A latest examine disputes the concept that international warming will shrink water-breathing animals like fish, discovering as a substitute that heat water air pollution creates bigger, however youthful fish resulting from elevated progress and dying charges. The analysis, which in contrast populations of Eurasian perch in waters heated by a nuclear energy plant to these in a reference space, calls into query generalized local weather change predictions and emphasizes the necessity for large-scale, semi-controlled experiments in pure settings.
A singular 24-year examine on freshwater fish subjected to heat water air pollution reveals alterations in progress and mortality charges, together with dimension modifications, nonetheless, the outcomes don’t utterly conform to preliminary predictions.
A brand new examine not too long ago printed within the journal eLife challenges the idea that aquatic creatures like fish will diminish in dimension resulting from international warming.
The analysis indicated that whereas hotter water pollution raised each the expansion and mortality charges, the end result was a inhabitants of youthful, albeit bigger fish. This discovery partially contradicts the overall predictions concerning the affect of worldwide warming on pure ecosystems, underscoring the necessity for these hypotheses to bear rigorous, large-scale experimental validation.
As aquatic ecosystems grow to be hotter, it’s predicted that animals corresponding to fish will develop quicker at a younger age however attain smaller physique sizes as adults. This sample has primarily been noticed in small-scale experiments, and though some research have examined this prediction in pure environments, these have largely been carried out on fish species subjected to fishing, where the process of fishing itself can influence growth rates and body size.
“Studies into the effects of warming waters on fish from large-scale, semi-controlled experiments in natural settings are rare, yet they can provide unique insights,” says lead author Max Lindmark, researcher at the Swedish University of Agricultural Sciences, Department of Aquatic Resources, Lysekil, Sweden. “We used a unique study system to investigate how warm water pollution has changed the death rates, growth rates, and size of fish over many generations.”
Image showing the Eurasian perch (Perca fluviatilis). Credit: Karel Jakubec
The team carried out their study in an enclosed coastal bay that has received cooling water from a nuclear power plant, making it 5–10°C warmer than the surrounding waters. They compared the fish species Eurasian perch from the enclosed bay and from a reference area in the adjacent archipelago over a 24-year time period. They combined data on catches with measurements of the fishes’ length-at-age (back-calculated throughout their life from “age rings” in hard structures), and then analyzed these using statistical models to investigate how the warm water pollution affected the age and size of the fish populations, as well as their growth and death rates.
While the researchers found statistically notable differences in estimated growth rates, death rates, and sizes of the fish populations between the heated and reference areas, not all of these changes were as they expected. Although female perch in the warm area grew faster, as the team anticipated, they continued to do so throughout life.
These fish, therefore, reached a large size-at-age – approximately 7–11% larger in the heated area at any age, when compared with the reference area. Moreover, the authors say the increase in the growth rate of younger fish due to warm water was so pronounced that even if death rates were higher because of warming, and resulted in a younger overall population of fish, the average size and relative abundance of larger fish was still higher in the heated area. This trend conflicts with the prediction that global warming would shrink fish over time, especially the large and old ones. In essence, ecosystem warming instead led to younger, but larger fish in this study.
“Our study provides strong evidence for warming-induced differences in growth and death rates among a natural population of an unexploited temperate fish species exposed to 5–10°C water temperature increases for more than two decades. These effects largely, but not completely, counteract each other – while the fish are younger, they are also larger on average,” says co-author Malin Karlsson, Water Manager at the Department of Nature and Environment, County Administrative Board of Västmanland, Sweden.
“These findings highlight that generalized predictions based on theories such as the temperature-size rule may have limited use for predicting changes at a population level and that both death rates and growth rates are important when studying temperature effects,” concludes senior author Anna Gårdmark, Professor at the Swedish University of Agricultural Sciences, Department of Aquatic Resources, Uppsala, Sweden.
“Although we only studied a single species, this unique climate change experiment suggests the effects of heating at the scale of a whole ecosystem, making its findings highly relevant in the context of global warming.”
Reference: “Larger but younger fish when growth outpaces mortality in heated ecosystem” by Max Lindmark, Malin Karlsson and Anna Gårdmark, 9 May 2023, eLife.
DOI: 10.7554/eLife.82996
