Dispersal Patterns of Lake Sturgeon in the Detroit-St. Clair River System

This presentation summarizes recent results for an ongoing project focused on helping fishery managers quantify the spatial extent, population structure, and abundance of the lake sturgeon (Acipenser fulvescens) that spawn in the Detroit-St. Clair river system.  Lake sturgeon are threatened across the Great Lakes basin due to the combined effects of overfishing, habitat loss, and negative interactions with invasive species.  A basic information need for conservation and restoration of this imperiled species is the abundance and spatial extent of remnant stocks.  The lake sturgeon that spawn in the Detroit-St. Clair river system (herein, DSCRS) represent one of the largest remaining remnant lake sturgeon populations in the Great Lakes, but their exact status and spatial structure is unclear.  The absence of this information makes it difficult for fishery managers to assess and manage threats at appropriate spatial scales.  Recent genetics analyses were unable to differentiate spawners from the Detroit and St. Clair rivers despite evidence that this species exhibits natal philopatry, while mark-recapture and short-term radio telemetry data suggest that multiple spawning populations may exist.  Our study is using acoustic telemetry to help managers determine the actual number of spawning groups in the DSCRS and their spatial extent.  One of the primary project objectives is to use acoustic telemetry to determine if lake sturgeon dispersal from spawning sites depends on spawning river and capture site within the river.  To address this objective, lake sturgeon were captured, implanted with acoustic transmitters with a 10-year battery life, and then released back into the environment.  Movements of individual animals were then tracked from March to early December 2012.  Analysis of tracking data showed that SCRS lake sturgeon have complex migration patterns with some individuals migrating as far 150 km during the period of observation.  There also was significant mixing of different release groups within the spawning rivers during certain periods.  Clear modalities in the time when individuals exited spawning rivers for feeding and/or overwintering grounds also was evident with one group leaving spawning rivers immediately after temperatures exceeded the preferred range for spawning while a second group remained in the spawning rivers until late fall.  Fish tracking data also led to the discovery of important sturgeon overwintering habitats in Lake St. Clair, which is currently listed as an area of concern.