Fishing may be less sustainable than believed

Fishery assessment models, which form the “backbone” of fisheries management, overestimate the sustainability of fisheries globally. This is the devastating conclusion reached by a new study.

The study was carried out by a team led by Graham Edgar of the University of Tasmania in Australia.

According to this study, which analysed 230 fisheries worldwide, fishery assessment models overestimate the sustainability of fisheries worldwide and populations of many overexploited species are in much worse condition than reported. These findings underline the need for much more cautious fisheries management strategies.

To ensure the sustainability of fisheries, managed catch limits must not exceed the productive capacity of fish stocks. They must also allow for the recovery of depleted stocks.

Fisheries management relies on complex stock assessment models that integrate extensive data related to fish biology, catch history, and management controls. These models, which may involve many different parameters, are prone to overfitting, which increases uncertainties in their estimates.

While simpler methods are often validated against these complex models, the actual accuracy of the models remains uncertain, since actual fish biomass is difficult to assess and rarely observed directly.

Therefore, global fisheries assessments, such as those conducted by the Food and Agriculture Organization of the United Nations (FAO), which is the international organization charged with assessing and ensuring the sustainability of fisheries, may be biased by model estimates that obscure the true decline of stocks.

Part of a school of sardines or herring. (Photo: Anthony R. Picciolo/NOAA/NODC)

To assess the accuracy of stock biomass estimates, Graham Edgar and his colleagues analyzed publicly available data on 230 of the world’s largest fisheries.

Edgar and colleagues compared stock sizes reported to fishery managers at the time of historical assessments with updated hindcast model estimates for the same year, using the most recent and complete data available.

The findings revealed significant biases in estimates of stock biomass, especially in overexploited stocks. Initial assessments often overestimated stock sizes, leading to underestimations of the severity of their depletion.

According to the study’s authors, probably 85% more stocks than currently recognized have fallen below 10% of their maximum historical biomass.

The study is titled “Stock assessment models overstate sustainability of the world’s fisheries.” It has been published in the academic journal Science. (Source: AAAS)