Press Release
New Study Maps Spawning Habitat of Bluefin Tuna in the Gulf of Mexico
Critical Area Intersects Deepwater Horizon Oil Spill
May 28, 2010
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Electronic tagging and fisheries catch data have revealed pronounced differences in preferred habitat of Atlantic bluefin tuna and yellowfin tuna in the Gulf of Mexico, despite their close ancestry, according to a new study published today in the peer-reviewed journal PLoS ONE. Bluefin tuna return to the same regions of the Gulf of Mexico during spring months to spawn. The bluefin are selecting cool, productive water masses in the slope waters of the Gulf of Mexico, which are predictable and can be observed from satellites. Yellowfin tuna are more widely distributed throughout the warm Gulf waters and occupy the region throughout the year. "The bluefins' habitat requirements are relatively exact so we can predict with reasonable accuracy where bluefin tuna are likely to be spawning at any given time based on oceanographic data continually being gathered by satellites and weather buoys," said lead author Steven Teo of the University of California at Davis. "This is in stark contrast to yellowfin tuna, which exhibit much more generalized environmental preferences.” The fidelity to breeding areas over time detected in this study is reminiscent of salmon returning to their natal stream to spawn. Bluefin tuna are among the most valuable fish in global markets. The International Commission for the Conservation of Atlantic Tunas (ICCAT, http://www.iccat.int) currently manages the Atlantic bluefin tuna as two distinct populations, with western Atlantic spawners of the Gulf of Mexico forming a distinct population genetically from the eastern spawners of the Mediterranean Sea. The western Atlantic stock has suffered a significant decline in spawning stock biomass since 1950, and a 20-year rebuilding plan has failed to revive the population or the North American fishery. The failure of the Gulf of Mexico spawning population to rebuild, as well as the scope of illegal and under-reported catches - particularly in the Mediterranean Sea - are of such major concern that the species was recently considered by the United Nations for endangered species listing in March of 2010. Targeted bluefin fishing has been banned in the Gulf for over twenty years, but bluefin continue to be captured accidentally on pelagic longlines, often resulting in mortality. The study shows that bluefin tuna are captured in the Gulf of Mexico from January through June each year, and the highest pelagic longline catch rates are in April and May, during the bluefin spawning season. The authors compared environmental preferences and spatio-temporal distributions of bluefin and yellowfin tuna as revealed by pelagic longline catch rates and scientific tagging cruise conducted by the Stanford University and Monterey Bay Aquarium team coupled with oceanographic data sets. Drawing on these data, a model was developed to determine the relative probability of catching bluefin and yellowfin tuna at a given place and time. This model showed that there are two major hotspot regions within the Gulf where bycatch occurs – one in the eastern Gulf of Mexico to the north of the Loop Current, and the other in the western Gulf of Mexico. Both regions are along the slope where the shallow continental shelf depth changes rapidly to the deep sea. It is within these hotspots that bluefin tuna prefer to spawn in circular, swirling water masses called “cyclonic eddies.” These eddies are more productive and slightly cooler than surrounding warm Gulf ocean currents. Yellowfin tuna, however, are much more widely dispersed throughout the Gulf of Mexico throughout the year. These findings indicate that it would be possible to utilize spatial management techniques to protect western Atlantic bluefin tuna on their breeding grounds in the Gulf of Mexico without compromising the yellowfin tuna fishery, which could be carried out in other areas during the critical bluefin tuna breeding times. Unfortunately, these findings also give cause for concern in light of the recent Deepwater Horizon oil spill. “Both catch data and electronic tags indicate the
Funding for this study was provided by the Lenfest Ocean Program, the Tag-A-Giant Foundation, the David and Lucile Packard Foundation, the Monterey Bay Aquarium Foundation, the National Oceanographic and Atmospheric Administration and the Disney Foundation. Habitat Utilization of the Gulf of Mexico by Bluefin Tuna (Figure 1) and Yellowfin Tuna (Figure 2) from PLoS ONE (Teo and Block, 2010) Maps show the probability of encountering a bluefin tuna (Figure 1) or a yellowfin tuna (Figure 2) when fishing with a pelagic longline in the Gulf of Mexico. Probability of encounter is indicated by color from high probability (red) to low (blue). Bluefin tuna are located along the slope waters in the western and eastern Gulf of Mexico (Figure 1), whereas yellowfin tuna are distributed throughout the Gulf of Mexico (Figure 2). Figure 1 Figure 2 |
Original Scientific PaperTeo, SLH and BA Block. 2010. Comparative influence of ocean conditions on yellowfin and Atlantic bluefin tuna catch from longlines in the Gulf of Mexico. PLoS ONE 5: e10756. doi:10.1371/journal.pone.0010756. Link to PRESS RELEASE, Summary or Full Text.
Learn more about the Deepwater Horizon spill and its potential effects on Atlantic bluefin tuna. Media CoverageJune 7, 2010: Oil Spill Comes at Worst Time for Endangered Bluefin Tuna, Inter Press Service May 31, 2010: Oil spill hit the Gulf waters for bluefin tuna spawning, Asahi (translated from Japanese) May 31, 2010: Spawning Habitat of Bluefin Tuna in Gulf of Mexico: Critical Area Intersects Deepwater Horizon Oil Spill, Science Daily May 28, 2010: Bluefin Tuna Spawning Mid-Spill Right Now, Mother Jones |
