Fast-growing fish risk dramatic fall in population

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

"Rabbits are doing pretty well compared to rhinos. Mice thrive while lions, tigers and elephants are endangered," said Malin Pinsky, assistant professor of ecology and evolution in the School of Environmental and Biological Sciences at Rutgers University in US.

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 his research, Pinsky found that in nearly all of the cases, overfishing was the culprit. "Climate variations or natural boom-and-bust cycles contribute to population fluctuation in small fast-growing fish, but when they are not over-fished, our data showed that their populations didn't have any more tendency to collapse than other fish," Pinsky said.

For example, this effect is apparent in sardines off the coast of southern California, whose populations have fluctuated naturally for thousands of years. However, these fluctuations are not enough to explain why so many fast-growing fish species have collapsed to less than 10 per cent of historical levels in recent decades, researchers said.

With the advent of efficient fishing vessels and techniques after World War II, population collapses started to occur much more frequently in sardines and anchovies, which are valued for pet food and fish oil, they said.

"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," said Pinsky.

Combining climate variability with high levels of fishing greatly increases the risk of collapse, Pinsky said. Pinsky's analysis relied on data from fisheries management agencies worldwide, and used mathematical analyses developed by collaborator David Byler in operations research and financial engineering at Princeton University.

The work is important, he notes, because species declines can affect the viability of sea life higher in the food chain and human societies that rely on fishing to supply food and economic support. The study was published in the journal Proceedings of the Royal Society B.