Narrator: This is Science Today. The California Cooperative Oceanic Fisheries Investigations, or CalCOFI, was instituted in 1949 in response to the collapse of the Pacific sardine fishery off California and Mexico . Researcher George Sugihara of the Scripps Institution of Oceanography, says the essential question was whether the collapse was due to fishing or to some environmental effects.
Sugihara: Problem is that those two things happened together. So they're tangled effects that can not be disentangled. And the CalCOFI surveys were intended to try to disentangle those effects.
Narrator: In a study based on CalCOFI data, Sugihara found that fishing not only leads to declining stock levels, but populations fluctuate more through time – putting them at greater risk of collapse than previously thought. Sugihara says another thing that happens is the average age of fish gets younger.
Sugihara: And what this does is it basically takes away the buffering capacity of a population. Those older fish can weather environmental effects like El Nino, etc. Whereas the younger ones may be more prone to mortality or whatever it is that's associated with these environmental fluctuations.
Narrator: For Science Today, I'm Larissa Branin.