Friday, December 10, 2010
When Your Powers Combine...
Atlantic bluefin tuna Thunnus thynnus are a highly migratory, pelagic, marine fish species. Although I have never personally indulged myself by eating this fish, I have little doubt they are delicious. How can I make such an assessment? Well, Atlantic bluefin tuna are one of the most endangered animals on the planet and most assessments suggest they are on the brink of extinction. The obvious solution to this problem would be to close down the Atlantic bluefin tuna fishery, but alas, as with most fisheries issues the solution is not so cut and dry. The demand for bluefin tuna is incredibly high and in some countries, like Italy, the fishery represents a culturally important event. Because of the importance and current status of Atlantic bluefin tuna, significant effort has been put forth to address questions regarding migrations and stock structure of the species.
Studying the movements of highly migratory species is a difficult task to say the least, but solutions to these difficulties are quite interesting. A suite of methods including otolith microchemistry, genetics and electronic tagging has been used to decipher the life history of this species. Block et al. (2005) suggested that using each of these methods individually would be insufficient, and combining these methods paints a more powerful, more complete picture of the life history of bluefin tuna in the Atlantic Ocean.
Using otolith microchemistry, Rooker et al. (2003) identified unique chemical signatures in the otoliths of age-1 Atlantic bluefin tuna from the western and eastern Atlantic. This information is important, because it can be used to classify adult bluefin tuna to natal origins and suggests that there are probably two separate spawning stocks. This information is augmented by the findings of Carlsson et al. (2007) who used both nuclear loci and mtDNA to distinguish differences between Atlantic bluefin spawned in the Gulf of Mexico and the Mediterranean Sea. Finally, electronic tagging by Block et al. (2005) revealed that bluefin tuna have trans Atlantic migrations and may show spawning site fidelity to the Gulf of Mexico and the Mediterranean Sea.
Of course there is significant room to expand on all of this research, but when the current information is combined, the life history of Atlantic bluefin tuna becomes clearer. Using otolith microchemistry and genetic analysis to examine the origins of adult tuna should provide information on the mixing of individual stocks, which could answer questions like which side of the Atlantic is producing more fish? This information would complement findings from electronic tagging studies quite nicely. Whatever direction this research takes, it is pretty clear that one method will not provide all of the answers needed to make proper management decisions. It is only in combining their powers that a clear life history and stock structure can be identified for this critically important species.
Block BA, Teo SL, Walli A, Boustany A, Stokesbury MJ, Farwell CJ, Weng KC, Dewar H, & Williams TD (2005). Electronic tagging and population structure of Atlantic bluefin tuna. Nature, 434 (7037), 1121-7 PMID: 15858572
Carlsson J, McDowell JR, Carlsson JE, & Graves JE (2007). Genetic identity of YOY bluefin tuna from the eastern and western Atlantic spawning areas. The Journal of heredity, 98 (1), 23-8 PMID: 17158466
Rooker, J.R., D.H. Secor, V.S. Zdanowicz, G. De Metrio, & L. Orsi Relini (2003). Identification of Atlantic bluefin tuna (Thunnus thynnus) stocks from putative nurseries using otolith chemistry Fisheries Oceanography, 12 (2), 75-84