David Morgan

Three species of the family Cichlidae have been reported from Western Australian waterways, including Tilapia zillii, Oreochromis mossambicus and Geophagus brasiliensis. While T. zillii was first found in 1975 and was successfully eradicated, O. mossambicus was first recorded in natural waterways of Western Australia in 1981, and has since spread to a further three river systems through either human-assisted dispersal or from flooding events. Recent research assessing the distribution and impact of the species in Western Australia suggests that O. mossambicus poses a serious threat to the unique aquatic fauna of Western Australian inland waters, including estuaries. The entry of other cichlids into the State’s waterways, including G. brasiliensis, which was first discovered in 2006, has the potential to impact Western Australia’s unique aquatic fauna in both inland freshwaters and estuaries.

Storm surge barriers are structures created across rivers, estuaries or tidal inlets to prevent coastal flooding. However, along with halting upstream water movement, they also have the potential to impede the movement of fishes. The Vasse and Wonnerup estuaries are located near the City of Busselton, Western Australia. Both estuaries have downstream storm surge barriers to prevent the flooding of low-lying coastal land and have ‘fish gates’ integrated into them to enable fish passage during the low flow period. Owing to poor water quality that regularly occurs immediately upstream of the Vasse barrier, fish kill events have regularly occurred there during summer and autumn with Black Bream being particularly vulnerable. However, no information existed on the movement patterns of Black Bream in the system nor on how fish passaged through the fish gates. This study aimed to determine the movement patterns and spatial and temporal distribution of the Black Bream within the Vasse-Wonnerup system using acoustic tags that were internally implanted in 41 Black Bream. The study revealed that Black Bream are highly mobile within parts of the system. Key habitats identified include the Wonnerup Inlet and the Deadwater with habitat further upstream of the either surge barriers not often accessed even when passage through the gates was not impeded. Crucially, the study revealed that the Black Bream that passaged through the Vasse fish gate only did so down a gradient (head loss), and once upstream of the barrier, did not (or could not) return downstream. Therefore, the study indicated that instead of the gates allowing the fish to escape from poor water conditions that occurred upstream, the Bream appear to be ‘stuck’, which initiating a review of the management of the fishgates for the mitigation of fish kills.

This study considers the impact of climate change on two aestivating species, Salamanderfish, Lepidogalaxias salamandroides Mees and Black-stripe Minnow, Galaxiella nigrostriata Shipway, from a drying region, Australia’s Southwestern Province. Lepidogalaxias salamandroides is unique in that it is the sole member of the family Lepidogalaxiidae basally placed as the sister taxon of all Euteleosteomorpha (Li et al., 2010). Both L. salamandroides and G. nigrostriata are highly restricted in distribution to the ephemeral, acidic wetlands in the extreme south-western corner of the region (Berra & Allen, 1989a, b; Morgan et al. 1998), and are small bodied, have relatively short life cycles and annually aestivate underground (Pusey, 1989). This study aimed to quantify any changes in their geographical range and losses of populations, identify the factors that best explain their current distributions, and assess the overall threats to the viability of remnant populations. We hypothesised that: (i) there has been a decline in the distribution of both species since previous surveys, and (ii) the environmental drivers of this distributional decline will be directly linked to climate change.

Covering nearly one-third of the Australian continent, Western Australia comprises five of Australia’s 10 ichthyological (fish) provinces and this includes the Southwestern, Pilbara, and Kimberley provinces, all of which are wholly contained within Western Australia, whereas the western edge of the Northern Province and the western portion of the Paleo Province also occur in Western Australia (see Unmack 2013, Morgan et al. 2014a, b). The study focuses on the fish fauna of the Pilbara Province, and was a joint initiative of the Rangelands NRM Coordinating Group and the Western Australian Government’s State NRM Program and co-funded by the Australian and State Governments.

Rivers, streams and wetlands of southwestern Australia support populations of fish found nowhere else in the world. Many of these species are threatened and populations are declining in both abundance and distribution. In order to help understand the drivers of these declines and devise management actions to halt them, this collaborative project aimed to fill key knowledge gaps relating to the ecology of three of south-western Australia’s most threatened freshwater fishes, the Western Trout Minnow, Balston’s Pygmy Perch and the Little Pygmy Perch, one of Australia’s ‘newest’ fishes.