Delination of Coastal Shark Habitat within North Carolina Waters Using Acoustic Telemetry, Fisher Independent Surveys, and Local Ecological Knowledge
Knowledge of shark habitat preferences and use patterns is important to effectively manage shark fisheries and account for interactions between sharks and species targeted by other fishery management or conservation efforts. To gain baseline knowledge of the availability and spatial extent of shark habitat in North Carolina waters, habitat was assessed at three spatial scales: coastal nearshore, whole estuarine, and estuarine microhabitat. The local ecological knowledge of North Carolina fishermen was also incorporated and compared with data collected using fishery independent means. Catch data and acoustic telemetry were used to assess shark habitat at the coastal nearshore scale. Sharks captured near Cape Hatteras could be grouped into warm water and cold water assemblages. Juvenile Dusky (Carcharhinus obscurus) and Sandbar (Carcharhinus plumbeus) Sharks were tracked using acoustic telemetry, and 12 of 15 tagged Sandbar Sharks were detected over an area from New York City to Savannah, Georgia. The spatial extent of potential juvenile Sandbar Shark habitat was influenced by a combination of sea surface temperature and chlorophyll a concentrations, with habitat restricted to an area in the northern portion of Raleigh Bay near the Hatteras Bight during winter. At the estuarine scale, boosted regression tree modeling of shark catch and environmental data from North Carolina Division of Marine Fisheries (NCDMF) gillnet and longline surveys were used to spatially delineate potential habitat for six species within Pamlico Sound. Inlet distance and temperature were among the most influential environmental factors associated with species presence, while salinity was the most influential factor on abundance. Potential habitat for most species was located on the east side of the sound near the inlets with the exception of the Bull Shark (Carcharhinus leucas) which showed hot spots of potential habitat near sources of freshwater input. At the estuarine microhabitat scale, catch and environmental data from a fishery independent survey conducted in Back and Core Sounds and a small scale acoustic array deployed around Middle Marsh in Back Sound were used to identify associations between species and with specific habitat types. Spatial overlap between species was generally low and species assemblages separated based on water temperature. Smooth Dogfish (Mustelus canis) and Spiny Dogfish (Squalus acanthias) occurred primarily during mid afternoon and Blacknose Sharks (Carcharhinus acronotus) occurring most often at night. A large Bull Shark tagged in another study accounting for the majority of tag detections and occurred within the array primarily during nighttime hours, most often on receivers deployed at two oyster reef sites and one sand flat site. Local ecological knowledge (LEK) of shark distributions and habitat preferences was gathered using structured interviews with North Carolina fishermen and their observations were compared with data from fishery independent surveys and primary literature to assess their accuracy. All hypotheses generated from LEK were classified as either supported or plausible. Overall, water temperature was identified as an important influence on shark species presence and assemblage composition, with factors such as salinity and potential interspecific interactions more important at finer habitat scales. The locations and spatial extents of shark habitats in North Carolina are influenced by dynamic environmental factors and may be affected by large scale perturbations such as climate change.