Climate change set to shrink fish

Through most of last year I spent my days researching climate change for my dissertation project. When I started I thought I ‘knew about Climate Change’ – how wrong I was! My dissertation looked at the way in which climate change is predicted to change the global distribution of malaria in the future (click here). Disease is not something that you would necessarily associate with climate change and here is another example of something you might not think was associated with climate change – size.

A new study has modelled the response of fish size to rising temperatures. Researchers looked at the impact on over 600 species of fish, between 2001 and 2050. They found that some species of fish could shrink by up to 24% as a result of global warming.

But why is that such a problem? Scientists have warned that climate change will affect marine ecosystems in ways that we never even imagined before. The problem for the marine ecosystem is, as water temperature rises, the level of dissolved oxygen in the water decreases. By decreasing oxygen availability there are several effects on fish, most notably on size.

The paper in question highlights two areas where this is going to be a problem. Firstly, it is predicted there will be an issue in the fishing industry. If fish size does decrease by 24%, that means fish biomass will also decrease. With fish stocks already at dangerous levels, this could have a significant effect not only on our diets, but also the livelihoods of fishermen around the world.

The other problem the study highlights is the effect a smaller body size would have on reproduction. A smaller female will produce less eggs and therefore further reduce the size of fish stocks. Additionally, by producing less offspring, there will be fewer chances of random mutation, leading to natural selection. This may weaken species ability to respond to a changing environment as a result of changing climate, increasing pollution or increasing predation.

This study highlights our need to carry out more research into the effects of climate change, particularly those effects that will influence our supply of food. As human population numbers rise we need to find ways to secure the food resources we have now, in order to protect our future.