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In addition to the supply of water for agriculture, irrigation dams of south-western Australia are important systems for recreational activities, including fishing (Molony & Bird 2002, Molony et al. 2002a). Lake Navarino (the reservoir created by Waroona Dam, figures 1 and 2, approx. 115° 55 E 32° 51 S) is the first major public access reservoir south of the Perth Metropolitan Area and is an important component of the Recreational Marron (Cherax tenuimanus') Fishery (RMF) (Molony 2001a, 2002a, 2003a, Molony & Bird 2002, Beatty et al. 2003a). Further, it is the most northerly irrigation dam that is regularly stocked with rainbow trout (Oncorhynchus mykiss) produced at the Department of Fisheries' Pemberton Freshwater Research Centre (PFRC) to support its recreational freshwater fishery (Molony 2001b, 2002b, 2003b, Molony in press). As such, Lake Navarino is strategically important to these two licensed fisheries. Together, these two fisheries generate approximately $400,000 per annum in license revenue state-wide (Molony 2001a, b, 2002a, b, 2003a, b, Molony et al. 2002a) that is directed into the research and management of recreational fisheries. Further, the recreational fisheries in Lake Navarino generate income to the nearby regional centre of Waroona.

Lake Navarino has not been completely filled since 1997 due to concerns with the upper sections of the dam wall (M. Rhodes, Water Corporation, pers. comm.). In 2002, the Water Corporation of Western Australia planned to repair and reinforce Waroona Dam and undertake other maintenance and refurbishment works within the basin of Lake Navarino. As a result, Lake Navarino was to be almost totally drained for at least nine months to allow the works to be undertaken. The draining ofLake Navarino would immediately removea strategically significant component of both the RMF (Molony 2001a, 2002a, 2003a, Beatty et al. 2003a) and the southwest freshwater angling fishery (SWFAF) (Molony 2001b, 2002b, 2003b). Further, the extended period of draining of Lake Navarino was predicted to seriously impact populations of endemic crustaceans and fishes, including marron. Natural recovery of aquatic populations following such an event has rarely been studied but was likely to have been slow due to several reasons. Firstly, natural recruitment into Lake Navarino from downstream was highly unlikely due to the height of the refurbished wall (approximately 50 m). Secondly, two perennial tributaries that flow into Lake Navarino are also small, and were known to contain relatively small populations of marron and another endemic crayfish the gilgie (Cherax quinquecarinatus). Thirdly, the reproductive biology of marron (age at first maturity of approximately 2 years, brooders with low fecundity (Beatty 2000, Beatty et al. 2003b) and gilgies (Beatty et al. in press) was expected to result in a slow natural re-establishment of stocks. Given the size of Lake Navarino (~150 ha), the recovery of the recreational marron fishery would have taken many years. Finally, populations of the two endemic fishes in Lake Navarino and the two tributaries, the western minnow (Galaxias occidentalis) and western pygmy perch (Edelia vittata) were known to be relatively small (Beatty pers. obs.) and should the draining have greatly reduced their numbers, particularly in the tributaries (where greatest abundances were known to exist), the degree and rate of natural recovery of populations was unknown. Therefore, the refurbishment works posed an eminent risk to stocks of key species within Lake Navarino, particularly to the recreational marron fishery.

Negotiations amongst the Department of Fisheries, Murdoch University and Water Corporation were undertaken in 2001 and an action plan to reduce the impacts of dam draining on the aquatic species within Lake Navarino was developed that would be compatible with the refurbishment works.

ISBN

1 877098 66 3

ISSN

1446-5868

Publication Date

4-2005

Series Number

12

Publisher

Department of Fisheries, Western Australia.

City

Perth

Keywords

Waroona Dam, Biodiversity, Fisheries, Resource management, Western Australia

Disciplines

Aquaculture and Fisheries | Biodiversity | Biosecurity | Environmental Indicators and Impact Assessment | Environmental Monitoring | Management Sciences and Quantitative Methods | Natural Resources and Conservation | Natural Resources Management and Policy | Terrestrial and Aquatic Ecology

Fisheries Research Contract Report No. 12 - Mitigation of the negative impacts on biodiversity and fisheries values of the refurbishment of Waroona Dam, south-western Australia (Final report for the Water Corporation of Western Australia)

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