Assessment of Wetland Habitat Use by Juvenile Fishes, with a Focus on Rock Bass Ambioplites rupestris, within the St. Clair River Delta, Michigan, USA

Abstract

Juvenile fish are an essential link to adult populations, and often inhabit distinct environments from larvae and adults. I sampled fish at nine sites within the St. Clair River delta in an effort to 1) describe the juvenile fish community, 2) determine the use of bay habitats as nursery grounds, and 3) assess the short-term growth of rock bass Ambloplites rupestris. Fish were collected monthly from May through August and in October of both 2011 and 2012 using hoop nets and minnow traps in shallow areas along the Middle Channel and its connected bays. Catch per unit effort (CPUE) was highest in the channel sites and in October, with emerald shiner Notropis atherinoides and other cyprinids dominating overall catch. When these taxa were removed to evaluate only young-of-the-year (YOY) fishes, rock bass accounted for almost 50% of the overall catch and were cosmopolitan throughout the system. CPUE and rare species richness for YOY fishes were greater at bay sites than channel sites, and YOY fish species richness was correlated with vegetation species richness, which was also higher in bay sites. Growth of YOY rock bass was assessed using RNA:DNA ratios, which were highest in the bay sites, as well as in late summer, indicating that these nursery grounds may allow faster growth, and that growth fluctuates seasonally. While community associations varied by site and month throughout the summer, bay habitats consistently had higher abundance and diversity of YOY fish, indicating that these habitats may be critical nursery grounds and should be highlighted as conservation and restoration priorities.