Climate change is huge cause for concern to many different ecosystems, including marine fisheries. Cheung et al. (2013) delves into the effects of rising sea surface temperature (SST) on the mean temperature of the catch (MTC). MTC is an index that represents the average inferred temperature preference of a species weighed by the annual catch. Overall, the results showed that the composition of marine fisheries catch is significantly related to changes in SST. More warmer water species are being caught at higher latitudes and fewer subtropical species are being caught in the tropics. This is cause for concern as many developing costal nations rely on the maritime industry, not only environmentally, but economically and socially as well.—Neha Vaingankar
W. W. L. Cheung, R. Watson, D. Pauly, 2013, Signature of ocean warming in global fisheries catch, Nature 497, 365—368.
W.W. Cheung and his colleagues at the University of British Columbia found that the global MTC increased each decade from 1970 untill 2006, specifically in non-tropical the northeast Pacific Ocean and northeast Atlantic Ocean. Over these years, global temperature preference increased at a rate of about 0.2 °C every decade, and the effects were even more pronounced in non-tropical areas. To quantify this, Cheung et al. created large marine ecosystems (LME’s) to account for most of the world’s fisheries. Overall, 52 were used. Spacing of fisheries depends on the best possible environment for those species to live in, including biotic and abiotic factors. Distribution of some marine fisheries has changed over time due to changes in these ocean conditions. In measuring the MTC, Cheung et al. inferred the temperature preference of each species on the basis of its modeled distribution from the “Sea Around Us Project” and the Food and Agriculture Organization’s fishery database.
Cheung et al. assessed the preference of fish species in different areas by calculating the MTC. Global warming leads to catching more warm water species overall and therefore a higher MTC. Cheung et al. found that continents towards the north of the globe, like Europe, North America, and northern Asia all show a higher rate of change in SST with MTC rising at higher latitudes, meaning warm water species are being caught further north. Cheung et al.also found that MTC changes and SST changes correlate in almost every LME implying that catching warmer water species is a result of changes in ocean temperatures. Tropical marine ecosystems also correlated to the MTC, which stabilized at twenty-six degrees Celsius.
Because MTC is the main index used in figuring out the effects of climate change on marine fisheries, Cheung et al. explains why MTC works. Firstly, in the North Sea, scientists compared the change in MTC from the catch data to that of data collected from deep-sea trawlers that scrape the bottom of the ocean for fish and other marine organisms. This shows that the MTC is consistent regardless of what depths the species are coming from. Another example of why MTC is a valid proxy to examine changes in composition of catches in a region in relation to the temperature preference of the exploited animals is because an increase in fishing conservation efforts is related to the temperature preference of the exploited species. However, the positive correlation between the two was only found in about 19 LMEs, which shows that the MTC trend is not a result of the depletion of large fish by fishing. Next, in the case of misreporting of catch data, initial MTC values were not significant. However, after fixing the catch values, the MTC rates of change became significant. This sort of change in significance was not seen when different SSTs were used to calculate species’ temperature preference.
Overall, the results show that the change in composition of marine fisheries catch is significantly correlated with the temperature increases in the ocean. These changes in temperature will have a large effect on the socio-economic situation of poorer countries in the tropics, which rely on these fisheries for their income.