Assessing the Spatiotemporal Distribution of Larval Lake Sturgeon Acipenser Fulvescens Within the St. Clair River Delta, Michigan

Abstract

Historically, the St. Clair River provided ample spawning grounds for many native fish species including lake sturgeon Acipenser fulvescens. Anthropogenic alterations to the river’s hydrology and substrate have resulted in the loss or degradation of important spawning and rearing habitat, which along with overharvest have reduced lake sturgeon populations to less than 1% of their former abundance. Recent research and management has recognized critical knowledge gaps relating to early life stages, with focused need for understanding movement patterns and habitat use of larval lake sturgeon. To assess larval drift and movement patterns, I deployed a series of D-frame drift nets and depth-stratified (i.e. surface, middle, and bottom) conical net sets in the lower St. Clair River. These surveys provided insight on the spatiotemporal distribution of larval lake sturgeon, longitudinally throughout the North and Middle channels and vertically within the water column. From 2013-2014, 874 lake sturgeon larvae were collected. Catch per unit effort (CPUE; No. larvae/hour), total length (TL; 0.1 mm), and developmental stage (i.e. full, partial, or no yolk sac) of larvae were quantified to assess changes in catchability and growth over time (i.e. weeks) and space (i.e. river zones). Significance of differences in CPUE and developmental stage were assessed using Kruskal-Wallis nonparametric tests, followed by Dwass-Steel-Critchlow-Fligner post hoc procedure for multiple comparisons, and TL was assessed using generalized linear model two-way ANOVAs followed by Least Squares Means post hoc procedure for multiple comparisons. Results showed that larvae drifted predominantly along the river bottom and were capable of maintaining their position in the river in spite of strong currents, suggesting the nature of larval lake sturgeon drift is more active than passive, indicating that riverine habitat is important for their early survival. This information has broad implications when setting

management priorities for lake sturgeon in large river systems, by identifying the interactions and attributes important for their early survival, which help managers consider feasible management options and implement the appropriate response.