A new study indicates that climate change may be stunting fish growth. Fish sizes in the North Sea have shrunk dramatically, and scientists believe warmer ocean temperatures and less oxygenated water could be the causes. Could this be the case for the Baltic Sea cod?
The researchers followed six commercial fish species in the North Sea over 40 years and found that as water temperatures increased by one to two degrees, an accompanying reduction in fish size was observed. More specifically they found the body sizes of several North Sea species to have decreased by as much as 29 percent over a period of four decades.
It is generally accepted among scientists that decreased body size is a universal response to increasing temperatures, known as the “temperature size rule”, but there has not been any empirical evidence displaying this response in marine fish species until now.
It is hard to say that temperature changes is the explicit reason for the reduced fish size observed as other factors such as fisheries-induced evolution and intensive commercial fishing — which favors larger specimens – could have influenced size. However, the authors of the study argues that fisheries-induced factors would not be likely to affect growth rates across species, which was observed in the North Sea study.
The findings of the study resonate earlier model-derived predictions that fish would shrink in warmer waters. In 2012 a research team at the University of British Columbia in Canada, carried out the first global projection of the potential for fish stunting in warmer, less oxygenated oceans. Where they predicted changes in ocean and climate systems by 2050 could result in fish that are 14 to 24 percent smaller globally.
Fish are in a constant challenge to get enough oxygen from water to grow, and the bigger the fish gets the worse the situation gets. The study highlights that temperature may be changing the fishes’ energy versus expension rates, which could result in smaller sizes. Given the situation in the Baltic Sea with increasing areas of reduced or no oxygen and the shrinking size of cod, the concluding remarks of the study highlighting the need for strategies to be developed to curb greenhouse-gas emissions or risk disrupting food security, fisheries and the very way ocean ecosystems work should be taken seriously by the Baltic Sea states.