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Q&A HOME • BRAD CHASE • MOLLY LUTCAVAGE
• STEVE WEINER • BARBARA BLOCK • BILL HOGARTH
Barbara Block
Barbara Block, co-founder of the Tuna Research and Conservation Center (TRCC) at the Monterey Bay Aquarium and a professor of marine sciences at Stanford University, has been tagging giant bluefin tuna primarily off of the Carolinas since 1996.
To date, Block and her team at the TRCC’s Tag-a-Giant Program have placed a total of 930 archival and satellite pop-up tags in bluefin.
This program has yielded important migration information, which formed the basis of a landmark paper that Block and eight colleagues published in the April 2005 edition of the scientific journal Nature. Block also has done extensive research on bluefin spawning in the Gulf of Mexico.
For more information on the Tag-A-Giant Program and the tagging results, visit <www.tunaresearch.org>.
Q: How would you characterize the changes in the New England bluefin fishery over the last few years? To what do you attribute these changes?
A: Our electronic tagging results indicate that as bluefin tuna increase their body size, they use more northern latitudes. There is a correlation between size of a fish and how far north they go. Thus, fish that were once using the Gulf of Maine in summer use areas off the Canadian Maritimes as they get larger.
The decline in abundance locally might signal that some strong year classes (e.g. the 1994 year class) have reached a size where their home range has expanded beyond our American fishery.
Alternatively, research indicates that Mediterranean bluefin make up some of our fishery and potentially overfishing on these fish in the east impacts their presence in our fishery.
Clearly we’ve shown that recruitment from both sides of the Atlantic fuels our coastal fisheries.
Q: What is the single most important management strategy that the US should pursue domestically?
A: It will be important to the future of our western bluefin tuna fishery to learn more about the Gulf of Mexico giant bluefin tuna and to ensure its future reproductive success.
We’ve shown recently that fish that breed in the Gulf of Mexico do so at relatively large sizes – 10-12 years of age on average – and for up to three years in a row.
The western Atlantic bluefin tuna that spawns in the Gulf of Mexico is reproductively isolated. We know this from the genetic research recently conducted in our laboratory. This also fits our tracking data, which shows fidelity of individuals year after year to the Gulf.
One-thousand-pound breeders still exist there – we tagged and measured two in the western Atlantic last season. These fish are relics of the virgin bluefin tuna population that occupied the Gulf in the 1960s. If they can spawn, it will ensure that the population will still have young bluefin with genes from their parents that provide the capacity for there to be giant bluefin tuna.
I think many of us in the west can see that the remarkable 1994 year class of bluefin tuna has potentially made it to the Gulf of Mexico to breed. And, potentially, their offspring – the one- and two-year-old fish that are prevalent along the North American coast today – are a piece of the future recovery for our fishery.
Q: What is the single most important management strategy that the US should pursue at ICCAT?
A: The Tag-a-Giant team has put in over a decade of research at great expense to generate results that managers can use. To translate our results into new policy, ICCAT needs to recognize that western and eastern fishers are fishing upon mixed populations on the foraging grounds in the North Atlantic. The electronic tagging data clearly show this.
Thus, high quotas set in the east are adversely impacting the western recovery. We need to reduce the eastern quota to improve the opportunity for a western recovery as their fish contribute to our local abundances.
We need to press for controls in the Mediterranean Sea as bluefin tuna that spawn inside the Mediterranean are contributing to our fisheries along the North American coast as adolescents.
The North American coastline essentially is a hot spot for fish from both spawning grounds. What we do not know in any given year is what proportion of the populations is from each side.
Our population is in decline and the east is more fecund. That suggests that eastern Atlantic spawned bluefin tuna have a major role in our fishery. The high eastern quotas, however, appear to be decimating the eastern population, and it’s unclear what proportion of these bluefin will make up our future fishery.
American managers should be using our data published in peer-reviewed US and European scientific journals to make this point to our colleagues at the table at ICCAT: Without controls on the central, eastern, and Mediterranean fisheries, our fishery in the western Atlantic will be adversely impacted.
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