Marius Masalar / Unsplash Timothy Clark, Deakin UniversityFish are the most diverse group of vertebrates, ranging from tiny gobies and zebrafish to gigantic tunas and whale sharks. They provide vital sustenance to billions of people worldwide via fisheries and aquaculture, and are critical parts of aquatic ecosystems.But fish around the world are getting smaller as their habitats get warmer. For example, important commercial fish species in the North Sea have declined in size by around 16% in the 40 years to 2008, while the water temperature increased by 1–2℃. This “shrinking” trend is forecasted to significantly exacerbate the impacts of global warming on marine ecosystems.The link between warmer water and smaller size is well known, but poorly understood. Our experiments keeping fish in warmer water offer some crucial clues – and may help us learn how to prepare for a warmer future with smaller fish.The temperature–size ruleFisheries are a potential confounding factor when studying the effect of warmer waters on fish, because fisheries often target large fish. Removing these larger fish from the population benefits the survival of fish that mature quickly and reproduce at a younger age, when they are smaller.This trait of maturing early can be passed through fish generations. Indeed, it can lead to a phenomenon known as “fisheries-induced...
