Seasonal Residency and Movement Patterns of Bonnetheads (Sphyrna tiburo) in Two Subtropical Estuaries and Coastal Waters of the South Atlantic Bight

Abstract

Tracking animal movements underpins our understanding of habitat linkages, stock definitions, and life-history vital rates. The bonnethead (Sphyrna tiburo) is abundant seasonally in southeastern United States (US) Atlantic coast estuaries; however, there is relatively little information regarding bonnethead ecology at the northern end of its distribution. We employed acoustic telemetry to document patterns of seasonal residency and movement for bonnetheads in North Carolina (NC) and Georgia (GA) estuaries, as well as other portions of the South Atlantic Bight (SAB). We acoustically tagged 21 bonnetheads in Beaufort Inlet Estuary, NC and 16 in Wassaw Sound, GA, and tracked those fish within estuarine arrays of 78 and 8 hydrophones in NC and GA, respectively. Bonnetheads were resident in NC and GA estuaries from March through November. Overall, detections were highly localized within individual estuaries, with most bonnetheads remaining in the area where they had been tagged, suggesting small core areas of movement (≤ 2 km) during seasonal residency. Conversely, 15 bonnetheads tagged in NC and 10 tagged in GA were detected in 14 other coastal hydrophone arrays in South Carolina, GA, and Florida (FL). The location and timing of these detections suggest that bonnetheads from distinct estuaries along the SAB overlap during late fall and winter months along the southeast US Atlantic coast, especially offshore of Brunswick, GA and Cape Canaveral, FL. Return rates for NC and GA bonnetheads were at least 25% and 19%, respectively, indicating a notable degree of estuarine-scale site fidelity.