Fish will migrate as temperatures warm, putting fisheries at risk

Morley et al. 2018, a paper published May 16, 2018 in PLOS one (open access) projects how warming ocean temperatures will affect the geographic distribution of 686 commercially important species around North America. We already know that species across the globe are migrating due to climate change: organisms that require cooler environments are moving towards the poles while species that tolerate warmer conditions find themselves with more space to live.

Species migration and shifting home ranges have serious implications for natural resource management, particularly fisheries. Fishing boats may have to travel further to find fish, using more time & fuel; fishing communities and livelihoods could be lost as fish move away; or fish in one country’s jurisdiction (EEZ), may move to another country’s. The key management issue is the uncertainty. Fishers need to know how fish will be distributed in the future to adapt to warming temperatures and preserve their income and livelihoods.

The recent study should help fishery managers, fishers, and other stakeholders prepare for the future as it contains the most comprehensive projection of fisheries migration under climate change to date. Using over a hundred thousand data points from U.S. and Canadian fishery surveys over the past 50 years, researchers examined the relationship between temperature, depth, and habitat to establish home ranges for 686 species on the North American continental shelf; then used several climate models to see how home ranges would change under different emissions scenarios (representative concentration pathways—or RCPs).

The authors mapped a few species’ projected migrations:

From Morley et al. 2018. Jack mackerel Trachurus symmetricus is in the left-most column, canary rockfish Sebastes pinniger is in the middle column, and walleye pollock Theragra chalcogramma is in the right-most column. Mean annual thermal habitat suitability during summer under RCP 8.5 is shown for twenty-year periods in the 21st century. Habitat quality is higher in areas of greater blue intensity. Gray areas indicate regions of the projection grid that are not suitable thermal habitat. White areas indicate regions not included in the projections (either land or deep water).

Understanding RCPs is important to understand most climate change research, so here’s a little explainer I used when blogging about a different climate change study examining ocean warming in MPAs:

An RCP is a scientifically backed estimate of radiative forcing (you can think of this as the amount of global warming) based on different emissions scenarios. Basically, an RCP estimates the amount of warming Earth will experience based on the amount of future emissions. It is important to note that RCPs are not climate models—they are scientifically standardized scenarios that can be used to set up models. The 4 recognized RCPs are: RCP 2.6, 4.5, 6, and 8.5.

Radiative forcing is a measure of the amount of energy trapped in the atmosphere. Greenhouse gasses have the largest forcing effect as they trap radiation (like a greenhouse!), which warms the planet.

Morley et al. model RCP 8.5, the worst-case scenario where politicians, governments and people don’t make meaningful change in the future, and RCP 2.6, the best-case scenario when the world gets its act together and drastically cuts emissions. Take a look at how different the outcomes are for fisheries:

From Morley et al. 2018. Mean direction and magnitude of fishery migration over the 21st century for seven regions of the North American shelf under (A) RCP 2.6 and (B) RCP 8.5.

What a difference! A high-emissions future will cause lots of problems for fisheries and the people that rely on them, but a low-emissions future seems much more manageable.

Morley et al. 2018 is an important paper for fishery managers and stakeholders to plan for the future, but a takeaway for anyone not involved in fisheries is that reducing emissions counts. Reducing emissions by any amount reduces corresponding ocean warming and subsequent fishery migration and the stress/suffering of people that rely on fisheries for food and livelihood.

On an individual level, the best thing you can do to reduce emissions is watch your diet. Large-scale mitigation will come from policy and institutional change that you have some input on with your vote. Register to vote here.

Max Mossler

Max Mossler

Max is an expert in environmental perception & policy. He is the managing editor at Sustainable Fisheries UW.


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