Fish stocks are collapsing globally as overfishing continues

A comprehensive analysis of global fishery stock assessments has revealed that the sustainability of many fish populations has been overstated, raising concerns about fisheries management and consumer awareness.

Around the world, numerous fish stocks are either severely threatened by overfishing or have already collapsed. A major factor contributing to this alarming trend is that policymakers have often disregarded the catch limits recommended by scientists. 

Global fish stocks are overfished 

Catch limits were intended as strict thresholds to protect fish populations. However, new findings show that even the scientific recommendations were often set too high. 

Four Australian research institutions have uncovered that a significantly greater number of global fish stocks are overfished or have collapsed than previously believed.

The study, published in the journal Science, was led by the University of Tasmania’s Institute for Marine and Antarctic Studies (IMAS). The research team compared past and recent stock assessments across 230 fisheries worldwide.

A new approach to stock assessments

To complement this research, two leading fisheries scientists, Rainer Froese from the GEOMAR Helmholtz Centre for Ocean Research Kiel and Daniel Pauly from the University of British Columbia, offered their perspectives on the findings. 

In a Perspective Paper also published in Science, these experts advocate for simpler, yet more accurate models, and suggest adopting a more conservative approach to stock assessments when there is uncertainty.

Stock assessments are regularly conducted to evaluate the impact of fishing on fish and shellfish populations within global fisheries management regions. These assessments guide efforts to prevent overfishing, rebuild depleted stocks, and protect marine ecosystems.

“Independent scientific monitoring is essential for accurately assessing fish stock sustainability,” said IMAS marine ecologist and lead author Graham Edgar.

“This study was an opportunity to compare the stock status estimated in a given year, such as 2010, with a more recent revised estimate for that same year – and we found that the earlier stock assessments were often too optimistic about the number of fish in the ocean.”

Inconsistencies in stock assessments 

The study revealed a pattern of inconsistencies in stock assessments, particularly with the most depleted fisheries. Fish stock biomass was overestimated by an average of 11.5%.

In the European Union (EU), for example, fisheries are primarily managed through allowable catch limits, known as quotas, which are set by the European Council of Agriculture Ministers based on scientific advice and recommendations from the European Commission. 

The study by Edgar and his team indicates that even the scientific advice has often recommended catch limits that were too high.

Collapsed fish stocks

The research also found that nearly a third of stocks classified by the Food and Agriculture Organization (FAO) as “maximally sustainably fished” had, in fact, crossed into the “overfished” category. 

Moreover, the number of collapsed stocks – those with less than ten percent of their original biomass – within the overfished category is likely 85 percent higher than previously estimated.

Improving fish stock assessments 

The study suggests several ways to improve the accuracy of fish stock assessments, including expanding independent fisheries monitoring and revising stock assessment protocols. 

“This could include establishing a ‘red team’ that looks at potential worst-case scenarios and works to prevent the collapse of fish biomass,” Edgar suggested.

“When an assessment finds a stock is overfished, fisheries management needs to make tough decisions about reducing fish catches to reverse the trend in stock declines. This includes reducing catch limits, which will ensure the fish stock can continue to support food and jobs into the future,” he added.

Measures to protect fish stocks 

The journal Science asked Rainer Froese and Daniel Pauly, two of the world’s most cited fisheries experts, to interpret the study’s findings. 

In their Perspective Paper, they call for the revision of current stock assessment models, advocating for simpler, more realistic models based on ecological principles. 

Taking precautions 

The experts also stress the importance of using the precautionary principle: when there is doubt, conservative estimates should be adopted to protect fish stocks.

“In essence, sustainable fishing is simple,” Froese said. “Less fish biomass should be taken than is regrown.” He emphasized that fish must be allowed to reproduce before being caught, environmentally friendly fishing gear must be used, and protected zones must be established. 

Reducing the catch of forage fish 

Additionally, it is crucial to preserve the functioning of important food chains by reducing the catch of forage fish such as anchovies, sardines, krill, or herring – principles that form the basis of ecosystem-based sustainable fishing. 

“Four of these five principles can be implemented even without knowledge of stock sizes,” Froese concluded.

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