A deep dive into stock assessments of fisheries around the world has revealed their sustainability is overstated – and it has implications for fisheries management and consumer awareness.
Many fish stocks around the world are either threatened by overfishing or have already collapsed. One of the main reasons for this devastating trend is that policymakers have often ignored the catch limits calculated by scientists, which were intended to be strict thresholds to protect stocks. But it has now become clear that even these scientific recommendations were often too high. These are the findings of four Australian research institutions who have revealed that far more global fish stocks are overfished or have collapsed than thought.
In a new study published in the journal Science, a research team led by the University of Tasmania’s Institute for Marine and Antarctic Studies (IMAS) compared past and recent stock assessments across 230 fisheries worldwide.
Alongside this research, two eminent fisheries scientists, Dr Rainer Froese from the GEOMAR Helmholtz Centre for Ocean Research Kiel and Dr Daniel Pauly from the University of British Columbia have provided their insights on the study. In their Perspective Paper, also published in the journal Science to coincide with the new study, the two fisheries experts call for simpler yet more accurate models and, when in doubt, a more conservative approach to stock assessments.
Stock assessments
Stock assessments are conducted regularly to measure the impact of fishing on fish and shellfish populations in global fisheries management regions. These assessments inform approaches for preventing overfishing, rebuilding overfished stocks and protecting marine ecosystems.
“Independent scientific monitoring is essential for accurately assessing fish stock sustainability,” said IMAS marine ecologist and lead author, Professor 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.”
The study showed an inconsistency in stock assessments, with a strong pattern of over-estimating a fishery’s population status for stocks that were most depleted. 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 on the basis of scientific advice and recommendations from the European Commission. The study by Edgar et al. shows that already the scientific advice has been recommending catch limits that were too high.
The research by Edgar et al. also shows that almost a third of stocks classified by the Food and Agriculture Organization (FAO) as “maximally sustainably fished” have instead crossed the threshold into the “overfished” category. Moreover, the number of collapsed stocks (those with less than ten per cent of their original biomass) within the overfished category is likely to be 85 per cent higher than previously estimated.
The study highlights ways to improve the accuracy of fish stock assessments, such as expanding independent fisheries monitoring and changing 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,” Professor Edgar said.
Photo: Nicolas Job / Ocean Image Bank
What to do about it?
“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,” Professor Edgar said.
The journal Science, where the study is published, asked two of the world’s most cited fisheries experts, Dr Rainer Froese and Dr Daniel Pauly, to interpret the findings. In their Perspective Paper, they advocate for simpler, yet more realistic models based on ecological principles, and call for more conservative stock assessments and management when uncertainties arise.
Dr Froese and Dr Pauly call for a revision of current stock assessment models. They advocate simpler, more realistic models based on ecological principles. They also call for greater use of the precautionary principle: when in doubt, conservative estimates should be used to protect stocks. “In essence, sustainable fishing is simple,” says Dr Rainer Froese. “Less fish biomass should be taken than is regrown.” Fish must be allowed to reproduce before they are caught, environmentally friendly fishing gear must be used and protected zones must be established. The functioning of important food chains must be preserved by reducing catches of forage fish such as anchovies, sardines, krill or herring – these are the principles of ecosystem-based sustainable fishing. Froese adds: “Four of these five principles can be implemented even without knowledge of stock sizes.”
Further information:
The research paper by Edgar et al., ‘Stock assessment models overstate sustainability of the world’s fisheries’, is published in Science and can be read here.
The Perspectives Paper by Froese and Pauly, ‘Taking stock of global fisheries: Current stock assessment models overestimate productivity and recovery trajectory’ can be read in Science here.