HomeGuest CommentaryDisappearing Redfish and DFO Math

Disappearing Redfish and DFO Math

The Department of Fisheries and Oceans (DFO) announcement in late January with respect to redfish puts a glaring spotlight on the numbers problem in its science and management divisions.

Its new research purports to show that the biomass of redfish in Area 1, despite there having been essentially no fishery, has declined since 2019 from 4.3 million tonnes to 2.8 million tonnes after growing exponentially for a decade.

This follows news in December 2023, that the estimated number of seals in our Atlantic waters is now 4.8 million rather than the nearly eight million a few years ago. As with so much in DFO, it is uncertain whether this reflects an actual change in the number of animals or statistical errors in DFO’s computing system; most likely it is a real decline, complicated by errors. In any case, it’s a serious problem.

Another astounding revelation by DFO last October was that they were changing the limit reference point (LPR) for Northern cod in 2J3KL to 315 kt rather than 800 kt calculated a little over a decade ago.

Under DFO’s current management framework, the LRP calculations determine the total allowable catch (TAC), so this error prevented the harvest of millions of tonnes of cod during the time the old LRP was in place. This foregone harvest not only condemned large numbers of fish to death by starvation as their population outstripped food supply, it deprived the Newfoundland and Canadian economy of potentially more than a billion dollars.

A fourth example of this kind of major error is evident in DFO’s 2020 stock assessment for 3Ps cod, which raised the LRP enough to move the stock’s status from the cautious to the critical zone. (Three years earlier, the 2017 assessment had expressed various “concerns,” noting that the model used had “overestimated spawning stock biomass in recent years.”)

Surely, it’s clear that so-called fixed reference points that are subject to massive change do not constitute a good foundation on which to base harvest management policy.

Returning to the redfish puzzle, it would be a mistake to attribute the one and a half-million tonne drop (from 4.3 million tonnes to 2.8 million tonnes) to “natural mortality.” In current fisheries discourse, “natural mortality” is a catchall phrase used to refer to all undetermined reasons why fish disappear — mainly predation, unrecorded harvest, disease and starvation. But the cause of the recent dramatic decline in Gulf redfish is actually quite clear.

We can eliminate predation as a main cause because there has not been a massive increase in any predator species. Foreign over-fishing could be a factor if the fish were on the nose or tail of the Grand Banks or on the Flemish Cap, but not in the well protected Canadian waters of the Gulf. And there have been no reports of disease. Meanwhile, the area’s shrimp stock has been declining over this same time period, and shrimp constitute an important part of the diet of adult redfish.

So, although other unknown factors such as warming waters may also be involved, we are left to conclude that the disappearance of all those fish is largely due to starvation.

Since we’re talking numbers, it would also be incorrect to conclude that the loss of biomass between 2019 and 2023 was 1.5 million tonnes (4.3 minus 2.8) when it was actually more. Gulf redfish at their current size are still growing, though more slowly than in the cohort’s first decade. Positing a growth rate of 1 cm/yr in length, we calculate the growth in the weight of an individual redfish at about 10–12 per cent per year, as compared with 25–40 per cent for cod.

In a simplistic model with an assumption of zero mortality and omitting other variables, this would mean the stock biomass would have grown by over 50 per cent from 2019 to the present — to 6.5 (4.3 plus 50 per cent) million tonnes.

Obviously that is unrealistic, but the conclusion remains that starvation has taken a huge toll on redfish in the past four years — perhaps as much as 3.5 million tonnes. With proper management and planning, much of that biomass could have been harvested. At a conservative price of 50 cents per pound, that much fish would theoretically be worth over 3 billion dollars. This kind of loss to the Canadian economy was one of the scenarios we predicted three years ago in our Navigator article, “Redfish: Bonanza or Boondoggle?”

So, what now?

At the 25-kilotonne annual rate of exploitation currently proposed, it would take just over one hundred years to catch all the redfish in today’s Gulf of St. Lawrence stock, even if we assumed no fish growth (impossible) and no new recruitment (unlikely.) Of course, redfish are a long-lived species, but they won’t live that long. Still, the scenario demonstrates the absurdity of basing harvest plans on those kinds of calculations.

Perhaps we need to ask, who’s doing the math at DFO?

By Barry Darby

Barry Darby is a retired fisherman and educator from Burin, N.L., who has done extensive research on the economics and sustainability of the fish harvesting sector.