Rehabilitating Elwood Canal and Elster Creek, Victoria:
	An Assessment of Impacts on Native Freshwater Fishes
	Continued
	Materials and Methods
Site Description
	The Elster Creek Catchment is highly modified from its natural condition and characterised by high-density urban development, high catchment imperviousness and a highly modified stream network with degraded instream habitat. Elster Creek is a short (approximately 15-20 km ) low altitude tributary stream of Port Phillip Bay. Elster Creek originates in the suburb of Bentleigh and flows north east across the coastal lowlands through the suburbs of McKinnon, Brighton East, Gardenvale and Brighton to its confluence with Port Phillip Bay at Elwood, approximately 20 km south east of Melbourne Central Business District. Elster Creek has a short estuarine reach with tidal influence extending approximately three kilometres upstream from the creek mouth to Glenhuntly Road Crossing where a drop structure restricts tidal influence.
	Elster Creek has been channelled throughout its length for the efficient conveyance of floodwaters. In the upper reaches, Elster Creek flows through underground culverts until surface flow is reinstated around Brighton East approximately 8 km downstream from the headwaters. Between Brighton East and New Street in Brighton, Elster Creek flows through an open concrete channel (Plate B).
		Downstream of New Street the Creek flows through an earthen channel through the Elsternwick Park Golf Course (Plate C) and a short section of narrow blue stone channel between St Kilda Street and Glenhuntly Road (Plate D).
	Similarly, The estuarine section has been channelised from this point downstream to the stream mouth (Plate E).
	Habitat available as cover to aquatic fauna is limited in the catchment. Although areas of aquatic vegetation exist (Plate G) in the lower reaches between Glenhuntly Road and New Street, the absence of native streamside vegetation (Plate D, H) results in an absence of other important habitat attributes such as organic debris (leaf litter and bark), rootmasses and woody debris. Furthermore, stream channel modification has eliminated other important habitat characteristics which are important to stream fish assemblages.
	Channelisation of Elster Creek has resulted in a loss of hydraulic diversity (pool, run, riffle, backwater cascade), loss of diversity in streambed composition (mud, sand, gravel, cobble and boulder) and absence of undercut banks. Channelisation has also resulted in a loss lateral connectivity with offstream wetlands which were once located in the lower reaches of the catchment before being reclaimed for urban development.
	Modification to the stream channel has also resulted in numerous barriers (drop structures, syphons, Plate F) which potentially restrict longitudinal movement of fish and other aquatic biota. This is of particular concern to migratory fish species that potentially occur in Elster Creek/Elwood Canal which require free passage between estuarine/marine habitats at some stage during their life.
	Increased catchment imperviousness has resulted in alteration of natural flow regimes, and has produced a highly responsive flow regime which reacts quickly to rainfall events. Alteration to the flow regime in combination with stream channelisation and clearing of riparian vegetation has resulted in a decoupling of aquatic and terrestrial ecological process that are vital for the maintenance of aquatic biodiversity. For example it is likely that ecological processes including nutrient cycling, foodwebs and habitat creation have all been disrupted.
Fish Collection
	Two fish surveys were undertaken in the lower reaches of the catchment downstream of the New Street Road Crossing. Fish surveys were conducted over the summer months (13 Dec. 2001 and 21 Jan 2002) to coincide with the period when migratory species would most likely be recorded in Elster Creek Catchment. On each occasion, a combination of netting and electrofishing techniques was used to maximise the likelihood of collecting all species inhabiting the lower reaches of Elster Creek and Elwood Canal. A portable backpack Smith-Root® model 12 electrofishing unit was used to collect fish in the freshwater reaches between Glenhuntly Road and New Street. A single pass electrofishing technique was used during which the operator fished ion an upstream direction. All habitats along the edges and in the middle of the channel were targeted, with fish stunned and retrieved. An assistant followed the operator collecting any animals missed by the operator. The total time taken to electrofish was recorded on each sampling occasion (Table 1).
	Netting techniques were restricted to the estuarine reach between the mouth of the creek and Glenhuntly Road. Two fine mesh larval nets and two eel fyke nets were deployed between Barkley Road and Addison Road. Nets were deployed in the late afternoon on an in coming tide to maximise the likelihood of collecting a representative sample of fish species. The total wetted time for each net was recorded on each sampling occasion (Table 1).
Sample Processing
	All fish collected were identified, counted and measured for length (to the nearest 1 mm - length to caudal fork) and weight (wet weight to the nearest 0.1 g for weights < 100 g and 1 g for weights > 100g). Nomenclature for fish species follows Allen (1989) and Paxton et al. (1990). For samples containing >30 individuals of a single species, a representative subsample of 30 specimens was counted and measured for length and the number of additional individuals of each species recorded.
	Table 1. Sampling techniques and effort* used in freshwater and estuarine reaches of the Elster Creek Catchment to collect fish.
Sampling Technique Reach Date Effort (hrs.) Electrofishing Freshwater 13 Dec 01 3.17 Larval nets (x2) Estuarine 13 Dec 01 4.5 Fyke nets (x2) Estuarine 13 Dec 01 4.5 Electrofishing Freshwater 21 Jan 02 2.67 Larval nets (x2) Estuarine 21 Jan 02 4.5 Fyke nets (x2) Estuarine 21 Jan 02 4.5 *Effort for netting techniques are given for individual nets. Effort for elctrofishing is total elapsed time and not electrofishing seconds
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