How do round gobies and ruffe threaten native Great Lakes fish?

The ruffe and the round goby are nonindigenous species that negatively impact the Great Lakes ecosystem. These invasive fish threaten native populations through the following mechanisms:

• Ruffe: This small, perchlike fish preys directly on the eggs of native fish species, which can significantly reduce the reproductive success of those populations.1
• Round Goby: As a bottom-dwelling fish, the round goby competes with indigenous species for essential habitat and food resources.1

The introduction of such nonindigenous species disrupts the established food web and poses a persistent challenge to the biodiversity of the Great Lakes.1