Movement and reproductive structure of lake sturgeon in Voyageurs National Park, Minnesota

We examined seasonal movement patterns and reproductive structure of lake sturgeon Acipenser fulvescens in Voyageurs National Park, USA. Lake sturgeon (n=243) were collected in the spring of 2007-2009 prior to spawning. Sixty sturgeon were implanted with Vemco V16 acoustic transmitters. Movement was monitored using an array of 13 stationary receivers in Namakan Reservoir and its major tributaries. A blood sample was taken from the caudal vasculature of 133 fish and analyzed for plasma steroid concentrations (testosterone and estradiol-17ß) using radioimmunoassay. Ninety-four females and 39 males were identified. Of the females 8 (9%) were considered gravid, while 11 (28%) of the males were considered ripe based on steroid concentrations. Linking these fish to daily movement summaries, we identified three tributaries as potential spawning areas. One of these tributaries, the Namakan River, may have multiple spawning sites. Evidence from plasma steroid concentrations also revealed that annual as well as periodic spawning of males may occur. We noted two spawning migration strategies. An initial upstream migration into the river that began in the summer and resumed in the spring; and complete migration to potential spawning locations in one trip that began in the early spring.