The Downside of Evolution in Action

From Yahoo News:

Fish have lost half their average body mass and smaller species are making up a larger proportion of European fish stocks as a result of global warming, a study published Monday has found.

“It's huge,” said study author Martin Daufresne of the Cemagref Public Agricultural and Environmental Research Institute in Lyon, France.

“Size is a fundamental characteristic that is linked to a number of biological functions, such as fecundity - the capacity to reproduce.”

Smaller fish tend to produce fewer eggs. They also provide less sustenance for predators - including humans - which could have significant implications for the food chain and ecosystem.

A similar shrinking effect was recently documented in Scottish sheep and Daufresne said it is possible that global warming could have “a significant impact on organisms in general.”

Earlier research has already established that fish have shifted their geographic ranges and their migratory and breeding patters in response to rising water temperatures. It has also been established that warmer regions tend to be inhabited by smaller fish.

Daufresne and his colleagues examined long-term surveys of fish populations in rivers, streams and the Baltic and North Seas and also performed experiments on bacteria and plankton.

They found the individual species lost an average of 50 percent of their body mass over the past 20 to 30 years while the average size of the overall fishing stock had shrunk by 60 percent.

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Without reading the original paper, it seems like pinning the effect on warming is a bit of a leap. It isn't like people haven't been selectively culling large fish... aka fishing.

And that bit about shep becomding smaller as a result of global warming is just bizarre; humans control sheep reproduction, so natural selection can hardly be acting there, and genetic drift would tend to be curtailed by human selection, plus, you can hardly blame global warming for genetic drift.

By Valhar2000 (not verified) on 22 Jul 2009 #permalink

I'd like to see data on how much sea temperatures have risen in the last "20-30 years" and a plausible mechanism for a change of just a couple of degrees (assuming that's what it is) causing a halving of average size. On land, it wouldn't be unreasonable to expect an increase in temperature to cause things to grow faster and larger.

And, like the first commenter, I'd want to know how they eliminated the effect of increases in fishing when, according to the article, they've been looking at the size of "fishing stock". These are surely questions any enquiring scientist would want to ask before accepting what he reads on "Yahoo News", particularly something that looks like a reprinted press release and has no link to the source.

By Julian Gall (not verified) on 22 Jul 2009 #permalink

#3: Thanks, that makes a lot more sense.

By valhar2000 (not verified) on 23 Jul 2009 #permalink

Julian #4,

On land, it wouldn't be unreasonable to expect an increase in temperature to cause things to grow faster and larger

Not unreasonable, but wrong in this case. Colder weather provides an advantage to larger animals because they have a lower surface-to-volume ratio, so they lose heat slower. That translates into needing to eat less per kg of body mass. All other factors being equal, of course...which they aren't, which is why you can have fairy penguins in the antarctic and 800-lb gorilla in the tropics.

What makes me scratch my head is that fish are cold-blooded. So surface-to-volume shouldn't be a factor; they aren't spending energy to keep their insides at a constant temperature. So what's the cold water advantage of being bigger?

This exact effect has previously been attributed to overfishing. Google search "overfishing smaller fish".