As sea temperatures rise, many fish species will have to relocate to find waters that can support them. But they won't have a lot of time to look for the right new home. For fish, it's survival of the fastest.
An international team of researchers examined over fifty years' worth of data dating back to the 1960s to determine the patterns of climatic and seasonal changes both on land and in the sea. Professor John Pandolfi of the University of Queensland summarizes their findings:
"Our research shows that species which cannot adapt to the increasingly warm waters they will encounter under climate change will have to swim farther and faster to find a new home. We examined the velocity of climate change (the geographic shifts of temperature bands over time) and the shift in seasonal temperatures for both land and sea. We found both measures were higher for the ocean at certain latitudes than on land, despite the fact that the oceans tend to warm more slowly than air over the land.
Unlike land-dwelling animals, which can just move up a mountain to find a cooler place to live, a sea creature may have to migrate several hundred kilometres to find a new home where the water temperature, seasonal conditions and food supply all suit it. Also, as seas around the equator warm more quickly and sea life migrates away — north or south — in search of cooler water, it isn't clear what, if anything, will replace it. No communities of organisms from even warmer regions currently exist to replace those moving out."
Land animals and plants are currently migrating towards the poles at a rate of about four miles per decade. However, the researchers found that sea animals will likely have to migrate at a rate many times faster than that to keep pace with the changing ocean temperatures. That sort of migration speed — particularly into increasingly unfamiliar waters — is far outside what fish are normally capable of, and it's an open question how many species could survive such treks intact.
There's also the question of the environment that awaits them. There's only so much water around the poles, and the organisms that already live there might not be able to deal with tons of new migrants. This is a thorny issue, and there's no easy solution for us or for fish. Right now, about all we can say is that fish should start swimming as fast as they can. What happens after that is anybody's guess.