Adult Lake Sturgeon Movements Associated with the Large Rivers of Green Bay, Lake Michigan

Spawning river fidelity of lake sturgeon is difficult to assign considering the relatively long inter-spawning intervals and the complexity of conducting assessments on large waterbodies with multiple spawning rivers, like Green Bay. In addition, movement patterns of adult sturgeon are likely impacted due to a relatively small population size compared to historic estimates (< 1%) and hydroelectric dams on most rivers which have altered spawning behavior.

 Green Bay lake sturgeon have been genotyped (N=907) and indirectly assigned to assumed spawning river groups (Menominee, Peshtigo-Oconto, and Fox-Wolf); but direct tagging studies have indicated mixing of adult sturgeon between genetically assigned spawning rivers. Using acoustic telemetry, we observed the movements of adult lake sturgeon (N=83) into five Green Bay rivers (Cedar, Menominee, Peshtigo, Oconto, and Fox). Acoustic receivers allowed us to identify seasonal and directional movement patterns of these sturgeon for multiple years. We identified that most (57%) of the sturgeon tagged within or adjacent to the mouth of one of three rivers (Menominee, Peshtigo, and Oconto) were only detected in the river where they were originally tagged. However, it was common (19%) to detect implanted sturgeon in more than one river. No detections occurred with the Cedar and Fox river receivers, so we have no evidence that these sturgeon from the Menominee, Peshtigo and Oconto rivers used the former rivers.

 A significant group (24%) of the lake sturgeon were not detected post-surgery which may be related to long inter-spawning intervals and a three year battery life of the original transmitters. We did not find any correlation between size or sex of the sturgeon as an explanation of movement. We are not able to confirm that upstream movements in April and May of each year was associated with spawning activity, since acoustic receivers were located downstream of known spawning sites. Movements were routinely detected during both spawning and non-spawning seasons; but most fish were only detected for a few days to weeks in the subject rivers and occupied the greater Green Bay waters for the remainder of the year. Genotypic assignments can corroborate that implanted fish originated from the rivers where they were tagged; but it appears from our acoustic telemetry data that mixing of these spawning stocks occurred during spring spawning periods.