Fierce invader steals nests from a native fish

Since the round goby arrived in the Great Lakes more than a decade ago, the small but feisty fish has spread rapidly and has caused local extinctions of a native species. Researchers now have identified just how the gobies take over.

In those places where the pencil-length bottom-dwellers have proliferated, populations of the mottled sculpin, an important prey species for larger fish, have crashed.