Upper Lake River Was Completed in 1965 As Part of the Poatina Power Scheme

South Esk – Great Lake Water Management Review

Scientific Report on Arthurs Lake

August 2003

Prepared by Hydro Tasmania

Table of Contents

1. Assessment of Issues and Status ...... 1 2. Formulation of Study Objectives ...... 7 3. Data Collection and Analysis...... 8 4. Environmental Management Options for Arthurs Lake...... 28

Scientific Report on Arthurs Lake August 2003

ARTHURS LAKE

1. ASSESSMENT OF ISSUES AND STATUS The Arthurs Lake investigation formed Technical Study 3 of the South Esk – Great Lake Water Management Review. Background information about the catchment, including Arthurs Lake, is given in the Environmental Review document (Hydro Tasmania, 1999). Community consultation and issues are discussed in the Community Consultation report (Hydro Tasmania, 2000). The Environmental Review document lists a number of issues, primarily environmental, associated with the management of Arthurs Lake. Additionally, several responses to questionnaires distributed to the community specifically referred to issues relating to the potential impact of low lake levels on trout fishing in Arthurs Lake. The main aim of this study was to make an assessment of the issues that have been identified through earlier work, undertake additional investigation to collect current data on the issues of importance and from this information develop potential options for achieving the management objectives.

Development History and Present Management Arthurs Lake is an artificial impoundment that inundated Morass Marsh and two natural water bodies, Blue and Sand Lakes. The construction of Arthurs Dam on the Upper Lake River was completed in 1965 as part of the Poatina Power Scheme. Water from Arthurs Lake is lifted into Great Lake, via a pumping station at Pumphouse Bay. This diversion has a maximum capacity of 5.1 cumecs. The water then flows through the Tods Corner Power Station into Great Lake, the Poatina Power Station into the South Esk catchment at Brumbys Creek, and finally through the Trevallyn Power Station into the Tamar Estuary at Launceston. In 1974, a set of three siphons was installed over the dam wall, which, in combination with a small riparian valve, facilitates the release of water, when necessary, from Arthurs Lake into the Upper Lake River. These are brought into operation when the lake water level exceeds 951.6 m above sea level (July-October) or 952.0 m above sea level (December-April), and have also been used to maintain water levels in Woods Lake in 1995 and 2000 (see Woods Lake Study). The lake has a notional operating range of 9.77 m, with full supply level at 952.82 m above sea level and normal minimum operating level at 943.05 m above sea level. As part of an informal agreement with the Inland Fisheries Service, an agreed minimum operating level of 948.0 m above sea level reduces the operating range to 4.82 m. This minimum lake level was established in 1993 in response to angler concerns, following discussions with the then Inland Fisheries Commission. Prior to this agreement, the level of Arthurs Lake had fallen below 947 m above sea level (see Figure 1), resulting in less-favourable fishing conditions, particularly in relation to boat access and navigation hazards. This has always been an informal agreement between Hydro Tasmania and the Inland Fisheries Service and has no regulatory backing.

South Esk – Great Lake Water Management Review 1 Scientific Report on Arthurs Lake August 2003

The lake is relatively shallow, with a maximum depth of 18 m at the dam wall, and covers an area of 64.6 km2, for a storage volume of 511 Mm3. Figure 1 shows the change in water level in Arthurs Lake since 1990 and the period during which the minimum level has been implemented. The plot shows that since 1993, the lake has been operated within a 3 m range, from 948 – 951 m above sea level (mASL). Under normal circumstances, operating procedures preclude spill from the lake. The primary spillway for Arthurs Lake, located on Arthurs Levee, is designed to spill overland rather than into a natural stream channel.

953 FSL 952.82 m 952

951

950 )

949

948 Agreed minimum 948.0 m 947

Lake level (mASL 946

945

944 NMOL 943.05 m 943 c-92 e 1-Jan-90 1-Jan-91 1-Jan-92 1-Jan-94 1-Jan-95 1-Jan-96 1-Jan-97 1-Jan-98 1-Jan-99 1-Jan-00 1-Jan-01 31-D Date

Figure 1: Water level in Arthurs Lake from 1990 to present. Full supply level (FSL), normal minimum operating level (NMOL), and the agreed minimum level (1993) are also shown

Inflows to the lake comprise several relatively small streams with a total catchment of over 161 km2. Figure 2 shows the major inflowing streams and their catchment areas. The inflowing streams are unregulated and drain relatively undeveloped countryside. The excellent water quality and natural discharge patterns make these streams ideal spawning grounds for the exotic brown (Salmo trutta) and rainbow (Oncorhynchus mykiss) trout. These species have been introduced into Arthurs Lake and now form one of the major recreational trout fisheries in the State.

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Figure 2: Map of Arthurs Lake and surrounds, indicating major inflowing streams and their catchment areas

Biological Issues The biological issues that were identified for Arthurs Lake during preliminary reviews were related to threatened native fish species and to the performance of the trout fishery.

Native Fish Arthurs Lake forms a significant part of the range of two endemic fish species, the saddled galaxias (Galaxias tanycephalus) and the Arthurs paragalaxias (Paragalaxias mesotes). Both species share a distribution that is restricted to Woods and Arthurs Lakes. Because of this restricted distribution, and the effects of predation from introduced trout, these species are listed under the Tasmanian Threatened Species Protection Act 1995. Under this legislation, both species are listed as ‘Endangered’. G. tanycephalus is also listed under the Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999, as ‘Vulnerable’. Crook and Sanger (1997) prepared a recovery plan for G. tanycephalus, which described the species as being uncommon in Arthurs Lake and abundant in Woods Lake. More recent work by the Inland Fisheries Service in March 2001 indicate that

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this relative distribution still holds, with 49 individuals caught in Woods Lake and 17 in Arthurs Lake (J. Jackson pers. comm.). P. mesotes was recently elevated to ‘Endangered’ status under the Tasmanian Act and, because of this, is also likely to be listed under the Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999. Eighty individuals were caught in Arthurs Lake in the March 2001 during the Inland Fisheries Service sampling (J. Jackson pers. comm.).

Fish Dispersal Arthurs Dam acts as a general barrier to fish species attempting to move upstream, although the only species likely to be affected are eels. While these animals are able to surmount obstacles such as the dam, it is likely that downstream factors, such as Woods and Trevallyn Dams, the absence of flows in the Lake River upstream of Woods Lake, and the land and water use patterns of the lower South Esk and Macquarie Rivers, have a significant effect on this species’ migrations and is likely to greatly reduce the number of individuals reaching this part of the catchment. The threatened species in Arthurs Lake are self-sustaining lake-based populations. Their past use of the Lake River between Arthurs Lake and Woods Lake for dispersal purposes is unknown, but has now been effectively blocked by Arthurs Dam.

Exotic Species Exotic fish species in Arthurs Lake comprise the two trout species, brown (Salmo trutta) and rainbow (Oncorhynchus mykiss). These are major predators of the endemic fish species and predation by trout is the predominant threatening process associated with the decline in native fish populations elsewhere in the State. The exotic water plant, Canadian pondweed (Elodea canadensis) is widespread in Arthurs Lake. This plant is a secondary prohibited aquatic weed introduced from North America. It prefers warm, shallow, slow moving water and forms fast growing, dense beds which out-compete native macrophytes. As a result, the distribution of native instream vegetation may be reduced and the habitats available to other aquatic organisms may be lessened. No comprehensive survey of the distribution or impact of Canadian Pondweed in Arthurs Lake has been undertaken to date and is not considered a significant issue for this storage.

Trout Fishery Arthurs Lake supports a large, self-sustaining population of the exotic brown trout (Salmo trutta) and a smaller population of the exotic rainbow trout (Oncorhynchus mykiss). Data on angling at Arthurs Lake collected by the Inland Fisheries Service, for the period 1996 - 99, indicate that between 34 – 43 % of licensed anglers (10 - 12,000), fish this water. The extrapolated harvest for 1998 - 99 was over 140,000 brown trout and almost 1,200 rainbow trout. The average number of days per fisher spent at the lake ranged from 6.25 in 1996 - 97 to above 8.5 in 1998 - 99. The data show an increasing trend in both actual number and percentage of fishers using the lake, although both catch per unit effort and the numbers of both brown and rainbow trout being landed appeared to peak in 1997 - 98.

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An assessment of the correlation between water level in Arthurs Lake and angler catches was undertaken, however the low resolution of the annual angler survey data limits the usefulness of the analysis. Overall it was found that water level, though not directly impacting on catch rates from Arthur’s Lake, tends to determine angling pressure on the lake. Higher water levels result in greater harvest as a result of greater angler numbers and angler effort, although catch rates per angler day do not appear to change noticeably. This may be the result of increased access to the fishery or to angler perceptions of better catches during periods of higher water. Overall, the data are symptomatic of a fishery that is pressured by neither water level management nor angler effort. In summary, Arthurs Lake provides the most significant recreational trout fishery in the catchment, has a high profile amongst anglers and has a relatively good catch rate.

Lake Management Issues During broad community consultations, most of the respondents indicated that water level management in Arthurs Lake was an issue of concern.

Lake Level Management The list of community concerns raised included aspects of lake and water level management, specifically the marking of navigation hazards and control of camping around the lakeshore. In terms of the recreational fishery, elevated water levels facilitate boating access to regions of the lake where this can be limited. In particular, the Cowpaddock Bay area in the north-west of the lake becomes progressively too shallow for boating as the water level approaches the agreed minimum of 948.0 m above sea level. This appears to be the primary reason for requests to raise the minimum level at least another metre. The primary reason given for having a higher water level in Arthurs Lake is the recent improvement in performance of the fishery, which has coincided with substantial increases in water level, and consequent inundation of littoral terrestrial vegetation. This produced an apparently bountiful food supply and supported improvements in trout numbers and condition. However, the maintenance of this aspect of the fishery is likely to rely more on seasonal changes in water level rather than maintaining a stable and elevated level.

Marking Navigational Hazards Sited in a region of periglacial features, and inundating a large area which was previously forested, Arthurs Lake has numerous navigation hazards, including logs, submerged tree stumps, significant reefs, and a very rocky shoreline. These hazards may be exacerbated by the seasonal fluctuations in water level in the lake. The primary responsibility for identifying and marking navigation hazards rests with Marine and Safety Tasmania, although both the Inland Fisheries Service and Hydro Tasmania may assist with this work from time to time.

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Lakeshore Camping The Parks and Wildlife Service has recently upgraded facilities at the Pumphouse Bay and Jonah Bay Campgrounds, which should ameliorate concerns about issues related to camping and access around the shore of the lake.

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2. FORMULATION OF STUDY OBJECTIVES The work carried out to investigate the issues raised by the environmental review and consultations with community members and other agencies, has produced greater insights into conditions within the lake. Of the range of issues identified, two appear to be predominant in Arthurs Lake. These are: that favourable environmental conditions are maintained to ensure the long- term survival of populations of threatened fish species; and that a water level regime is maintained that supports a productive recreational fishery in the lake. To assist with the identification of appropriate management options for Hydro Tasmania, the objectives for data collection within this study are: 1. Threatened Species: review existing data on the population status and size structure of G. tanycephalus and P. mesotes and supplement these with additional data where necessary to identify conditions that will facilitate successful spawning and long-term survival of these species; and examine the habitat preferences of both fish species so that the potential impact of any change in lake level management on these species can be identified. Due to a lack of necessary data, no further studies are planned to investigate appropriate lake levels to maintain present performance of the trout fishery, however the following management objective is proposed: 2. Recreational Trout Fishery: identify an appropriate management regime that will satisfy angler expectations and concerns about water levels and fishery performance.

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3. DATA COLLECTION AND ANALYSIS

Threatened Species Surveys by Inland Fisheries Service Both G. tanycephalus and P. mesotes are listed as threatened species. Recent surveys by the Inland Fisheries Service have recorded moderate numbers of both species in Arthurs Lake. Figure 3 shows the location of the six sites used for electrofishing sampling of the near-shore adult populations of both threatened species by the Inland Fisheries Service. The technical study of threatened species in Arthurs Lake aims to determine some of the presently unknown life history parameters of both species, including spawning seasonality and habitat preferences, as well as the species’ distribution and abundance.

Figure 3: Map of Arthurs Lake, showing the six electrofishing sites used in the Inland Fisheries Service threatened species sampling program

Abundance The Inland Fisheries Service has regularly monitored numbers of native fish in Arthurs Lake since 1997, as part of the Recovery Plan for G. tanycephalus (Crook & Sanger, 1997). These data were collected by the Inland Fisheries Service, with

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funding from the Natural Heritage Trust, and have been made available to Hydro Tasmania for the purpose of this technical study. Table 1 shows the overall abundance of both species caught using standardised capture effort (15 minutes electrofishing at each of the 6 sites) over 12 sampling events since September 1997. No planktonic catch data were available for this period.

Year Mar-Apr Jun-Jul Sep-Oct Dec G. tany. P. meso. G. tany. P. meso. G. tany. P. meso. G. tany. P. meso. 1997 23 23 32 ? 1998 24 55 11 18 3 60 1999 28 28 50 30 3 12 13 55 2000 9 138 ? ? 0 8 2001 17 80 Total 213 507 Table 1: Number of G. tanycephalus and P. mesotes caught at six sites in Arthurs Lake from September 1997 to March 2001

The relative abundance data in Table 1 indicate that most G. tanycephalus were caught over the spring-autumn of 1997 - 98 and the autumn-winter of 1999. Relatively low numbers of this species have been caught since June 1999. On the other hand, P. mesotes was most abundant in the summer-autumn period in all years. P. mesotes tended to outnumber G. tanycephalus by over 2 to 1, but this varied between sites and sampling events. A total of 213 G. tanycephalus and 507 P. mesotes were captured in Arthurs Lake. Over the same period, and with the same sampling effort, 689 adult G. tanycephalus and no P. mesotes were caught in Woods Lake. Table 2 shows the total numbers of each threatened species caught at each site during the Inland Fisheries Service sampling program. Site locations are indicated in Figure 3.

Site / species EF 1 EF 2 EF 3 EF 4 EF 5 EF 6 Total G. tanycephalus 130 29 11 28 5 10 213 P. mesotes 151 77 44 56 39 140 507 Table 2; Numbers of G. tanycephalus and P. mesotes caught over the 12 sampling events conducted by the Inland Fisheries Service threatened species sampling program between September 1997 and March 2001

Site-specific data indicate that G. tanycephalus was most prevalent at site 1 (near the dam wall), with numbers at this site accounting for more than half the total catch and being 4 times greater than the next most abundant sites (sites 2 and 4). Very few G. tanycephalus were caught at the most exposed site, site 5. The data for P. mesotes indicate a more evenly distributed population; with the greatest abundances being recorded at sites 1 and 6 (Jonah Bay). However, the abundance at other sites was generally high compared to G. tanycephalus numbers. Site 5 produced the lowest numbers of P. mesotes.

Size The Inland Fisheries Service has carried out twelve sampling events since September 1997, catching mostly adult fish using the electrofishing methods

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described above. The size of the fish caught may be a useful indicator of the development and progress of size cohorts in the population. Figure 4 illustrates the size data presented as length-frequencies for each of the twelve sampling events.

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14 Sep 1997 13 12 11 G. tanycephalus (n=23) 10 P. mes otes ( n=23) 9 8 7 6

Number of fish 5 4 3 2 1 0 134 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 130 100-104 105-109 110-114 115-119 120-124 125-129 a Size class (mm)

12 Dec 1997 11 10 9 G. tanycephalus (n=32) 8 P. mesotes (no data) 7 6 5 4 Number of fish 3 2 1 0 134

b 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 130 Size class (mm) 100-104 105-109 110-114 115-119 120-124 125-129

18 Apr 1998 17 16 15 14 G. tanycephalus (n=24) 13 12 P. mes otes ( n=55) 11 10 9 8 7 Number of fish 6 5 4 3 2 1 0 134 c 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 100-104 105-109 110-114 115-119 120-124 125-129 Length (mm) 130

Figure 4 (a-c): Length – frequency data for G. tanycephalus and P. mesotes captured in Arthurs Lake from September 1997 to March 2001

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6 Oct 1998 5 G. tanycephalus (n=11) 4 P. mes otes ( n=18) 3 2 1 Number of fish 0 134

d 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 130 Size class (mm) 100-104 105-109 110-114 115-119 120-124 125-129

21 20 Dec 1998 19 18 17 16 G. tanycephalus (n=3) 15 P. mesotes (n=60) 14 13 12 11 10 9

Number of fish 8 7 6 5 4 3 2 1 0 134 e 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 130 Size class (mm) 100-104 105-109 110-114 115-119 120-124 125-129

14 Apr 1999 13 12 11 G. tanycephalus (n=28) 10 P. mes otes ( n=28) 9 8 7 6

Number of fish 5 4 3 2 1 0 134 f 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 100-104 105-109 110-114 115-119 120-124 125-129 Size class (mm) 130

Figure 4 (d-f): Length – frequency data for G. tanycephalus and P. mesotes captured in Arthurs Lake from September 1997 to March 2001

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14 Jun 1999 13 12 11 G. tanycephalus (n=50) 10 P. mes otes ( n=30) 9 8 7 6

Number of fish 5 4 3 2 1 0 134 g 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 Size class (mm) 100-104 105-109 110-114 115-119 120-124 125-129 130

4 Sep 1999 3 G. tanycephalus (n=3) 2 P. mesotes (n=12) 1

Number of fish 0 134 h 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 100-104 105-109 110-114 115-119 120-124 125-129 Size class (mm) 130

24 Dec 1999 23 22 21 20 19 18 G. tanycephalus (n=13) 17 P. mes otes ( n=55) 16 15 14 13 12 11 10 Number of fish 9 8 7 6 5 4 3 2 1 0 134 i 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 130 Size class (mm) 100-104 105-109 110-114 115-119 120-124 125-129

Figure 4 (g-i): Length – frequency data for G. tanycephalus and P. mesotes captured in Arthurs Lake from September 1997 to March 2001

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26 n=34 Mar 2000 25 24 23 22 21 20 19 G. tanycephalus (n=9) 18 P. mesotes (n=138) 17 16 15 14 13 12 11 Number of fish 10 9 8 7 6 5 4 3 2 1 0 134 j 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 130 Size class (mm) 100-104 105-109 110-114 115-119 120-124 125-129

sh Sep 2000 2 G. tanycephalus (n=0) 1 P. mesotes (n=8)

No. of fi 0 134 k 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 130 Size class (mm) 100-104 105-109 110-114 115-119 120-124 125-129

14 n=33 Mar 2001 13 12 11 G. tanycephalus (n=17) 10 P. mes otes ( n=80) 9 8 7 6

Number of fish 5 4 3 2 1 0 134 l 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-99 130 Size class (mm) 100-104 105-109 110-114 115-119 120-124 125-129

Figure 4 (j-l): Length – frequency data for G. tanycephalus and P. mesotes captured in Arthurs Lake from September 1997 to March 2001

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These data indicate that G. tanycephalus follows a similar growth pattern to that of the Woods Lake population, with fish recruiting into the adult, near-shore population at around 50 mm in the spring-summer, although there was some indication of recruitment in the early autumn of 1998. They then spend 12 - 18 months as adults, with large-sized individuals usually disappearing from the population during the winter months. If this interpretation is correct, it indicates that the adult G. tanycephalus usually have one or, at best, two spawning seasons available. From a management perspective, this indicates that one bad year would have a major effect on the population and two consecutive bad years would threaten the viability of the entire population. P. mesotes appears to recruit into the adult near-shore population at around 30 mm, in both spring and autumn. Those that recruit in spring appear to leave the population the following winter, while those that recruit in autumn appear to leave the population the following summer, giving a period of about 9 months, or, at most, two spawning seasons, in the adult near-shore population. Fulton (1990) describes their preferred habitat as rocky margins of lakes, and McDowall (1996) indicates that this species ‘has never been found commonly’, being discovered only in the mid-1970s.

Current Study Data To collect additional and more recent data, native fish surveys were conducted by both Hydro Tasmania and the Inland Fisheries Service (Native Fish Conservation section). The aim of this additional work was to complement the long-term data collected during Inland Fisheries Service Recovery Plan monitoring for G. tanycephalus (Crook and Sanger, 1997), with surveys targeting a wider variety of habitat types with increased fishing effort. Fyke-net surveys were conducted using fine mesh; single 5 m wing fyke nets fitted with trout/platypus exclusion screens. Hydro Tasmania sampling consisted of the deployment of four fyke nets placed at each of seven sites around Arthurs Lake (as shown in Figure 5 and listed in Table 3). With the exception of one site located adjacent to Neil Island, the study sites were located around the periphery of the lake. Five of the sample sites were located in less that 1.5 m of water, while deep sets (approximately 5m) were conducted off Jones Rivulet and Sandlake Bay. The majority of sites were situated in areas with a sparse to moderate cover of aquatic plants. The location of the Inland Fisheries Service Recovery Plan sample sites is shown in Figure 3 (map in previous section). Sites were generally located in areas of rocky substrate in water depths less than 1.5 m. Surveys were conducted in July, September, and December 2001, and April 2002. Fish were sampled by backpack electrofishing for a total of 15 minutes at each of the six sites, supplemented by fyke nets deployed overnight. While the 2001 - 2002 Inland Fisheries Service surveys initially used both fykes and electrofishing methods, later survey were conducted using only electrofishing, as presumably Inland Fisheries Service considered this method adequate for comparison with historical Recovery Plan monitoring data.

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Site Location Characteristics Afy02 On the western shore of Creely Bay (this is Sparse macrophyte cover adjacent to the Inland Fisheries Service electrofishing site EF2); Afy04 On the eastern (sheltered) shore of Neil Island Moderate macrophyte cover and rocky substrate (this site is a little to the south of the Inland Fisheries Service electrofishing site EF4); Afy05 Along the shore of Phantom Bay (this site is Dense macrophyte cover between the Inland Fisheries Service electrofishing sites EF3 & EF6); Afy07 Around the mouth of Tumbledown Creek, in the Some macrophyte cover north of the lake; Afy08 Around the mouth of Jones Rivulet, in the north of Moderate macrophyte cover the lake; Afy09 South of Jones Rivulet Deep set, macrophyte cover Afy10 Off Sandlake Bay Deep set, 30 m inshore, chara beds Table 3: Details of the sample sites used in the technical study

Figure 5: The location of sites used in the technical study, and sampled by the IFBC. Four fyke nets were set overnight at each sites during each sample. Sites afy 09 afy 10 were deep set sites while the remainder were shore set in less than 1.5m.

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Saddled Galaxias (Galaxias tanycephalus)

G. tanycephalus Catch Rates Numbers of G. tanycephalus collected from the seven technical study sites surveyed between August 2001 and July 2002 are shown in Table 4. A total of 63 G. tanycephalus were captured during the survey, the majority of which were captured from sites Afy02 and Afy04. Sites where fykes were deployed in deeper water returned the lowest catches of saddled galaxias during the survey. Highest catches of fish were recorded from the March and July 2002 surveys (n = 28 and n = 22 respectively). Summarised results from the Inland Fisheries Service recovery plan monitoring for 2001/2002 are shown in Table 5. A total of 50 fish were caught in the Inland Fisheries Service surveys, most of which were captured at sites EF1 and EF3. Highest catches were recorded in July 2001 and April 2002. With the exception of the April 2002 sample, Inland Fisheries Service surveys used both electrofishing and fyke nets to capture fish. While it is not possible to quantitatively compare the relative efficiency of these sample methods, it is interesting to note that electrofishing captured marginally more fish than fyke netting when the April 2002 sample is excluded. The results from both Hydro Tasmania and Inland Fisheries Service surveys show a high degree of spatial and temporal variability, with relatively low catches for the amount of fishing effort expended regardless of method. Historical Inland Fisheries Service Recovery plan data from 1997 to the present, discussed earlier, also shows a high degree of within and between year variability, making temporal assessment of historical standardised catch rates difficult.

Sampling Period Site Aug 01 Sep 01 Dec 01 Mar 02 Jul 02 Site totals Afy02 0 0 2 7 8 17 Afy04 0 2 0 8 10 20 Afy05 0 0 0 5 2 7 Afy07 3 1 0 2 0 6 Afy08 0 1 0 8 0 9 Afy09 0 0 0 0 2 2 Afy10 1 1 0 0 0 2 TOTAL 4 5 2 28 22 63 Table 4: Number of G. tanycephalus caught with fyke nets at seven Hydro Tasmania technical study sites in Arthurs Lake during surveys conducted between August 2001 and July 2002. Bracketed numbers represent CPUE (fish per net hour). Nets were set for overnight soak.

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Sampling period July 01 September 01 December 01 April 02 Site Totals Site Fyke Shock Fyke Shock Fyke Shock Fyke Shock EF 1 0 9 - 1 - 1 - 9 20 EF 2 - - - 1 - 3 - 3 7 EF 3 10 2 0 0 0 0 - 1 13 EF 4 - - 1 2 0 0 - 1 4 EF5 0 1 - 1 1 0 - 1 4 EF 6 1 1 0 0 0 0 - 0 2 TOTAL 11 13 1 5 1 4 - 15 50 Table 5: Number of G. tanycephalus caught at the Inland Fisheries Service Recovery Plan sites in Arthurs Lake during four surveys, from July 2001 to February 2002. Fyke nets were deployed overnight, and electrofishing runs were standardised at 15 minutes shock time. Sites that were not sampled are indicated by (–) in the appropriate cell.

G. tanycephalus Size Structure Figure 6 contains G. tanycephalus length frequency histograms for each of the 5 sampling events undertaken as part of the technical study, while Figure 7 shows length frequencies of the data collected during Inland Fisheries Service Recovery Plan monitoring. Analysis of population size structure is a useful indicator of spawning time and the development and progress of size cohorts in the population. When collected with a time step of sufficient resolution for the target species (eg quarterly for saddled galaxias), length frequency data can provide an indication of recruitment success or failure, and hence is a useful tool in fish population management. The histograms in Figure 6 and Figure 7 shows changes in length frequency of G. tanycephalus population samples over the year. Unfortunately, some of the histograms contain data from only a handful of individuals and so limited inferences can be drawn from them. However, analysis of cohort progression using both Hydro Tasmania and Inland Fisheries Service data generally shows that larval G. tanycephalus recruit to the adult population at a length of approximately 45 mm, and while individual cohorts are difficult to follow with the limited data available, there appears to be recruitment to the adult population after the December sample, between March and July. Examination of the March and July 2002 data in Figure 6 shows evidence of 3 cohorts in the sample population, presumably due to additional resolution provided by increased sample sizes in these months. Inland Fisheries Service historical saddled galaxias length frequency data contained in the June 2001 status report for this study confirms that larval saddled galaxias recruit to the adult population at around 45 mm, however up to four cohorts were identified from the recent data. With the exception of the April 2002 Inland Fisheries Service electrofishing data, very few individual between 85 and 110 mm were collected during the year during both the Hydro Tasmania and Inland Fisheries Service sampling programs, and the reasons for this are not clear. Sample sizes of the Inland Fisheries Service data are too small to draw any inferences regarding the potential for gear selectivity between electrofishing and fyke netting.

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3 G. tanycephalus Arthurs Lake Survey (IFSBC) 14-15th August 2001 n = 4 2 Number 1

0 0 102030405060708090100110120 Fork Length (mm)

3 G. tanycephalus Arthurs Lake Survey (IFSBC) 25-26th September 2001 2 n = 5 Number 1

0 0 102030405060708090100110120 Fork Length (mm)

3 G. tanycephalus Arthurs Lake Survey (IFSBC) 3-4th December 2001 2 n = 2 r Numbe 1

0 0 10 20 30 40 50 60 70 80 90 100 110 120 Fork Length (mm)

Figure 6: Length frequency data for G. tanycephalus from August 2001 to June 2002 collected by the Inland Fisheries Service Biological Consultancy for the Arthurs Lake technical study.

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4 G. tanycephalus Fyke net n=11 Arthurs Lake Survey (IFS) July 2001 Electrofishing n=13 3

2 Number

0 0 102030405060708090100110120 Fork Length (mm)

3 G. tanycephalus Arthurs Lake Survey (IFS) Fyke net n=1 September 2001 Electrofishing n=5 2 Number 1

0 0 102030405060708090100110120 Fork Length (mm)

3 G. tanycephalus Arthurs Lake Survey (IFS) Fyke net n=1 December 2001 Electofishing n=4 2 Number 1

0 0 102030405060708090100110120 Fork Length (mm)

Figure 7: Length frequency data for G. tanycephalus caught by the Inland Fisheries Service in Arthurs Lake from July 2001 to April 2002

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Arthurs Paragalaxias (Paragalaxias mesotes)

P. mesotes Catch Rates Table 6 shows numbers of P. mesotes collected from the technical study sites between August 2001 and July 2002. A total of 60 Arthurs paragalaxias were captured during the survey. The highest catch rates were recorded from site Afy02 (Creely Bay). Deep set fyke sites (Afy09 and Afy10) returned the lowest catches of P. mesotes during the survey. Highest catches of fish were recorded from the March and July 2002 surveys (n = 31 and n = 11 respectively) while only two fish were captured in December 2001. Observed ‘catch dynamics’ were generally similar to those reported for saddled galaxias, with similar site and seasonal maxima. Inland Fisheries Service recovery plan monitoring data for 2001/2002 are shown in Table 7. A total of 93 fish were caught in these surveys, most of which were captured at sites EF1, a rocky site adjacent to Arthurs dam wall. Highest total catches were recorded in April 2002, when the sole method of sample collection was electrofishing via standardised methods. With the exception of the April 2002 sample, Inland Fisheries Service surveys used both electrofishing and fyke nets to capture fish. While it is not possible to quantitatively compare the relative efficiency of these sample methods, electrofishing captured marginally more fish than fyke netting when the April 2002 sample is excluded from the data, an observation that was also made with the saddled galaxias data. In a similar pattern to the saddled galaxias data, the results from both Hydro Tasmania and Inland Fisheries Service surveys show a high degree of spatial and temporal variability, with relatively low catches for the amount of fishing effort expended regardless of method. Historical Inland Fisheries Service Recovery plan data from 1997 to the present, reported in the June 2001 status report for this study, also shows a high degree of within and between year variability, making temporal assessment of historical standardised catch rates difficult.

Sampling Period Site Aug 01 Sep 01 Dec 01 Mar 02 Jul 02 Site total Afy02 2 1 0 14 6 23 Afy04 1 0 0 4 3 8 Afy05 0 3 0 5 1 9 Afy07 3 2 0 5 0 10 Afy08 0 0 0 3 1 4 Afy09 1 1 1 0 0 3 Afy10 0 2 1 0 0 3 Sample total 7 9 2 31 11 60 Table 6: Number of P. mesotes caught with fyke nets at seven technical study sites in Arthurs Lake during surveys conducted between August 2001 and June 2002

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Sampling period July 01 September 01 December 01 April 02 Site totals Site Fyke Shock Fyke Shock Fyke Shock Fyke Shock EF 1 0 3 - 4 - 5 - 29 41 EF 2 - - - 0 - 0 - 2 2 EF 3 3 0 3 0 4 0 - 1 11 EF 4 - - 4 8 5 0 - 3 20 EF5 0 0 - 0 0 0 - 1 1 EF 6 0 2 1 1 1 3 - 10 18 TOTAL 3 5 8 13 10 8 - 46 93 Table 7: Number of P. mesotes caught at the Inland Fisheries Service Recovery Plan sites in Arthurs Lake during four surveys, from July 2001 to February 2002. Fyke nets were deployed overnight, and electrofishing runs were standardised at 15 minutes shock time. Sites that were not sampled are indicated by – in the appropriate cell.

P. mesotes Size Structure Figure 8 and Figure 9 show the length frequency distribution of samples taken during 2001 - 2002 as part of the Hydro Tasmania technical study and Inland Fisheries Service Recovery Plan monitoring respectively. As discussed previously, samples for the latter program were collected by both fyke netting and electrofishing. Data from these surveys indicate that larval recruitment to the adult population appears to start at approximately 25 mm in length. Once again, low catch rates of Arthurs paragalaxias make interpretation of cohort progression difficult, however it is apparent that most histograms contain only one cohort. Data collected by the Inland Fisheries Service in July 2001 and April 2002 is the exception to this rule, with two cohorts apparent in the histograms, particularly in the latter data. These data confirm historical Inland Fisheries Service Recovery Plan data discussed earlier that showed larvae recruitment to the adult population at approximately 25 mm in length, and reported a minimum of two cohorts from length frequency data.

South Esk – Great Lake Water Management Review 22 Scientific Report on Arthurs Lake August 2003

3 P. mesotes Arthurs Lake Survey (IFSBC) 14-15th August 2001 n = 7 2 Number 1

0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Fork Length (mm)

4 P. mesotes Arthurs Lake Survey (IFSBC) 25-26th September 2001 3 n = 9

2 Number

0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Fork Length (mm)

3 P. mesotes Arthurs Lake Survey (IFSBC) 3-4th December 2001 n = 2 2 Number 1

0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Fork Length (mm) Figure 8 (a-c): Length frequency data for P. mesotes caught by the Inland Fisheries Service Biological Consultancy from August to June 2002 for the Arthurs Lake technical study

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7 P. mesotes 6 Arthurs Lake Survey (IFSBC) 3 March 2002 5 n = 31

3 Number 2

0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Fork Length (mm)

5 P. mesotes Arthurs Lake Survey (IFSBC) 4 July 2002 n = 11 3 ber m u

n 2

0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Fork length (mm)

Figure 8 (d-e): Length frequency data for P. mesotes caught by the Inland Fisheries Service Biological Consultancy from August to June 2002 for the Arthurs Lake technical study

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3 P. mesotes Fyke net n=3 Arthurs Lake Survey (IFS) July 2001 Electrofishing n=5 2 er b Num 1

0 0 102030405060708090100110120 Fork Length (mm)

5 P. mesotes Fyke net n=8 4 Woods Lake Survey (IFS) Electrofishing n=5 September 2001

Number 2

0 0 102030405060708090100110120 Fork Length (mm)

3 P. mesotes Fyke net n=10 Arthurs Lake Survey (IFS) December 2001 Electrofishing n=8 2 Number 1

0 0 102030405060708090100110120 Fork Length (mm)

8 P. mesotes 7 Arthurs Lake Survey (IFS) Electrofishing n=46 April 2002 6 5

Number 3 2

1 0 0 102030405060708090100110120 Fork Length (mm) Figure 9 (a-d): Length frequency data for P. mesotes caught by the Inland Fisheries Service in Arthurs Lake from July 2001 to April 2002

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Summary Although a variety of habitats were surveyed during the technical study and the Inland Fisheries Service Recovery Plan monitoring programs, habitat preference information derived from the study is limited but useful. Data from the deep-set fyke nets indicates that both species occur at depths of up to 5 m, however numbers of fish collected from these sites were very low in comparison to the shallow sites. While Crook and Sanger (1997) and Fulton (1990) described saddled galaxias and Arthurs paragalaxias as occupying rocky lake margins, the results from the Arthurs Lake Technical Study and closely related Woods Lake Technical Study show that both species are also found associated with areas of aquatic plant cover (eg. Afy05), and so these areas should not be discounted as important habitat for both species. Dedicated studies are required before the habitat preferences for both species can be refined. The surveys showed that both species recruited to the adult population during 2001/2002, indicating that successful spawning during the previous spring. While both species are relatively short lived, Arthurs paragalaxias populations are particularly vulnerable in the case of recruitment failure due to the fact that there are only up to two cohorts present in the lake at any time. Historical Inland Fisheries Service catch records show that Arthurs paragalaxias has not been collected in Woods Lake since the late 1980s and Inland Fisheries Service Recovery Plan and Hydro Tasmania technical studies conducted in 2001 - 2002 also failed to detect its presence in the lake, and so it is highly likely that it is either locally extinct or very low in numbers. The reasons for this localised extinction are not clear, but the Inland Fisheries Service speculates that it may be related to lake level management. Ongoing technical studies for Woods Lake planned for 2002/2003 should shed some light on this question. Consequently, P. mesotes has recently been nominated for listing as ‘endangered’ under the Environment Protection and Biodiversity Conservation Act 1999, and if P. mesotes is extinct in Woods Lake, Arthurs Lake would then be the sole remaining location for this endangered species. Given this, it is critical that populations in Arthurs Lake are protected and monitored to ensure the continued survival of the species.

Lake Level Management The principal public concern identified during community consultation was lake level variations, with opinions varying between those who thought that the lake was managed at levels that are too low through to those who thought that fishing over the last several season has been exceptional, and that there should be no change to current lake level management regimes. No respondents advocated a decrease in lake levels. Consultation with the Inland Fisheries Service has indicated that Arthurs Lake has been fishing particularly well over the last several years, and it has been supporting an increasing number of anglers over successive seasons. Water level in the lake during this period has been maintained over the 948 mASL minimum level, and has generally been above 949 mASL. While the Inland Fisheries Service is satisfied with the current minimum lake level agreement, and would be happy to see it formalised in some way to ensure that the water level is maintained, there is some angler support for an increased minimum lake level of 949 m above sea level.

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Hydro Tasmania has only a limited scope to raise the current minimum lake level due to the high cost and questionable environmental benefits of doing so. An increase in the minimum lake level would result in increased risk of spill and potential loss of valuable water that would normally be used to generate electricity through the Poatina Power Scheme. As the capacity of the Arthurs Flume pumping system and Arthurs Dam siphons is finite, there is no capacity to reduce spill risk by modifying the operation of these assets without major capital expenditure. Hydro Tasmania would also forego some generation potential if the minimum lake level was raised. The biological benefits of increasing the minimum lake level are unclear, however boat anglers are likely to benefit by increased ease of access to shallow.

Conclusions

Current Lake Level Agreement While some respondents to the public consultation process advocated an increase in the minimum lake level, Arthurs Lake is currently ranked as one of Tasmania’s most productive fisheries. The current informal agreement to maintain a minimum lake level of 948 m above sea level is supported by the Inland Fisheries Service, indicating that the current level management regime is adequate to maintain the fishery. Aside from increased boating access to shallow bays, the recreational fishery benefits that might arise from increasing the minimum lake level are unclear, and there would be some cost to Hydro Tasmania by doing so. However, the current minimum lake level agreement is informal, and while there is acceptance of the agreement, the wider perception is that there is little incentive for Hydro Tasmania to adhere to it, particularly with the introduction of Basslink and the potential changes to operation that may accompany it. It is recommended that Hydro Tasmania formalise a minimum level agreement between itself and the Inland Fisheries Service.

Threatened Species The Arthurs Lake Technical Study has shown that the current lake management regime appears to maintain native fish populations, as both species appear to be successfully spawning within Arthurs Lake. While the technical study has increased general knowledge regarding both species habitat preferences, large knowledge gaps remain regarding the biology and ecology of both G. tanycephalus and P. mesotes. The findings of the study indicate that there is little scope or justification to increase the minimum lake level for management of threatened species, as the current management regime appears adequate in sustaining galaxiid populations. The exact implications of lowering the current minimum lake level are not clear, but the risk of poor water quality, habitat loss and degradation would increase. Moreover, any increase in risk to populations of saddled galaxias and particularly Arthurs paragalaxias is highly undesirably given the extremely limited distribution, and the National and State conservation status of both species. It is also recommended that Hydro Tasmania review and support appropriate Recovery Plans for both species. Funding should be made available to support University studies to further investigate the life history and ecology of both the Arthurs paragalaxias and the Saddled galaxias.

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4. ENVIRONMENTAL MANAGEMENT OPTIONS FOR ARTHURS LAKE As indicated earlier, the two predominant issues for Arthurs Lake are threatened species and lake level management. This section lists some options that may be considered to help manage the issues identified.

Lake Level Management Hydro Tasmania has direct control over outflows from Arthurs Lake, through the pump and flume system, which transfers water to Great Lake and, to a lesser extent, the siphons and riparian outlet, which allow water to be discharged from the dam into the Upper Lake River. These structures facilitate control of the lake level, although the limited capacity of the pump means that water level management is an exercise in medium- (seasonal) to long-term (annual) planning. The lake is managed by Hydro Tasmania to provide water to the Poatina Power Scheme, via Great Lake, avoiding both the possibility of spill and the level falling below the agreed minimum. To date, the present operational regime has been successful in achieving these goals. However in light of the interest in maintaining yet higher water levels in the lake, there are a number of options

Increase the Pumping Capacity from Arthurs Lake Increasing the pumping capacity from the lake may allow higher minimum levels to be maintained without increasing the risk of spill. This would require expansion or duplication of the pump, flume and canal system presently in place, and this is likely to involve significant capital expenditure.

Raise the Minimum Lake Level to 949.0 Metres Above Sea Level This would directly address community concerns about low water levels for boating, especially in favoured areas like Cowpaddock Bay, and would be looked on favourably by the angling community in general terms. It imposes further restrictions to operating flexibility and is likely to cost Hydro Tasmania the foregone generating potential from the extra metre of water. In addition, without infrastructure changes, this would also increase the risk of spill from the lake.

Maintain Existing Conditions The existing lake management has been successful in maintaining a relatively healthy native fish population and a productive trout fishery, while operating the lake so as to avoid both spill and low water levels.

Threatened Species Management Although conditions in Arthurs Lake appear to be suitable for maintaining populations of P. mesotes and G. tanycephalus, these species, because of their short life span, remain vulnerable to negative changes in environmental conditions should they persist for one year or more.

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A priority for any management option should be to ensure that nothing is done which has a detrimental effect on the environmental conditions of the lake, in terms of pelagic and in-shore rocky habitats. Options for these species’ management include: translocating populations of both species to suitable nearby habitats; funding research into the environmental requirements of both species in Arthurs Lake; and maintain existing conditions.

Translocations The Recovery Plan for the Saddled Galaxias (Crook and Sanger, 1997) proposed, as a long-term objective, that all available options for translocation should be evaluated. Both species are lake-based and would require similar habitats to those that existed in Arthurs Lake before impoundment. Although there are no trout- free lakes in the Lake River catchment, two small lakes to the north of Arthurs Lake may provide suitable habitat. These are Little Lake and Gunns Lake, which connect to Arthurs Lake via the Jones Rivulet. Successful translocations would provide alternative populations of these species, which would be available for restocking of Woods and Arthurs Lakes, should the populations decline dramatically. The establishment of additional populations may also assist in improving the conservation status of the species.

Research the Environmental Requirements of the Threatened Fish Species This option would extend the information gathered by the present technical study in Arthurs Lake. It would require extensive sampling of a range of habitat types and water depths. It may also require an investigation of the rates of predation by trout. While management of the lake’s water quality by Hydro Tasmania does not appear to have caused any problems for the threatened species, major changes to water level management may. It will be important to know the risks associated with this in terms of the environmental conditions required by the threatened species. This work could be carried out by Hydro Tasmania staff, by Inland Fisheries Service staff with resource assistance provided by Hydro Tasmania, or by supporting an Honours student.

Maintain Existing Conditions The populations of threatened species in Arthurs Lake appear to be in good condition, with regular spawning and recruitment evident since Inland Fisheries Service sampling commenced in 1997. There is no known reason why these conditions should not persist indefinitely under the existing management regime.

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References Crook, D.A. and Sanger, A.C. 1997, Recovery Plan for the Pedder, Swan, Clarence, swamp and saddled galaxias. Inland Fisheries Commission, Hobart and Environment Australia Biodiversity Group, Canberra. Fulton, W. 1990, “Tasmanian freshwater fishes” Fauna of Tasmania Handbook 7, University of Tasmania, Hobart. Hydro Tasmania, 1999, Environmental Review: South Esk – Great Lake Hydro Catchment, Hydro Tasmania, Hobart. Hydro Tasmania, 2000, Community Consultation Report: South Esk – Great Lake Hydro Catchment, Hydro Tasmania, Hobart. McDowall, R.M. (ed) 1996, Freshwater fishes of South-eastern Australia, revised edition, Reed Books, Chatswood.

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