The trophic role of a large marine predator, the tiger shark Galeocerdo cuvier

Abstract

Tiger sharks were sampled off the western (Ningaloo Reef, Shark Bay) and eastern (the Great Barrier Reef; GBR, Queensland and New South Wales; NSW) coastlines of Australia. Multiple tissues were collected from each shark to investigate the effects of location, size and sex of sharks on δ13C and δ15N stable isotopes among these locations. Isotopic composition of sharks sampled in reef and seagrass habitats (Shark Bay, GBR) reflected seagrass-based food-webs, whereas at Ningaloo Reef analysis revealed a dietary transition between pelagic and seagrass food-webs. In temperate habitats off southern Queensland and NSW coasts, shark diets relied on pelagic food-webs. Tiger sharks occupied roles at the top of food-webs at Shark Bay and on the GBR, but not at Ningaloo Reef or off the coast of NSW. Composition of δ13C in tissues was influenced by body size and sex of sharks, in addition to residency and diet stability. This variability in stable isotopic composition of tissues is likely to be a result of adaptive foraging strategies that allow these sharks to exploit multiple shelf and offshore habitats. The trophic role of tiger sharks is therefore both context- and habitat-dependent, consistent with a generalist, opportunistic diet at the population level.

Resource use of great hammerhead sharks (Sphyrna mokarran) off eastern Australia

“…The δ 34 S values ranged across food webs relying on benthic epiphytes (Moncreiff & Sullivan, ), seagrasses and macroalgae (Belicka et al ., ) and marine particulate organic matter (Benstead et al ., ). By comparison, δ 13 C values of great hammerhead tissues ranged between −13 and −17‰, which are indicative of coastal macrophytes (−14) and pelagic phytoplankton (−18; Hobson, ), but were narrower than those of coastal and estuarine species such as G. cuvier or Carcharhinus leucas (Valenciennes 1839) (Ferreira et al ., ; Matich et al ., ). Great hammerheads occupy a carbon niche breadth similar to that of white sharks (Estrada et al ., ; Kim et al ., ) and a wider range of trophic levels (δ 15 N values) than G. cuvier or C. leucas (Ferreira et al ., ; Matich et al ., ).…”

Effects of pre‐treatments on bulk stable isotope ratios in fish samples: A cautionary note for studies comparisons

“…), a consensus has yet to be reached on the preferred pre‐treatment. A number of recently published studies used either no pre‐treatment (e.g …”

“…A number of recently published studies used either no pre-treatment (e.g. 8,[32][33][34] ), a distilled water rinse followed by a chloroform/methanol 2:1 rinse (e.g. 35 ), or cyclohexane rinses (e.g.…”

“…). Studies of the foraging ecology of elasmobranchs are no exception with a recent increase in published papers using the stable isotope approach (e.g …”

“…Studies of the foraging ecology of elasmobranchs are no exception with a recent increase in published papers using the stable isotope approach (e.g. [6][7][8][9] ). Due to the life history of elasmobranchs, their wide-ranging migration patterns and concern about their population decline, 10 the stable isotope approach for their study is particularly useful, as samples can be collected non-lethally (e.g.…”