As I write this, the world's foremost climatologists, ecologists and earth scientists are meeting in Berlin to decide whether or not the 'Anthropocene' should become an actual epoch. Originally conceived by Eugene F. Stoermer in the 1980s, the specifics of this anthropocentric period are highly contested. William Ruddiman, who will be making his case at UCL this coming Tuesday, asserts that humans have impacted the environment for thousands of years longer than the couple of hundred years since the industrial revolution usually cited as the Anthropocene. Regardless of the timescale, one thing is certain - present environmental conditions are such that human agency is an increasingly important factor and we are already beginning to see the effects of anthropogenic climate change.
A report by the International Fund for Agricultural Development (IFAD) identifies temperature as one of the climate change impacts on fisheries. Fish and most marine non-mammals are poikilotherms - they have no internal mechanism for heat regulation and are reliant on their surrounding environment to maintain an optimal body temperature. Therefore as climate change proceeds to increase ocean temperatures, fish and other organisms will migrate north to cooler waters in order to secure their optimal temperatures. An analysis of 50 fish species in UK and Irish waters found that 70% responded to increasing temperatures by changing their distribution, with an increase in typically warm-water species and a marked decline in colder-water species. In this scenario there will be winners and losers with fish migrating to higher latitudes, providing a larger marine stock. By contrast, tropical and warmer latitudes will experience a decline potentially threatening the livelihood of some of the poorest coastal communities.
Rising sea surface temperatures also poses a threat to marine habitats, which in turn disturbs fish ecosystems. Coral reefs provide a habitat for a variety of fish species, particularly in the vital juvenile stage of the life cycle. However, as temperatures rise they become increasingly susceptible to the process of coral bleaching and fish species are severely limited in their choice of spawning ground. On top of the pressures of temperature rise, coral reefs are vulnerable to the threat of ocean acidification, which will be discussed in the next post.
Really interesting post, Marko. There are two things that interest me, that I'm sure you'll touch upon in the future. Firstly, I'd be interested to know whether the areas projected to see the highest rises in water temperature are anywhere in or near the vicinity of the largest fish stocks in the world. I'd also be interested to know whether you think the increase in global sea temperatures as a whole, or more specific localised extremes will have a greater effect on fish populations.
ReplyDeleteHi Ali! I'll try to answer your questions the best I can. The problem with trying to forecast changes in fisheries, and therefore adapt or mitigate, is that over 80% of global marine fisheries are not formally assessed (Costello et al. 2012). This is clearly an impediment in the conservation of fisheries and is one of the first things that needs to be fixed.
DeleteThat said, we know how important coral reefs are in providing spawning grounds, habitats and food sources for species that comprise part of the global catch. According to SST change records from 1901 to 2012 by the EPA, some of the areas that experienced the greatest rises corresponded to areas with extensive coral reef habitats. These include the Indian Ocean, areas off the coast of East Africa, Australia's Great Barrier Reef and parts of the Pacific off the coast of China, Japan and South East Asia. Modelling by Xie et al. 2009 suggests that these areas will also see greater rises in SST as CO2 increases in the future. These factors, coupled with existing resource exploitation by multinationals, suggests that reef stocks and the local fisheries they support will be among the worst affected. Hope that was helpful!