BioEd Online

Fish are shifting their homes northwards, according to an analysis of North Sea populations. The authors warn that climate change is probably to blame for the move, which could drive some commercially fished species out of the sea completely.

Allison Perry of the University of East Anglia in Norwich, UK, and her colleagues looked at data for 36 species of fish that live near the bottom of the North Sea. Between 1962 and 2001, the North Sea warmed by about 0.6 °C. The team found that, in response, 15 species had shifted as much as 400 kilometres into cooler waters. A further six species had moved into deeper waters in their search for cooler living conditions.

Previous work has shown other species moving away from warming environments, including insects, plants and mammals (see ' Global warming alters US wildlife'). But the fish seem to be moving more quickly, perhaps because there is little to obstruct them.

If surface temperatures rise as climate models predict, Perry says that blue whiting (Micromesistius poutassou) and redfishes (Sebastes)spp. might completely withdraw from the North Sea in the next 50 years. The loss of such commercial species would severely affect fisheries, suggests the report in Science¹.

"We will see dramatic changes to the whole North Sea ecosystem," says Geir Ottersen from the Institute of Marine Research in Norway. "Even a change of one degree can affect fish, who are also under pressure from fishing."

Baby blues

Warmer temperatures not only prompt fish to move, but may also affect their ability to reproduce. "Cod are going to have trouble as the water warms," says Perry. And juvenile North Sea herring seem to have difficulty thriving in warmer waters.

"Fishing management needs to take even more precautions if we are going to let stocks of fish rebuild," Perry says.

A hotter North Sea isn't all bad news. Some species, such as the northern cod (Gadus morhua), "grow faster, as long as they are able to find food", says Ottersen. However, as some species move further than others in response to changing temperatures, predators may be separated from their normal prey.

"Warming temperatures just change things, for some species it can be favourable," says Ottersen. "It doesn't mean that biodiversity has to decline."