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Small fish 'twice as vulnerable' to collapse as bigger species

 

May 03 2011 Lewis Smith

 

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Sardine fishing in Monterey Bay

Jonathan Blair / © Monterey Bay Aquarium

Stocks of small fish such as anchovy and sardines are up to twice as likely to collapse through overfishing as those of larger, iconic species including bluefin tuna and cod, scientists have found.

The discovery overturns conventional wisdom which regards small species, whether on land or at sea, as being better protected from collapse.

Researchers analysing records of more than 200 fisheries going back half a century discovered that against expectation the populations of smaller fish were twice as likely to collapse as the bigger species.

"We were expecting to see a strong pattern with large, top predators showing the highest probability of collapse," said Malin Pinsky, of Stanford University. "We were really surprised to find that just isn't the case."

"The important lesson is that all species of fishes can collapse once humans decide to eat or use them, from sardines to swordfish. You hear the old adage, 'Don't sweat the small stuff,' but for fisheries, we do have to care about the little guys. This really contrasts with what scientists, managers and the conservation community have often assumed up until now."

Small fish, just like mice on land, had been thought to be more resilient because they are fast-living creatures with short individual lifespans and high rates of reproduction. In contrast, larger species tend to have longer lifespans but markedly lower rates of reproduction.

The assumption has been that because the smaller fish could reproduce so fast they would be better at recovering from fishing pressures than bigger species, particularly predators at the top of the food chain. But the analysis by researchers from the US and Canada showed them to be more vulnerable.

"Local managers and fishermen have known about individual fishery collapses for years," said Professor Stephen Palumbi, of Stanford University. “It took looking at 50 years of data and hundreds of fisheries to realize that these collapses among small species actually add up to a whole lot. Bringing a halt to overfishing is the best way to reduce collapses in the future.”

More than 25 per cent of the world’s fisheries consist of small fish and scientists suggested that fishery managers have vastly overestimated the capacity of small fish to recover from fishing which has led to population crashes.

Moreover, they suggested that fisheries managers pay closer attention to data from catches of large, trophic fish and fail to understand or pay enough attention to the needs and frailties of smaller species when considering how many can be caught without causing stocks to slump.

“Fast species collapse just as often as species with slower life histories,” the researchers reported in the journal Proceedings of the National Academy of Sciences.

“We found collapsed stocks in short-lived species, such as summer flounder (Paralichthys dentatus) and Spanish mackerel (Scomberomorus maculatus) and among small, fast-growing species like capelin (Mallotus villosus) and herring (Clupea harengus and Clupea pallasii).

“Although these collapses are well known to local fisher-men and managers, the general prevalence of collapse among these types of species has not been recognized.”

The researchers added: "The high harvest rates on many short-lived species also mean that errors in setting harvest rates can have particularly severe consequences."

An example cited by the researchers was the sardine fishery in Monterey Bay, off California, where stocks took decades to recover from overfishing.

Data sets used in the analysis came from the Food and Agriculture Organization of the United Nations and Dalhousie University. The two are together considered the most comprehensive collection of scientific fisheries data in the world.

The research team made its discovery while looking at the data sets in the hope of identifying a means of predicting when fisheries are likely to collapse and thus knowing when to make emergency interventions. They concluded there is no easy shortcut to make such a prediction and that the only reliable method is constant monitoring.

 

 

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