Trophic pathways and foodweb structure of Cockburn Sound and Owen Anchorage

Researchers from Edith Cowan University and Murdoch University are collaborating on a project, supported by Department of Primary Industries and Regional Development, within the larger WAMSI Westport Marine Science Program to investigate the foodweb structure in Cockburn Sound. Foodweb structures are crucial to identify critical animal and plant species, and understand energy flow from the humble seaweed to an apex predator. This is being done by combining gut content analysis (GCA) and stable isotope analysis (SIA).

GCA involves identifying recently ingested food items. This has highlighted that crustaceans play a crucial role in the foodweb as they are consumed by most fish species and make a huge contribution to many including baitfish (see figures below). Some species (e.g. Butterfish) are opportunists feeding on a very broad range of prey allowing them to tolerate shifts in prey abundance.

Stable isotopes of a consumer will reflect those of its food sources following the premise “you are what you eat” and provides a longer term understanding of energy transfer. A large suite of fish, invertebrate and macrophyte species has been processed for SIA. Collaboration with other projects has allowed little penguins, dolphins, and Australian sea lions to be included. Once fully compiled, a statistical model will determine the food sources and energy transfer throughout Cockburn Sound, and provide its first comprehensive foodweb.

While at early stages, the conceptual foodweb below based on GCA alone shows the major prey items consumed by fishery species, with bold lines denoting prey making a particularly large contribution to the diet of a predator. Research will be built upon in 2023 to help inform investigations being completed as part of the Westport Program for the proposed terminal in Kwinana.

Further information regarding this, and other projects within the WAMSI Westport Marine Science Program can be found at:

Authors: Roisin McCallum, Daniel Cox, Mitchell Haywood, Glenn Hyndes, James Tweedley