Meeting Abstract
Southeast Florida experiences an enormous seasonal influx of upper trophic level marine predators each year as blacktip sharks (Carcharhinus limbatus) migrate south to overwinter in nearshore waters. These sharks form aggregations ranging from a few individuals to thousands. The sharks are often found in very shallow water, only a few meters from popular swimming beaches which raises concerns about potential negative interactions. To quantify shark abundance and distribution, an aerial survey was conducted during peak season (December – April) from 2011-2017. A low altitude (150m) survey flight was flown from Government Cut (South Beach, Miami) to Jupiter Inlet at approximately biweekly (2011-2014) or weekly (2015-2017) intervals. A high definition video camera recorded a transect from the beach to approximately 200m offshore. Segments of the survey transect were demarcated by inlets, and the number of sharks found within each segment was counted to calculate shark density. During the seven year study, the greatest shark density was consistently found in February and March. Although sharks were seen throughout the entire 132km length of the survey transect, significantly greater numbers of sharks were found at the northernmost third of the transect in Palm Beach County (Boynton Beach Inlet to Jupiter Inlet) where densities exceeded 1,000 sharks km-2. The habitat throughout the transect is largely consistent, so it remains unclear why the sharks are not distributed farther south. Southward migrating sharks might simply stop once they reach appropriate conditions and warming oceans might eventually restrict their migration to increasingly higher latitudes.
