The northern Atlantic cod fisheries off the Canadian coast are famed for being one of the most disastrous examples of overfishing and mismanagement. The stocks once supported several million tonnes of fish, and shaped the lives of those living on Canada’s eastern coast for half a millennia. But after heavy unsustainable fishing in the 60s and then again in the 80s, the stock eventually collapsed to 1% of its previous level and in 1992 fishing for cod was banned.

The slow and almost non-existent recovery over the following decade and a half led some to suggest that the stocks would never fully recover, and that they had been fished too extensively. But new research, carried out by the Memorial University of Newfoundland, suggests that after decades of limited recovery, the stocks might now be on the up again. The researchers document how the numbers seem to have increased off Newfoundland and Labrador from tens of thousands, to several hundred thousand tonnes, and growing.

^{Dr Sherrylynn Rowe, who coauthored the paper, shown tagging a large cod off the coast of Newfoundland and Labrador. Laura Wheeland c/o Dr. George Rose.}

The number of cod was depleted to such a low level that for over a decade after the ban on cod fishing, there was little evidence for spawning or migration along the coasts of eastern Canada. Surveys found that individual fish were in poor condition, and those that were spawning were doing so at much smaller sizes than expected, a behavior no doubt driven by the over harvest of the largest fish. One large aggregation of overwintering and spawning cod persisted, however, in a small fjord at Trinity Bay on Newfoundland.

But at the beginning of 2007, this surviving population worryingly also started to decline. Using trawl and acoustic surveys, the researchers actually found that fish instead seemed to have migrated out from the fjord and along a once well-known spawning and migration corridor offshore, populating depleted regions with a wide range of cod ages and sizes. This seems to have been linked to an increasingly healthy stock of another species of fish, the capelin.

“The important take-away from this study is that with favourable environmental conditions, in this case the increase in capelin as a key food for this stock, and a severe reduction of fishing, even the most decimated fish stocks have the potential to recover,” explained Dr George Rose in a statement. Rose led the study, which is published in the Canadian Journal of Fisheries and Aquatic Sciences. “Without a doubt, maintaining low removals of this stock over the past decades has been essential to recovery. While the timing of a full recovery remains uncertain, continued protection from excessive fishing remains essential to achieving that outcome.”

This study goes to show that recovery of fish numbers can occur given limits on how many can be taken from the oceans, even for stocks as depleted as that of the northern Atlantic cod, so long as the environment in which they live is also properly managed. Other stocks of cod in the North Sea, which were equally overfished, also seem to be bouncing back, and have even been removed from the red list of fish which we should avoid eating.

^{Main image credit: *saipal/Flickr CC BY 2.0}