Lenanton, R. C. J., Dowling, C.E., Jackson, G. and Fairclough, D. V.

Western Australian Fisheries & Marine Research Laboratories, Department of Fisheries,PO Box 20, North Beach WA 6025, Australia

The increasing ocean temperatures and frequency of extreme climatic events that are predicted to continue over coming decades will modify biological communities in shallow coastal environments. Such an extreme event occurred in the eastern Indian Ocean in the summer 2010-11, when ocean temperatures up to 4-5 ºC above average combined with an unseasonal and anomalously strong poleward-flowing Leeuwin Current (LC) triggered a marine heatwave off the west coast of Australia. These conditions persisted during the following two years. Long-term fisheries catch and effort and research monitoring databases, in conjunction with validated amateur observations were interrogated to determine whether, in shallow coastal waters≥ ~30°S, the unusual oceanographic conditions enabled not only the recruitment of tropical fishes, but also their survival and maturation during and following the marine heatwave. While several tropical species were shown to have recruited and over-wintered in 2011 and 2012, only Rabbitfish (Siganus sp.) was shown to have reproduced ~ 200-300nm south of its historical southern limits. Recruitment failure was observed following a return to more typical summer conditions during 2013/14. The investigation confirmed the importance of the emerging contribution of validated information from amateur observers to complement fisheries catch and effort and research monitoring data. The study underlines that short time-series of observations cannot alone demonstrate range extensions. Rather longer-term programs that collect information on recruitment, survival, and reproduction are required to adequately monitor the effects of a changing environment on coastal fish communities and associated fisheries.