Global Warming and Overfishing Among Suspected Culprits in Fish Size Decline

by Ella

A recent study has shed light on a concerning trend among various fish species, indicating that some are experiencing significant reductions in size. However, researchers are cautious about attributing this phenomenon solely to one factor, as overfishing, global warming, and food availability all emerge as potential drivers.

Conducted by an international consortium of scientists hailing from 17 universities, the research initiative received support from the German Centre for Integrative Biodiversity Research (iDiv) and was spearheaded by experts from the University of St Andrews’ Centre and the University of Nottingham. The findings, published in the journal *Science*, encompassed data spanning the past six decades, involving a diverse array of animals and plants.


While the trend of size reduction was most pronounced among fish, it manifested differently within other groups of organisms, including plants and invertebrates, where shifts in size were more diverse. The study’s comprehensive approach revealed a complex tapestry of changes occurring across species, with some growing larger while others shrink.


Maria Dornelas, senior author of the study and a professor at the University of St. Andrews, commented on the findings, stating, “We think this suggests that when large organisms disappear, other ones attempt to fill their ecological niches and capitalize on the newly available resources. Recognizing and delving into this complexity is crucial if we are to unravel the mechanisms underpinning changes in body size over time.”


Prior research had already noted a decrease in the size of trophy fish in fishing competitions, primarily affecting larger species. The current study further highlighted the reduction in body size as a result of both individual shrinkage within species and the replacement of larger species by smaller counterparts.


“In some regions, we’re witnessing a decrease in the size of thorny skate individuals while smaller-bodied species like mackerel are becoming more abundant,” remarked Inês Martins, the lead author from the University of St. Andrews. “Whether this is influenced by human dietary preferences or warming habitats, large fish are facing considerable challenges.”

The study also unveiled an intriguing trend, with a few large organisms being replaced by numerous smaller ones, while the overall biomass of species within a particular habitat remains constant. This unexpected outcome suggests that ecosystems tend to adapt to change by balancing reductions in body size with concurrent increases in population density.

Researchers are continuing to investigate the factors contributing to these fluctuations in body sizes, with some species experiencing growth exceeding 10 percent. They have proposed that these changes may be linked to the effects of global warming and overconsumption, both characteristic features of the Anthropocene era, which describes humanity’s substantial impact on the planet during the current geological epoch.

Maria Dornelas emphasized the broader implications of the study’s findings, stating, “It’s evident that the widespread replacement of species occurring globally has measurable consequences. Shrinking organisms have significant effects because the size of animals influences their role in ecosystem functioning and their contribution to human sustenance. Larger fish typically have the capacity to feed more people than their smaller counterparts.”



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