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Fisheries and aquaculture: multiple risks from climate change

FAO report predicts "an ocean of change" for fishers and fish farmers

Photo: ©FAO/F. Mattioli
West African fisherman put out to sea in a rough surf.
11 December 2009, Rome - Marine capture fisheries already facing multiple challenges due to overfishing, habitat loss and weak management are poorly positioned to cope with new problems stemming from climate change, a new FAO study suggests.

Small island developing states—which depend on fisheries and aquaculture for at least 50 percent of their animal protein intake—are in a particularly vulnerable position.

Inland fisheries—90 percent of which are found in Africa and Asia—are also at risk, FAO's study found, threatening the food supply and livelihoods of some of the world's poorest populations. Warming in Africa and central Asia is expected to be above the global mean, and predictions suggest that by 2100 significant negative impacts will be felt across 25 percent of Africa's inland aquatic ecosystems.

And fish farming stands to be affected as well. Nearly 65 percent of aquaculture is inland and concentrated mostly in the tropical and subtropical regions of Asia, often in the delta areas of major rivers at the mid- to upper levels of tidal ranges. Sea level rise over the next decades will increase upstream salinity, affecting fish farms.

The study, "Climate change implications for fisheries and aquaculture," which includes contributions from experts from around the world, including from the Worldfish Centre, Globec, NACA, Fisheries and Oceans Canada and the University of East Anglia, is one of the most comprehensive surveys to date of existing scientific knowledge on the impacts of climate change on fisheries and aquaculture.

Covering some 500 scientific papers, the picture FAO's review paints is one of an already-vulnerable sector facing widespread and often profound changes.

"High confidence" scenarios

According to the FAO study, certain general impacts on marine and aquatic systems as a result of large-scale changes related to temperature, winds and acidification can be predicted "with a high degree of confidence."

At "rapid time scales" of a few years increasing temperatures will have impacts on the physiology of fish due to limited oxygen transport to tissues at higher temperatures. This will result in changes in distributions of both freshwater and marine species, with most marine species ranges being driven toward the poles, expanding the range of warmer-water species and contracting that of colder-water species.

At the mercy of temperature

Since most aquatic animals are cold-blooded, their metabolic rates are strongly affected by environmental conditions, especially temperature. Changes in temperature can have significant influences on the reproductive cycles of fish, including the speed at which they reach sexual maturity, the timing of spawning and the size of the eggs they lay.

So in addition to changing where fish are found, there is "high confidence" that climate change will cause changes in abundance as well as in "recruitment," the life cycle processes through which young fish enter the fertile and exploitable adult population as they reach maturity.

Populations at the poleward extents of their ranges will likely increase in abundance with warmer temperatures, whereas populations in more equatorial parts of their range will decline.

For fish farming, temperature increases in temperate zones could exceed the optimal range for many of the organisms that are being cultured today.

Trouble spots

Cod in the North Atlantic, for decades a troubled fishery, will likely be hard hit. Temperature-related fluctuations in plankton populations there are already impacting the survival rates of young cod. Cod stocks in the Gulf of Maine and Georges Bank are at the species' southern-most limit and are particularly vulnerable. Models project that cod survival in the Gulf of Maine will decline. Similarly, simulations suggest that in the Northeast Atlantic increasing temperatures will lead to declines in North Sea cod populations.

Species adapted to cool and narrow temperature conditions, such as Atlantic salmon, "may be extirpated from their present habitats because of the combined impacts of warming, changing habitats, introduced competitors and predators and increased parasitism," the report found.

Antarctic krill have already declined between 38-75 percent per decade since 1976 probably as a result of the reduction in winter sea ice around the western Antarctic Peninsula. This has significant implications for the Southern Ocean food web, where krill are the primary food for penguins, seals, and whales.

Coral reefs have long been identified as being at particular risk from climate change impacts related to increasing temperatures, acidity, storm intensity and sea levels. They provide habitat for one-quarter of all marine species and are important sources of protein and income for many developing countries.

Sector crucial for millions of the world's poorest people

Some 520 million depend on fisheries and aquaculture as a source of protein and income. For 400 million of the poorest of these, fish provides half or more of their animal protein and dietary minerals.

Many fishing and coastal communities already subsist in precarious and vulnerable conditions because of poverty and rural underdevelopment, with their wellbeing often undermined by overexploitation of fishery resources and degraded ecosystems.

One crucial issue, the report notes, relates to how well such communities will be able to adapt to change. For example, while many African coastal fisheries are not likely to face huge impacts, the region's "adaptive capacity" to respond to climate change is low, rendering communities there highly vulnerable even to minor changes in climate and temperature.

"Urgent adaptation measures are required in response to opportunities and threats to food and livelihood provision due to climatic variations," FAO's report concluded.