Biological Investigation of the Endangered Northern Madtom in the North Channel St. Clair River

Abstract

AbstractAquatic organisms and the habitats they live in are declining globally, yet managers often lack even basic biological information for individual imperiled species. This makes assessment of the current status, management needs, and recovery targets for these species challenging. One such organism is the Northern Madtom Noturus stigmosus, a small, bottom‐dwelling catfish of the family Ictaluridae. Northern Madtom are listed as endangered in the state of Michigan and the province of Ontario, with only a handful of isolated populations known in each region. To address life history uncertainties and to provide fisheries managers with baseline information to inform decision making, the Michigan Department of Natural Resources annually sampled Northern Madtom in the St. Clair River using minnow traps and amassed the largest known data set for this species. We handled 871 individuals from 2010 to 2022, with yearly catch rates ranging from 0.17 to 1.33 individuals/trap. Age estimates derived from otoliths and dorsal spines of 17 individuals showed no clear pattern of bias, indicating that nonlethally collected dorsal spines provide a suitable age estimation method. We developed an age–length key to assign ages to all individuals in our data set, calculated growth parameters, and determined that annual mortality rates across all ages ranged from 46% to 69%. Diet analysis revealed that caddisfly (order Trichoptera) larvae were the dominant prey item and fecundity averaged 178 eggs/female. We compared microsatellite allele frequencies and mitochondrial DNA haplotypes among samples collected in the St. Clair River and the Detroit River. Significant evidence of genetic structure was present, indicating limited gene flow and suggesting that separate management of these two populations may be warranted. Collectively, these data provide context for managers interested in the development of biological reference points and planning for the conservation and management of this species.