Algal beds and threatened aquatic fauna in Great Lake: Current status, responses to lake level and management recommendations

Major changes in the flora and fauna of Great Lake have occurred since management of levels for hydro power generation commenced in the 1920's. Early records of Great Lake (e.g. Legge and Cramp, in Banks 1973) indicated that the lake had extensive areas of emergent and submerged macrophytes associated with shallow, shelving shorelines. These macrophyte communities were associated with several waterbird species infrequently or no longer observed at the Lake. Davies and Sloane (1988) described the major changes in characteristics of brown trout populations in the lake since the 1920's, noting a major 'boom' period in the fish population during the 10 - 20 years following construction of the Miena Dam. They attributed increases in fish growth rates and size to increases in access to freshly inundated shorelines, with associated increases in food availability. The period from the 1940's to the present was characterised by much lower and relatively stable growth rates of trout. During this period, the lake shore has been dominated by a characteristic 'bath-tub ring' (hereafter BTR) consisting of periodically inundated and exposed boulder-cobble armoured substrate. The BTR zone is also typified by absence of finer sediment grain sizes, largely due to the relatively high wave energies during periods of inundation, and an absence of terrestrial or aquatic vegetation