Coastal fisheries appear resilient to marine heat waves

Photo: Pexels/Peter Simmons

The global fisheries industry feeds billions of people and so fears of stocks running lower and lower as a result of overfishing and climate change are adding to concerns over long-term food security.

According to new research, however, we can be somewhat optimistic because fish stocks in coastal regions seem to be copying well with warming marine temperatures.

A team of scientists have found this after assessing the effects of climate change on commercially important fish such as flounder, pollock and rockfish based on data from long-running scientific trawl surveys of continental shelf ecosystems in North America and Europe between 1993 and 2019.

Their analysis included 248 marine heat waves during which extreme temperatures affected shallow coastal marine ecosystems.

To their surprise, the researchers found that “marine heat waves in general don’t show major adverse effects on regional fish communities,” as they put it, despite some declines in biomass during these periods. This sounds like good news, the scientists say.

“There is an emerging sense that the oceans do have some resilience, and while they are changing in response to climate change, we don’t see evidence that marine heat waves are wiping out fisheries,” explains Alexa Fredston, lead author of the study who is a postdoctoral associate in the Global Change Research Group at the Rutgers School of Environmental and Biological Sciences.

Marine heat waves do not seem to have marked impacts beyond natural variability in these ecosystems, according to the researchers.

“The oceans are highly variable, and fish populations vary quite a lot,” says Fredston, an assistant professor of ocean sciences at University of California, Santa Cruz. “Marine heat waves can drive local change, but there have been hundreds of marine heat waves with no lasting impacts.”

Another question was whether marine heat waves caused changes in the variety of fish species in coastal fish communities because during heat spells species preferring cold water migrate away while those more preferring warm water increase in number in a phenomenon known as tropicalization.

The findings suggest fish preferring cooler water can find safe havens during marine heat waves and return once temperatures cool down.

However, the data did include exceptions. Some marine heat waves had greater impacts such as the 2014-2016 one in the Northeast Pacific known as “the Blob,” one of the largest on record. This event led to a 22% loss of biomass in the Gulf of Alaska. Meanwhile, however, a marine heat wave in 2012 in the Northwest Atlantic led to a 70% gain in biomass.

Nonetheless, these weren’t large changes compared to natural variability in biomass and similar effects weren’t seen after most other marine heat waves, the scientists explain.

“We found that these negative impacts are unpredictable and that other heat waves had no strong impacts,” notes Malin Pinsky, an associate professor in the Department of Ecology, Evolution and Natural Resources at Rudgers. “This means that each heat wave that hits is like rolling the dice: Will it be a bad one or not? We don’t know until it happens.”