Something similar happened in California when the government began protecting sea otters, which had been driven to near-extinction. They also eat a lot of fish and shell fish. By the 1980's, sea otters had grown so numerous that the abalone and other shell fish--once abundant--became practically non-existent along the coast of Monterey County, and fisheries were also adversely affected.
California also has a Sea Lion problem where they climb aboard moored boats and sink them. Male Sea Lions can weigh 1500 lbs.
Our Grey seal males go about 500 lbs, it is only a matter of time until they move to areas that have moored boats that we will find out if like the California Sea Lions they want to climb onboard.
For now the Chatham seal Colony has brought whites into shallow water with has a sandy bottom which makes aerial spotting of the cruising shark much easier. Chatham has become a white shark taggers paradise. - Tom