Feeding selectivity of a guild of piscivorous fish in mangrove areas of north-west Australia

Abstract

Piscivorous fish are unusually abundant in mangrove creeks in the Dampier region of north-west Australia (20°40′S.,1 16°40′E.). Penetration of mangroves by predators is relevant to the role of such waters as nursery grounds. Caranx ignobilis, Carcharhinus limbatus, Scomberoides commersonianus and Scornberomorus semifasciatus were the most numerous predators. More than 50% of suitably sized potential prey fish species were consumed; the most common prey were Atherinidae, Gobiidae, Ambassis sp. and Sillago spp. Small (1-9 cm), permanently resident species constituted 60% of prey, and juveniles of larger species made up the balance. Feeding selectivity was assessed on three electivity indices and caution in their use is emphasised. Although the results conflicted, only the linear index could be statistically tested and two interesting points emerged. Firstly, of the three most common prey species, two were positively selected and one negatively selected, and the remainder were consumed in approximate proportion to their abundances. Secondly, the indices gave similar rank order preferences, with Atherinidae, Sillago spp. and Harengula sp. the most preferred and Ambassis sp. the least preferred.