Somatic condition, growth and distribution of Atlantic bluefin tuna (Thunnus thynnus) in the Gulf of Maine.

摘要

Atlantic bluefin tuna (Thunnus thynnus), a highly migratory apex predator, utilize temperate feeding grounds to place their tissues into positive lipid balance following reproduction and subsequent migration to northern latitudes. Commercial fishermen target Atlantic bluefin tuna between June and October, but landings have declined 70% from 2004-2009 suggesting adult bluefin tuna may no longer be utilizing the Gulf of Maine as a foraging ground. A series of linear and additive models fitted to multiple fishery dependent datasets identified significant declines in the somatic condition of Atlantic bluefin tuna in the Gulf of Maine. Significant changes in the somatic condition of Atlantic herring, increases in the landings of the commercial herring fleet and changes in Atlantic herring gonad size were also identified. New growth parameters were estimated for Atlantic bluefin tuna sampled in the western Atlantic and these are significantly different than previous estimates for bluefin tuna greater than eight years of age. Finally, there has been a significant shift in the distribution of Atlantic bluefin tuna surface schools greater than 350 kilometers to the east over the past 28 years. Significant associations between Atlantic bluefin tuna and Atlantic herring schools were also identified, but long-term shifts in Atlantic herring distributions did not follow the same trend as Atlantic bluefin tuna. These results suggest bottom-up and top-down mechanisms are responsible for the changes in somatic condition and distribution of Atlantic bluefin tuna in the Gulf of Maine.