A Population Study of Northern Madtom in the St. Clair - Detroit River System, Michigan

Abstract

The northern madtom (Noturus stigmosus) is a small Ictalurid catfish historically found in isolated populations throughout Western Lake Erie and the Ohio River Basin. Until recently, northern madtom were considered extirpated from most of their historic range in Michigan; however, monitoring of constructed spawning reefs in the St. Clair Detroit River System revealed northern madtom on and near these new reefs. Northern madtom are vulnerable to extinction due to their rare occurrence and lack of knowledge about their habitat requirements. I investigated selected reefs and rocky substrate sites in the Detroit River and the St. Clair River Delta to determine the presence and abundance of northern madtom. Overall, I collected thirty-seven northern madtoms in 2013 and 2014, and was also able to use data from another twenty-six fish collected in a previous study in 2011. Northern madtom abundance and occurrence was highly correlated (Pearson, r = 0.803) to preferred locations based on a habitat suitability index using bathymetry and surface current velocity. There was no correlation between age of reef and abundance of northern madtom. However, northern madtom were only observed in close proximity to rocky substrate which supports the notion that they prefer rocky substrate and constructed spawning reefs are helping their populations to recover. I also aged otoliths, pectoral spines, and dorsal spines from northern madtom; ages observed ranged from one to five years. A Von Bertalanffy growth curve was fit to the estimated ages and measured total lengths (mm); results were an asymptotic length ( 𝐿∞) equal to 142mm and growth rate (K) equal to 0.4025. I collected five northern madtom that were not aged; these were smaller than the estimated at age one total length (67mm), which shows evidence of natural reproduction occurring in these waters.