Global fisheries overestimating stocks beyond sustainability: UVic researchers

Scientists at UVic published an analysis Thursday of data from 230 fisheries worldwide, finding that due to overestimates of stocks, they may be catching more than is sustainable every year.

The university says estimates of how many fish are available in a fishery, known as stock assessments, are made on a regular basis and used by managers and scientists to inform their approaches to prevent overfishing, rebuild overfished stocks, and protect marine ecosystems. 

The analysts compared past estimates of stock size in the 230 fisheries with new estimates for the same year made with more recent data. The study included data from Canadian fisheries, including in B.C.

“We wanted to know if we’re being overly optimistic about how much fish is out there,” Amanda Bates, a professor of biology, ecologist, and co-author of the study, told 1130 NewsRadio.

“What we found is that on average, across all of these stocks — so this isn’t true for all stocks, but on average across the 230 stocks — we’re overestimating how much fish is out there by 11 per cent.”

Bates says that 11 per cent makes a big difference over time as fish populations decrease and the world “fishes its way down the food chain.”

“We’ve already removed a lot of those fish, so the populations, many of them, are at the edge of what might be sustainable into the future. And if we’re being overly optimistic on average about how much fish is out there, that means we could allow fish to be caught and crash populations,” she said.

Bates says analyzing the risk of sustainability is comparable to looking at the health of the financial stock market, adding that many factors have to be considered.

She says the fisheries and species in those fisheries were chosen for study not only for being overfished, but also for their proximity to waters rapidly warming due to climate change. 

“And oftentimes, stock assessment models may not explicitly incorporate climate change into their projections,” said Bates. 

“What I really hope is that this pushes some debate and discussion about the details of individual stocks and thinking about ‘how are we managing these stocks?’ And ‘Is there a way that we can develop our models or the context around our stock assessments that is going to improve our pragmatic estimates of sustainability?'”

Bates said that, thanks to its publication in the major journal “Science,” the study is already getting attention from the global fisheries community.

“That’s already starting a major discussion, including with some of the managers and some of the biggest fishery stocks in the world. We’re already even having a personal discussion with some of those people, talking about our data, what we’ve done, and what we think the implications are,” said Bates.

“Hopefully, this will initiate some debate and careful thought about what we can do in this world that is rapidly changing, but also where we’re managing stocks on a knife’s edge.”

She says population collapse has been successfully avoided in the past and hopes that many of the 230 fisheries can eliminate their estimation biases before their next stock assessment. 

—With files from Michael Williams.