New research published in Global Change Biology finds that of 22 studied tuna stocks, 20 have already shifted their ranges due to climate change, with even more significant shifts predicted in the near future. The analysis encompassed six of the seven most economically important tuna species, including albacore, Atlantic bluefin, and yellowfin. Some major tuna stocks are starting to move away from where coastal fishing fleets can easily reach them, while others are moving into new habitats that might not be able to support a large number of predatory fish.
This study not only analyzed range shifts that have already happened over the last few decades, but predicted future shifts under a high carbon emissions scenario. Overall, it points to potentially widespread economic disruptions that the tuna industry needs to begin planning for.
“Many fish species [not just tuna] are shifting, moving to colder water and greater depths,” lead study author Maite Erauskin-Extramiana, a PhD student at the Spanish research institute AZTI, told Earther. “Some freshwater fish have moved upstream in rivers, while warm water fish species in the ocean have been reported to be expanding their distribution limits.”
When it comes to tuna, these range shifts are likely to be important for fishing nations: If you’re only catching tuna in one place and the fish move elsewhere, a lot of people could be put out of work very quickly. In addition, the mass migration of large predators into new environments can lead to ecological disruption. The new habitats tunas are moving to may have different food or less food available, resulting in all kinds of problems for them, or for the fish that live there already.
“We just do not how tunas and the oceanic ecosystems will perform in the new situation,” Haritz Arrizabalaga of AZTI, the study’s senior author, told Earther.
Arrizabalaga noted that the shifts may indicate good news in some cases, as some tuna stocks are likely to increase or become more easily accessible to some fishing fleets. But overall, the high value of today’s tuna fisheries makes the implications of these results alarming. Grantly Galland, a Regional Fisheries Management Organization Officer with the Pew Charitable Trusts who was not involved with the study, noted that Pew estimates the global tuna catch is worth at least at least 42 billion at the final point of sale.
“We know from examples of smaller, shorter changes to tuna distribution, caused by local or regional environmental variability or stock decline, that these changes can negatively affect fishing operations,” Galland said. “ If larger, longer range shifts become the norm, the effects we’ve observed locally may be intensified and may occur over a wider area.”
Galland also emphasized that the largest threat currently facing tunas and tuna fisheries is not climate change-induced range shifts, but overfishing— Pacific bluefin tuna, for example, has been reduced to about 3 percent of what it was before humans started fishing it.
The study’s authors stressed that some of the negative economic effects can be minimized if fishing nations, especially smaller fishing ones that rely on locally accessible stocks, start planning now. This kind of planning can include investing in newer boats or fishing gear and renegotiating fishing agreements with other nations so that they’re not left behind when the tuna leave their waters.
As for what consumers can do, well, it may be time to start getting into California rolls.