World Ocean Census - Extract 11 - Blue fin tuna: seafood, satellite tags and census

14 March 2010

The majesty of the bluefin tuna has awed humans throughout our history. Their power, grace and predatory prowess have propelled them to iconic status in many societies. However, their delicious flavor is contributing to their decline. Bluefin tuna, known in the Japanese market as kuromaguro, is in high demand worldwide and commands premium prices, even as stocks steadily wane. Hence, the effort put into catching this iconic seafood has reached huge proportions.

Experts are now warning that bluefin stocks cannot handle this pressure, and much work is being done to gather information about the species in an attempt to better manage it. Says Barbara Block, chief scientist of the Census of Marine Life Tagging of Pacific Predators (TOPP) program, “Their population is on the brink of collapse, and it has happened on our watch, in my lifetime. We have the science today to rebuild populations and prevent them from going the way of the cod.”

Bluefin tuna is one of the species being intensively studied by Census researchers. Scientists using satellite tags to track bluefin migration and diving behavior have found that these giants of the sea will routinely cross entire ocean basins during their annual movements. Tuna that were tagged while swimming together in Ireland have been found more than 4,800 kilometers (3,000 miles) apart less than eight months later. Results are proving that traditional management strategies for these tuna – and the notion that ocean space has boundaries – don’t take into account these vast migrations, making successful conservation of the stock unlikely. Bluefin tuna don’t respect boundaries drawn by humans. Because of their global-scale migrations, fishing in European waters affects stocks in the Gulf of Mexico, and bluefin poaching in the Southern Ocean affects North Pacific stocks. Collaborative, cross-boundary management is emerging as a key necessity if tuna stocks are to recover and survive.

Tagging efforts by Census researchers and affiliated groups – such as the Tag-a-Giant Foundation, the Large Pelagics Research Center and the Pelagic Fisheries Conservation Program, to name just a few – are helping to improve management efforts by providing a clearer picture of how these iconic fish use ocean space. Increased understanding of their ocean habitat, coupled with oceanographic data collected by sophisticated electronic tags, is helping scientists to better comprehend how environmental conditions affect tuna feeding and spawning ecology. Ultimately, this knowledge could help prevent their demise.

Text and images reprinted with permission from World Ocean Census: A Global Survey of Marine Life by Darlene Trew Crist, Gail Scowcroft and James M. Harding Jr., Firefly Books, 2009.

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