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Climate change threatens global fish stocks

Ocean warming has already affected global fisheries in the past four decades, the new study showed.

Ocean warming has already affected global fisheries in the past four decades, a new international study has found, driving up the proportion of warm-water fish being caught and posing a threat to food security worldwide.

The new study, conducted by researchers from the University of Tasmania’s specialist Institute for Marine and Antarctic Studies and the University of British Columbia and published in the journal Nature, warned that climate change adaptation plans were needed immediately.

“We have demonstrated that climate change impacts have already been operating for several decades. Many people think that climate change impacts are some futuristic and speculative thing which we can defer thinking about, but this study shows it is here and now and has already impacted global ocean life that we depend on,” said one of the study’s authors, Dr Reg Watson, Professor of Fisheries and Ecosystem Modelling and a Research Scientist at the University of Tasmania’s Institute for Marine and Antarctic Studies.

The researchers analysed data on the species of fish being caught and their preferred ocean temperature in 52 ocean ecosystems between 1970 and 2006.

They identified “an increasing dominance of catches of warmer waters species at higher latitudes and a decrease in the proportion of catches of subtropical species in the tropics.”

This graphic presents concepts from the study published in Nature. The thermometers are representative of trends in ocean temperature over time and the fish are representative of trends in catch composition over time. They do not represent specific values. Graphic by The Pew Charitable Trusts' ocean science division,

“Such changes in catch composition have direct implications for coastal fishing communities, particularly those in tropical developing countries, which tend to be socioeconomically vulnerable to the effects of climate change,” the authors warned in their paper.

“Continued warming in the tropics to a level that exceeds the thermal tolerance of tropical species may largely reduce catch potential in this region.”

Australia at risk

David Booth, Professor of Marine Ecology at the University of Technology, Sydney, said the authors of the study used the best data available on the temperature preferences of nearly 1000 fish species and changes in their catch distribution over 30 years to show a strong link with climate change increases in ocean temperature.

“In particular, tropical fisheries may lose significant numbers of species and see declining catch rates as a results of climate change temperature rises. Australia has over half of its fishing area in tropical waters and is one of the countries at risk,” said Professor Booth, who was not involved in the study.

“Much of the tropical Pacific and Indian ocean islands have subsistence fisheries that rely on fish as part of local diet and protein uptake. Climate change sea temperature rise will affect them most of all.”

The new study was one of the first on a global scale to show how climate change sea surface temperature rise will affect fish distributions, Professor Booth said.

Professor Jessica Meeuwig, Director of the University of Western Australia’s Centre for Marine Futures (Oceans Institute), said the study provided compelling evidence for the effects of climate change on fisheries catches.

“It is also an elegant use of one of the few global data sets we have for the ocean: fisheries data,” said Professor Meeuwig, who was not involved in the study.

“Recognising that the species targeted by fisheries are under pressure from climate change means that our approach to the exploitation of these species needs to be extremely conservative, erring on the side of under- rather than over-exploitation and opening new fisheries only with great caution.”

The results of this study ring a significant warning bell with respect to many Australian endemic southern fishes, including blue gropers, Professor Meeuwig said.

“These cold water species will have difficulties shifting southward as subtropical species move in given the lack of appropriate shallow water habitat off the continental shelf.”

Global problem

James Smith, Research Fellow in Fisheries at University of New South Wales said the new study “cleverly uses existing catch data to explore range shifts on a global scale.”

“This large-scale data confirms the many local and single-species studies showing range shifts in fish species,” said Dr Smith, who was also not involved in the study.

“The findings are sound, and may in fact underestimate the problem, given that it doesn’t take into account small spatial shifts in fishing effort, as fishing grounds shift to follow the shifting fish.”

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