Surprising recovery for some fish populations, but others still suffer

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According to a new study, over-exploited fish species are capable of recovering from low populations, but some fish species have been so extensively over-fished that they may never recover.

This study, which examined the resiliency of 153 different species of fish and invertebrate whose populations had been reduced to less than 50 per cent of their 'sustainable yield', found that over-fishing actually enhanced the ability of some species to bounce back.

"My hypothesis, based on prior studies, was that marine stocks that had been overexploited for a long time would have a harder time coming back," said Philipp Neubauer, a post-doc researcher at Rutgers University in New Jersey who is one of the co-authors of the study, according to a news release. "So this was a bit of a surprise."

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The key to this recovery, according to the researchers, are the adaptations that happen in the species in response to the stress from over-fishing. They found that some species tend to mature faster than they did before the over-fishing, giving them a larger breeding population faster. However, there's a point where the over-fishing can drive the species to the point where recovery is more difficult, so an important part of this is imposing limits on the catch, to allow the species time to bounce back.

"Nature is not as fragile as we might suppose," said study co-author Olaf Jensen, an assistant professor of marine and coastal sciences at Rutgers, according to the statement. "Just because a fish stock has been overexploited for a long time doesn't mean we should give up on it."

However, for some species, such as cod, things aren't looking so good. It's been 20 years after the Canadian government shut down Newfoundland and Labrador's commercial cod-fishing industry, and even after all this time, their population is nowhere close to what scientists thought it would be by now.

Cod fishing off the east coast of Canada was fairly consistent and sustainable up until the late 1950s, but from that point until the mid-1970s, this species was heavily over-fished, which caused a total collapse of cod populations in 1992. Population decline isn't always due solely to over-fishing, as environmental factors can have a large influence as well, but over-fishing does put an enormous strain on the population and can severely limit a species chances of recovery.

"Here we are two decades after enormous depletion of cod stocks... and people are still wondering about the prospects of recovery," said Jeff Hutchings, a Dalhousie University biology professor who is another co-authored the study, according to the CBC.

"Our study really suggests that recovery is quite unlikely now for cod because of our failure to act when we could have."

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The study, titled Resilience and Recovery of Overexploited Marine Populations was published online today in the journal Science.

(Images courtesy: Jonathan Hayward/The Canadian Press, UNEP)

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