Seasonal offshore/inshore migration of round gobies

Abstract

Since the invasion of round gobies (Neogobius melanostomus) to Lake Michigan, they have become integrated into both nearshore and offshore food webs. Round gobies can be found in relatively shallow water (<20 m) during summer, but nearly disappear from these depths in early fall. They have been collected, occasionally, offshore in depths greater than 70 m during warm seasons. These observations and other anecdotal evidence suggest that round gobies migrate offshore during fall and return to nearshore water in spring. To study this, a remotely operated vehicle was used to conduct video transects at various depths.Sampling showed that round gobies migrated away from the shallowest (10 m) site in early October, with larger gobies moving offshore first, and were almost exclusively found deeper than 20 m by November. Round gobies remained offshore (>30 m) until mid-May, when they began the return to nearshore habitat. The cues to start offshore and return migrations were not the focus of this project, but fall offshore migrations coincided with decreasing temperatures nearshore in fall, and in spring, the offshore movement of the thermal bar.