An investigation by the National Museum of Natural Sciences (MNCN-CSIC) and the National University of Colombia, published in Nature Ecology & Evolution, reveals that the chronic warming of the oceans is causing an annual decline of up to 20% in fish biomass.
The study analyzed more than 700,000 estimates of biomass change in 33,990 populations between 1993 and 2021 in the Mediterranean, North Atlantic, and Northeastern Pacific.
Marine heatwaves: contrasting effects
Marine heatwaves, increasingly frequent, do not affect all species equally:
- In warm waters, populations can plummet by up to 43.4% when they exceed their thermal comfort zone.
- In cold waters, some species temporarily thrive, increasing their biomass by up to 176%.
However, these increases are transitory and can lead to management errors if interpreted as sustained increases.
The risk of overexploitation
Researcher Shahar Chaikin warns that if managers increase fishing quotas based on temporary biomass increases, there is a risk of causing population collapse when temperatures return to normal or chronic warming prevails.
Researcher Juan David González Trujillo adds that, unlike short-term weather fluctuations, constant warming exerts continuous negative pressure on fish populations.
Necessary management strategies
The study proposes a three-level fisheries management framework:
- Rapid response: immediate measures in the face of extreme heatwaves to protect vulnerable populations.
- Long-term planning: structuring policies considering the sustained decline in biomass.
- International cooperation: since species cross borders seeking their ideal thermal zone, management must be coordinated among countries.
A global problem
The loss of fish biomass directly affects global food security, as millions of people rely on the oceans as their primary protein source. Moreover, the decline in fish alters the balance of marine ecosystems, affecting predators and the entire food chain.
Researcher Miguel B. Araújo emphasizes that managers must carefully balance localized increases with global declines to avoid overexploitation.
Ocean warming is a constant stress factor that threatens the resilience of fish populations. Although some species may benefit temporarily, the overall trend is a sustained decline that requires urgent international management measures. The only viable strategy is to prioritize long-term resilience, planning fisheries policies that consider an increasingly warm ocean.
