The Nurse Shark, Mating and Nursery Habitat in the Dry Tortugas, Florida
Harold L. Pratt, Jr. and Jeffrey C. Carrier
Abstract.—A 12-year study of nurse shark Ginglymostoma cirratum reproduction in the islands of the Dry Tortugas, Florida has shown continued use of a 0.8-square-hectare shallow lagoon by sharks in all life stages from neonate through adult. Adults breed here every year during the June and July mating season. Juveniles use the same lagoon until they are about 185 cm total length (TL). When not in the lagoon, evidence from remote sensing shows that the sharks spend a large part of their time at or near the base of the seaward fringing reef. The sharks’ distribution in this area takes advantage of natural geological and biotic habitat features. To determine habitat use, movements, and behavior, we have tagged 242 nurse sharks (31.5–275 cm TL), including 103 adults, and placed transmitters on 49 adults. Tag recaptures have shown that most males return annually to mate and most females return at 2-year or longer intervals. Our repeated capture and recapture of juveniles of all sizes from neonate to 165 cm substantiates the additional use of this same sea grass lagoon as primary and secondary nursery grounds. The surrounding octocoral and fringing reef habitats are important to the reproductive cycle of adults. It may take the juxtaposition of these three habitats to create a mating refuge.