the Department of Fisheries and Oceans announcement to suspend the blue mackerel and spring herring fishery in the southern Gulf of St. Lawrence caused waves at the opening of the fishing season.

This decision will have repercussions for the fishing industry on several levels since these species are fished not only for commercial purposes, but are also used as bait in the lobster, snow crab and Atlantic halibut fisheries. Given the precarious state of the exploitable adult part of these populations, also called stocks, closing the fishery is the right decision.

As fisheries ecology researchers, we are interested in the dynamics of commercially exploited fish stocks. Here we explain the causes that led to the suspension of the spring mackerel and herring fishery in the southern Gulf of St. Lawrence, as well as its implications for the fishing industry.

High adult mortality

The latest inventory valuation of Atlantic mackerel and spring herring in the southern Gulf of St. Lawrence revealed high mortality rates in adult fish. Despite significant reductions in commercial catches over the past 20 years, with quotas falling from 75,000 tonnes to 4,000 tonnes for mackerel and from 16,500 tonnes to 500 tonnes for spring herring, fishing mortality has remained too high to support inventory growth, especially for mackerel.

In addition to the high fishing pressure, the natural mortality of fish from predation has also increased rapidly, a detailed phenomenon in southern Gulf of St. Lawrence herring.

the gray sealnow 16 times more abundant than in the 1960s, is the main predator of herring.

The northern gannet populations on Bonaventure Island and Rocher aux Oiseaux, which are also large consumers of herring and mackerelare also at high levels.

Red tuna is another large predator responsible for the high mortality of adult herring. Its abundance has increased rapidly in Gulf waters over the past decade.

Adverse environmental conditions

The current record lows for mackerel and spring herring are also due to reduced recruitment to these stocks.

Recruitment is the arrival of a new annual cohort into the adult stock. It has remained relatively low for herring since the 2000s, and for mackerel since the 2010s. This reduction in recruitment strength is probably related to environmental conditions that have become unfavorable for the larvae. Indeed, during the first weeks of life, when young fish measure only a few millimeters and present a high risk of mortality, their survival depends directly on the success of feeding on their main prey, microscopic crustaceans called zooplankton.

However, the rapid warming of the southern Gulf of St. Lawrence over the past two decades has changed the composition, distribution and developmental time of zooplankton organisms. This led to a spatial and temporal shift between the emergence of mackerel and spring herring larvae and the production of their preferred prey. This discrepancy weakened the survival rate of larvae and caused recruitment failure, preventing the recovery of fish stocks.

The recovery of stocks will depend, in part, on the return to favorable conditions for the survival and recruitment of larvae. Unfortunately, short-term climate projections do not allow us to foresee a return to colder years, favorable to the survival of the larvae.

Expected bait shortage

The impact of the spring herring and mackerel fishery closures extends beyond the commercial fishery for these two stocks. These species are the main bait for lobster and snow crab traps, as well as hooks targeting Atlantic halibut and bluefin tuna.

These fisheries, among the most lucrative in the Gulf, are enjoying good times, having brought in more than $1.3 billion to fishers in Quebec and the Atlantic in 2020.

This exacerbates the already high demand for bait. Anticipated additional costs related to the supply of bait can accentuate the rapid rise in the prices of the most prized resources of the Gulf of St. Lawrence.

What are the options?

The ultimate solution to the current crisis is to continue strict management measures for the mackerel and herring stocks affected by the suspension of fishing, in order to preserve a sufficient number of spawners while waiting for environmental conditions conducive to their recovery. However, as these species do not reach the minimum capture size until they are three to four years old, no short-term effects of management measures can be expected. We must be patient.

In the short term, fishermen in the southern Gulf of St. Lawrence will have to compensate for the shortage of bait by sourcing mackerel from abroad. In Europe, for example, the stock is healthier. The direct and environmental costs of this transport do not make it an ideal long-term solution. The fall herring fishery, which remains open, could also allow fishermen to stock up later in the season.

However, an innovative solution is under study. Alternative baits could be developed to completely replace herring and mackerel in shellfish traps.

Research teams are currently working on developing an effective recipe for making such baits using marine by-products — materials resulting from the processing of seafood products that can be used for purposes other than human consumption.

The manufacture of alternative bait from species such as redfish, the large-scale fishing of which should soon resume in the Gulf of St. rapidly increasing in numberis something worth considering.