As for predation by grey seals on fish stocks, scientists sometimes shy away from precisely identifying the impact on the biomass. According to a person I spoke to, scientists apparently said that seals did not eat large quantities of cod and other fish. Regardless of what people say, a seal eats a ton of fish each year.
According to one of my friends, it is simple: one thing he knows for sure is that seals do not eat strawberries. They eat fish and there are a lot of them. So it is clear that one way or another, there is an impact on the biomass.