When I started reading this, I thought you were going to say the seals had learned to associate your canoe with an easy meal. Pprobably a lot easier for a seal to grab a lassoed silver than it is to grab one unfettered. We ran into the seal circus one year in a lagoon we fish. The seals would grab hooked fish, sometimes biting them and sometimes just letting them go. They kept this up a whole lot longer than we found amusing.
Are these harbor seals or sea lions? Our encounters were all with harbor seals.