A marine heatwave can stress fish, shift their ranges and disrupt food webs. Low biological productivity can reduce the energy available to the same ecosystems. A global analysis shows that when those two conditions occur together, the risk of extreme fishery losses rises sharply.
Researchers analyzed thousands of fishery time series spanning more than a thousand species and hundreds of regions. Instead of treating temperature and productivity as separate pressures, they examined compound events: periods when unusually warm water coincided with unusually low primary productivity. Those combinations were associated with the most severe low-catch outcomes in many systems.
The distinction matters because climate impacts rarely arrive one at a time. Fish can sometimes tolerate a brief temperature anomaly if food remains abundant, and a temporary productivity decline may be survivable under otherwise favorable conditions. When metabolic demand rises in warm water while the base of the food web weakens, populations can face simultaneous physiological and ecological stress. Fishing fleets then encounter fewer fish, displaced stocks or both.
The effects were not uniform. Tropical and subtropical regions often face greater exposure because many species already live close to upper thermal limits, while high-latitude systems may experience different combinations of warming, productivity change and species redistribution. Target species also differ in mobility, life history and dependence on local food-web conditions. A single global average therefore cannot describe every fishery.
For management, the work argues for monitoring compound risk rather than relying on sea-surface temperature alone. Early-warning systems could combine temperature forecasts with indicators of chlorophyll, upwelling or other measures of productivity. If managers know that a stock is entering a period of high metabolic stress and weak food supply, temporary changes in catch limits or fishing effort may reduce additional pressure.
The analysis also has consequences for communities that depend on seafood for income and nutrition. Extreme catch failures can produce price shocks and economic losses far beyond the vessels that land the fish. Regions with limited ability to switch species, move fleets or import food are especially vulnerable to compound climate events.
The study does not imply that every marine heatwave will cause a fishery collapse. It shows that the context surrounding heat matters. As the ocean warms, the probability of overlapping extremes may change even where average productivity remains similar. Future fisheries planning will increasingly need to ask not only how hot the water will become, but what else is happening in the ecosystem at the same time.
