I have read the Senate report The Sustainable Management of Grey Seal Populations: A path toward the recovery of cod and other groundfish stocks. The senators show a deficit of logical thinking. Perhaps most fundamentally, the cull they are supporting is not an "experiment" in any scientific sense of the term, and will tell us virtually nothing about the workings of the ecosystem.
I am a scientist who has studied marine mammals off eastern Canada for the past 35 years. The concept of a seal cull to improve Maritime groundfish stocks is not scientifically defensible. It is simply not known whether seals have a positive or negative effect on groundfish populations. A large cull of grey seals in the Maritimes will not help our understanding.
The world´s largest population of grey seals breeds on Sable Island on the eastern Scotian Shelf. Current surveys show that while seal populations on Sable Island are still increasing somewhat, so also now are the groundfish populations. These trends may or may not be related but clearly there is no case whatsoever for a seal cull on Sable Island. All diet studies to date have concluded that cod comprise a very minor component of grey seal diets on the Scotian Shelf.
In the southern Gulf of St Lawrence, groundfish stocks are in worse shape and have declined while seal populations have increased. This does not mean that seals caused the groundfish decline. There are many other species in this ecosystem that consume cod (the greatest of which are cod themselves and other fish), and many other factors affecting ecosystem changes.
For instance, there is a substantial biomass of small fish-eating whales and dolphins in the southern Gulf of St Lawrence, and cod-eating sperm whales in the Cabot Strait. Should they be culled too for this experiment? Actually, "experiment" is the wrong word, because there is no replication and no control. If the seals were removed and the groundfish increased, or the groundfish decreased, it would tell us nothing much at all about the relationship between the species. What is the "scientific plan" to determine what the cause and effects would be?
Grey seals were part of the ecosystem in these waters before humans set eyes on them, and coexisted with very large groundfish populations until mechanized fisheries appeared, so, in effect the "experiment" has already been done, and the conclusion is: groundfish and seals can coexist in large numbers, when not over-exploited by fisheries.
We have a woeful history of manipulating ecosystems. There is sometimes a case for trying to remove non-native species with large impacts, but these attempts often backfire. Removing native species is scientifically indefensible, and, from my perspective, morally wrong.
