The ruby-red slice of maguro presented on a piece of nigiri sushi does nothing to convey the sheer power of Pacific bluefin tuna. These top ocean predators can grow to be twice the size of lions; at top swimming speed, they’re faster than gazelles. But it’s been a huge challenge to halt the decline of these incredible fish.
The Pacific bluefin population is down to just 2.6 percent of its unfished level—yet it continues to face intense fishing pressure. The fish are prized commercially, command staggering market prices, and are difficult to manage because they cross through national and international waters on trans-Pacific migrations.
Monterey Bay Aquarium has long advocated for use of the best available science to inform management decisions that can bring the Pacific bluefin population back to a healthy level. Now researchers at the Aquarium, together with colleagues from Harvard University and the National Museum of National History, have identified new evidence of migration trends that underscore the need for comprehensive fishing restrictions and enforcement across the Pacific—especially in the Western Pacific, where all Pacific bluefin spawn, and where most of the fish are caught.
The source of spawning-age fish
The analysis, published in Science magazine, concludes that—in many years—the majority of spawning-age bluefin tuna in the Western Pacific are migrants who left the waters off Japan when they were just one to two years old, and spent the next four to six years on rich feeding grounds off the coasts of California and Mexico, before returning to the Western Pacific.
If too many of the young fish are caught in the Western Pacific before they can make the migration east, there won’t be enough returning fish years later to maintain or recover the already-depleted population.
And if fishing pressure is too great in the Eastern Pacific, the fish won’t survive to make the migration back to their spawning grounds near Japan.
“These fish were passing through two gauntlets, in the west and in the east, before they had a chance to spawn,” said Dr. Andre Boustany, the Nereus Principal Fisheries Investigator for the Aquarium. “Many fish have to pass through both the Western and Eastern Pacific Ocean. So by taking too many of them out in both locations, we end up with a severely depleted population.
“We need much better management of the fishery in the west, and to continue to at least maintain current management in the east,” he added.
Continue reading Science shows a path to recover Pacific bluefin tuna