Life histories of galaxiid fishes in Arthurs Lake and Great Lake, Tasmania, and effects of water level fluctuations on their populations

Collectively, Arthurs Lake and Great Lake, central Tasmania provide natural habitat for six galaxiid species, four of which are considered to be threatened (Arthurs Lake: Arthurs paragalaxias (Paragalaxias mesotes) and saddled galaxias (Galaxias tanycephalus); Great Lake: Great Lake paragalaxias (Paragalaxias eleotroides) and Shannon paragalaxias (Paragalaxias dissimilis)). The other two galaxiid species (spotted galaxias (Galaxias truttaceus) and climbing galaxias (Galaxias brevipinnis)) are not considered to be threatened, but are also likely to be important to the aquatic ecosystem of Great Lake.

Arthurs Lake and Great Lake are high priority impoundments within the Tasmanian hydro-electric power scheme. Recently, both lakes have experienced prolonged periods of relatively low water levels. Low water level conditions can cause significant environmental and socio-economic risks with legal consequences if either power supply or survival of the threatened fish species is jeopardised. To mitigate these risks, Hydro Tasmania has established: (1) social and environmental risk bands which govern how water levels in the Arthurs Lake and Great Lake can be drawn down, and (2) agreed water level arrangements for Arthurs Lake with the Inland Fisheries Service to minimise risks to fish in this lake. In recent years, Hydro Tasmania has also supported research into the dynamics of the charophyte communities in Great Lake and their associated biota to gain an understanding of how water levels influence these important habitats in this lake.

Given the findings of recent work undertaken on golden galaxias (Galaxias auratus) populations in Lake Crescent and Lake Sorell, central Tasmania, reduced water levels or unseasonal water level fluctuations are likely to negatively impact on galaxiid populations in Arthurs Lake and Great Lake; particularly their ability to breed and recruit due to losses of critical habitats and spawning cues. However, prior to this study, little was known about the life histories and habitat requirements of the galaxiid fishes in in Arthurs Lake and Great Lake; thus, how best to manage water levels to protect their populations.

This study examined interactions between fish populations, hydrology and habitats. Specifically, the broad objectives of the study were to:

1. Examine the biology and ecology of galaxiid fishes in Arthurs Lake and Great Lake (especially the threatened endemic species).
2. Identify water level management issues, to assist sustainable management of populations of these fishes in these lakes, particularly during periods of low water levels.
3. Investigate relationships between fish populations, critical habitats and lake hydrology.