text size: smaller reset larger

 

 

Like fish out of water: the impact of climate change on fisheries

Sample of freshwater lake fish, whose populations could be at risk from climate change
Sample of freshwater lake fish, whose populations could be at risk from climate change

Lake Tanganyika, situated within the western rift of the Great Rift Valley, is the world's longest and second deepest freshwater lake, holding almost 20 per cent of the world's liquid freshwater supply. A unique ecosystem rich in biodiversity, this vast body of water supports over 350 fish species. It also provides a critical food source in East Africa, but in recent years fish productivity has diminished, and catches have shrunk. Subject to year-round high temperatures, the lake is not an obvious candidate to suffer from climate change, but scientists have discovered that rising temperatures in recent years have affected the vital mixing of the lake's nutrients, and believe this is causing its fish population to decline.

From 25 to 40 per cent of the animal protein consumed in the region has traditionally been fish, although only a few fish species, including the giant and small Nile perch, are eaten by the people of the four countries that border the lake - Burundi, Tanzania, Zambia and the Democratic Republic of Congo. But over the last three decades fish yields have plummeted, and the impact on the local economy has been severe. Large-scale commercial fishing began in the mid-1950s but industrial fisheries, which boomed in the 1980s, have subsequently collapsed. Currently there are around 45,000 people directly involved in the fisheries operating from almost 800 sites, with around one million people dependent on the fishery sub-sector. With fish populations in decline, these livelihoods are in jeopardy.

An essential mix

Deep freshwater lakes are dependent on the circulation of nutrients from the colder, denser water in the depths to the warmer, less dense layers near the surface. These vital nutrients support the lake's food chain by sustaining algae populations on which the fish feed. A study published in Nature in 2003, however, reported that warmer air temperatures (up by 0.6°C) above the lake's surface and less windy weather in the region were reducing the mixing of nutrients and contributing to the collapse of Tanganyika's fish stocks. While overexploitation is known to be a problem in some localised areas around the lake, the changes in fish population are too great to be attributed solely to increases in fishing. The Lake Tanganyika fisheries currently yield around 200,000 tonnes of fish per year but another study, also published in Nature in 2003, provides further evidence of climate change by revealing that the lake's productivity, measured by the amount of photosynthesis in aquatic plants, had decreased by 20 per cent. This could easily account for the 30 per cent decrease in fish yields.

Fishermen on Lake Tanganyika (Dave Midgley)
Fishermen on Lake Tanganyika
Dave Midgley

Large freshwater lakes are unlikely to be the only fishery systems to be affected by climate change, states a recent DFID-funded report. Inland fisheries will also be affected by changing water levels and flooding, while coastal ecosystems will be affected by severe weather events, rising sea temperatures and bleaching of coral reefs.

In comparison to South and Southeast Asia, fisherfolk in Africa are fewer in number, but the low per capita GDP of the region means that a greater proportion of fisherfolk live in poverty. In Africa small-scale fisheries and related activities, including trade and processing, provide income to rural communities where alternative employment opportunities are often scarce or non-existent. It is anticipated that the semi-arid regions, including Angola and Mauritania, that are reliant on coastal or inland fisheries, will be the most vulnerable to the impacts of climate change. These, like most African countries, have low adaptive capacity for climate change. And, although coastal fisheries communities often have access to alternative income sources, they are more likely to be squeezed out in the trends of increasing demographic pressures, such as urbanisation.

Urgent action required

Climate change is clearly another threat to the already overstretched fisheries and associated vulnerable communities in many parts of the world. Policies need to be developed for better management of resources, but also to enhance the resilience of fishing communities to deal with the threat of climate change, alongside other threats such as HIV/AIDS, political marginalisation, inequity and poor governance. At the end of August 2005, African governments unanimously adopted the Abuja Declaration on Sustainable Fisheries and Aquaculture in Africa, a strategy that focuses on capture fisheries, developing aquaculture, improving fish market chains, increasing benefits from fish trade, and supporting decision makers with information. But if the fisheries sector in Africa is to provide the economic and social benefits that are required in the next 10-20 years and beyond, the potential impacts of climate change need to be taken into account by policymakers and included in national action plans.

Note: A recent DFID-funded workshop held in London in September 2005 will produce a briefing on current knowledge and research needs to support efforts to mitigate climate change impacts on fisheries, particularly on the most vulnerable communities. This will be published through a 'New Directions in Fisheries' series produced by the FAO/DFID Sustainable Fisheries Livelihoods Programme.

Date published: November 2005

 

Have your say

 

The New Agriculturist is a WRENmedia production.

This website uses cookies to improve your experience. By continuing to browse the site you are agreeing to our use of cookies.
Accept
Read more