Diet and prey preference of juvenile lemon sharks Negaprion brevirostris

摘要

Sharks are often regarded as opportunistic asynchronous predators that feed on the most abundant prey. In the present study, 2 populations of juvenile lemon sharks Negaprion brevirostris were investigated from Bimini, Bahamas, with well-defined home ranges facilitating the estimation of prey preference. Stomach contents were quantitatively analysed from 396 lemon sharks with data on prey species and abundance obtained from quantitative sampling of mangrove and sea-grass faunal communities to elucidate preferences with respect to prey type, prey size and location. Yellowfin mojarra Genes cinereus dominated the diet of juvenile lemon sharks (> 50 % by weight and percentage index of relative importance, %IRI), even when present in lower abundances in the environment. Preference was determined and compared using abundance, %IRI values and original weight of prey, with the latter preferred due to their close relationship with energetic intake. Juvenile lemon sharks do not feed indiscriminately, but exhibit prey preference and size selection. Juvenile lemon sharks at Bimini demonstrated a hierarchy of prey preference: parrotfish (Scaridae) > mojarra (Gerreidae) > toadfish (Batrachoididae) > filefish (Balistidae) > grunts (Haemulidae) > barracuda (Sphyraenidae). High overlap between shark diet and mangrove communities revealed the importance of mangroves to lemon sharks and their prey. Lemon sharks fed disproportionately on intermediate sized teleosts and crustaceans, with maximum prey size of nursery-bound sharks primarily limited by availability in the environment. We conclude that sharks can be highly plastic foragers, capable of selective feeding, but will switch to more opportunistic foraging when environmental conditions deteriorate.