Warmer seas will limit food supply from fisheries

(Credit: Getty Images)

Climate change is beginning to disrupt the complex, interconnected systems that underpin the world’s fisheries and the food they provide, report researchers.

Fish provide a vital source of protein for over half the world’s population and more than 56 million people work for or subsist on fisheries.

For a new study in Science, researchers looked at historical abundance data for 124 species in 38 regions, which represents roughly one-third of the reported global catch. They compared the data to records of ocean temperature and found that warming negatively affected eight percent of populations and positively affected four percent.

“We were surprised how strongly fish populations around the world have already been affected by warming, and that, among the populations we studied, the climate ‘losers’ outweigh the climate ‘winners,'” says Christopher Free, a postdoctoral scholar at the University of California, Santa Barbara’s Bren School of Environmental Science & Management.

Region had the greatest influence on how fish responded to rising temperatures. Species in the same region tended to respond in similar ways. Fishes in the same families also showed similarities in how they responded to changes. The researchers reasoned that related species would have similar traits and life cycles, giving them similar strengths and vulnerabilities.

Gains and losses

When examining how the availability of fish for food has changed from 1930 to 2010, the researchers saw the greatest losses in productivity in the Sea of Japan, North Sea, Iberian Coastal, Kuroshio Current, and Celtic-Biscay Shelf ecoregions. The greatest gains occurred in the Labrador-Newfoundland region, Baltic Sea, Indian Ocean, and the Northeastern United States.

Although the changes in fisheries productivity have so far been small, vast regional discrepancies exist. For instance, East Asia has seen some of the largest warming-driven declines, with 15 to 35 percent reductions in fisheries productivity.

“This means 15 to 35 percent less fish available for food and employment in a region with some of the fastest growing human populations in the world,” Free says. Mitigating the impacts of regional disparities will pose a major challenge in the future.

One-two punch

The findings highlight the importance of accounting for the effects of climate change in fisheries management. This means coming up with new tools for assessing the size of fish populations, new strategies for setting catch limits that consider changing productivity, and new agreements for sharing catch between winning and losing regions, Free explains.

“Knowing exactly how fisheries will change under future warming is challenging, but we do know that failing to adapt to changing fisheries productivity will result in less food and fewer profits relative to today.”

Preventing overfishing will be a critical part of addressing the threat that climate change poses to the world’s fisheries. “Overfishing presents a one-two punch,” says Free. It makes fish populations more vulnerable to warming, while warming hinders the recovery of overfished populations.

Further, ocean warming is just one of many processes affecting marine life and the industries that rely on it, Free says. Ocean acidification, falling oxygen levels, and habitat loss will also impact marine life. More research is necessary to fully understand how climate change will affect fish populations and the livelihoods of people that depend on them.

Source: UC Santa Barbara