Aiye! Is this from a horror movie!?

This is a sea lamprey that left the scar on the steelhead trout we just viewed. It was still attached to the trout when we captured it in the seine. The sea lamprey is an exotic that gained access to Lake Erie and the upper Great Lakes with the creation of the Welland Canal around Niagra Falls. They are parasites of the trouts and salmons, and I have even seen their scars on species like catfish and carp.

A parasite uses another organism, with no benefit, and usually harm to the host (the prey).

It's commonly believed that the sea lamprey was the demise of the native Lake trout, exotic coho salmon and rainbow trout populations in the 1950's and 1960's. Due to its evil looks, it made for an excellent scapegoat for overfishing and human pollution inhibiting (stopping) the salmonoid young's growth. The sea lamprey certainly didn't help as a final factor, but we should understand the main causes for decline were human activity.