Fine-scale distribution and occupancy modelling of the threatened pugnose shiner (Notropis anogenus) in the St. Lawrence River, Ontario, Canada1

Understanding population-level habitat requirements is important for the effective conservation of imperilled species, especially for those with fragmented distributions. This study examined fine-scale distribution of the threatened pugnose shiner (Notropis anogenus) in the upper St. Lawrence River, Ontario, Canada. Occupancy modelling, multivariate analyses, and co-occurrence modelling were used to identify environmental correlates of pugnose shiner distribution and species associations in an embayment area, Thompson’s Bay. The pugnose shiner was most abundant in outer bay sites that were cooler, less turbid, had a higher pH, and had more submerged aquatic vegetation than the inner bay sites. The probability of pugnose shiner occupancy increased with distance from the inner bay and with the presence of Chara vulgaris, and decreased with increasing conductivity. The pugnose shiner positively co-occurred with seven species, including the blackchin shiner and blacknose shiner, and negatively co-occurred with bluegill. Centrarchid species were dominant across Thompson’s Bay. This has important conservation implications because some native centrarchid predators are increasing in abundance, coincident with climate change, which may threaten the persistence of rare and imperilled cyprinids such as pugnose shiner.