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Following a dream, and tuna, with electronic tagging


Following giant tunas as they move across the ocean has always been a challenge. A decade ago, the thought of tagging and tracking more than 1,000 bluefin tunas was only a dream. Now it's been done, and an even more ambitious goal of following thousands of open-ocean predators representing two dozen marine species across the North Pacific has been initiated.

Stanford scientist Barbara Block discussed the current understanding of oceanic animal migrations in a lecture titled "Hot Tuna: Electronic Tracking of Giant Bluefin Across the Open Sea," during a symposium on new approaches to marine conservation at the annual meeting of the American Association for the Advancement of Science in Seattle on Feb. 13.

Marine sciences Professor Barbara Block, left, has pioneered the use of electronic tags to study the behavior of large migratory fish, including tuna, sharks and billfish. Courtesy Barbara Block

As the Charles and Elizabeth Prothro Professor of Marine Sciences at Stanford and director of the Tuna Research and Conservation Center (TRCC), a collaboration between the Monterey Bay Aquarium and the university, Block has pioneered the use of electronic tags to study the behavior of large migratory fishes, including tunas, sharks and billfishes. She and her team of doctoral students, postdoctoral associates and aquarium personnel have tagged highly migratory fishes throughout the Atlantic and Pacific oceans. For the past decade, her work has focused on the North Atlantic to document the migrations of bluefin tunas from the Eastern Seaboard of the United States across the Atlantic Ocean to the Mediterranean Sea.

Barbara Block, a professor of biological sciences at Stanford University, surgically implants an electronic archival tag in a 500-pound bluefin tuna off the coast of Massachusetts last October. The tags provide researchers data about the remarkable migrations of these tuna across the Atlantic. Courtesy: Barbara Block

This work has helped determine that Atlantic and Pacific bluefin tuna undertake extensive migrations back and forth across entire ocean basins. These findings are critical in helping to craft international management schemes for tuna fisheries. Giant bluefins are the most valuable fish in the ocean, worth tens of thousands of dollars each in places like the Tokyo fish market, where they are sliced into the highest quality sashimi. Increasing pressure on the natural resource has led to controversy on how to allocate the bluefin quotas worldwide.

In January, as residents of the Eastern Seaboard huddled behind closed doors in record cold, the Atlantic bluefin tuna Tag-A-Giant (TAG) team was out on the rough waters off the coast of Morehead City, N.C. The TAG program is a long-running collaboration among the TRCC, Duke University and regional sportfishers, who compete to catch and tag giant bluefin tunas, which then are tracked across the Atlantic. After seven days at sea, TAG scientists had placed 100 electronic tags in 100 fish -- each weighing between 300 and 700 pounds. The TAG program has placed more than 800 electronic tags in bluefin tuna since 1996.

Marine sciences Professor Barbara Block, above right, and her team of doctoral students, postdoctoral associates and aquarium personnel have tagged highly migratory fish in the Atlantic and Pacific oceans. Courtesy: Barbara Block

In the Pacific, researchers from Block's program have placed more than 200 electronic tags in bluefin tuna that frequent the coasts of California and Mexico.

"When you look at the data, it's easy to forget how hard this work is," Block said. "Doing surgery on a 500-pound tuna on the deck of a rolling vessel in the middle of winter is as hard as it gets. It takes a dedicated team to make this all work, but when you see a track from three years of a bluefin's life, moving back and forth across an ocean basin, it makes all the hard work worthwhile."

Marine researchers prepare to surgically implant an electronic archival tag in a bluefin tuna caught in waters off the North Carolina coast in January 2003. Courtesy: Barbara Block

With more than 800 Atlantic bluefin tagged, their tracks tell an amazing story.

"We can now see the 'hotspots' for bluefin tuna in the Atlantic," Block explained. "We're discovering the migration corridors these animals are using to travel from place to place. We are recognizing that the tunas we see off the coast of the Carolinas in the winter might be at the Flemish Cap off Canada by spring, and all the way to the Mediterranean by summer. And then they'll make the journey back by the end of that year to the western Atlantic close to the point where we tagged them. Piece by piece, we are assembling a picture of how these animals are using their environment."

Local fishermen were enlisted to help catch Atlantic bluefin tuna for tagging. The tag data allow scientists to document where the animals travel over seasons and even years. Courtesy: Barbara Block

The tuna tag data allow scientists to document where animals go over seasons and even years, and are critical to understanding the dynamics of the Atlantic tuna populations. In recent years Block has worked closely with the International Commission for the Conservation of Atlantic Tunas (ICCAT) to help integrate new information from the electronic tags into its bluefin tuna management strategies.

TOPP researchers

Beginning in late 1999, an even more ambitious program, called Tagging of Pacific Pelagics (TOPP), was undertaken by Block and colleagues Dan Costa of the University of California-Santa Cruz and Steven Bograd of the National Marine Fisheries Service (NMFS). Over the next seven years, in collaboration with dozens of other researchers, they plan to tag and track 5,000 animals representing more than 20 different species across the North Pacific.

TOPP, one of seven pilot field programs with the international Census of Marine Life, will make use of a variety of electronic tags to follow the movements of fishes, sharks, sea birds, pinnipeds, cetaceans, sea turtles and even Humboldt squid. An international team of more than 65 TOPP collaborators will monitor the migrations of these animals in the context of the conditions in the water surrounding them, in an effort to learn not only where they go but also what factors control their movements.

"People have been studying animal migrations for many years," said Costa, who has worked extensively on marine mammals, "but this is the first time that anybody has tried to take a larger, ecosystem-scale approach. By working in a broad collaboration, we can start to ask questions about how the whole open ocean system works."

The magnitude of the task is daunting. Over the first three years of the program, the TOPP team has coordinated a dozen workshops, with representative experts on each animal group as well as oceanographers, computer modelers, database managers, educators and journalists. The result of these workshops was a research plan that extends to 2010.

At the same time, the TOPP team managed to deploy more than 800 tags on 17 different animal species. These pilot field studies were focused on testing new and existing technologies and refining the methods for large-scale deployments. Through these studies, new electronic tagging technologies are being developed and several significant discoveries have been made, Block said. "We're studying the Pacific Ocean from the top predators' viewpoint for the first time in human history," she noted. "We're already seeing a story about Pacific bluefin beginning to unfold, and it's amazing."

Tunas, sharks and seals

And now, in addition to tagging bluefin, Block and her TOPP colleagues from NMFS and ICCAT are tagging all three tuna species that gather off the California and Mexican coasts: bluefin, yellowfin and albacore. TOPP researchers also are tagging numerous shark species -- including white, mako, blue and salmon sharks -- that range from Alaska to Baja California.

These fishes cross the largest ocean on Earth to move from one feeding area back to a breeding region. How and when such migrations occur has been a mystery, Block said: "We are watching salmon sharks do things we never expected them to do. We also have brought together a dedicated group of leatherback sea turtle biologists to tag animals in Costa Rica, and we're going to figure out how to keep these animals from going extinct. It's a very exciting time for the TOPP program, and we're just getting started."

One realization TOPP scientists had as they began shaping their research collaboration was that the animals themselves could provide valuable information about their ocean habitats. Because many of the electronic tags collect oceanographic data, such as water temperature, tagged animals can act as "autonomous ocean sensors," going places and collecting data that would be costly and difficult for humans to obtain.

"Northern elephant seals swim from Northern California to Alaska's Aleutian Islands in about six months," Costa explained. "And every day they'll make 50 to 60 dives to depths of 500 to 600 meters [1,500-1,800 feet]. Since the tags they wear record the water temperature every 10 seconds, every one of those dives represents a detailed thermal profile of the ocean. In many cases, these are the only data we have about the subsurface ocean conditions at that particular place and time."

TOPP scientists also are beginning to recognize that the data they gather, similar to those collected on Atlantic bluefin tunas, may provide useful information to resource managers working in the North Pacific. "Right now the Pacific open ocean is one of the last frontiers on our planet," Block said. "We don't have the basic information that would be needed to ensure the long-term health of this ecosystem. Our objective is to garner the knowledge that will lay the foundation for future management."

By better understanding how large oceanic animals use the ocean and how they interact with their environment as well as the humans that rely on it, TOPP scientists hope to create new tools to help shape ocean policy.

"If we can predict how large predators use the ocean and what are the common points of interaction between sea turtles, tunas, whales and seabirds -- where, for example, they all might come together to feed -- we can better understand how humans can develop sustainable fisheries without as much turtle and seabird bycatch," Block concluded.

Randall E. Kochevar is the science communication manager at the Monterey Bay Aquarium in Monterey, Calif.


Barbara Block

New technology turns marine animals into ocean explorers (2/25/04)