Estimation of mortality of juvenile blacktip sharks, Carcharhinus limbatus, within a nursery area using telemetry data

A population of young blacktip sharks (Carcharhinus limbatus) was monitored over three years to determine their mortality rates using a series of acoustic listening stations. Based on these data it was possible to use several mortality estimators, including indirect life history based methods and direct methods such as the Kaplan-Meier and SURVIV methods, to estimate natural, fishing, and total mortality. Kaplan-Meier (61-91%) and SURVIV (62-92%) methods provided nearly identical total mortality rates during the first six months of life. This agreement suggests that these estimates are accurate for this population. All natural and fishing mortality occurred within the first 15 weeks of the study. This suggests that young sharks are most vulnerable to all types of mortality during this period. Sharks that survived beyond the first 15 weeks successfully left the nursery and were presumed to have migrated southward during fall months. These results provide critical information concerning the early life history of sharks and the importance of nursery areas to the survival of young animals.