In the early days of ocean acidification research, experiments were simple, says benthic ecologist Jim Barry. Some involved plopping fish into containers of high-carbon seawater. This sort of lab test allowed researchers to observe animals’ physiological responses to our ocean’s changing chemistry.
These days, many studies attempt to address the more difficult question of how acidification and ocean warming might affect interconnected marine species. “What you can’t learn from tests of fish in a jar,” Barry says, “is how climate change affects the way energy moves through a food web.”
That line of inquiry may start in the pages of scientific journals, but it leads somewhere more intimate: our dinner plates.
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.
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.