For more than three decades, Barry Hutchins from the Western Australian Museum has been monitoring the annual arrival of pulses of tropical fish larvae at Rottnest Island, and the above two damselfish species have always figured prominently. These tropical species do not breed at Rottnest and it appears that larvae originate from the Houtman Abrolhos Islands off Geraldton, where these species are known to breed. Oceanographic studies by Alan Pearce (Department of Fisheries and Curtin University) have demonstrated that they are carried down in the Leeuwin Current to the waters around Rottnest, which has been their southernmost limit along the Western Australian coast.
The Western Australian ’marine heat wave‘ in early 2011 resulted in ecological changes ranging from devastating fish mortality at a number of localities to a variety of tropical fish, including whale sharks and manta rays, being found well south of their normal ranges. The first-ever sighting of a larval scissortail sergeant at the Busselton Jetty Underwater Observatory attracted Alan’s attention. Observatory Manager, Sophie Teede reported seeing the three centimetre long fish in mid-March 2011, when the water temperature at the jetty reached 23°C (and had even been above 25°C two weeks previously). This individual was spotted around the observatory windows until early May. The following March, two individuals were sighted.
Alan’s investigation of the ocean currents and water temperatures have led him to suspect that these damselfish species could be found between the Capes during March and April. He would greatly appreciate being notified of any sightings of larval or juvenile damselfish by divers or collectors. Thankfully, Redmap is now up and running in Western Australia and is an ideal tool to collect any observations of scissortail sergeant (Abudefduf sexfasciatus) and the Indo-Pacific sergeant (A. vaigiensis) anywhere south of Rottnest Island in Western Australia. If you suspect you have spotted them in the Capes area (i.e. Busselton to Augusta) please log your report through Redmap we can put you in touch with Alan and his ongoing research.