Tropics face fish famine due to climate change, report warns

The first study to look at how climate change will affect food supplies offshore warns of severe declines in fish stocks in some of the world's poorest regions

Suzanne Goldenberg, guardian.co.uk 8 Oct 09;

Fish populations in the tropics could fall by as much as 40% over the next half century because of global warming, jeopardising a vital food source for the developing world, a new study published today has found.

The waters off Indonesia - which rank among the most plentiful areas for fish today - could see supplies fall by well over 20% by 2055 because of changes in ocean conditions. Fishermen operating in US coastal waters (excluding Alaska and Hawaii) could also face large declines in fish stocks, as would those working off Chile and China.

"Fish are very sensitive to temperatures, and when the temperatures warm because of climate change, the fish will move away. And some of the species - those that can't swim that far - may locally go extinct," said William Cheung, lead author of the study.

The study, conducted by the Sea Around Us project at the University of British Columbia, is the first to look at how climate change will affect food supplies offshore. It is published in the journal, Global Change Biology.

But not all regions would be losers. Cooler climates would see their catch potential rise by between 30% and 70% by 2055, with Norway, Greenland, Alaska and the east coast of Russia seeing the biggest increases. This is because fish will migrate northwards as the oceans warm to seek out suitable cooler waters.

But while the overall productivity of the world's oceans will remain roughly the same, the sharp declines in fish stocks in Asia, the Caribbean, and semi-enclosed seas like the Mediterranean could cause severe shortfalls in some of the poorest regions of the world.

Sub-saharan Africa and south Asia are already threatened with food shortages because of climate change. A study last week by the International Food Policy Research Institute projected sharp declines in rice and wheat crops by mid-century because of global warming, which could see more than 25 million malnourished children around the world.

In many parts of Africa and south-east Asia, people depend on fish and seafood for half of their animal protein.

"It is devastating," said Daniel Pauly, a marine biologist at the University of British Columbia who worked on the study. "Basically you have lots of people living at the edge of the sea. They depend on fisheries, not in the way we do in northern countries. So income-wise and consumption-wise they are affected directly by the decline in catch."

The study used computer modelling to gauge the effects of climate change on more than 1,000 species of fish, from krill to shark, across the 20 largest fishing zones.

It did not take into account the effects of ocean acidification - caused by more carbon dioxide dissolving in seawater and which scientists expect will reinforce the effects of warming on the oceans. "We think that our estimates should be considered conservative because adding ocean acidification into the equation would further decrease future fishery potential," said Cheung. He said a follow-up study would look at the effects of acidification.

The scientists found that the warming seas were driving fish from their current habitats, with for example, tropical mainstays like snapper moving north. Some will successfully migrate to colder waters - reflected in the projected increase in fish populations in more northern waters. But others will not survive the changes. "Not all of them will make it. They can handle it only by shifting more energy to resisting the higher temperatures, which means less growth and less potential for harvesting," said Pauly.

The study did not focus on individual species. However, scientists said the changes brought by warming seas would see the decline and possible disappearance of familiar fish even in colder waters, like those off Britain. Cod stocks will flee British waters for Iceland, Norway and Greenland.

Tropical Regions To Be Hardest Hit By Fisheries Shifts Caused By Climate Change
ScienceDaily 8 Oct 09;

Major shifts in fisheries distribution due to climate change will affect food security in tropical regions most adversely, according to a study led by the Sea Around Us Project at The University of British Columbia.

In the first major study to examine the effects of climate change on ocean fisheries, a team of researchers from UBC and Princeton University finds that climate change will produce major shifts in productivity of the world's fisheries, affecting ocean food supply throughout the world. The study is published October 7 in the journal Global Change Biology.

"Our projections show that climate change may lead to a 30 to 70 per cent increase in catch potential in high-latitude regions and a drop of up to 40 per cent in the tropics," says lead author William Cheung, a researcher at the University of East Anglia in the UK who conducted the study while at UBC.

"Many tropical island residents rely heavily on the oceans for their daily meals. These new findings suggest there's a good chance this important food source will be greatly diminished due to climate change."

Previous studies have looked at how climate change affects global food supply but were limited to land-based food sources. These studies have also predicted that tropical areas will see a decline in land productivity.

The team, led by UBC Fisheries professor Daniel Pauly, also found that regions with the highest increase in catch potential by 2055 include Norway, Greenland, Alaska and the east coast of Russia. Meanwhile, regions with the biggest loss in catch potential include Indonesia, the United States (excluding Alaska and Hawaii), Chile and China.

While greater catch potential in colder regions might appear beneficial, the authors caution that more research is needed to account for the multitude of dynamic factors that affect every ecosystem.

"We need to keep the big picture in mind when looking at the 'winners' and 'losers' of climate change," says Pauly. "Major shifts in fish populations will create a host of changes in ocean ecosystems likely resulting in species loss and problems for the people who now catch them."

"While warmer waters might attract new species to colder regions, the rise in temperature might make the environment inhospitable to current species in the region that cannot move to even higher latitudes. Often these species are important to the diets and culture of native subsistence fishermen."

The team's projections also show that Canada's overall catch potential will remain approximately the same. The west coast may see a decrease of almost 20 per cent from 2005 to 2055 while the east coast may get a 10 per cent boost.

The study analyzed 1,066 species ranging from krill to sharks that constitute roughly 70 per cent of the world's catch. The authors used models that include a large number of environmental and biological factors that affect fisheries. They ran these models through two climate change scenarios, one more conservative than the other, and measured the impact of the scenarios on fish distribution from the years 2005 to 2055. The authors did not include the highest emission level scenario considered by the Intergovernmental Panel on Climate Change, which would have produced even more dramatic results.
Adapted from materials provided by University of British Columbia, via EurekAlert!, a service of AAAS.