Climate change is emerging as the latest threat to the world's fast declining fish stocks, which could affect millions of people who depend on the oceans for food and income, says a new report by the United Nations Environment Programme (UNEP).
The report, In Dead Water, says climate change may slow down the global flow of ocean currents, which flush and clean the continental shelves and are critical to maintaining water quality, nutrient cycling and the life-cycle patterns of fish and other marine life in more than 75 percent of the world's fishing grounds.
"In developed countries, the degradation of traditional fishing grounds will have commercial effects on the fishing industry sector and fleets," said Stefan Hain of UNEP's World Conservation Monitoring Centre. "The effects in developing countries and SIDS [Small Island Developing States] will be more direct, i.e. on coastal communities and populations, which depend on marine resources for sustenance and livelihoods."
Fifty million people could be at risk by 2080 because of climate change and increasing coastal population densities, according to a Food and Agriculture Organisation (FAO) policy brief on the impact of climate change on fisheries. "Projections suggest that these combined pressures could result in reef loss and a decline in fish availability for per capita consumption of approximately 15 percent by 2015."
|The high catches that currently allow exports may become a thing of the past, and a high dependence on fish for protein could threaten the health of many thousands as catches shrink|
Coastal fishing communities face a double whammy of reduced fisheries resources and increased risks of coastal flooding and storm surges, said the FAO brief, Building adaptive capacity to climate change: Policies to sustain livelihoods and fisheries. "Impacts of climate change are an additional burden to other poverty drivers, such as declining fish stocks, HIV/AIDS, lack of savings, insurance and alternative livelihoods."
The UNEP study, the first of its kind by UNEP scientists, was conducted in collaboration with universities and institutes in Europe and the United States, which found that the number of marine dead zones - oxygen deficient areas - have increased from 149 in 2003 to over 200 in 2006, mostly in coastal waters. These zones are linked with pollution and the projected growth in coastal development, and this number is expected to multiply in a few decades.
Christian Nellemann, editor-in-chief of the UNEP report, pointed out that the "impoverished will take the greatest toll both in terms of reduced food supply, but also breakdown in their economy and their primary opportunity to move out of poverty. This is an emerging catastrophe of an unprecedented scale, and the efforts in the next two decades will determine the lives of hundreds of millions for centuries ahead.
He said West Africa, where several million people live along the coast and the fisheries provide the primary income and food resource, could be among the worst affected by climate change and industrial overfishing - including bottom trawling - combined with coastal pollution. "Here, an increasingly larger portion, often exceeding 80 percent to 90 percent of the fishery harvest, is caught by non-local vessels, such as from the European Union.
The report also found that up to 80 percent of the world's primary fish-catch species are exploited beyond or close to their harvesting capacity: advances in technology, combined with subsidies, mean the world's fishing capacity is 2.5 times bigger than can harvest fisheries sustainably.
Higher sea surface temperatures in the coming decades threaten to bleach and kill up to 80 percent of the globe's coral reefs, which are major tourist attractions, natural sea defences and nurseries for fish.
There is also growing concern that carbon dioxide emissions will increase the acidity of seas and oceans; this in turn may negatively affect calcium- and shell-forming marine life, including corals, but also tiny ones such as planktonic organisms at the base of the food chain.
Impact on poor countries
The FAO paper noted the link between fisheries and poverty reduction. "The sector and its related activities are important for economic output and growth, and employs over 155 million people worldwide - 98 percent from developing countries."
It cited a recent study on the vulnerability of national economies and food systems to climate impacts on fisheries, which found that African countries were most vulnerable to the likely impacts of climate change on fisheries. "This is in spite of over 80 percent of the world's fishers being in south and Southeast Asia, and fish catches being greater in Latin America and Asia."
Climate change will change the distribution, conservation and use of the water of the earth and its atmosphere. African fisheries are particularly at risk because semi-arid countries with significant coastal or inland fisheries have high exposure to future increases in temperature, and the linked changes in rainfall and coastal current systems.
The high catches that currently allow exports may become a thing of the past, and a high dependence on fish for protein could threaten the health of many thousands as catches shrink. Low capacity to adapt to change due to their comparatively small or weak economies and low human development indices could set back development in countries like Angola, Congo, Mauritania, Mali, Niger, Senegal and Sierra Leone.
In African countries like Ghana, Namibia, Senegal and Uganda, the fisheries sector contributes over six percent of gross domestic product. Rift Valley countries such as Malawi, Mozambique and Uganda, and Asian river-dependent fishery nations, including Bangladesh, Cambodia and Pakistan, are also vulnerable.
Impact on freshwater fisheries
In the short term, climate change is expected to affect freshwater fisheries through changes in water temperature, nutrient levels and lower dry-season water levels. Dry-season flow rates in rivers are predicted to decline in south Asia and in most African river basins, leading to reduced fish yields, according to the FAO.
In the longer term, larger changes in river flows are anticipated as glaciers melt, reducing their capacity to sustain regular and controlled water flows.
Researchers found that lake fisheries have already begun to feel the impact of climatic variability, affecting fish production.
. In Lake Chilwa, Malawi, a 'closed-basin' lake, dry periods have become more frequent and fish yields are declining.
. In Lake Tanganyika, Tanzania, fish yields have dropped because of declining wind speeds and rising water temperatures, which have reduced the mixing of nutrient-rich deep waters with the surface waters that support fish production. This, along with overfishing, may be responsible for the declining fish yields from the lake.
. Lake Chad's area fluctuates extensively, but follows a declining trend. In 2005 it occupied only 10 percent of the area it was in 1963, with further decreases predicted in the coming century. Fish catches have not fallen to the same extent, but the overall productive potential of the lake is declining.
Upside of global warming
Snow and glacier melt in the Eurasian mountains, which stretch from the Caucasus Mountains to the Himalayas, may also result in changes in the flows of the Indus, Brahmaputra, Ganges and Mekong, which sustain major river and floodplain fisheries, as well as supply nutrients to coastal seas, the FAO paper said.
"Predictions for consequences of flow regimes are uncertain but increased runoff and discharge rates during this process may boost fish yield through more extensive and prolonged inundation of floodplains. In Bangladesh, a 20 percent to 40 percent increase in flooded areas could raise total annual yields by 60,000 tonnes to 130,000 tonnes.
"These potential gains may be counterbalanced by greater dry-season losses due to lower dry-season flows and greater demands on water resources for irrigation, threatening fish survival and making them more susceptible to capture. Damming for hydropower, irrigation and flood control may also offset any potential fishery gains," the FAO paper noted.
The FAO suggested policy action for mitigation and adaptation such as raising awareness of the impacts of climate change to ensure that the special risks to the fishery sector are understood and used to plan national climate change responses.
Mitigation targets should be set, using mechanisms like the Kyoto Protocol. Mangroves should be restored and coral reefs protected, which will contribute to carbon dioxide absorption, coastal protection, fisheries and livelihoods.