Study’s pens keep swans from weedy feed in Swan River

Study’s pens keep swans from weedy feed in Swan River

HOW more black swans will affect seagrass regrowth is being studied by Edith Cowan University student Caitlyn O’Dea at her floating pens at Mosman Park, Nedlands, Crawley, Attadale and Como in the Swan River.

“With climate change it is expected there will be less seasonal wetlands for the swans in the South West, and they’ll move to permanent water bodies like the Swan River estuary,” Ms O’Dea (22) said.

There are an estimated 500,000 black swans world wide and the species is not threatened, but they do follow seasonal rains to feed and breed in WA.

Ms O’Dea’s two-year study for her environmental management masters degree is backed by $6300 from the Ecological Society of Australia and the university’s Joondalup-based School of Science.

Photo: Andrew Ritchie

The study will test how more swans on the river and their greater grazing will affect the estuary’s three species of underwater seagrasses, including the most-common paddle weed.

The swans use their long necks to reach down underwater and pull the grasses from the riverbed, before eating the plants.

Ms O’Dea’s pens have been designed to keep the birds away from patches of the shallow sand flats at five test sites in the river.

Photo: Andrew Ritchie

“To simulate regrowth we’ve removed a quarter, half, three-quarters and all the weed in sections of each pen’s patch,” she said.

Weekly checks for the past two months have measured how well the un-grazed, varying densities of weed have regrown.

The tests have another two months to run, before any results are published next year.