Meeting Abstract
South Florida witnesses an enormous migration of marine apex predators each year as massive aggregations of blacktip sharks (Carcharhinus limbatus) overwinter in nearshore waters. The narrow shelf and close proximity of the Gulf Stream Current to the Palm Beach County (PBC) shoreline constrain tens of thousands of sharks to the shallow, coastal environment. This natural bottleneck provides a unique opportunity to estimate abundance. Over a 39 month period, a biweekly aerial survey was flown along the length of PBC and the number of sharks was directly counted. Shark abundance peaked in the winter (January-March) and declined precipitously to nearly zero in the summer months. Shark abundance was correlated with water temperature with sharks found in large numbers only when sea surface temperature ranged from 21-24° C. A subset of sharks was instrumented with acoustic transmitters and 70% of instrumented individuals were detected at various locations along the eastern seaboard. Sharks appear to follow their preferred temperature, traveling as far north as Delaware Bay in the summer before returning to overwinter in south Florida. The straight line movements from point to point represent a minimum travel velocity of up to 31 km-day. These baseline abundance data can be compared to future studies to determine if shark population size is changing and if sharks are restricting their southward migration as global water temperatures increase.
