The influence of ontogeny and environment on the diet of lookdown dory, Cyttus traversi

Abstract

Research on trophic relationships is an important component in the move towards an ecosystem approach to fisheries management. The diet of lookdown dory, Cyttus traversi, was determined from examination of stomach contents of 239 specimens of 13.9–50.7 cm total length (TL), sampled at depths of 220–744m on Chatham Rise, New Zealand. The diet was characterised by the macrourid fish, Coelorinchus oliverianus, the natant decapods, Lipkius holthuisi, Campylonotus rathbunae, Sergestes spp., Notopandalus magnoculus, and Pasiphaea spp., and the galatheid, Munida gracilis. Multivariate analyses using distance-based linear models, non-parametric multi-dimensional scaling and similarity percentages indicated the best predictors of diet variability were depth and fish length. Diet changes associated with depth were most apparent in the crustacean prey. Changes in the diet with ontogeny suggested four ontogenetic trophic units: pelagic (<13.9 cm TL), juveniles (13.9–25.8 cm TL; benthopelagic invertebrate feeders), maturing females and males (26–39.5 cm; benthopelagic omnivores) and mature females (>40 cm TL; benthopelagic piscivores/omnivores).