Bluefin Tuna in the Gulf of Mexico

Today in the journal PLoS ONE, TOPP scientists Drs. Barbara Block and Steve Teo published a study focusing on habitat suitability for yellowfin and bluefin tuna.  This study is important for a number of reasons.  First and foremost, it illustrates one of the key principals that underpins the TOPP program, and much of the work we do around the world – that it is possible, by marrying electronic tag data with oceanography, to gain a sufficient understanding of ecosystem function to enable more effective management of ocean resources. 

Specifically, this study shows that when bluefin tuna enter the Gulf of Mexico, they are going to specific locations, where cool, productive water in “cyclonic eddies” makes its way along the continental slope.  So during April and May, when they are spawning, bluefin tuna are relatively concentrated – whereas yellowfin tuna remain disbursed broadly throughout the Gulf.  This suggests that it would be possible to protect the bluefin, which are accidentally caught on longlines intended for yellowfin, by restricting fishing in those specific areas where the bluefin are spawning; but that such restrictions need not reduce yellowfin catch rates since they are more uniformly distributed.

 
 Map shows the probability of encountering a bluefin tuna when fishing with a pelagic longline in the Gulf of Mexico.  Probability of encounter is indicated by the colors from high (red) to low (blue). Bluefin tuna are located along the slope waters in the western and eastern Gulf of Mexico.

 

This is especially important for bluefin tuna, whose numbers have declined to less than 20% of what they were just a few decades ago.  If we can improve management of the “western stock,” which breeds in the Gulf of Mexico (as opposed to the “eastern stock” that breeds in the Mediterranean), this would be a significant step for the population as a whole.

Unfortunately, the implications of the paper also carry a down side for bluefin, in light of the current situation in the Gulf.  It appears that one of the key breeding grounds, in the eastern Gulf of Mexico, is currently being impacted by the Deepwater Horizon oil spill.  We don’t know what effect this will ultimately have on the spawning tuna or their offspring, but we have been working in the lab on how to measure stress genomically and we hope to move forward applying some of the work to the Gulf of Mexico tuna populations.  We are currently collaborating with scientists from other labs in the region to investigate these questions further.