Assessment of the vertical distribution of larval lake sturgeon drift in the Peshtigo River, Wisconsin, USA

Drift nets have been used to document reproductive success of lake sturgeon Acipenser fulvescens. Current net designs and methods for collecting drifting larvae only sample a portion of the water column, which require assumptions of either a benthic or uniform distribution of larvae when estimating abundance or production. The objective of this study was to describe the vertical distribution of larval lake sturgeon in the Peshtigo River, Wisconsin, and to determine if drift was benthic or uniform in distribution. A net was designed to assess the vertical distribution of drifting larvae in 0.2-m increments at depths up to 1.4 m; however, during this sampling, maximum depth did not exceed 0.78 m. The distribution of larval lake sturgeon was neither benthic nor uniform. Only 5% of larvae were captured in the lowest 0.2-m increment, followed by 18% from 0.2 to 0.4 m, 41% from 0.4 to 0.6 m, and 36% from 0.6 m to the surface. Although results will likely differ among years, systems, and the precise location of sampling, our study illustrates the importance of and provides a technique for testing assumptions of the vertical distribution of larval lake sturgeon drift.