Climate Change Shrinking Global Fisheries

(CN) – Fisheries around the world are in decline as ocean temperatures rise due to climate change, according to a study published Thursday.

A bluefin tuna weighing 600 pounds is ensnared near the mouth of a fish trap at a depth of 82 feet. (Danilo Cedrone/U.N. Food & Agriculture Organization)

Sustainable catches have dropped by as much as 35 percent in some regions of the world and by an average of 4.1 percent across the globe from 1930 through 2010, according to a Rutgers-led study published in Science.

“We recommend that fisheries managers eliminate overfishing, rebuild fisheries and account for climate change in fisheries management decisions,” said Chris Free, a researcher at Rutgers who is now a 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.”

Scientists at Rutgers-New Brunswick and the U.S. National Oceanic and Atmospheric Administration studied the impact of ocean warming on 235 populations of 124 species in 38 ecological regions around the world. Species included various fish species, crustaceans like shrimp, and mollusks such as sea scallops.

Using ocean temperature maps to estimate temperature-driven changes in the sustainable catch by matching such data with population counts tracked over the 80-year period, the decline appears steady.

“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 at Rutgers. “These aren’t hypothetical changes sometime in the future.”

The steepest losses in population occurred in the Sea of Japan, Iberian Coastal, Kuroshio Current and Celtic-Biscay Shelf regions. All of these ecological regions are either adjacent or in proximity to countries where seafood is a considerable portion of the regional diet.

Seafood is an increasingly indispensable source of nourishment as the global population continues to balloon, particularly in coastal developing countries where it provides up to half the animal protein eaten.

More than 56 million people worldwide work in the fisheries industry or subsist on fisheries.

While much of the news from the study is grim, some species that prefer warmer water have benefited.

“Fish populations can only tolerate so much warming, though,” said Olaf Jensen, a professor at Rutgers and senior author of the study. “Many of the species that have benefited from warming so far are likely to start declining as temperatures continue to rise.”

Nevertheless, the study found fishery populations have spiked off the northeastern coast of the United States, where a curtailment of 19th century fishing industry practices has allowed fish to recover.

The Baltic Sea and the Indian Ocean have also witnessed a recovery and expansion of fisheries over the study period.

The scientists involved in the study touted the ability to show present-day effects of climate change, as opposed to the typical reliance on forecast models.

“Something I think is unique about this study is that we quantified effects that have already occurred to fisheries, rather than forecasting the future, which is much more fraught with uncertainty,” said co-author Kiva Oken, a scientist at the University of Washington.

The contemporary data should provide fishery managers with the data they need to make decisions and to curb overfishing, which will only exacerbate the problems presented by increasing oceanic temperatures, the study said.

Additional study will be needed, particularly of tropical regions which were left out of the present study, Free said.

Rising temperatures are only one effect of climate change on oceans, as the impact of increased acidification, declining oxygen content and the death of coral reefs will also need to be accounted for.

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