New study warns of overestimation of fish stocks

Nearly 60% of fish species are systematically overestimated in their abundance, according to a new study. This leads to overfishing. The phenomenon also affects Canada.

“We show that on average the fish quantity estimates are overestimated by 11 per cent,” said Amanda Bates, a biologist at the University of Victoria who co-authored the study published Thursday in the journal Science“There is an overestimation of fish stocks even in fisheries that can be described as sustainable.”

Estimates of fish biomass in the waters are critical to setting fishing quotas. If those estimates are overestimated, quotas are too high. “It was because of poor estimates that we had the collapse of the cod fishery in the 1990s in Atlantic Canada,” says Boris Worm, a biologist at Dalhousie University who has worked extensively on this topic.

Mr Worm notes that more than half of the 290 fish populations studied, covering 128 species, are sustainably fished, compared with 38% that are overfished. There is an overestimation of populations in some sustainable fisheries, but it is decreasing.

Canada also affected

Overestimation is present for eight of the 12 fish species studied in Canada. “The good news is that we are now taking action against this overestimation,” says Mr. Worm. “For two years, Fisheries and Oceans has taken the courageous decision of a moratorium on Atlantic mackerel.”

Atlantic mackerel fishing was reopened this summer but at only 470 tonnes, ten times less than in 2021.

Ray Hilborn, a University of Washington biologist who often clashes with colleagues sounding the alarm about overfishing, believes that Science should not have accepted this study. “We have known for more than ten years that there is an overestimation. We do not understand the reasons for this overestimation but we take it into account by reducing the quotas.”

These quota corrections to account for overestimation don’t work, according to Graham Edgar, a biologist at the University of Tasmania in Australia who is the lead author of the study. Science. “The most recent estimates are also too high, so the corrections have not eliminated the error in the models.”

Scenarios

The solution is to consider multiple scenarios for fish populations when setting quotas, Worm said. “If you add up the optimistic, pessimistic and disaster scenarios, and assess the probability of each, you can make better decisions. If you had known that a disaster scenario had a high probability for cod 35 years ago, you might not have had a collapse in the fishery.”

Mr. Hilborn supports this approach of establishing quotas with disaster scenarios.

Canadian catches of Atlantic cod peaked at half a million tonnes in the 1980s. After the collapse of the cod fishery, 30,000 Canadian fishermen were left unemployed.

Watch a video about cod fishing in the Magdalen Islands