San Diego

Are there plenty more fish in the sea? The question continues to reverberate around most of the world's fishing grounds, but scientific data on the subject can sometimes prove elusive.

That's why researchers whose interests include species conservation and oceanography, as well as fisheries management, are keen to get more reliable information on the movements of marine animals. This month, on the Pacific seaboard of the United States, marine biologists took a big step towards their goal of understanding these migrations.

Size matters: measuring and tracking tuna helps researchers assess the status of fish populations.

Researchers returned to San Diego from the ocean on 17 August after snagging and electronically tagging 80 tuna as part of the Tagging of Pacific Pelagics (TOPP) project, which aims to track bluefin tuna, several types of shark and albatross, elephant seals, leatherback sea turtles and other free-ranging species.

TOPP is part of an ambitious global undertaking called the Census of Marine Life, funded by the New York-based Alfred P. Sloan Foundation, the US Office of Naval Research and several other agencies. The census is intended to chart the diversity, abundance and distribution of marine organisms in the world's oceans over the next decade.

“The tagging will create a data set by observing animals that will present a better picture of the ocean,” says Jesse Ausubel, an environmental scientist at Rockefeller University in New York who coordinates the Sloan Foundation's funding of TOPP, which involves 60 biologists, oceanographers and computer scientists.

The tagging project is the first of about a dozen similar schemes around the world that will be carried out as part of the marine census, and exploits the latest technological advances in tagging devices that can be attached to animals. Its tags store data on species location, water temperature and depth. The project uses both archival tags, which are recovered when species are caught or found dead, and transmitting ones — some as small as a deck of cards — that send information regularly for analysis via a French satellite instrument called ARGOS.

Barbara Block, a marine biologist at Stanford University in California who has pioneered tuna-tagging projects in the Atlantic Ocean (see Science 293, 1310–1314; 2001), is leading TOPP in the Pacific. “The fishing was so good we ran out of electronic tags,” she says of this month's voyage.

TOPP's participants have also launched tagging operations to track salmon sharks off Alaska, blue sharks off Los Angeles, humpback whales off Oregon, and albatross near Hawaii and the Galapagos Islands.

George Boehlert, director of Oregon State University's marine laboratory in Newport, who studies the physical environments in which marine species live, says that data obtained from the tagging will help researchers to understand why animals venture to certain oceanic regions.

The information will complement that obtained from several other exploratory systems. For example, elephant seals, which plunge to depths of more than 600 metres several times an hour when at sea, will be monitored by the Argo float system that is being deployed to chart deep ocean currents and their impact on climate (see Nature 415, 954–955; 2002).

Researchers hope that the tagging of tuna and other species will reveal migratory routes that will help biologists to understand Pacific fisheries. The project brings together groups of researchers from fields that do not traditionally interact. “Everyone is now on the same playing field,” says Block.

→ http://www.toppcensus.org