Hot, hot, hot. Fish the world over are migrating to escape global warming.

For several years now, some fishers have been noticing changes in their nets. In places, new species are being caught. Sea bass and red mullet have moved north into British waters. Pacific salmon have swum to the Beaufort Sea, where – according to Dan Pauly of the University of British Columbia in Vancouver, Canada – the Inuit have no name for them.

Elsewhere, staple catches are vanishing fast.

But whether this is a global effect and what is behind the change have been unclear. Are fish being ousted from their original habitats as climate change warms the waters? Are disappearances due to overfishing?

Now, Pauly and colleagues have found that the mix of fish in all the world’s major fisheries has changed since 1970, as fish that prefer warmer waters move in. The average temperature preference of fisheries has risen by nearly 1 ºC in temperate regions. The effect correlated closely with local increases in sea surface temperatures, but not with fishing pressure or other oceanic features such as currents.

Ominously, the temperature preference of tropical fisheries also rose initially, until the 1980s, then levelled off. Cooler-water species moved out, but there are no heat-loving species to replace them, says Pauly’s colleague William Cheung. The species that are abandoning tropical fisheries may also be the most important food species for coastal communities that subsist on fishing.