Effects of body size, age and maturity stage on diet in a large shark: ecological and applied implications

Abstract

Ontogenetic diet shifts are a widespread phenomenon among vertebrates, although their relationships with life history traits are poorly known. We analyzed the relative importance of body size, age and maturity stage as determinants of the diet of a marine top predator, the copper shark, Carcharhinus brachyurus, by examining stomach contents using a multiplehypothesis modeling approach. Copper sharks shifted their diet as size and age increased and as they became sexually mature, incorporated larger prey as they grew, and had a discrete shift in diet with body size, with only individuals larger than %200 cm total length able to prey on chondrichthyans. Body size was the most important trait explaining the consumption of chondrichthyans, while age determined the consumption of pelagic teleosts. Pelagic teleosts were consumed mostly by mediumaged sharks, a result, probably, of a risk-reducing feeding strategy at young ages coupled with either a senescence-related decline in performance or a change in sensory capabilities as sharks age. Copper sharks of all sizes were able to cut prey in pieces, implying that gape limitation (i.e., the impossibility of eating prey larger than a predator's mouth) did not play a role in producing the diet shift. Our results suggest that, contrary to the current practice of setting minimum but not maximum size limits in catches, any plan to conserve or restore the ecological function of sharks, through their predatory control of large prey, should aim to maintain the largest individuals.

Food habits of the rough rayRaja radula(Chondrichthyes: Rajidae) from the Gulf of Gabès (central Mediterranean Sea)

“…These ontogenetic shifts in feeding biology indicate that R. radula has sufficiently plastic foraging behaviour to change from one strategy to another. Diet shift with size is a pattern widely observed in elasmobranchs (Lucifora et al 2009). This shift can be associated with changes in morphometric characteristics, food preference with growth and swimming capacities of the species, as has been observed for other rajids (Farias et al 2006).…”

Predator–prey relationships and foraging ecology of a marine apex predator with a wide temperate distribution

“…Although the species differ in each region, there are consistent global-scale predator-prey links between Notorynchus cepedianus, triakid sharks, myliobatid rays and marine mammals (Appendix 1). As larger sharks are often the only predators of mesoconsumers, such as other chondrichthyans and pinnipeds, N. cepedianus may perform a similar role in0 regulating meso-consumer population numbers throughout their distribution (Lucas & Stobo 2000, Heithaus 2004, Lucifora et al 2009). Both the consistent predator-prey links over large spatial scales and the differences over the finer scales show the importance of incorporating spatial and temporal variability in dietary analysis to explore predator-prey relationships.…”

Feeding habits of the Magellan skate: effects of sex, maturity stage, and body size on diet

“…Furthermore, these results confirm that ontogenetic shifts in diet of B. magellanica are more a function of predator size rather than any other life-history traits. Diet shifts with size is a pattern widely observed in elasmobranchs (Ebert, 2002;Treolar et al, 2007;Lucifora et al, 2009), but there is no unique explanation for it.…”