Researchers warn of global decline in fish growth as overfishing intensifies

Scientists have warned that overfishing and environmental stress are steadily reducing fish growth rates worldwide, with many species now growing more slowly and reaching smaller sizes than they did a century ago.

The findings come from a study conducted by researchers at Australia’s James Cook University, which analysed nearly 7,700 growth records covering 1,479 marine species between 1908 and 2021.

The researchers found a long-term decline in fish growth performance beginning around 1908, with the steepest drops recorded among species heavily targeted by commercial fisheries.

Fish growing slower, shrinking in size

Helen Yan, who led the study during her PhD programme, said human activity is reshaping marine ecosystems at a biological level, not just in population numbers.

According to her, managed fisheries have experienced an average 9% decline in growth performance over the last century, meaning fish are either growing more slowly or reaching smaller adult sizes.

“Managed fisheries experienced an average 9-per cent decline in growth performance over the last century,” she said.

The study explained that growth performance reflects the trade-off between how fast a fish grows and how large it ultimately becomes, making it a key indicator of ecosystem health.

Fishing pressure identified as the main driver

Researchers say size-based commercial fishing practices, where larger fish are preferentially removed, are the primary driver of the trend.

While climate change may intensify the effects, the study found fishing pressure itself remains the dominant factor behind shrinking fish sizes.

The impact is most visible in temperate regions, where fishing activity is highest and long-term exploitation has been more intense.

Ecosystem risks and food security concerns

Scientists warned that smaller and slower-growing fish could disrupt marine food webs, reduce overall fishery yields, and make populations harder to rebuild over time.

They stressed the need for stricter catch limits, stronger habitat protections, and long-term monitoring systems to track biological changes in fish populations.

The study adds to growing evidence that sustained human pressure on oceans is altering marine life in ways that could have long-term consequences for global food security and biodiversity.

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