Climate change may directly affect fishery production along many pathways. Fish reproduction, growth and migration patterns are all affected by temperature, rainfall and hydrology. Changes in these parameters will therefore shift patterns of species abundance and availability. Saltwater intrusion caused by rising sea levels may threaten freshwater fisheries while, at the same time, creating opportunities for catching and cultivating high-value brackish or marine species . Changes in precipitation will affect seasonal flooding patterns that drive inland fish production. While greater wetseason flooding may boost production in some inland fisheries, drier dry seasons may threaten stocks of both wild and cultured fish.
Fish in Cambodia
Fisheries are critical to human well-being in Cambodia, where fish provide up to 80 per cent of all animal protein in the diet. Capture fisheries and aquaculture contribute about 10 per cent of Cambodia's gross domestic product and are even more important in terms of local livelihoods. Fishing and related activities are the primary sources of income for about one third of the people living around Tonle Sap and a secondary source of income for half of those who live around Cambodia's great lake.
Climate change in Cambodia
Climate change is occurring now. The average temperature in Cambodia has increased since 1960 by 0.8°C, and with it the frequency of unusually hot days and nights has increased as well. A further 0.3-0.6°C increase is expected by 2025. Alternative estimates put the expected warming at 0.7-2.7°C by the 2060s. Temperature increases will be more severe from December to June. All climate change models agree that rainfall in Cambodia will increase, but the magnitude of change is uncertain.
Estimates of the increase vary from as little as 3 per cent to as much as 35 per cent. Models predict that the increase in rainfall will occur during the wet season, bringing more flooding, and that precipitation in the dry season will be unchanged or lower. Rainfall is expected to increase more in the lowlands than in the highlands, with precipitation and flooding increasing predominantly in the central agricultural plains, which are already vulnerable to flooding and drought. Climate change will bring more extreme weather events such as storms, heat waves, droughts and floods. Damage from intense cyclones has increased significantly in Cambodia in recent decades and may worsen.
Implications for Cambodian fisheries
Runoff throughout the Mekong Basin is expected to increase by 21 per cent by 2030. This will intensify sediment loading in Cambodia's rivers, lakes and wetlands, with higher nutrient levels boosting fishery productivity. However, this effect may be offset by sediment retention behind the many dams that are likely to be constructed upstream.By 2030, climate change may raise the wet season flood level of the Tonle Sap lake by 2.3 meters, extending feeding grounds and encouraging fish production. On the other hand, dams to be developed in the Mekong Basin will store water during the moonsoon and thus will decrease wet season flood levels. The net result of these two processes is unknown.
It is similarly difficult to predict the specific effects of climate change on fish species composition and abundance in Cambodia. Patterns of change in fertility, recruitment, nutrition and growth will depend on both species and interactions between species. Some of the 500 or so Cambodian freshwater species will thrive in a changed climate, while others may die out . An assessment is needed of climate change effects on the commercially dominant species that comprise the bulk of the catch.
Cambodian fish catches are increasingly made up of species such as Henicorhynchus spp. ("trey riel" in Khmer) that are considered unstable because their abundance is largely driven by the annual flood pattern, as they grow quickly and die young. This emerging boom-and-bust cycle may be amplified by the higher hydrological variability predicted with climate change, bringing very high year-to-year fluctuations in fish abundance, with years of high abundance followed by years of shortage.
Extreme weather events could further harm fish production in Cambodia by causing loss of aquaculture stock and destroying fishing and aquaculture infrastructure. Changes in fishery production are likely to have the greatest impact on people who depend on fishing as their primary livelihood activity. As these people are often poorer and more marginal than those who own land and have other primary sources of income, the effects of climate change on fisheries will harm those least equipped to cope.
Issues for Local Adaption Strategies
A recent global study classified Cambodia as highly vulnerable to the effects of climate change on fisheries (see Figure 2). These findings were based on assessments of Cambodia's dependence on fisheries, the magnitude of expected climate change in the country, and its adaptive capacity. This vulnerability makes it important that Cambodian fisheries receive the support necessary to adapt to and cope with climate change. Yet the current Cambodian National Adaptation Program of Action for climate change (NAPA) does not prioritise adaption planning for capture fisheries in lakes, rivers and wetlands, despite their importance to the national economy and their vulnerability to climate change.
Infrastructure development upstream – which is a threat more immediate than climate change and whose effects will combine with those of climate change – calls for a response that includes investment in fishery forecasting and management in the context of changes in flow regime.
An ecosystem stressed by overfishing is more likely to collapse when subjected to climate change. Policies to prevent overfishing and ensure the sustainable use of fish stocks help build ecosystem resilience to climate change.
A key to successful adaptation is diverse livelihoods. Livelihood diversity helps ensure that, if one economic option temporarily closes, people can resort to other options for making a living. Poverty reduction strategies that help diversify livelihoods and improve poor people's access to natural resources also help build adaptive capacity for climate change.
Fishing communities in Cambodia have coped with environmental variability for many years, developing strategies of adaptation to fluctuation. Understanding and supporting these adaptive strategies and removing barriers to adaptation are steps toward preparing fishery-dependent communities to cope with climate change.
Some adaptation strategies in other sectors may adversely affect fisheries. Hydropower dams and irrigation structures can improve water management and availability in the dry season, but they can also block fish migrations and reduce fishery productivity. It is therefore critical to take fisheries into consideration in adaptation planning, thereby ensuring that adaptation measures in one sector do not become counterproductive in another.
Fisheries and aquaculture can help solve other adaptation problems. As rising sea levels and increased flooding may render some existing farmland unsuitable for cropping, fish cultivation can provide alternative livelihoods and offset these losses. Further, water and nutrients from fishponds can improve farm productivity and sustain it under drought. Conserving wild fisheries and enhancing aquaculture should be considered twin strategies of adaptation to climate change.
Conclusion
Most fisheries are highly variable by nature and subject to environmental change, including climate change. Hydropower dam construction, intensified fishing pressure and macroeconomic drivers are likely to affect Cambodian fisheries more immediately and visibly than climate change. Building fisher communities' capacity to adapt to these more immediate changes goes hand-in-hand with improving their capacity to adapt to climate change. A far-reaching strategy to improve adaptive capacity and strengthen resilience promises to reduce poverty and enhance food production now and in the years to come.
December 2009
