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Global study reveals how extreme marine heat, very low primary productivity, especially when they occur together or in sequence — are associated with sharply higher odds of very low fisheries catches.

A global analysis by researchers at The University of British Columbia (UBC) and the University of Bern has found that extreme ocean temperatures and unusually low primary productivity can combine to substantially increase the risk of very low fisheries catches .

Image by Michelle Maria from Pixabay

Examining conditions between 1991 and 2019, the researchers found some of the greatest effects in tropical regions, small-island nations, and communities dependent on seafood for food and livelihoods. Primary productivity is an indicator of the amount of energy entering the marine food web. When unusually high temperatures coincide with—or are followed by—extremely low productivity, fish and shellfish may face multiple environmental pressures at once.

“Our findings show why fisheries managers need to consider more than temperature alone ,” said Dr. William Cheung, lead author and professor in UBC’s Institute for the Oceans and Fisheries. “Understanding how different extremes interact will be essential for anticipating risks to fisheries and the communities that depend on them.”

The danger of compound extremes

Image by Stephanie from Pixabay

Globally, two consecutive years of extreme high ocean temperature increased the odds of an extreme low catch by about 40 per cent. The odds approximately doubled when extreme heat in the previous year was combined with extremely low productivity, compared with non-extreme conditions.

Co-author Thomas Frölicher, professor at the University of Bern, said that, “the frequency and intensity of temperature extremes and their compound events with other extremes are increasing under climate change. This is why looking at sequences and combinations of extremes is so important for assessing marine climate risks and informing adaptations.”

Risks are global but not evenly distributed

The risks identified in the study are not evenly distributed around the world.

Strong relationships between extreme heat and low catches appeared in the Humboldt and California Current systems, the tropical eastern Pacific, and several tropical and small-island regions. Low-productivity extremes produced a somewhat different pattern, affecting parts of the Arctic, North Sea, Caribbean, western Arabian Sea and South Pacific.

Peru’s anchoveta fishery provides a stark example

Anchovies. Image by Engin Akyurt/Pixabay

One of the strongest examples in the study comes from Peru. In Peru’s anchoveta fishery, prolonged high-temperature anomalies were associated with more than nine times the odds of an extreme low catch. Median catches during these events were approximately 60 per cent lower than under non-extreme conditions.

“Prolonged high-temperature anomalies here were associated with more than a ninefold increase in the odds of extreme low catches, accompanied by median catch declines of approximately 60 per cent,” said co-author and IOF PhD student Isabella Morgante .

Many of the regions experiencing elevated climate risks are also places where fisheries contribute substantially to food security, livelihoods and local economies. “For a fishery of enormous economic and nutritional importance, a decline of this magnitude is not simply an ecological event. It can affect processors, fishing fleets, employment, government revenues, food supply chains, and communities dependent on the fishery,” said Cheung.

Tuna can move away from the communities that depend on it

The implications are particularly significant for tropical island nations. In the Solomon Islands, medium and large pelagic fisheries experienced up to 41 times the odds of low catches during extremely low-productivity conditions. The analysis links this pattern partly to the eastward movement of tuna, including skipjack, during El Niño events.

“Fish do not necessarily disappear when ocean conditions change. They can move,” said co-author Dr. Juliano Palacios-Abrantes. “Shifts in distribution not only alter how many fish are available, but where they are available. For fishing communities, that distinction is critical because the movement of fish can change access to resources even when the species itself remains productive elsewhere.”

Sharks, small pelagics and invertebrates among the most sensitive

Sharks. Image by baechi from Pixabay

Sharks and rays, small pelagic fishes, and commercial invertebrates were among the most sensitive species across the extreme-event categories. Coral reef-associated fisheries face particular challenges because many reef species have relatively narrow thermal tolerances and depend on structurally complex habitats that can themselves be damaged by extreme warming and coral bleaching.

“Coral reefs are at risk to temperature extremes that cause bleaching and mortality. In the Maldives, reef-associated fisheries were highly sensitive to lagged temperature extremes, with odds ratios exceeding four and typical catch losses of approximately 25 per cent,” said Cheung. “In the Galápagos, shark and ray fisheries were particularly sensitive to high-temperature extremes. Warming alters the vertical and geographic distribution of species and therefore their availability to fishing fleets.”

Commercial invertebrates in the United Kingdom were particularly vulnerable when high temperatures and low productivity occurred together, highlighting how compound extremes can affect fisheries in temperate as well as tropical environments.

Adaptation will be essential

The findings indicate that fisheries management must prepare for both gradual ocean warming and increasingly frequent extreme events.
“Fisheries that depend heavily on a single species or fishing strategy may be particularly exposed ,” said Cheung. “Diversification, better monitoring and flexible management can help spread that risk.” He pointed out that some small-scale fisheries are already more diversified than highly specialized industrial fisheries.”

“Monitoring and prediction is also important,” said Frölicher. “Early information, early warning systems, and being more climate-responsive and flexible about developing temperature and productivity extremes could give fisheries managers and fishing communities time to adjust fishing strategies, harvest levels or other activities before an extreme event reaches its full impact.”

“Climate adaptation will require greater international support for vulnerable countries, particularly where scientific monitoring, forecasting and management capacity is limited,” said Palacios-Abrantes. “Some of the greatest risks occur in tropical and subtropical waters, small-island regions and fisheries that are important for food security and local economies.”

“Compound climate extremes represent a growing fisheries risk, and the burden will not be shared equally, said Cheung. “There is no single solution. Fisheries will need better monitoring, improved forecasting, flexible harvest rules, diversification, and stronger international support.”

Large fisheries declines linked to compound and extreme climate events was published in Nature Communications.

Tags: anchovies, Arctic, climate change, coral, faculty, fisheries, Galápagos, heatwaves, IOF postdoctoral fellows, IOF students, Juliano Palacios-Abrantes, Maldives, marine catches, marine invertebrates, pelagic fish, Peru, Research, sharks, Solomon Islands, William Cheung