Conservation of Fish Assemblages in Protected and Open Embayments Required for Maintenance of Biodiversity in the Upper St. Lawrence River

The cumulative effects of water level regulation and the alteration of habitat by humans and the invasive hybrid cattail Typha x glauca pose threats to nearshore fish assemblages.  We contrasted fish assemblages in open and protected nearshore habitats within the Thousand Islands region of the upper St. Lawrence River to examine how fish-habitat associations and fish assemblage structure differed based on environmental characteristics in each habitat type. We sampled nearshore fish assemblages as well as measured a suite of physical habitat variables in eight littoral embayments. Two distinct patterns of fish assemblages were described by a principal component analysis (PCA) and nonmetric multidimensional scaling model consistent with samples collected from  protected  and open nearshore habitats.  The PCA suggested that the open habitat assemblage was associated with increases in species of Notropis minnows, round goby Apollonia melanostomus, yellow perch Perca flavescens, bluegill Lepomis macrochirus, white sucker Catostomous commersonii and tessellated darter Etheostoma olmstedi while the protected habitat assemblage was associated with tadpole madtom Noturus gyrinus, northern pike Esox lucius, central mudminnow Umbra limi, and pumpkinseed  Lepomis gibbosus. Canonical correspondence analysis of fish abundance and environmental variables identified substrate, fetch, temperature and chl a as the most influential variables structuring fish assemblages among nearshore habitat types. Restoration and conservation strategies in the upper St. Lawrence River should focus efforts on increasing connectivity among nearshore habitats to provide refugia from suboptimal habitat conditions and enhance nearshore spawning and nursery habitat.