Warming oceans may be having an unexpected effect on fish

Larger animals around the world are getting smaller, most noticeably fish, with smaller species increasing in abundance.

This is thought to possibly be a result of the warming planet due to climate change, according to a new study published in the journal Science. One prime example of this phenomenon was observed in the thorny skate fish, a North Atlantic fish, which has shrunk significantly on average since 1960.

“In some locations, for example, smaller and smaller individuals of thorny skate fish are being observed, while smaller-bodied species like mackerel are increasing in abundance,” Inês Martins, lead author of the paper and macroecology researcher at the University of York, said in a statement.

The exact reason for this pattern isn’t apparent, but the researchers think that warming oceans may be a significant driver, as well as overfishing.

“Whether it’s because of what humans prefer to eat, or their habitats getting warmer, big fish just can’t seem to catch a break,” Martins said.

This pattern was observed in several of the 4,292 species involved in the study, primarily in fish, plants and invertebrates.

“For other organisms, we have less data available and we don’t really see any changes from the average [but] it is unquestionable that we are observing quite big changes in biodiversity and the type of biodiversity we find in different places,” Martins told The Guardian.

Other smaller species of fish were also seen to have increased in population. This follows the theory of an ecosystem self-regulating the amount of biomass (total mass of living creatures) constant, with larger organisms being replaced by increased numbers of smaller ones.

“We think this suggests that, when large organisms disappear, other ones try to take up their place and use up the resources that become available,” Maria Dornelas, co-author and biodiversity professor at the University of St Andrews, said. “Recognizing and exploring this complexity is imperative if we want to understand the mechanisms involved in how body size is changing through time.”

These findings are essential regarding how the Earth’s changing climate will impact species around the world, and the ripple effects that those impacts will have through ecosystems. Loss of larger fish may heavily affect the fishing industry.

“Our study highlights the importance of considering changes in species’ characteristics at both the individual level and across species if we want to understand the effects of environmental change and human influences on biodiversity globally,” co-author Franziska Schrodt, an associate professor of biodiversity and geodiversity at the University of Nottingham, said.

“Unfortunately, we currently lack data on many organisms other than fish to draw clear conclusions – future research will benefit from a greater investment in these kinds of measurements, particularly when exploring food webs and other species interactions.”

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