The future of our fisheries under climate change
By Dr. William Cheung, Director of Science and Associate Professor
Nippon Foundation–UBC Nereus Program
Institute for the Oceans and Fisheries
The University of British Columbia
The oceans, through marine fisheries, provide important ecosystem services to our society in terms of income, jobs, food, and cultural value. However, the future sustainability of these services is uncertain because of climate change, which is altering ocean conditions. The ocean is getting warmer, more acidic, and less oxygenated. Sea surface temperature is increasing at a rate of 0.12 degrees Celsius per decade, and pH has decreased by 0.1 unit since the 1950s . Changing ocean conditions redistribute fish stocks, reduce fisheries catches, and challenge fisheries management, thus affecting biodiversity and human security. We can still solve these problems, but swift actions to mitigate and adapt to climate change are needed.
Fisheries respond to a changing ocean
Marine organisms’ biological performance, particularly that of fish and invertebrates, is sensitive to changing ocean conditions. Marine organisms perform optimally within a specific range of water temperatures. When waters become too hot or cold, performance (such as growth and reproduction) decreases, and ultimately mortality increases. Temperature changes also affect the ocean’s primary productivity, the ultimate source of energy to fuel most marine food webs, with observed and projected decreases in large areas of the ocean.
Fish stocks respond to climate change partly through distributional shifts. Range shifts of marine fishes and invertebrates have been most common toward higher latitudes and deeper waters, in general following temperature velocity at rates of tens to hundreds of kilometers per decade . Areas where environmental conditions exceed species’ biological limits thus see decreases in abundance, or local extinction in severe cases.
Computer simulation models that analyze all exploited fishes and invertebrates in the world suggest that the rate of range shifts of these marine species would be 65 percent higher under the high-emission scenario relative to the strong carbon mitigation scenario . An intense rate of local extinctions is projected in tropical oceans. In some areas, such as the Indo-Pacific, more than 30 percent of the species may become locally extinct by 2050 because temperature, oxygen, and other conditions will exceed levels that these species have experienced in past centuries . In contrast, the Arctic may see an increase in species richness because of warming, loss of sea ice, and an increase in primary production. However, the Arctic is also a hotspot of ocean acidification, adding uncertainty to the future of polar biodiversity .
Climate change-induced impacts on marine fish stocks are already affecting capture fisheries. From 1970 to 2006, subtropical and higher latitude regions have seen increased catches of warmer water species, while equatorial waters have seen a decrease in the catch of subtropical species . Recruitments of many fish stocks globally have decreased during this period, which is partly attributed to ocean warming .
Challenges to fisheries management and food security
Global fisheries will be substantially impacted by climate change under the business as usual scenario. Recent studies project that global fisheries catch will decrease by 3 million tonnes per degree Celsius of atmospheric surface warming . Concurrently, fisheries will be challenged by changes in species composition through species turnover (species gains and local extinctions because of distribution shifts). As a result, fisheries are projected to lose around US $10 billion in revenue per year globally if greenhouse gas emissions are not mitigated .
Moreover, hundreds of millions of people who previously relied on consuming fish to meet their nutritional needs may face malnutrition . Tropical developing countries (e.g., the Indo-Pacific and West Africa) are especially vulnerable. Impacts there will be severe since these populations are highly dependent on fish for food and livelihoods, and they are relatively less equipped to deal with these impacts. In addition, the Arctic is projected to be highly vulnerable due to a rapid rate of warming and loss of sea ice that causes a high rate of species invasion, while intensive acidification makes impacts on future fisheries in the region still more uncertain.
Climate change-related impacts on fish stocks are challenging fisheries management by disturbing trans-boundary stocks management, reducing accuracy of scientific management advice, reducing effectiveness of management strategies, and enhancing conditions for using illegal fishing methods.
In addition, shifts in stocks are leading to disputes about quota sharing between countries, as seen in the case of Atlantic mackerel fisheries. In the 2000s, thanks in part to the warming North Atlantic, the distribution of Atlantic mackerel shifted poleward, causing greater abundance of Atlantic mackerel in Iceland and the Faroe Islands . In 2010, these two jurisdictions unilaterally increased their catch quota from a total of 27,000 tonnes to 280,000 tonnes per year. This led to a major dispute in the sharing of quota between countries fishing this species in Europe and destabilized the co-management of the species, to the extent that the Marine Stewardship Council withheld its certification of Atlantic mackerel fisheries as sustainable.
The case of cod in the Gulf of Maine is another example of how rapidly warming waters have complicated fisheries management. Waters in the Gulf of Maine — which is at the southern boundary of Atlantic cod distribution — have warmed in the last decade at a rate faster than 99 percent of the global ocean . Empirical evidence suggests that increased water temperatures have reduced recruitment and increased mortality in the region’s Atlantic cod stock, linking cod collapse directly to the rapid warming of ocean waters . Over the past decade, fisheries managers have restricted cod harvesting in the Gulf of Maine, yet even these strict quota limits could not reverse quickly declining cod stocks.
Shift in species distribution may also result in an increase in spatial overlap between targeted and bycatch species, potentially increasing bycatch and discards in fisheries. In developing countries that lack alternative livelihoods, the loss of fisheries catch potential may promote the use of destructive, often illegal, fishing methods, leading to ecosystem damage and loss of biodiversity .
Better communication of scientific knowledge about climate change and fisheries would also facilitate adaptation to potential changes and impacts.
The way forward
Solutions to this grand challenge are still available and within reach. The world has set the goal to limit global warming to 1.5 degrees Celsius above preindustrial levels through the Paris Agreement. Achieving this goal would largely reduce the impacts of climate change on global fisheries to a level that fishers, business, and managers can adapt to.
Adaptation includes protecting and restoring ecosystems, fish stocks, and habitats; reducing fishing capacity and pollution; diversifying livelihoods; and promoting social security and better communication of information about future changes. Ecosystems that are well protected from human stressors are less sensitive to ocean warming, particularly in the case of biogenic habitats such as kelp and corals. Maintaining a diversity of fish populations also helps species to adapt to climate change. Fishers with varied livelihood options could be less dependent on resources that may dwindle under climate change. Better communication of scientific knowledge about climate change and fisheries would also facilitate adaptation to potential changes and impacts.
We are now at a crossroads for seafood sustainability. We are changing our oceans in unprecedented ways. Good science and collaborative efforts to develop and support solutions are necessary to ensure a future of sustainable fisheries.
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