A dose of optimism for Atlantic cod

It’s been almost 20 years since the Atlantic cod fishery collapsed, leading to a moratorium that remains in place to this day.

“We thought after four or five years, we would see some recovery,” explains Ken Frank, research scientist with the Bedford Institute of Oceanography and an adjunct professor with Dalhousie’s Department of Oceanography. “But then 10 years went by, and now almost 20. We got worried that the ecosystem was stuck in an alternate state, or that a deep, permanent change had taken place.”

But there’s evidence to suggest the tides are turning. Dr. Frank is one of the collaborators on a new study, published this week in the journal Nature, that is the first to show signs of recovery in Atlantic cod and other groundfish populations. Other researchers involved in the study include Brian Petrie, a colleague of Dr. Frank's who did his PhD at Dalhousie and who recently retired as an adjunct professor, as well as researchers at Queen’s University.

The paper explores just why the cod stocks were slow to rebound: it’s that forage fish such as capelin and Atlantic herring exploded in numbers when the larger, predatory fish disappeared. The smaller fish choked out the ecosystem, feasting on cod eggs and fish in earlier stages of their life-cycle.

But after several years, the numbers of the smaller fish became too much for the ecosystem to support and now it seems the balance has swung back to the larger predators.

“If you remove a link in the ecosystem, or diminish it, you get this rippling effect – a reverberation,” explains Dr. Frank. “That’s why it’s taken 20 years to start to reassemble.”

That said, there’s still cause for caution. These are early results, and there are some signs that the recovery has quite a ways to go. For example, the physical size of some of the fish—such as haddock—is about half of what it once was.

“What we’re documenting is the initial stage of recovery...it’s hard to say whether the system will ever be fully the way it was before,” says Dr. Frank.

Which is why that even if further research finds continued recovery, any decision to end the moratorium will have to be made carefully, with considerably more analysis.

“It’ll have to be a slow process to make sure that we don’t go down the same road again.”