Changes in climate cause certain fish species to shrink, while others grow larger, according to a recent study.

In a groundbreaking study published in Nature Ecology & Evolution, researchers from Australia's Institute for Marine and Antarctic Studies have analysed the effects of climate change on fish sizes. The study, led by Asta Audzijonyte, delved into the size changes of 335 species of fish, including tiny ones, giant fish, and sharks, using data collected through a reef monitoring program that has run for three decades and a citizen science program involving 100 divers who conducted underwater surveys with a standard method.

The study investigated fish size in two main ways: comparing fish of the same species in different locations and examining how species in one location would be affected by climate change-induced warming over time. The findings suggest that climate change is causing fish to morph in size, with some shrinking and others growing.

Interestingly, the study shows the complexity of species' responses to warming in our oceans. While certain fish species, particularly those from tropical waters, have grown larger in connection with climate change, others like the Baltic cod have shown a reduction in size due to fishery-induced genetic changes. The warming oceans can alter fish size and populations, which may disrupt marine ecosystems and biodiversity.

The bigger fish tended to get bigger, and the smaller fish usually got smaller. A population of fish experiencing warming waters changed by nearly 20% for 0.5 degree [Celsius, or 0.9° Fahrenheit] of warming, observed over the last two decades. This shift in size has significant implications for the marine environment and the management of fisheries.

The implications for these size changes are not fully understood, but they would certainly have an impact on the marine food web. As fish get smaller, they're more vulnerable to predation, which could lead to higher mortality rates. The study's findings highlight the need to study the effects of these size changes on the marine ecosystem.

The study did not focus on commercially fished species, but on a wide range of fish living in Australian waters. The data was collected through a reef monitoring program that has run for three decades and a citizen science program. The changes in temperature through time, in response to climate change, had a stronger impact on fish size than changes of temperatures in space.

The study's findings suggest that there is a lot that is still not known about the temperature-size relationship in the wild. This research underscores the importance of continued monitoring and research to understand the intricate ways in which climate change affects our oceans and the life within them.

The article was originally published on Mongabay.