Date: Sep 12, 1998 Source: NewScientist (
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Dr. Molly Lutcavage, a research scientist at the New England Aquarium, reports new findings that suggest the distribution of adult, spawning-size giant Atlantic bluefin tuna (Thunnus thynnus) is much broader than previously considered. These findings add to the intense debate over the population of a species that is commercially valuable to fishermen yet strictly regulated by fisheries management officials.
Dr. Lutcavage and her colleagues Dr. Richard Brill from the Pelagic Fisheries Research Program at the University of Hawaii, Greg Skomal and Brad Chase from the Massachusetts Division of Marine Fisheries, and Dr. Paul Howey from Telemetry 2000 in Columbia, Maryland, hold new information about bluefin tuna migration and possible spawning habitats. This new data calls attention to the possibility that bluefin tuna traveling through New England waters spawn, or lay eggs, in much broader regions of the mid-Atlantic, between Bermuda and the Azores, than previously thought. Since bluefin tuna are managed under the theory that there are two different stocks or groups (western and eastern Atlantic), these findings argue for reconsideration of current assumptions about migration, spawning habitats and stock structure.
In September and October of last year, twenty bluefin tuna of reproductive size, from 75 to 115 inches long (estimated ages 8-18 years), were tagged off the New England coast using pop-up satellite tags. The tags, attached by researchers working with New England harpoon, purse seine, and rod and reel bluefin fishermen, were pre-programmed to release or "pop-up" monthly from March through July, 1998. The tags are about the size of a cigar, with a five-inch long antenna. Once released, the tags not only transmit location, but also reveal historical data about water temperature during the tuna's travels. Seventeen out of 20 tags were recovered after being on the bluefin tuna for as long as 9 1/2 months, a span of time that is unprecedented with pop-up tags. Five of the tags released from the tuna on the eastern side of the western Atlantic management line at 45 degrees west longitude, an international fisheries management boundary established by the International Commission fo! r the Conservation of the Atlantic Tuna (ICCAT).
"Tuna clearly have a very complex and broad migration pattern. Since the 1980s, scientists concluded that there were two, separate bluefin tuna stocks. Now it looks as though the same tuna that travel through New England waters also swim near the Azores. We now have an opportunity to quickly gain a better understanding of bluefin migration and potential spawning areas, and pop-up tag technology is proving to be a very effective research tool to gather data," said Dr. Lutcavage. "In fact, in just the past two years, scientists around the world have begun to use these tags to learn more about other pelagic (open ocean) tuna, sharks and billfish."
Giant Atlantic bluefin tuna are the largest living species of tuna, reaching up to 10 feet in length and weighing more than 1,400 pounds. As they are commercially valuable and believed by many to be a depleting resource in the eastern Atlantic, bluefin tuna are at the center of a heated debate. Tuna regulators have been recommending increasingly stricter quotas, while fishermen claim they see more bluefin tuna in a week than regulators say exist in the entire North Atlantic all year. In fact, the last two stock assessments for the western Atlantic zone reveal that the population of bluefin tuna is on the rise. Currently, bluefin tuna are managed by fishing area quotas, size limits and spawning area protection measures. However, compliance with these regulations only occurs in the western Atlantic fishing grounds and surrounding seas off the coasts of the U.S. and Canada.
Understandably, New England fishermen are eager to take part in the scientific research of bluefin tuna to learn whether or not adhering to restrictions in the western Atlantic is worthless because of the lack of management compliance in the eastern Atlantic. In another first, Dr. Lutcavage and colleagues have undertaken a international collaboration with Canadian Department of Fisheries and Oceans researcher Dr. Julie Porter and Canadian bluefin tuna fishermen. The new partnership will target both New England and Canadian giant Atlantic bluefin tuna in the 1998 fishing season. In late August, the first Canadian bluefin tuna was tagged with a pop-up technology. The tag is scheduled to pop-up in 9 1/2 months.
The 1998 tagging study was funded by the East Coast Tuna Association and through donations by cooperating fishermen. "On-going collaborations with fishermen contribute priceless information about bluefin tuna, a source of knowledge that has until now been untapped as a research resource," said Rich Ruais, Executive Director, East Coast Tuna Association. "Through this joint research with the New England Aquarium, some light will be shed on critically important questions which might allow future development of a fair and efficient long-term, Atlantic Ocean-wide conservation program for Atlantic bluefin tuna."
Regulators need to have better information on exactly where bluefin tuna spend their time and where they reproduce to ensure that tuna stocks are properly managed and not overfished. A highly migratory and fast-swimming species, bluefin tuna spend much of their time foraging off the continental shelf, and then probably disperse to spawning areas to lay eggs. It has been assumed that bluefin tuna spawn primarily in the Mediterranean and in the Gulf of Mexico. Before these recent results from pop-up tagging research, there was little reason to question these assumptions. Despite the intense interest in bluefin tuna, their travels and behaviors are not well understood or documented, and their life cycles are believed to be exceedingly complex. By understanding the whole cycle of the bluefin tuna's life, fisheries managers can make informed decisions about appropriate management and conservation measures.
Augmenting these tagging efforts, New England Aquarium researchers also conduct aerial surveys, remote sensing, and hydro-acoustic tracking studies of bluefin tuna. Through a new study with Johns Hopkins Applied Physics Laboratory in Baltimore, MD, the National Marine Fisheries Service, the National Environmental Satellite Distribution and Information Service of NOAA, and Arete Associates of Tucson, AZ, Dr. Lutcavage is testing cutting-edge LIDAR and Synthetic aperture radar technology to learn more about bluefin tuna. In a process similar to radar, LIDAR emits a laser light that bounces off an object creating a 3-D image. In this manner, researchers hope to learn how many bluefin tuna are swimming below the ocean's surface, therefore gaining a more accurate count of the total population. Synthetic aperture radar technology may be used to detect the distribution of surface-swimming bluefin tuna over a broad geographic area.
New England Aquarium Conservation Director Greg Stone is a US Senate-appointed member of the International Commission for the Conservation of the Atlantic Tuna (ICCAT), a 23-member-country organization charged with determining all legal quotas of North Atlantic bluefin tuna and other large open-ocean fish. Dr. Lutcavage serves as scientific technical advisor to the Bluefin Working group of the Scientific Advisory Committee of ICCAT. All data regarding bluefin tuna is presented to ICCAT, who issue guidelines biennially.
