Kate Wing's Blog
Fishing makes fish populations unstable
April 21, 2008
Posted by Kate Wing in Reviving the World's Oceans
I'm always excited to see new papers from George Sugihara's lab, because his group of researchers is applying new math to old problems. Since you can't count all the fish in the sea, regulators rely on estimates produced by stock assessments, which use models to extrapolate an idea of the total population size from a sample of caught fish. The underlying approach to these models has changed little over the decades, even though we've learned much more about how fish and fisheries actually behave. Sugihara brings his background in finance to bear on fish population dynamics, with interesting results.
The latest papers appear this month in Nature and the Canadian Journal of Fisheries & Aquatic Sciences and they look more in depth at the question of what is it about fishing that's driving the instability. In CANJFAS, Hsieh looks at the spatial distribution of 29 species in Southern California and finds that exploited fish populations are more likely to shift their location along the coast in response to changes in ocean conditions. In Nature, they drill down more deeply to the root causes.
Using the fifty year CalCOFI dataset (which is a very long time in ocean science) they looked at three hypotheses:
- Fishing pressure varies and that variability is amplified by natural processes, making populations themselves more variable
- Fishing pressure drives fish to be smaller and younger, which makes them more sensitive to environmental changes and that causes instability
- By changing the age and size structure of the populations, fishing changes the inherent demographics of the population, making it less stable.
#3 won out, which should start pointing our management in a new direction because it says there's a fundamental problem with catching bigger, older fish. It's not just that it exacerbates other problems (hypothesis #2), like changing ocean temperatures or the availability of prey, but it inherently destabilizes the population. Perhaps we should be giving Rainer Froese's ideas a second look and tracking not only the number of fish caught, but the demographics of the population left behind.
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