A study has produced the strongest evidence yet that climate change is forcing hundreds of valuable fish species toward the poles.
The paper, published in the ICES Journal of Marine Science on Friday, concludes that Canadian and Arctic waters may end up with more species and greater abundance.
But fisheries in the tropics, where people depend more heavily on seafood, may become hollowed out.
"The variety of species available for fisheries in the tropics will decrease," said co-author William Cheung of the University of British Columbia.
"It may be good news for the Arctic — our projections are that the Arctic will be a hot spot for species invasion. There will be more variety of fish species available for the Arctic region."
Previous studies have suggested that warming ocean waters will affect the distribution of fish stocks. Cheung's paper gives the clearest and broadest picture yet of those effects.
More than 800 species studied
Using a combination of three different mathematical models and the latest climate data, he forecast the probable distribution of 802 commercially exploited fish species. Those species include commonly harvested fish such as cod, tuna, herring and halibut.
On average, Cheung found the fish are slowly moving toward the South and North poles at a rate of between 15 and 26 kilometres a decade. The effect is more pronounced in the Arctic, where warming is happening the quickest.
He checked his conclusions by using the same method to model the past movements of fish. When Cheung compared the modelling results with actual fisheries data, the two matched up.
"We found that, overall, our projections are consistent with the observations in the last 30 years."
Some countries already seeing new species
Cheung warns that the finding means challenges as well as opportunity.
How the invasive species will interact with existing species and ecosystems is unknown. Their movements are also likely to create problems for international fisheries management, as stocks shift across different jurisdictions.
"They could destabilize existing management agreements between countries."
That's already happening in some parts of the ocean, he said.
Scandinavian countries are negotiating how they'll deal with changes in the location of Atlantic mackerel stocks.
"Norwegian fisheries are already changing noticeably."
Cheung cautioned northern countries not to rush to exploit new fish stocks until scientists have a chance to learn what's happening with them and how they'll interact with existing populations. He praises a U.S. decision to enact a moratorium on new commercial fishing in the Arctic.
Canada has enacted no such fishing ban.
"We know from our previous experience that if we don't manage the fisheries well, it will collapse quite easily. It would be much better to be conservative and careful at first."
Cheung said his study points to the need for governments to start thinking now about how climate change will affect natural resources such as fisheries in the future.
"Things are much more easy to manage when there's not a vested interest already there," he said.
"We really need to look into these long-term projections and scenarios and start to think about how the fisheries should be managed now."