Golfo Dulce: critical habitat and nursery area for juvenile scalloped hammerhead sharks Sphyrna lewini in the Eastern Tropical Pacific Seascape

Scalloped hammerhead sharks Sphyrna lewini are endangered and threatened by fisheries. Along the Eastern Tropical Pacific Seascape (ETPS) adults are protected from fishing near oceanic islands, but juveniles are captured by various fishing gear in coastal areas that require identification and protection. We used passive acoustic telemetry to track movements of ten juvenile S. lewini (L_T = 87–102 cm) in Golfo Dulce, a sheltered embayment along the southwestern coast of Costa Rica where neonates and juveniles are in high abundance, to assess juvenile residency patterns. Tagged sharks were detected for up to 372 days (245 days average). Average residency was high during the first month after tagging (Residency Index = 0.65 ± 0.14) and decreased exponentially after, but remained high for eight consecutive months on two individuals. One juvenile female shark (~1 year old), remained in the vicinity of the array for 9 months, returned after 11 months, and moved more than 400 km offshore to adult habitat where it was caught 3.5 years after tagging. We found that at Golfo Dulce there is: (1) high residency of juvenile S. lewini for at least a month, (2) juvenile presence for up to a year, (3) continued use during multiple years, and (4) connection between this juvenile habitat and offshore adult habitat. This collective evidence suggests that Golfo Dulce is a critical habitat for juvenile survival and recruitment into adult populations of S. lewini in the ETPS, and adds evidence for use of this area as a juvenile nursery.