Characteristics of Spawning Lake Sturgeon in the Upper Black River, Michigan

Abstract

The population of lake sturgeon Acipenser fulvescens in Black Lake, Michigan, is confined to a smaller spatial habitat than was historically available, which has led to concern over the future viability of the population. Biological data were collected from spawning lake sturgeons in the Upper Black River in 2001 and 2002 to assess the size of the spawning run and the condition of spawning fish relative to other populations. A 1.6-km section of the total 11 km of available habitat in the Upper Black River was an important spawning location for lake sturgeon. Spawning fish were captured and data were collected at the spawning sites from 115 adults in 2001 and 104 adults in 2002. Fish gender was determined by the presence of ripe gametes. The male : female sex ratio was 1.55:1 in 2001 and 2.06:1 in 2002. Weight at length for spawning lake sturgeons was comparable to that of other studied populations, and the average size at age of spawning lake sturgeons was slightly higher than for spawning fish from the Sturgeon River, Michigan, an open tributary to Lake Superior with a self-sustaining population. Consecutive-year spawning was documented for 10 male lake sturgeons, which showed an average increase in total length and weight of 1.6 cm and 1.15 kg, respectively. Age estimates predicted by a von Bertalanffy model for the spawning adults predicted males representing 25 different age-classes ranging from age 12 to age 63 and females representing 29 different age-classes ranging from age 20 to age 70. On the basis of our observations of ripe gametes, growth of the annual spawners, and overall condition of the spawning fish, we conclude that the spatially restricted habitat in Black Lake was sufficient to support adult lake sturgeon growth and gamete production.