Scientists warn that fish are getting smaller, why?

Scientists collected data from thousands of species on the seabed to reach one conclusion: their size is shrinking. The study, published in the journal Science, analyzed 4,292 mammals, invertebrates, fish, amphibians, reptiles and plants that live in the depths of the oceans.

The team, made up of scientists from 17 universities around the world, explained that species such as the spiny ray, a North Atlantic fish that can grow up to a meter in length, are among the animals that have become smaller. The same thing happens, and even to a greater extent, to some species of fish, plants and invertebrates.

In fact, a study published in the journal Nature said that the same thing was happening to salmon, a problem that would not only affect the ecosystem but also the fishing industry around the world.

However, species that were already small in size have grown in abundance, changing the composition and functioning of ecosystems.

But what is the reason for the bodily change?

Although the causes of the change in the body sizes of species are still being investigated by scientists, one could find a good clue in the consequences of global warming and the excessive consumption of some fish.

Dr Inês Martins, from the University of York, told The Guardian that the main finding is that not only is body size shrinking, but organisms are becoming smaller through a combination: the replacement of other species and their population changes. This means, in Martin's words, that species that were already small are replacing larger ones.

“These trends were most evident among fish, where we saw clear evidence of a reduction in body size. For other organisms, we have less data available and we don't really see any change from the average,” Martin continued, highlighting that, likewise, this represents a large alteration in global biodiversity.

Martin warned that the fact that organisms become smaller has important effects, since the size of animals influences, not only the functioning of ecosystems, but how humans benefit from them. For example, larger fish can usually feed more people than smaller ones.

Dr Franziska Schrodt, a co-author from the University of Nottingham, also told The Guardian that we currently lack data on many organisms other than fish to draw clear conclusions. Therefore, both she and Martin stressed the importance of more future research to get an idea of ​​what lies ahead in the coming years.

“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.”

Species size shrinking, affecting ecosystems

Dr. Inês Martins, the lead researcher from York University, stated, "The core finding is that the body size is not just predominantly shrinking but that organisms are becoming smaller through a combination of species replacement and changes within species populations.

Within some species, individuals are becoming smaller and smaller. And larger species are being replaced by smaller ones when they disappear. These trends were most evident among fish, where we saw clear evidence of shrinking body size. 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."

Many smaller organisms were replacing small numbers of large organisms, maintaining constant biomass, which supports the idea that ecosystems compensate for changes, the paper also noted.

Professor Dornelas emphasized, "It's clear the widespread species replacement we see around the world is having measurable consequences. Organisms becoming smaller has important effects as the size of animals mediates their contribution to how ecosystems function and how humans benefit from them. Bigger fish can usually feed more people than smaller fish."

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