Movements and Habitat Use of Juvenile Lake Sturgeon in the Namakan River of Northwestern Ontario

Lake sturgeon (Acipenser fulvescens) are listed as a Threatened Species in Northwest Ontario and Special Concern in Minnesota, with those present within the Namakan River being of management concern for stakeholders on both sides of the international border.  Information on the ecology of juvenile sturgeon (i.e., those <60cm in length) is lacking in this system, and across the species’ range in general.   We initiated a study of juvenile sturgeon in the summer of 2010 to address several aspects of their ecology, including the use of an acoustic telemetry positioning system to determine fine scale (10 m²) movements and habitat use.

We used gillnets (mesh sizes 38-76mm) to sample juvenile sturgeon from June-July, 2010. A total of 106 juvenile sturgeon were captured with the majority (85%) being captured within Bill Lake, a small (134 ha) and deep (>30 m) lake along the rivers upper watershed. Ten fish from Bill Lake were surgically implanted with acoustic transmitters (Vemco V13). An array consisting of four acoustic receivers (Vemco VR2W) and two synchronizing reference position transmitters (Vemco V16) were determined sufficient to cover the study area. The receivers were deployed from 23 July to 23 Oct and recorded a total of 699,122 detections. The data were then processed and imported into ARCGIS to produce 12,583 locations. The number of individual fish locations ranged from 89 to 5,081 with three fish producing the majority (84%) of the total locations.  Analysis of movement data shows that individual variation is high, with no predictable patterns exhibited by all tagged fish. Assessments of habitat use and availability within Bill Lake results in juvenile sturgeon showing preference for habitats characterized by depths greater than 10 m and high flows (>.4 m/s).