From the Great Lakes Echo: 

“Sea lamprey – unlike the silver and American brook species – come from the Atlantic Ocean, accidentally introduced to the Great Lakes through shipping canals.

Like the native silver lamprey, sea lamprey are parasitic, with sharp teeth and a sucking disc mouth that allows them to feed on the blood of host fish. Also like the silver lamprey, they are harmless in their early stages of development. 

Sea lamprey spend the first four years of their life as larvae in the soft bottom and banks of lakes or streams, according to the New York Department of Environmental Conservation. 

As they mature, they change into the harmful predator threatening the Great Lakes today, said Yu-Weng Chung-Davidson, a senior research associate on Li’s team.”