Visibility is not great and the water is bracing, but soon Booth, who is a professor of marine ecology at the University of Technology, Sydney and chief scientist of the Sydney Institute of Marine Science, and his student begin their search.

To the average snorkeller, weedy seadragons are invisible. But within an hour Mr Sanchez-Camara has found 15.

"These ones all seem much smaller than the ones in Botany Bay," he says.

Weedy seadragons are found in southern Australian waters, from Port Stephens, just north of Sydney, to Geraldton in Western Australia. But virtually nothing was known of their ecology until the past few years.