Seasonal Distribution and Habitat Associations of Bull Sharks in the Indian River Lagoon, Florida: A 30‐Year Synthesis

Abstract

AbstractMany coastal shark species use shallow estuarine regions as nursery habitat, but there are considerable gaps in our understanding of the seasonal distribution and habitat use patterns of sharks within these systems. We compiled all available sampling data from the Indian River Lagoon (IRL) along Florida's central Atlantic coast to examine the distribution of bull sharks Carcharhinus leucas. The data synthesized in this study spanned the 30‐year period 1975–2005 and included information on the seasonal distribution, size structure, and habitat associations of 449 bull sharks. For comparison, data from an additional 106 bull sharks captured in shelf waters adjacent to the IRL were also examined. The IRL is dominated by young‐of‐the‐year (age‐0) and juvenile bull sharks, which were most abundant during spring, summer, and autumn. Shark captures were most often associated with shallow freshwater creeks, power plant outfalls, ocean inlets, and seagrass habitats with temperatures greater than 20°C, salinities of 10–30‰, and dissolved oxygen concentrations between 4 and 7 mg/L. Juvenile bull sharks were found in waters with higher mean salinities than were age‐0 sharks. Although the IRL is one of the most important bull shark nursery areas on the U.S. Atlantic coast, catch‐per‐unit‐effort data indicate that bull shark abundance decreases with increasing latitude within and north of the IRL, suggesting that the IRL is the northern limit of functional nursery habitat for this species in the northwest Atlantic Ocean.