Researchers have found new evidence that global warming is affecting the size of commercial fish species, reporting for the first time that juvenile fish are growing larger, as well as confirmation that adult fish are declining as sea temperatures rise. The results are published in the British Ecological Society Journal of Applied Ecology.
Researchers from the University of Aberdeen looked at four of the most important commercial fish species in the North Sea and west of Scotland: cod, haddock, whiting and saithe. They found that juvenile fish in the North Sea and west of Scotland have become larger while adult fish have become smaller. These changes in body size were related to rising sea temperatures in all areas.
Idongesit Ikpewe, lead author of the study, said: “Changes in both juvenile and adult size coincided with a rise in sea temperature. Importantly, we have seen this pattern in the North Sea, which warming rapidly, and the west of Scotland, which has experienced only moderate warming, and these findings indicate that even a moderate rise in sea temperature could affect body sizes. commercial fish species. “
In the short term, the decisions could lead to a decline in commercial fishing output, affecting an industry worth around £ 1.4 billion to the UK economy and one that employs more on twenty-four thousand people, according to records from the House of Commons research library.
Idongesit Ikpewe said “Our decisions have a significant and direct impact on the fisheries sector. The decline in adult body size is likely to reduce commercial fishing output. However, in the long run, the youngsters who are grows faster and more compensated, to some extent., for the final loss of yield, as although the increase in length (and, therefore, weight) per person may be small, fish are more childhood is much more numerous. It is this result that we now need to explore. “
To mitigate the effects of global warming and increase sustainable yield, the authors state that temperature changes should be incorporated into forecasts used in fisheries management.
The results are also likely to affect marine ecosystems. “Of the four species we looked at, three (cod, whistle and saithe) are fish-eating predators towards the top of the food chain so they play an important ecological role in the game. ecosystems in which they live.Because the size of a predator determines what prey they can target, changes in the body size of these fish species or predator relationships can be affected, by potential impact on the structure of the food web. ” said Idongesit Ikpewe.
The maximum extent that fish can reach is determined by the supply and demand of limited resources such as oxygen. Warmer water is usually warmer but also increases metabolic levels and hence demand for oxygen. Fish in warming waters may reach a size where they can no longer get the oxygen needed to maintain metabolic demands, thus limiting the size of an adult body.
It has been shown previously in laboratory experiments that ectotherms (animals with cold blood) develop faster at warmer temperatures but reach a smaller body size. This phenomenon, known as the ‘temperature magnitude rule’, has been observed in a number of animals, plants and bacteria. However, to date, few empirical studies have shown a link between temperature rise and faster growth in fish.
In this study the researchers examined the body size of cod, haddock, whistle and saffron at different age groups and compared trends in juvenile and adult lengths with low annual sea temperatures.
They obtained the data from Trawl Bun International Studies provided by the International Council for the Study of the Sea. This provided 30 years of independent primary fishing trawler data from 1970 to 2017 for the North Sea and 1986 to 2016 for the west of Scotland.
Although the findings provide strong empirical evidence for changes in fish size and growth rate in warming oceans, the study was limited to terrestrial species (living close to the seabed) in areas across the UK. Other species of commercial importance to the UK such as mackerel and herring were not considered in this study.
“The next step in our work is to consider the regulatory implications of shaping these numbers. “Idongesit Ikpewe said.” The idea is to work out what the size changes we have seen could mean for future fish production and production under different warming conditions “.
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