Seasonal movement patterns and habitat preferences of age-0 lake sturgeon in the lower Peshtigo River, Wisconsin

Efforts to restore lake sturgeon Acipenser fulvescens to former population levels in the Great Lakes will benefit from a thorough understanding of the species' early life history. The rehabilitation of this species will be aided by identifying nursery habitats in riverine environments through characterizing the habitat use and movements of age-0 fish. The objectives of this study were to determine the habitat preferences and movement patterns of age-0 lake sturgeon in the lower Peshtigo River, Wisconsin, a tributary of Lake Michigan. Fish were captured from June through October 2002 and 2003 by means of wading, snorkeling, haul-seine, and backpack electrofishing surveys, and radio transmitters were attached to individuals larger than 74 g. For each capture and relocation site, habitat features were evaluated by measuring water depth, velocity, and temperature and by characterizing substrate type and macroinvertebrate assemblage. Age-0 lake sturgeon were collected and relocated at water depths less than 2 to over sand substrates and at current velocities less than 0.60 m/s. Capture and relocation sites were dominated by dipteran larvae, and the median macroinvertebrate density was lower at these sites than in the remainder of the study area. Macroinvertebrate diversity index values were also lower at capture sites than in the overall study area. Daily movements of age-0 lake sturgeon showed that fish exhibited greater activity after dark, whereas seasonal movement patterns were related to changes in water temperature, particularly during fall months as fish moved from the river to Green Bay. These results suggest that shallow, riverine areas with sand substrates, low current velocity, and a predominance of dipteran larvae should be protected as important nursery habitats in Great Lakes tributaries that support spawning populations of lake sturgeon.