Population status and demographics of lake sturgeon (Acipenser fulvescens) in the St. Marys River, from 2000 to 2007

The St. Marys River, the sole outflow of Lake Superior, was historically inhabited by lake sturgeon (Acipenser fulvescens); until recently it was unclear whether a population was still present in the river. From 2000 to 2007, the population status of subadult and adult lake sturgeon in the St. Marys River was characterized. Setlines were deployed at multiple water depths (2-20 m) for 3400 setline nights. Biological measurements including total length and weight were recorded and each individual was affixed with unique identification tags before being released. A total of 192 unique lake sturgeon were captured with a recapture rate of 16%. The population size of lake sturgeon in the St. Marys River was estimated to be near 500 individuals. Fish captured exhibited a mean weight of 13 kg (range 2-37 kg) and a mean total length of 125 cm (range 80-175 cm). The mean age of lake sturgeon captured was 20 years (range 7-59 years) and 36 age classes were represented. Lamprey wounds were observed on 23% (N = 53) of sturgeon and nearly 19% (N = 44) of lake sturgeon had visible external parasites classified as Argulus spp. This study suggests that a recovering lake sturgeon population exists in the St. Marys River, however, it remains unclear as to whether this is a self-sustaining population reproducing in the river. Additional information is needed on metapopulation dynamics, habitat use, and younger age classes to assess recruitment success and population status.