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The oceanic preyfield available to offshore foraging seabirds of the Abrolhos Islands, Western Australia

Wellington, Max (2015) The oceanic preyfield available to offshore foraging seabirds of the Abrolhos Islands, Western Australia. Honours thesis, Murdoch University.

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The Abrolhos Islands in the south-east Indian Ocean host large breeding colonies of tropical seabirds such as sooty terns, wedge-tailed shearwaters and brown noddies. These birds forage widely for epipelagic and mesopelagic prey in the waters of the surrounding south-east Indian Ocean. In this study, an opportunistically collected set of night-time surface plankton samples from waters off the Abrolhos Islands was examined to ascertain the distribution and abundance of potential prey items available to seabirds and linked to concurrently recorded oceanographic conditions. A wide diversity of macro-zooplankton including larval and juvenile fishes, cephalopods and phyllosoma was found in the surface plankton samples including numerous species previously identified in the diets of the seabirds. Larvae and juveniles of oceanic meso-pelagic fishes such as Myctophidae, Phosichthyidae and Gonostomatidae dominated the samples although a range of neritic fish species were also recorded. The warm, southward flowing Leeuwin Current was prevalent over the study area and the associated field of meanders, anti-cyclonic and cyclonic meso-scale eddies added considerable oceanographic complexity. Sea-surface temperature and fluorescence explained some of the variation in surface fish assemblages and, likewise, delineated oceanographic features were also found to have a moderate structuring effect on surface fish assemblages. Interestingly, larvae and post-larvae of the beaked salmon Gonorynchus greyi, a neritic fish species and known preferred prey species, were particularly abundant in an anti-cyclonic eddy located 150 km beyond the shelf-edge. This species has a long pelagic larval duration of up to three months and the westward trajectories of anti-cyclonic eddies may facilitate supply of this prey species to the offshore foraging areas of some seabirds. Use of remotely sensed sea-surface temperature, altimetry and chlorophyll a imagery could assist in the delineation of these oceanographic features, to aid further investigations of seabird foraging and prey availability.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Beckley, Lynnath
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