Fish stocks fluctuate with seawater temperature

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Year-to-year fluctuations in seawater temperature are partly responsible for the much slower ups and downs in the abundance of marine fish stocks. This is the conclusion of a global study conducted by Wageningen University & Research, among others. Fish biologists have observed slow fluctuations in fish stocks for centuries, but the causes have remained largely unclear. This study shows that decades-scale fluctuations are naturally present in fish populations due to their sensitivity to water temperature.

The reaction of a fish population to temperature depends on the lifespan of the species and its position in the food chain. For ephemeral fish that feed on plankton, a climatically favorable year quickly leads to population growth. This effect is considerably slower in long-lived predatory fish.

Climate change

The results can provide insight into the effects of climate change on marine fish populations. Climate change will lead not only to a gradual increase in seawater temperature, but also to greater year-to-year fluctuations in fish populations. The researchers therefore also carried out simulations using climate change scenarios. Peter van der Sleen, a researcher at Wageningen University & Research, who led the study, says that “the simulations do not raise hope: climate change may lead to greater fluctuations in fish stocks, with consequences on the functioning of marine ecosystems and fisheries”.

Herringbone annual rings

The basis of this study is formed by research on growth rings in fish. Van der Sleen says, “It may sound strange, the growth rings of fish, but fish, just like trees, also form growth rings. They do this in their “otolith,” a bone-like structure analogous to our ear bones. A good year for a fish leads to a wide ring; a bad year to a narrow one. Based on tree ring data, the researchers established the links between seawater temperature and fish growth. “We used methods similar to those used to measure tree growth rings,” says Van der Sleen. “It was a revelation to discover how sensitive fish growth is to temperature fluctuations. For some of the fish species studied, otolith growth patterns over life matched climatic patterns almost perfectly.

This, however, did not explain the slow fluctuations of fish populations: “What an individual fish does, in terms of growth, is not necessarily the same as the growth of a population as a whole. Much theoretical research has been conducted on the effect of demographic factors (such as the lifespan of species) on variations in population density. We combined this information with our results on fish otoliths. »

The researchers’ next step was to extend the growth of individual fish to that of populations. Van der Sleen explains that “lack of data on the thousands of species of marine fish that we wanted to study, we built simple mathematical models. These simulate the effect of year-to-year temperature fluctuations on fish populations, based on estimated lifespan and its position in the food chain. We were surprised to see that the slow fluctuations in fish stocks we simulated corresponded very well to the variation in observed fish stocks.

The research has been published in Communications Biology.

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More information:

Peter van der Sleen et al, Interannual temperature variability is a major driver of low-frequency fluctuations in marine fish populations, Communications Biology (2022). DOI: 10.1038/s42003-021-02960-y

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Wageningen University

Fish stocks fluctuate with seawater temperature (2022, January 17)
retrieved 17 January 2022

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