Fast-growing fish face dramatic fall in population

In a counterintuitive discovery, new research has found that ocean species that grow quickly and reproduce frequently -- such as sardines -- are more likely to experience dramatic plunges in population than larger, slower growing fish such as sharks or tuna.

The situation is in stark contrast for life on earth.

"Rabbits are doing pretty well compared to rhinos," said Malin Pinsky, assistant professor of ecology and evolution at Rutgers, The State University of New Jersey in the US.

"Mice thrive while lions, tigers and elephants are endangered," Pinsky explained.

After studying population changes in 154 species of fish worldwide over 60 years, Pinsky was surprised to see marine equivalents of rabbits and mice collapsing to low levels - still shy of extinction but serious enough to disrupt ocean food chains or fishing-based societies.

In nearly all of the cases, overfishing was the culprit, the research identified.

"Climate variations or natural boom-and-bust cycles contribute to population fluctuation in small fast-growing fish, but when they are not overfished, our data showed that their populations did not have any more tendency to collapse than other fish," Pinsky noted.

"Overfishing is a problem throughout the world and across all species, including slow-growing fish like sharks, many of which are in serious trouble," said Pinsky.

"But it turns out that fishery collapses are three times more likely in the opposite kinds of species - those that grow quickly," he said.

The findings appeared in the journal Proceedings of the Royal Society B.