Some widely publicized papers suggesting that fishes and fish catches will be smaller in the future are based on false assumptions

Two physiologists, Sjannie Lefevre and Göran E. Nilsson, from the Department of Biosciences, the University of Oslo, have together with a colleague, David J. McKenzie at the University of Montpellier, published a paper in Global Change Biology this week showing that some highly cited and publicised modelling studies are based on erroneous physiological principles and facts. These models are suggesting that fishes will become smaller in the warmer climate expected in the future.

The authors behind these modelling studies may be prominent fisheries biologists and modellers, but unfortunately some fundamental assumptions made in the models are simply incorrect, says Sjannie Lefevre. For once, they got the geometrical principles guiding the surface area of fish gills completely wrong, and they also make the unfounded assumption that the capacity of fish to take up oxygen from the water limits their ability to grow. It is troublesome that these inaccurate assumptions have been allowed to go unnoticed by fish physiologists, but they are partly hidden in the formulas used and in some obscure statements made in these papers.

Lefevre, McKenzie and Nilsson say that they do not deny the possibility that fishes may become smaller in the warmer future, although there is currently not much firm evidence for this, but any such predictions must be based on verified mechanisms and experimental evidence.