Meeting Abstract
Southeast Florida experiences an enormous seasonal influx of upper trophic level marine predators each year as blacktip sharks (Carcharhinus limbatus) form massive aggregations 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 four year period, a biweekly aerial survey was flown along the length of PBC and the number of sharks within 200m of shore was directly counted. Shark abundance peaked in the winter (January-March) at over 12,000 individuals, and declined to nearly zero in the summer months. This corresponds to a maximum density of over 800 sharks km-2. Because these numbers represent only the sharks immediately adjacent to the shoreline, they are a gross underestimate of the total number of sharks present. Shark abundance was inversely correlated with water temperature with sharks found in large numbers only when water temperatures were less than 25°C. 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.
