The number of collapsed stocks—those with less than 10% of their original biomass—is likely to be 85% higher than previously estimated, according to the research.
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A new study has revealed that fish stocks around the world may be in worse condition than previously thought, due to overly optimistic stock assessments.
The research, conducted by Australian scientists and published this month in Science, highlights that scientific recommendations for catch limits have often been set too high, contributing to the ongoing crisis of overfishing and stock collapses.
In the European Union (EU), fisheries management relies heavily on catch limits, or quotas, which are set by the European Council of Agriculture Ministers based on scientific advice. However, the study by Edgar et al. shows that even these scientifically advised quotas have been overestimated, leading to inadequate protection for fish stocks.
Two of the world’s leading fisheries experts, Dr. Rainer Froese from the GEOMAR Helmholtz Centre for Ocean Research Kiel and Dr. Daniel Pauly from the University of British Columbia, provided their insights on the study’s findings in a Perspective Paper published in Science on 22 August, calling the data "troubling".
They advocate for simpler, more realistic models based on ecological principles, and they urge the use of more conservative stock assessments, particularly when uncertainties are present.
The study analyzed data from 230 fish stocks globally and found that assessments often exaggerated the abundance of fish and underestimated the time needed for stocks to recover.
This issue is particularly severe for stocks already depleted by overfishing, where overestimates led to "phantom recoveries," where stocks were mistakenly classified as recovered while they continued to decline.
"This resulted in insufficient reductions in catch limits when they were most urgently needed," explained Froese in a press release. He further noted that this problem persists, as known overestimates in recent years have not been corrected in current stock assessments.
The study also revealed that nearly a third of the stocks classified by the Food and Agriculture Organization (FAO) as “maximally sustainably fished” have actually crossed into the “overfished” category. Additionally, the number of collapsed stocks—those with less than 10% of their original biomass—is likely an astonishing 85% higher than previously estimated.
Froese and Pauly attribute these distortions to the complexity of standard stock assessments, which often involve over 40 different parameters, including fish life history, catch details, and fishing effort. This complexity can lead to unreliable results, as many required input parameters are unknown or difficult to estimate. This forces modelers to rely on less reliable values, skewing results towards expected outcomes, the scientists said.
To address these issues, Froese and Pauly call for a revision of current stock assessment models, advocating for simpler, more ecologically grounded approaches. They also emphasize the importance of the precautionary principle, suggesting that conservative estimates should be used when there is uncertainty to better protect fish stocks.
“The principles of ecosystem-based sustainable fishing are straightforward and not difficult,” Froese and Pauly state:
“Take out less than is regrown; let fish grow and reproduce before capture; use fishing gear with low impact on the environment and on other species; provide refuge or no-take areas as reservoirs of genetic diversity; and maintain functional food webs by reduced fishing of forage species, such as anchovies, sardines, herring, or krill.”
