Recovery of overfished ocean populations depends on swift action

Halifax, NS – A secret to recovery in ocean populations that have been depleted by overfishing is quick decision action at the first sign of overfishing, according to a new study co-authored by University of Dalhousie biologist Jeff Hutchings. The paper was published in Science last week.

“Here we are, two decades after the greatest numerical loss of a vertebrate in Canadian history, and we’re in a position where stocks are actually declining further, in some cases, and most stocks are remaining stable at very low levels,” says Dr. Hutchings. “Our work provides a means of interpreting that.”

The study has implications far beyond just cod. Hutchings and his collaborators looked at more than 150 marine fish and invertebrate stocks worldwide, modeling recovery times for 184 recorded depletion events.  

“There’s good news and sobering news,” he says. “It appears that marine fishes, in general, are much more resilient and better able to recover than perhaps we had previously thought. That means that if action is taken to reduce fishing mortality immediately, at the first signs of overfishing, then there’s a very good chance that the population will recover within as short a period of time as 10 years.”

However, if action is delayed, or if fishing is allowed to continue at relatively high levels after the depletion has taken place, recovery is much slower, if at all.

(The study defines recovery as a stock, or population, returning to biomass at maximum sustainable yield, or BMSY: the level at which a population is large enough to produce the maximum catch over the long term without depleting the stock.)

“In the case of severely depleted stocks, such as our cod stocks, we did not take effective action at the first signs of overfishing,” says Dr. Hutchings. “Secondly, we permitted fisheries to take place just a few years after the moratorium in 1992, and those fisheries — even though they were described as small-scale — almost certainly nipped the bud in any recovery that was taking place.”

While he believes mistakes were made 20 years ago, he hopes the findings make the case for avoiding such mistakes in the future.

“It should provide a strong scientific incentive for politicians, for fisheries managers, to take meaningful, rapid action to reduce catches at the first signs of overfishing,” he says.

Reported by Ryan McNutt, Dalhousie University