Overfishing hits all creatures great and small

On land, the pattern is a sadly familiar one: when an ecosystem is threatened, it is the large predators that usually suffer the greatest decline and therefore are most in need of protection. Logic would seem to dictate that the same pattern should apply at sea, but new research has demonstrated the opposite. It's the small fry at the low end of the marine food chain that may be more prone to population collapse.

A small body size does not improve the odds when fish species are faced with population collapse.

In the past six decades, smaller species that are commercially fished have had up to twice as many stock collapses as fishes higher up the food chain, according to a study published on 2 May in theProceedings of the National Academy of Sciences¹."There's been a lot of attention on top [ocean] predators, with good reason, because a lot of them are in trouble," says Malin Pinsky, an ecology graduate student at Stanford University's Hopkins Marine Station in Pacific Grove, California, and co-author on the paper. "But it turns out that there actually have been a lot of collapses at the other end of the food chain as well. We weren't expecting to see that."

Large fish species are sensitive to industrial-scale fishing, so managers tend to impose stricter fishing regulations for them. Highly productive smaller fish are thought to be hardier, so they are taken at a higher rate. Although individual stocks of small fish species have collapsed — the Pacific sardine in the 1940s, for example — fishermen and fisheries managers have, in the past, considered those to be isolated cases, Pinsky and his colleagues write.

"It really wasn't until our study that we realized that all these individual collapses among small fishes actually add up to a lot," says Pinsky. "All kinds of species, including the small ones that we used to think were incredibly resilient, are also vulnerable to overfishing."

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http://www.nature.com/news/2011/110503/full/news.2011.262.html