Duration and drift of larval lake sturgeon in the Sturgeon River, Michigan

Recovery of lake sturgeon populations in the Great Lakes basin is now a focus of binational, federal, provincial, state and tribal management agencies; however, efforts to restore and rehabilitate stocks will be ineffective until early life history strategies are understood. Defining the extent and duration of larval drift will help to protect and re-establish populations of lake sturgeon, Acipenser fulvescens. The stages of early-life, from egg to about 250 mm total length (TL), are believed to be the most vulnerable to factors affecting survival. Drift of larvae was monitored during 8 of the 9 years between 1992 and 2000 using drift nets set 14, 26, 35, 45 and 61 km below the spawning site on the Sturgeon River, Michigan. Natural river water levels varied between years and influenced drift sampling and success of spawning and hatch. Between 1992 and 2000, total annual catch of drifting larval lake sturgeon varied from three to 423 individuals, with 978 larvae collected over the 8 years. Larvae drifted as a \u27plug\u27 and became more dilute and spread out over time with distance downstream. This study has shown that (i) lake sturgeon larvae drift to 26 river kilometers (rkm) below the spawning site within 15 to 27 days after spawning and to 45 rkm within 25 to 40 days after spawning; (ii) the average size of the larvae increases with distance downstream; (iii) drifting larvae are not distributed uniformly in space or time; (iv) two peaks in spawning were common and spawning seems to be related to the phase of the new moon in years without heavy spring flows; and (v) that the lower river may be an important habitat for young-of-the-year sturgeons