Ocean temperature is one of the primary environmental factors that determine the geographic range of a species. A paper published recently in the journal Fish and Fisheries has used computer modelling to project the global impact of climate change on biodiversity with reference to 1,000-odd fish species. The study has shown that the only way for the tropical fish, with their inability to regulate their body temperature, to survive in warming oceans would be to migrate to cooler waters at higher latitudes. The warming of the oceans would affect the sub-polar species differently. A two-to-four-fold limit to temperature tolerance compared to tropical species and a very limited species diversity would have a big impact in the polar regions. Local extinctions in the sub-polar, tropical, and semi-enclosed regions as well as migration of species to cooler latitudes would affect nearly 60 per cent of present fish biodiversity. Such a mass-scale disturbance is very likely to disrupt the marine ecosystem. Though warming oceans would affect fish whether they live at the surface level or at depths, the shift to an extent of 600-odd km would be seen in the case of surface-living species.
Local extinctions in the tropics will have a great effect on food security of developing countries. According to the Food and Agriculture Organisation, the direct impact of climate change on fisheries would be more pronounced in the developing and least developed countries where about 42 million people work directly in the sector. Two-thirds of the most vulnerable countries are in tropical Africa. It is a fact that reliance on fish protein is directly related to the level of development. In the developing countries, 2.8 billion people depend on fish products for 20 per cent of animal protein. The only way to reduce the magnitude of the impact is to take urgent measures to check the current trend of carbon pollution and limit the average global temperature rise to 2 degrees C by 2100, as against the anticipated 6 degrees. Dwindling fish catch will be one of the many adverse consequences of uncontrolled global warming. Several studies published since the Intergovernmental Panel for Climate Change’s 4th Assessment Report show that carbon emissions are rising faster than expected, and worldwide action to bring them down brooks no delay.
Science Editor with @The_Hindu, Chennai, India.
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