Occurrence at the Busselton Jetty
Mosaic Leatherjackets can be seen daily in the waters around the Busselton Jetty and the Underwater Observatory. Varying cohorts, from the juvenile stage to the mature adult are common throughout the year. They are most commonly observed feeding amongst the jetty piles occasionally as a mature adult pair. During the 2012 Underwater Observatory season a juvenile Mosaic leatherjacket was observed sheltering inside the bell of the Net-Patterned Jellyfish. They are a beautiful sight as they pass close by the windows flashing their brightly patterned bodies and raising their dorsal spine up and down.
The Mosaic Leatherjacket is brightly coloured with orange spots over a blue-purple base. They also have a prominent dorsal spine able to be raised and lowered, however it is not known to be venomous. One of the larger species of southern leatherjacket, the Mosaic Leatherjacket reaches a maximum size of 60 centimetres. Juvenile and females of this species are deep bodied, with the adult male being quite oval and slender. This change in body shape of the male occurs as the fish matures, where some of its bony skeleton is resorbed to create more of a torpedo shaped body. The male Mosaic Leatherjacket also tends to have larger fins, and combined with their slender body shape would improve their swimming agility and performance, which is probably important during courtship.
The early life history of this species is one of the most fascinating among the leatherjackets. Once hatched, juvenile Mosaic Leatherjackets seek out a pelagic jellyfish, the Net-Patterned Jellyfish Pseudorhiza haeckeli. They then live under the bell of the jellyfish, first feeding on a diet of planktonic larval crustaceans and as they grow feeding on morsels of the Net-Patterned jellyfish’s food . Once they are too large to shelter beneath the jellyfish they settle onto reefs in estuaries, sponge gardens and sheltered bays, before moving offshore to depths of 80 metres at maturity.
The Mosaic leatherjacket is widespread along the southern coast of Australia, from Shark Bay, WA to the southern coast of Queensland.
Other common names include Deep-bodied leatherjacket
Edgar, G. (1997) Australian Marine Life: The Plants and Animals of Temperate Waters. Australia
Hutchins, B and Swainston, R. (1986) Sea Fishes of Southern Australia. Swainston Publishing, Australia
Hutchins, Barry. (2000) Under Southern Seas: The Ecology of Australia’s Rocky Reefs. UNSW Press, Australia
Kuiter, R H. (1996) Guide to Sea Fishes of Australia. New Holland Publishers, Australia
Morrison, S and P., Storrie, A. (2003) Beneath Busselton Jetty. Department of Conservation and Land Management, Western Australia