Movement patterns of juvenile lemon sharks Negaprion brevirostris within Atol das Rocas, Brazil: A nursery characterized by tidal extremes

Movement patterns and habitat use of juvenile lemon sharks Negaprion brevirostris were monitored at Atol das Rocas, Brazil, an atypical nursery area for this species, characterized by extreme tides and a lack of seagrass flats and mangroves. Twenty-three sharks carrying transmitters were monitored using an array of bottom-fixed automated receivers during 3 trips over a total of 60 d. Transmitters were recorded on receivers over 13 000 times, and the majority of sharks were detected more than 100 times. Newborn sharks (60 to 80 cm total length, TL) showed restricted but repeated movements between small tide pools on reef flats at low tide and a small, shallow, nearby tidal creek at high tide. Larger sharks (up to 106 cm TL) sampled 6 and 20 mo after the study in March 2000 frequented the tidal creek and several other locations at high tide and a variety of larger pools at low tide, and in general exhibited more extensive movements within the atoll than did newborn sharks. Sharks approaching 2 yr of age were generally observed in specific pools or shallow water locations within the atoll during high and low tides, but also expanded their movements to include more of the atoll. Throughout the study, young lemon sharks appeared to concentrate movements within shallow-water low-tide refuges and separate high tidal areas. Movement patterns of sharks in Atol das Rocas differ from those at other well-studied lemon shark nursery locations, where individuals continuously occupy shallow flats and mangrove habitats. Nevertheless, lemon sharks in general restrict their movements to shallow-water habitats regardless of the specific nursery area occupied. This behavior is most likely related to predator avoidance. This study provides an example of the interaction between the physical environment and the biology of animals - in this case, the influence of the physical characteristics of a nursery area and the behavioral ecology of young lemon sharks.