Pacific bluefin tuna

Posted by on May 23, 2010 in Articles | 1 comment

Pacific Bluefin Tuna (Thunnus orientalis)
(used with permission from the Inter-American Tropical Tuna Comission)

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

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.

Bluefin at Tskuji Fish Market

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 our 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, Michael Domeier (while at PIER) launched a baseline study aimed at answering some of these intriguing questions. Since then 34 electronic tags (17 pop-up satellite tags and 17 surgically implanted archival tags) have been deployed on bluefin from 60 to 110 lb. off of Southern California and Mexico. Nearly half of the surgically implanted archival tags were recovered by the purse seine fishery off Baja California and one was recovered by a longliner off Japan. Our research has demonstrated that juvenile bluefin tuna remain in the eastern Pacific year round, seasonally migrating between southern Baja and the California/Oregon border (see figure at right). Eventually the juveniles begin to sexually mature and migrate back across the Pacific to their spawning grounds. The impact the eastern Pacific purse seine fleet is having on the overall population of bluefin is not known, but the fact that we recovered so many tags from this fishery leads us to believe that this issue needs more attention.

See Published results in:
 Domeier, M.L., D. Kiefer, N. Nasby-Lucas, A. Wagschal, and F. O’Brien. 2005. Tracking Pacific bluefin tuna (Thunnus thynnus orientalis) in the northeastern Pacific with an automated algorithm that estimates latitude by matching sea-surface-temperature data from satellites with temperature data from tags on fish. Fishery Bulletin 103:292-306

We gratefully acknowledge the support of the George T. Pfleger Foundation

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