John Dory Zeus faber (Linnaeus, 1758) feeding off Galicia and in the Cantabrian Sea: Dietary shifts with size

Abstract

Between 1990 and 1997, stomach contents of 647 Atlantic John Dory Zeus faber (Linnaeus, 1758) measuring from 5-58 cm, were analysed volumetrically. The species was found to be almost entirely icthyophagous: fishes constituted more than 99 % of its diet by volume, or 75 % in terms of number. Among these, there are some commercially and ecologically important gadoids and clupeoids. Using clustering and multi-dimensional scaling methods, four length ranges with a different diet composition were found: smaller fishes, measuring 5-9 cm, fed mainly on invertebrates (mysids and Allotheutis spp.) and small benthic fishes (e.g., gobiids and Callionymus maculatus Rafinesque-Schmaltz, 1810). In the transitional length range, 9-12 cm, Gadiculus argenteus Guichenot, 1850 replaced the invertebrates. From 12-30 cm, Z. faber's diet basically comprised gadoids, such as Micromesistius poutassou (Risso, 1826), G. argenteus and Merluccius merluccius (Linnaeus, 1758), whereas specimens longer than 30 cm fed on larger fishes, including M. poutassou, clupeoids (mainly Sardina pilchardus Walbaum, 1792), and Cepola rubescens Linnaeus, 1766. Feeding was more intense in the smallest length range, and within each length range, a different diet composition by depth strata was also observed.