Claim: Global Warming is Reducing Fish Numbers

Guest essay by Eric Worrall

According to climate models fish numbers dropped substantially between 1930 and 2010.

Climate Change Shrinks Many Fisheries Globally, Rutgers-Led Study Finds

Climate change has taken a toll on many of the world’s fisheries, and overfishing has magnified the problem, according to a Rutgers-led study in the journal Science today.

Ocean warming led to an estimated 4.1 percent drop in sustainable catches, on average, for many species of fish and shellfish from 1930 to 2010. In five regions of the world, including the East China Sea and North Sea, the estimated decline was 15 percent to 35 percent, the study says.

“We recommend that fisheries managers eliminate overfishing, rebuild fisheries and account for climate change in fisheries management decisions,” said Chris Free, who led the research while earning a doctorate at Rutgers and is now a post-doctoral scientist at the University of California, Santa Barbara. “Policymakers can prepare for regional disparities in fish catches by establishing trade agreements and partnerships to share seafood between winning and losing regions.”

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“We were stunned to find that fisheries around the world have already responded to ocean warming,” said Malin Pinsky, study co-author and associate professor in Rutgers’ Department of Ecology, Evolution, and Natural Resources. “These aren’t hypothetical changes sometime in the future.”

The study reports that the effects of ocean warming have been negative for many species, but also finds that other species have benefited from warming waters.

“Fish populations can only tolerate so much warming, though,” said senior author Olaf Jensen, an associate professor in Rutgers’ Department of Marine and Coastal Sciences. “Many of the species that have benefited from warming so far are likely to start declining as temperatures continue to rise.”

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Read more: https://news.rutgers.edu/climate-change-shrinks-many-fisheries-globally-rutgers-led-study-finds/20190221

The abstract of the study;

Impacts of historical warming on marine fisheries production

Christopher M. Free, James T. Thorson, Malin L. Pinsky, Kiva L. Oken, John Wiedenmann, Olaf P. Jensen

Science 01 Mar 2019:
Vol. 363, Issue 6430, pp. 979-983
DOI: 10.1126/science.aau1758

Climate change is altering habitats for marine fishes and invertebrates, but the net effect of these changes on potential food production is unknown. We used temperature-dependent population models to measure the influence of warming on the productivity of 235 populations of 124 species in 38 ecoregions. Some populations responded significantly positively (n = 9 populations) and others responded significantly negatively (n = 19 populations) to warming, with the direction and magnitude of the response explained by ecoregion, taxonomy, life history, and exploitation history. Hindcasts indicate that the maximum sustainable yield of the evaluated populations decreased by 4.1% from 1930 to 2010, with five ecoregions experiencing losses of 15 to 35%. Outcomes of fisheries management—including long-term food provisioning—will be improved by accounting for changing productivity in a warmer ocean.

Read more (paywalled): http://science.sciencemag.org/content/363/6430/979

I think it is remarkable how scientists can eliminate the uncertainty of sketchy historical data, and the complexities of international fisheries management, major wars, and geographic differences between regions by plugging a few numbers into a climate model.