Warming Arctic will let Atlantic and Pacific fish mix

Climate change is heating up the planet, and species are moving toward the poles, up mountains and deeper into the oceans. For most, there’s a natural end to this journey — the edge of a continent, for instance, or the summit of a mountain.

For fish and sea creatures in the Northern Hemisphere, though, there is no such physical barrier to their movement — only one of temperature. And once the Arctic Ocean warms enough for them to move in, they can keep moving, right on through to the other side of the world. A new study finds that by end of the century, dozens of fish species will have moved into the Atlantic from the Pacific, and vice versa. The research appears January 26 in Nature Climate Change.

Loïc Pellissier of the University of Fribourg in Switzerland and colleagues investigated how 515 species of fish would respond to climate change over the coming century. For each species, they forecast where suitable habitats would open up as the oceans warm and Arctic ice melts. By 2100, they predict, 41 Atlantic species could move into the Pacific and 44 Pacific species could enter the Atlantic.

From the human fish-eater point of view, that wouldn’t necessarily be a bad thing. Ten of the species predicted to move are highly commercial. They include Atlantic cod, American plaice (a type of flounder) and yellowfin sole. Fishing opportunities have already opened up off of Greenland because of climate change, and more could develop as the Arctic region warms.

But with those new opportunities comes the risk of overexploiting them, the researchers warn, saying that “care will be needed in fishing these high-latitude stocks.” And fishing in the Arctic, even when it’s a bit warmer, could be incredibly dangerous.

The timing of the fishes’ arrival in their new ocean homes isn’t certain, but species that reproduce by producing thousands or even millions of eggs, such as Alaska pollock, could be among the first to arrive when conditions become suitable, the scientists note.

Also difficult to predict is what will happen to the local food web once those species arrive. The ultra-cold Arctic passage from the Atlantic to the Pacific has been shut off to fish species for much of the last 2.6 million years. But the arrival of new species could have far-reaching effects on local food webs. The arrival of apex predator species, such as Atlantic cod and lingcod, could have particularly large effects, as their meal choices ripple through the food web. The researchers say that predicting those effects is “the next modeling challenge,” but there may be effects similar to what’s been seen when invasive species enter ecosystems. Invaders often upend food webs, causing some species to decline and even become extinct.

The Atlantic-Pacific fish exchange won’t end at the close of the century, as this study’s simulation did. “Arctic warming is expected to continue beyond 2100,” the researchers note, “thus one can expect that the extent of faunal interchange will continue to increase.” And the changes to the ocean ecosystems will continue long after we’re all gone.