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A wily redfish
DFO  R. Larocque

Redfish in the Gulf of St. Lawrence belong to two closely related species, the deepwater redfish (Sebastes mentella) and the Acadian redfish (Sebastes fasciatus). As its name suggests, the deepwater redfish predominates in deep water and its range lies farther north than that of the Acadian redfish. Historically, redfish and Atlantic cod were the most abundant groundfish in the Gulf. Following intensive fishing, the population collapsed in the early 1990s which led Fisheries and Oceans Canada (DFO) to impose a moratorium on the Gulf groundfish fishery in 1995, one that is still in effect today.

Since the beginning of the moratorium, DFO has closely monitored fluctuations in this reduced population by means of the bottom trawl survey conducted each summer aboard a research trawler. For several years, the redfish showed no signs of recovery. Then in 2005, surprise: the survey detected strong recruitment by small redfish born in 2003. Obviously, these small redfish stirred the hopes of biologists and the redfish fishing industry. But this wave of optimism was unfortunately cut short since in 2008 and 2009, the abundance of these small redfish fell dramatically: they apparently disappeared from the Gulf before reaching the minimum commercial fishing size. In fact, this was not the first time the redfish played a trick of this kind on biologists. The redfish born in 1988 also appeared to be very abundant, but they disappeared from the Gulf after a few years before reaching the size permitted for fishing. What happened?

The first hypothesis that springs to mind is that these young redfish died. Although this hypothesis cannot be rejected entirely, it is not the explanation that most scientists put forward since there are a variety of indications that lead them to believe that these small fish simply left the Gulf. In fact, genetic analyses indicate that they were not born in the Gulf so it is possible that they returned to their spawning grounds after growing in the Gulf for several years. Indeed, it seems that the typical Gulf species that supported the fishery prior to the moratorium was the deepwater redfish, while the two strong recruitment episodes in 1988 and 2003 involved the Acadian redfish, which feels less at home in the Gulf than in the Atlantic.

The biology of the redfish still holds many mysteries in store; the work and analyses done by Maurice Lamontagne Institute researchers will perhaps help solve some of them.

Martin Castonguay