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sustainable fisheries management

Pacific bluefin tuna (Thunnus orientalis)

One of the largest and most powerful fish in the sea is the bluefin tuna. These fish can reach a size of 1,400 lbs and swim across an ocean basin in only a few weeks. Bluefin have a very broad thermal range occurring from the Gulf of Mexico to the chilly waters of Iceland. Bluefin tuna occur in the Atlantic, and the north and south Pacific. In both the Atlantic and south Pacific, population levels are 20% or less of what they were only 20 years ago.

The current status of bluefin populations may be largely attributed to the high value of the fish in the Japanese sashimi market, where one animal can demand as much as $80,000 dollars. The north Pacific population appears to be the only one of the three that has not been severely over-harvested. There is currently no management of bluefin in the north Pacific, a cause for worry given the status of the other populations.

Blue Fin Tuna Map

Bluefin tuna geographic range (used with permission from the Inter-American Tropical Tuna Commission)

Effective management plans require an understanding of stock structure and movement patterns. Most research to date has focused on small bluefin tuna near Japan. At present we know little about the movements of bluefin in the eastern Pacific, especially the larger animals. Based on the available information the following story has been put forth. Bluefin appear to spawn only in waters off southern Japan. Late in their first year, some individuals swim east. Data suggests that when the sardine population off of Japan diminishes, bluefin leave the area. Off the coast of Mexico and California, bluefin are most abundant in the summer and fall months, after which they seem to disappear.

Some questions that PIER’s research is directed to answer include:

  • What happens to the bluefin when they leave Californian and Mexican waters?
  • Do they migrate back to Japan each year or remain in the eastern Pacific until they mature and return to the spawning grounds off Japan?

During the summer of 2000, PIER launched a baseline study aimed at answering some of these intriguing questions. Since then 17 pop-up satellite tags have been deployed on bluefin from 60 to 110 lb. off of Southern California and Mexico. PIER has also expanded its research to include archival tags which unlike the satellite tags need to be recovered by fishermen in order to recover the data. Both of the tagging techniques will assist us in learning more about where the fish are during the winter and spring and whether they return to Japan each year. By tagging large animals near reproductive maturity it may be possible to determine whether the waters off of Japan truly constitute the only spawning site or if others exist. Data PIER collects will help protect the last remaining healthy population of bluefin tuna in the sea.

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The Pfleger Institute of Environmental Research, PIER, is a non-profit 501(c)(3) organization based in Oceanside, California.