Movement of smallmouth bass within the Beaver Island Archipelago, northern Lake Michigan

Fish movement may vary across a wide array of aquatic ecosystems and may be related to the overall size of the system inhabited. We investigated movement of smallmouth bass in Lake Michigan because this information is lacking for larger systems. A total of 16 smallmouth bass were surgically implanted with ultrasonic transmitters within the Beaver Archipelago, northern Lake Michigan. During 2007–2008, a maximum of one location per individual was recorded daily during three specific tracking periods – pre-spawn, spawning, and post-spawn – to determine diurnal movement patterns. Movement was evaluated as site fidelity, minimum displacement rate, maximum excursion rate, and distance from shore. Smallmouth bass exhibited greater maximum excursion rates during the spawn period compared to pre-spawn. Movement rates did not differ between tracking periods; however, movement rates were greater during the spawn period in 2007 than 2008. Both sexes moved further offshore to deeper water during post-spawn, but females were located further offshore than males during this period. Annual site fidelity was more evident during post-spawn than during spawning for both sexes. Two smallmouth bass emigrated outside of the Archipelago, suggesting this population may be more “open” in terms of individuals moving throughout northern Lake Michigan than previously thought. These results indicate smallmouth bass may move greater distances in larger aquatic systems and therefore larger management units (in terms of total area) should be established in Lake Michigan to account for these greater excursion distances.

► Movement of smallmouth bass differed between sexes and time periods.
► Annual site fidelity of smallmouth bass was more evident during post-spawn.
► The Beaver Archipelago smallmouth bass population is open in terms of migration.
► Movement of smallmouth bass may be greater in larger aquatic systems.
► Smallmouth bass management should include all of northern Lake Michigan.