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.
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.
In a new study published in the journal Science, an international research team compared past and recent stock assessments across 230 fisheries worldwide.
“Independent scientific monitoring is essential for accurately assessing fish stock sustainability,” said IMAS marine ecologist and lead author of the study, 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.
“Depleted fish stocks are often the most contentious,” Professor Edgar said. “When 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.”
IMAS researcher and co-author, Dr Nils Krueck, said stock assessment scientists around the world acknowledge the issues highlighted in the study.
“I believe it’s vital to bring these issues into focus, as it will lead to improvements in the way we do our assessments and ultimately improve fisheries management globally.”
IMAS marine ecologist and study co-author, Associate Professor Chris Brown, said the rising trends in the biomass of overfished stocks noted in some stock assessments often disappeared in later assessments, suggesting they were too optimistic about the pace of recovery in overfished stocks.
“When management put limits on catches, many overfished populations have failed to recover as quickly as expected, so our study suggests the assessments tools being used are too optimistic about the real recovery potential,” he said.
The study also found that fish stocks with low economic value, or in areas with rapidly rising sea temperatures, were more susceptible to inaccurate assessments.
“Stocks with low economic value will usually have less scientific information to inform the assessments – and this may impact the ability to accurately assess stock status,” Associate Professor Chris Brown said.
“Meanwhile, fish stocks in ocean warming hotspots are often under-estimated, as stock assessments are not well tuned to populations extending their range into cooler regions – which is happening much faster than expected.”
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.
“Our study clearly shows we need to take a much greater precautionary approach to protect our vital fish stocks around the world – for sustainable fisheries and healthy oceans, and ultimately for our own food security.”
Citation: Graham J. Edgar et al. ,Stock assessment models overstate sustainability of the world’s fisheries. Science 385,860-865 (2024).DOI:10.1126/science.adl6282
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