A new study analyzing more than 230 fisheries has found that their sustainability is likely overstated worldwide, and previous estimates of the number of fish in the ocean globally may have been too optimistic.

The study, conducted by University of Victoria marine ecologist Amanda Bates alongside collaborators at the University of Tasmania鈥檚 Institute for Marine and Antarctic Studies, was published in the journal Science on Aug. 22, and the findings could have implications for the management and long-term sustainability of fisheries according to the university.

"Currently, in many fisheries, we may be catching more fish than is sustainable. Fisheries feed the livelihoods of many coastal people, and our cultures are intimately tied to fisheries and fishing practices. If we care about future generations and want healthy ocean systems, we need to rethink how we鈥檙e managing our fisheries," said Bates in a news release.

Estimates of how many fish are available in a fishery, called stock assessments, are made regularly and considered the "gold standard" for the scientific management of fisheries. Stock assessments are used by managers to prevent overfishing, rebuild overfished stocks and protect marine ecosystems.

In the study, researchers conducted a retrospective analysis that compared past estimates of stock size in worldwide fisheries with new estimates for the same year made with more recent data. The study included data from Canadian fisheries, including Pacific herring fisheries in the Strait of Georgia and western Vancouver Island.

The study showed an inconsistency in stock assessments, with results differing between the past estimates and the more recent estimates. There was a pattern of overestimating the size of stocks that were the most depleted, and assessments were often too optimistic about the pace of recovery. They say fish stock biomass was overestimated by an average of 11.5 per cent.

鈥淎 bias towards overestimating fish stocks in overfished fisheries could lock in stock collapse, as the decline in fish may not be noticed until it鈥檚 too late to take precautionary measures,鈥� noted Bates in the release. 鈥淚f we want to avoid collapses in fisheries around the world, which would have far-reaching impacts on ocean health and food security, a more precautionary approach to fisheries management is vital.鈥�

Stocks that were in areas with rapidly rising sea temperatures and those that had low economic value were also found to have more inaccurate assessments.

The study concluded that there "is room for improvement" in how stock assessments are conducted, and it laid out 10 practices that, when implemented together, could increase their accuracy. The practices include expanding independent monitoring of fisheries, changes to assessment protocols including the implementation of a 鈥渞ed team鈥� that looks at potential worst-case scenarios, and the expansion of monitoring in marine protected areas where fishing is prohibited.