Diets of sharks from estuaries and adjacent waters of the North-eastern Gulf of Carpentaria, Australia

Abstract

Sharks were collected over 2 years (six field trips) from the offshore prawn trawling grounds in Albatross Bay (7-45 m depth), from shallow (< 5 m) nearshore waters, and from the adjacent inshore waters of the Embley River estuary. Stomachs from 11 shark species were collected and analysed gravimetrically (% dry weight). Four species (Carcharhinus cautus, C. dussumieri, C. tilstoni and Rhizoprionodon acutus) were represented in all three regions. Seven general food categories (Mollusca, Penaeidae, Brachyura, Stomatopoda, Other Crustacea, Teleostei and Other) were used to describe their diets. Nearly all sharks were primarily piscivorous, and the teleost diet is discussed in detail. Hemigaleus microstoma was not piscivorous and cephalopods represented 94.7% of its diet. Teleostei constituted less than 70% of the diet for three other species: C. amblyrhynchos offshore (64.3% Teleostei, 18.6% Penaeidae, 11.6% Mollusca), C. dussumieri offshore (52.5% Teleostei, 21.8% Stomatopoda, 10.1% Penaeidae), and R. acutus nearshore (59.3% Teleostei, 17.6% Cephalopoda, 10.3% Brachyura). Offshore, there was a strong correlation between estimates of consumed prey biomass and of trawled prey biomass, suggesting that these sharks feed in a density-dependent manner.