Global changes to fish distributions are expected to continue in coming decades with predicted increases in ocean temperatures and the frequency of extreme climatic events. In the eastern Indian Ocean during the 2010/11 summer, sea surface temperatures 4–5 °C above average and an unseasonal, anomalously strong, Leeuwin Current (LC) triggered a “marine heatwave” along the west coast of Australia, with elevated water temperatures persisting for a further two years. Peak LC flows in summer/autumn transported pelagic early life history stages of summer-spawning coastal subtropical and tropical fishes southwards. This study examined whether the heatwave enabled the arrival, persistence and reproduction of such species in waters ≥∼32°S using a range of available datasets. Juveniles of Chaetodon assarius, Trachinotus botla, T. baillonii, Polydactylus plebeius, Psammoperca waigiensis and Siganus sp. recruited into nearshore waters at ≥∼32°S in 2011. Polydactylus plebeius survived until the summer of 2012/13. Trachinotus spp., P. waigiensis and Siganus sp. survived over consecutive winters, with Siganus sp. establishing a self-recruiting, breeding population two years later. A return to more typical summer water temperatures by 2013/14 was associated with an apparent recruitment failure of Siganus sp. This is a rare example of a tropical vagrant surviving to breed in temperate regions. Confirmation of range extension beyond existing limits of this and other tropical species will be primarily dependent on either continuous or intermittent recruitment from this recently established southern breeding population. Commercial fisheries catch and effort data were of limited use in this study because they were not designed to record small catches of unusual and/or non-target species. In contrast, fisheries-independent recruitment surveys recorded tropical juveniles and validated amateur observations provided important information on unusual species. The study confirmed the emerging contribution of ‘citizen scientists’ working with researchers to document climate related impacts in the marine environment.
Lenanton, R. C. J., Dowling, C. E., Smith, K. A., Fairclough, D. V., & Jackson, G. (2017). Potential influence of a marine heatwave on range extensions of tropical fishes in the eastern Indian Ocean—Invaluable contributions from amateur observers. Regional Studies in Marine Science, 13, 19–31. https://doi.org/10.1016/j.rsma.2017.03.005