© 2005 International Council for the Exploration of the Sea
Sources of variation in the feeding ecology of the piked spurdog (Squalus megalops): implications for inferring predator–prey interactions from overall dietary composition
a Southern Seas Ecology Laboratories, Darling Building DP 418, School of Earth and Environmental Sciences, University of Adelaide Adelaide, SA 5005, Australia
b Primary Industries Research Victoria PO Box 114 Queenscliff, Vic 3225, Australia
*Correspondence to J. M. Braccini: tel: +61 8 83036224; fax: +61 8 83034364. e-mail: matias.braccini{at}adelaide.edu.au.
Sources of variation in dietary composition were examined in the piked spurdog (Squalus megalops). The species is an opportunistic predator that consumes a wide range of prey items. When importance of prey was measured by weight or occurrence, S. megalops preyed largely on molluscs and teleosts. However, when number of prey was considered, the main items were crustaceans. A bootstrap analysis showed that considerable variability can be expected in the importance of prey items in the species' overall diet. Regional, seasonal, and ontogenetic differences in dietary composition were found, but there were no differences between mature and immature sharks or between males and females. The spatial and temporal variation in diet exhibited by S. megalops and the intrinsic natural variability of the dietary composition of this opportunistic predator suggest that studies that infer predator–prey interactions from overall diet are likely to miss information on the ecological relationships among species and thus account for only part of these interactions.
Keywords: Australia, diet, predator–prey interactions, shark, variation
Received 12 January 2005; accepted 14 April 2005.