Monday, September 21, 2009

Bluefin sampling with the "Nantucket Tuna Blast"

On a rainy weekend, 12-13 September 09, the 2nd “Nantucket Tuna Blast” tournament took place on the beautiful island of Nantucket, MA. Twenty-nine captains and their crews were competing for the heaviest bluefin caught by trolling. Since these fish were to be brought to the weighing station round (not dressed), it gave us a great opportunity to maximize our sampling efforts.
During this year we have observed many bluefin in the size range of 60-65”. These fish, presumably of western Atlantic stock, are considered immature, and thus are important to our study on maturity schedules of west Atlantic bluefin tuna.

So, what exactly are we doing?
Atlantic bluefin tuna are managed as two separate stocks, east and west. Natal homing is assumed to be the predominant reproductive behavior, where fish return to spawn in their native waters, which so far have been documented in the Mediterranean Sea or the Gulf of Mexico and the Florida Straits. Mixing of eastern and western fish occurs on feeding grounds such as the Bay of Biscay and the Mid-Atlantic Bight.
The current theory is that the two stocks have different maturity schedules, or ages of sexual maturation. Mediterranean spawners mature between the ages of 3-5 years old, whereas western Atlantic spawners are believed by some to mature between the ages of 10-12 years. This great discrepancy might be a result of a sampling bias and not represent the actual age of maturity of all western origin bluefin. Over the last 30 years some bluefin fishermen and scientists have suggested that smaller fish are capable of spawning in areas of the west Atlantic Ocean other than the Gulf of Mexico or Florida Straits. Among these suggested alternative spawning grounds are the Gulf Stream edge, the Bahamas and the Caribbean Sea.
We are examining the possibility that the presence of primarily large spawners caught as bycatch in the Gulf of Mexico during the spawning season, does not exclude other spawning behaviors. Sampling of tissues involved in bluefin reproduction from various size classes of fish, during and outside of the reproduction season, is crucial for the understanding the specie’s reproductive physiology.

Sampling with the Nantucket tournament
Learning about the Nantucket tournament from our tagging partner, Capt. Eric Stewart of the FV Tammy Rose (and The Hookup, Inc), we knew that it would be a great opportunity to increase our sampling. Tournament director, Jonas Baker, immediately offered his help with obtaining the samples, and the Kaisers, Thea and Pete, a long time tuna fisherman and a charter captain, generously offered to host us. The captains and crews were all happy to help with our scientific effort and weighing station master, Dave Berard, graciously assisted throughout the tournament.
The tournament was a great success and we sampled eleven fish, seven females and four males, and obtained blood and reproductive tissues. All of the bluefin were between 88-162 lbs., measuring 53-65”.

Collaborating with fishermen in bluefin tuna research has been at the heart of our program. Such coordinative efforts are critical for obtaining more information on Atlantic bluefin tuna’s biology.
We’re grateful for the opportunity to obtain samples at the Nantucket Tuna Blast and to spread the word about our Tag a Tiny tagging program. We also want to send a big thank you for the assistance we received by all participants!
Gilad Heinisch

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