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Feature Articles
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Bluefin tagging program: Tag placements continue; researchers plan data use in assessments
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This article is reprinted with permission of Commercial Fisheries News, the Northeast's fishing newspaper for over 30 years, ©2003 Compass Publications Inc. Commercial Fisheries News is published monthly; annual subscriptions are $21.95. To subscribe or request a sample issue: call (877) 263-4496; fax (207) 367-2490; e-mail (cfoster@fish-news.com); or click on the hot link.
by Lorelei Stevens
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From left, Jeff Gavigan and Mark Genovese place a bluefin tag. They are in the skiff of the White Dove Too. The purse seiner put out 63 pop-up archival tags last summer and fall. (Steve Wilson New England Aquarium photo)
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BOSTON, MA - The practice of affixing pop-up archival tags to bluefin tuna has been perfected over the last six years to the point of seeming almost routine, but there's nothing routine about the skill it takes to do the job or about the information these amazing devices are generating.
Last summer and fall, researchers and fishermen working in cooperation with Molly Lutcavage and Steve Wilson of the New England Aquarium and Rich Brill of the Virginia Institute of Marine Science (VIMS) put out 66 high-tech tags, which were paid for with funding from the National Marine Fisheries Service.
All of them were supposed to pop-up on June 1 and begin transmitting via satellite the extraordinary data that will enable scientists to map out exactly where each fish has been during all those months. But a number of the tags have already reported data that is helping to identify the bluefin's elusive wintering areas and depth and temperature preferences.
Of the tags, 63 were put out by the purse seiner White Dove Too over the course of eight sets in the Great South Channel and east of Chatham between July 17 and Oct. 10. The charter boat Cookie Too put out another two tags and one was placed by Sean Smith of the Canadian Department of Fisheries and Oceans off Nova Scotia.
Jon Lucy of the VIMS Sea Grant program, aboard the Yorktown, VA-based Striker, deployed two additional tags in January off North Carolina. These tags were programmed to pop up in November.
Researchers and fishermen working on the tagging project plan to continue tagging in the Gulf of Maine and Canada this year, Lutcavage said.
"We're also doing trans-Atlantic work," she added. "They're tagging fish in Turkey right now with tags we've supplied to our European collaborators."
In another promising development, computer modelers and scientists working with the International Commission for the Conservation of Atlantic Tunas are now trying to come up with ways to actually use the groundbreaking tagging information on fish migration patterns in stock assessments, according to Lutcavage.
"A number of ideas on how to do this are already underway," she said. "This is what it's all about."
Central Atlantic
Also last year, researchers, including Lutcavage, conducted an extensive study of highly migratory species in the central Atlantic between May and August.
The goal was, in part, to see if there was evidence to support the hunch of many scientists and fishermen that bluefin tuna spawn in the middle of the Atlantic, well outside the Gulf of Mexico, which has traditionally been identified as the bluefin's primary spawning ground.
Two legs of the cruise were conducted by the Eagle Eye Two and two legs were conducted by the Shoyu Maru II, a Japanese research vessel.
Although the cruise didn't succeed in catching any bluefin for study, it was productive, according to Lutcavage.
"This was the second year of extensive oceanographic study of the area. We caught yellowfin, bigeye, skipjack, and swordfish. So, extensive work was done on food habits and distribution of those species," she said.
"The only objective we didn't achieve was to catch bluefin," Lutcavage added with mock frustration. "But it's just as possible that they were there and we just failed to catch them. We were just one boat in a very big ocean."
However, other commercial vessels fishing between the central Atlantic and the east edge of the Gulf Stream did catch bluefin and offered up gonads for testing. The reproductive analyses are being conducted by graduate student Jen Goldstein of the New England Aquarium and the University of Massachusetts Boston in cooperation with other scientific collaborators.
Gulf of Maine gonads
Goldstein also has been examining gonads taken from bluefin tuna entering the Gulf of Maine in June and July over the last three years. Preliminary results of this work indicate that about one third of the fish sampled in June and July - males and females - could have recently spawned or were capable of spawning.
Although more work needs to be done before any definitive case can be made, Lutcavage said these early results were intriguing.
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2002 Central N. Atlantic Longline Sets
Yellow: F/V Eagle Eye II leg 1 May 6-28
Green: F/V Eagle Eye II Leg 2 June 8-20
Blue: R/V Shoyo Maru Leg 1 June 23-July 12
Red: R/V Shoyo Maru Leg 2 Muly 26-August 17
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"The presumed spawning period for bluefin has been in the Gulf of Mexico in April and May," she said. "But this (reproductive analysis) suggests to us that there may be additional spawning areas or that bluefin don't always spawn when they're capable of spawning."
Lutcavage emphasized that this idea isn't new. Woods Hole Oceanographic Institution scientist and bluefin research pioneer Frank Mather first broached the alternative spawning site theory more than 30 years ago," she said.
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