WASHINGTON, DC – Climate change will dramatically alter marine ecosystems, wreaking havoc on many fisheries and exacting a huge economic toll, researchers reported today at the annual meeting of the American Association for the Advancement of Science.
Despite being overexploited, the world’s fisheries are still profitable: In 2003, they generated more than $24 billion in wages for fishermen, profits for companies and payments to resource owners, says Rashid Sumaila, an economist at the University of British Columbia in Vancouver. Yet those profits – and in some cases the fisheries themselves – are threatened by a variety of ill effects brought about by climate change, he notes. Warming seas and rising atmospheric concentrations of carbon dioxide will cause oceans to acidify, the habitable ranges of many species to shift substantially, and the size of adult fish to decline, to name just a few.
Climate models suggest that by the year 2100, sea-surface temperatures will be between 1.9° and 2.8° Celsius higher than they were in the 1890s, says Jorge Sarmiento, a marine biogeochemist at Princeton University in Princeton, New Jersey. As a result, changes in the patterns and rates of upwelling that bring nutrients to the surface, among other factors, will cause primary productivity – the amount of biomass generated by the ocean’s food chain – to decline between 2 and 16 percent by the end of the century. While some areas, such as the Southern Ocean surrounding Antarctica, will see slight increases in biological productivity, many areas, including much of the tropical and temperate seas, will see substantial decreases, the models suggest. For example, he notes, in 2090 the combined productivity of North Atlantic fisheries will be about half what it was in 1860.
As has been noted for large numbers of land-based species of plants and animals, the habitable ranges of many fish species will shift poleward as climate warms. At high latitudes, where warming tends to be greatest, those shifts will be dramatic, says William Cheung, a marine ecologist at the University of East Anglia in Norwich, England. For example, in the North Sea and the Arctic Ocean north of Scandinavia, ranges will shift northward, on average, more than 40 kilometers per decade between now and 2050, he reports. Such shifts could have a dramatic influence on fishing grounds, causing local extinctions of species along the southern fringes of some fisheries, for example.
Cheung also noted that warmer seas will cause the size of adult cod to decline about 10 percent by 2050. If the potential effects of ocean acidification and decreases in dissolved oxygen content are included, body size could drop as much as 40 percent. Altogether, effects of climate change could trim yields from fisheries in tropical latitudes and many areas of the Southern Ocean in half by 2055.
Although yields from Arctic fisheries will increase in coming years, those in other areas will drop off woefully. Due to changes in ocean chemistry and declines in fish body size, more than 70 percent of fishing nations will see declines in the tonnage of fish netted. As a result, about 60 percent of those countries will see declines in the profitability of their fisheries, says Vicky Lam, a fisheries economist at the University of British Columbia in Vancouver. In some cases, countries will see declines in profitability of as much as 40 percent.