Honey, I Shrunk the Fish

Today's blog is going to be looking at the phenomenon of fish shrinking due to the warming of the ocean. The title may seem a little gimmicky and I'm not going to deny that it is. However, since the ocean is warming due to anthropogenic climate change, maybe we should all be taking some responsibility for the effects.

Cheung et al. released a paper earlier this year reporting that they had used a model to show changes in body weight of over 600 species of fish due to the increased temperature of world's oceans. This paper was reported widely, for example here and here, because the results were fairly surprising. The model not only looks at the the physiological effects that cause fish to become smaller, but also how changes in species distribution will impact body weight. I think figure 1 in the paper (below) really helps to illustrate exactly what this study found.

It's pretty easy to see from these figures what's going on. In A, we can see how temperature at the bottom is expected to increase and  from B we can see that oxygen concentration in the ocean is expected to decrease alongside this. C shows how fish are expected to shrink in size, and that their distribution will move to higher latitudes. The overall picture is that fish weight is expected to decrease by 14- 24% from 2001 to 2050. This varies by region, with fish body weight expected to decrease by 24% in the Indian Ocean, while in the Pacific the decrease is projected to be 14%.

There are of course some uncertainties in this paper, which is to be expected given that this is a model and that this is the first study of its type. Firstly the study is limited by the difficulties associated with projecting future climate and ocean conditions. The global trends it predicts are only validated against 2 earth system models. The model also does not include some unknowns such as how fish may adapt to climate change or how other factors such as changes to trophic levels and human stresses such as overfishing may impact future fish size. However, I feel that Cheung makes an exceptionally valid point in that this is the first study of its kind, and future studies can build and improve upon the methods used in this paper. To be honest, the results presented aren't particularly detailed anyway so there seems to be a lot of scope for further work and a more analysis of exactly how the body weight of fish is expected to change. I would also say that there isn't really any consideration of how this issue will effect fisheries and human consumption of fish and its economic impacts.

So, to wrap up this blog, I think this is an important paper because it is the first to look specifically at how fish body weight will be effected by climate change, however there is much further work that can be done to build on from this paper. I think the authors state this fairly explicitly within the paper, and even in the abstract they say that the work provides a ''new dimension to understanding'' impacts of climate change. However, while researching this paper I stumbled across this apparently notorious climate skeptic blog. He seems to argue that warming will actually cause increased photosynthesis that will increase oxygen in the ocean...he also rejects the argument that fish weight will decrease overall across the 610 species used in the paper by using another paper that looks at field observations of just one species. I'm not sure I'm quite taken by this argument. I accept that some areas of climate change research have a long way to go, however I don't think it's acceptable to reject the entire basis of papers because of this. Despite not being perfect studies such as Cheung et al.'s undertake the vital task of helping to forward scientific research, which is of great importance seeing as science is  a constantly evolving subject.