Meeting Abstract
The migratory behavior of the blacktip shark (Carcharhinus limbatus) in the Western Atlantic has been anecdotally described but not empirically studied. The sharks are thought to migrate from nursery areas along the southeastern coast of the United States in the summer, to South Florida, where they remain in large aggregations (up to 800 sharks km-2) from January to April before returning northward. The first recorded description of the blacktip migration states that they occur north of Cape Hatteras, North Carolina “only as a rare stray.” Given that this description was published over 70 years ago, their range might have shifted poleward in response to warming ocean temperatures, as has been demonstrated in many other marine species. To investigate the current migratory pattern of this population, 27 blacktip sharks were instrumented with acoustic transmitters, while they overwintered in South Florida, and passively tracked along the eastern coast of the United States in cooperation with the Florida Atlantic Coastal Telemetry (FACT) and the Atlantic Cooperative Telemetry (ACT) networks. Eighteen of the 27 individuals (67%) were detected after instrumentation. Three of those 18 individuals (17%) were detected far north of the previously reported North Carolina boundary, off Delaware Bay, NJ (1) and Long Island, NY (2). Five individuals were detected at the original capture location in South Florida the following winter, including two of the sharks that were detected in Delaware Bay and Long Island. This study provides the first empirical evidence of blacktip sharks completing a full migration cycle and suggests that their northern distribution may have expanded poleward.
