Question of the month

During an interview with Mike Hammill, person in charge of marine mammal research at the Maurice Lamontagne Institute, Whales online asked him the following question :

Are seals responsible for the collapse of cod fish stocks in the Gulf of St. Lawrence ?

M. H. :

Seals are not responsible for the collapse of cod fish stocks in the Gulf of St. Lawrence but they may have played a part in the tragedy. The collapse of cod fish stocks in the Gulf is due, instead, to over-fishing and this over-fishing is the result of a complex situation in which various parties are implicated :

Fisheries scientists did not take into account environmental changes which affected cod productivity. Briefly, a drop in temperature in the Gulf reduced cod productivity, but the scientists did not discover this immediately. The quotas were therefore established using a productivity rate superior to reality which lead to a situation of over-fishing.
Fishermen resorted to practices such as declaring takes that were smaller than the they were in reality, leading once again to a situation of over-fishing.
Scientists ignored warnings from certain fishermen who had noticed the decrease in cod stocks.
Politicians refused to follow scientists’ recommendations when they finally became aware of the problem at the end of the 1980s.

And the seals in relation to all of this? Since the 1970s,the populations of grey and harp seals have doubled. These two species are both predators and competitors of cod. Even though seals consume very little of the larger cod that interest fishermen, they attack the smaller fish and in this way decrease the number of cod that survive and become large enough for the fishermen. As well, in consuming the prey sought after by cod, seals are also likely to affect cod fish stocks as less nourished cod will have a weaker productivity.

Normally, the predation and competition presented by seals should not have had a huge impact on cod fish stocks. But because the stocks were already fragile, due to over-fishing, perhaps they suffered from this additional pressure. Nevertheless, seals are not the only predators or the only competitors of cod,there are other species of fish, whales, and marine birds. At present we cannot evaluate the exact part played by seals in relation to these other predators.

To know more about over-fishing and the collapse of cod fish stocks in the St.Lawrence

Portrait of Mike Hammill