"From a strictly environmental perspective, countries in the higher latitudes will see the most pronounced impact from climate change on fishing," said Edward Allison, director of policy, economics and social science at WorldFish. "But economically, people in the tropics and subtropics likely will suffer most, because fish are so important in their diets and because they have limited capacity to develop other sources of income and food."

Of the 33 nations deemed most vulnerable 19 were already classified by the United Nations as "least developed" because of their particularly poor socioenomic conditions.

Researchers from the WorldFish Center, the University of East Anglia, UK, Simon Fraser University, the Centre for Environment, Fisheries and Aquaculture Science, the University of Bremen, Germany, and the intergovernmental Mekong River Commission looked at 132 national economies. They analysed environmental, fisheries, dietary and economic factors, reporting their work in Fish and Fisheries.

The countries that will experience the largest environmental impact of climate change were not necessarily the most vulnerable. In vulnerable nations, fish plays a large role in diet, income and trade but there’s not much capacity to adapt to problems caused by climate change, such as loss of coral reef due to warmer ocean temperatures and lakes becoming parched by temperature and precipitation changes. For example in the most vulnerable countries fish makes up at least 27% of daily protein intake, compared to 13% in non-vulnerable countries, and there are scant resources for alternative protein sources.

The 33 highly vulnerable nations were Malawi, Guinea, Senegal and Uganda in Africa, Bangladesh, Cambodia, Pakistan and Yemen in Asia, and Peru and Colombia in South America.

The researchers say that these countries should be a priority for adaptation efforts that will allow them to endure the effects of climate change and maintain or enhance the contribution that fisheries can make to poverty reduction.

"We believe it is urgent to start identifying these vulnerable countries, because the damage will be greatly compounded unless national governments and international institutions like the World Bank act now to include the fish sector in plans for helping the poor cope with climate change," said Allison.

Climate change can affect factors such as the upwelling of nutrient-rich water along coastlines, coral reef health, and water levels and temperatures in inland lakes. Inland freshwater habitats could also be damaged by intrusions of salt water as sea levels rise.

"Fisheries are already under tremendous pressure from overfishing, habitat loss, pollution and a range of other factors," said Steve Hall, director general of WorldFish. "Climate adaptation measures must go hand in hand with efforts to confront other threats if these countries are to succeed in building sustainable livelihoods for fish-dependent people."

Now the researchers will continue to "refine their ability to link climate change to fish productivity and to social and economic conditions". This study found a scarcity of data on the social and economic impacts of fisheries at the country level, particularly for subsistence fishing and small island states. In fact, 60 countries were excluded from the study’s final listing because of insufficient data but many of these – such as Kiribati, Myanmar, Somalia and the Solomon Islands – are likely to be highly vulnerable to the effects of climate change.