should help reveal even more about deep-sea life. Magnetic sensors may soon tell scientists not only when marine creatures are eating but what they're eating, by measuring how wide they open their jaws. And Block, who is with the Tagging of Pacific Pelagics project, an international effort to study migration in the northern Pacific, recently helped place the first "real time" tags on the dorsal fins of salmon and blue and mako sharks. Sharks bask to help regulate body temperature, so their tagged fins are often above water, capable of instantly transmitting their location to computer screens.
Research "volunteers." Oceanographers, who are trying to learn how the seas relate to the atmosphere and weather patterns, may bring tagging needed money and support. Tuna and mammals are excellent collectors of the data oceanographers need to help construct more-accurate profiles of the water, such as temperature, salinity, and chlorophyll levels. Block calls animal data collection the new paradigm in ocean research. "It will help our animals earn their keep."
Sims, meanwhile, after spending nine hours aboard his boat without spotting a single shark, is unperturbed. "You have to balance days like today with our real successes," he says, removing tags from the harpoons he had readied "just in case." Indeed, he has collected so much data already that he'll be plenty busy back at the lab. "Besides," Sims says, "if this were easy, everyone would be doing it."
advertisement
