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The Toolondo Reservoir Brown Trout Fishery | FN0135 |
Alan Baxter
April 1998 |  |
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The Results of Trout Management Group Fish Population Surveys 1980-1994 inclusive.
Introduction
Barton Swamp, the precursor of Toolondo Reservoir, was first stocked with salmonids in 1946 when 100 'yearling' rainbow trout, Oncorhynchus mykiss, were released. The reservoir was built in 1953 and the first recorded salmonid stocking of Toolondo Reservoir was in 1965 when 27,000 'advanced yearling' rainbow trout were released. The next stocking of salmonids was in 1980 when 15,000 chinook salmon, O. tshawytscha, were released. At that time the Department was attempting to establish additional chinook salmon waters. Lake Burrumbeet, near Ballarat, was also stocked with chinook salmon in 1980.
The first release of brown trout,Salmo trutta, was of 44,000 fish (average length approx. 180mm) in 1982 which coincided with a severe drought which set back trout stocks throughout Victoria. In 1983, after the drought had broken, the number of trout stocked was increased to 55,000 to compensate for the smaller size (average length 100mm) and reduced survival rate of the smaller trout.
The average annual stocking has been 40,000 and since 1987 this has been a combination of brown trout and rainbow trout at the request of local anglers. A brief, recent stocking history is given in Table 1.
Table 1: Recent salmonid stocking history for Toolondo Reservoir (Number x 1,000)
| 1980 | 15 CS | 1984 | 30 BT | 1988 |
| 1992 | 20 BT, 20 RT |
| 1981 | 0 | 1985 | 40 BT | 1989 |
| 1993 | 35 BT, 5 RT |
| 1982 | 44 BT | 1986 | 40 BT | 1990 |
| 1994 | 35 BT, 5 RT |
| 1983 | 55 BT | 1987 | 20 BT, 20 RT | 1991 |
| 1995 | 35 BT, 5 RT |
Fish Population Surveys
Netting surveys have been conducted in most years since 1980. There was no survey in 1983 and the reservoir was surveyed twice in 1982 and 1993. A number of gill nets of varying mesh sizes were set overnight and cleared the next morning. Mesh nets are to a degree selective for species and size and this is why a range of mesh sizes was used. The catch was weighed and measured.
The primary parameters monitored were:
- the composition of the catch by species;
growth rates;
condition (as measured by the Fulton's Condition Factor, K); and
catch per unit effort (CPUE).During this period, 1980-'94, a Creel Survey and a Catch Effort Return Program (CERP) were also run at various times which complemented the results of the netting surveys.
Species Composition
Before the brown trout fishery became established in about 1984, redfin, Perca fluviatilis, were the dominant species of fish taken in the netting surveys, followed by tench, Tinca tinca, and then brown trout. Prior to stocking, occasional brown trout were taken and these were believed to have entered the reservoir via the channel from Rocklands Reservoir as no trout spawning occurs in the streams entering Toolondo Reservoir.
In latter years the catch was dominated by brown trout. In the mid to late 1980's, the reservoir had developed a reputation for trophy size brown trout, and 3 to 4kg, good conditioned trout were not uncommon.
Growth Rates
Initially, it was not possible to readily age the trout caught in the gill netting surveys. Scale readings had been shown to be unreliable in temperate Victorian lakes as the growth checks were not prominent enough to be detected.
This changed with the introduction of finclipped trout in 1987. By varying the sequence of finclips, it was now possible for both fisheries managers and anglers to readily age the finclipped trout they caught. History had shown that the majority of brown trout in Victoria's temperate lakes were dead by age 4 and rainbow trout by age 2. Prior to fin clipping, the largest trout taken in the surveys were estimated to be age 4. Mesh selectivity trials conducted by the TMG between 1978 and 1980 had shown that 89mm nets would readily catch 2 year old lake trout and this was the smallest mesh size used.
Details of the largest (assumed to be 4yo), average and smallest (assumed to be 2yo) brown trout taken in surveys is given in Fig 1.
Figure 1: Largest, mean and smallest brown trout taken in gill netting surveys between 1980 and 1994.
The finclip of the largest brown trout caught in 1995 indicated that it was actually 5yo and this was the first confirmed record of a 5yo brown trout in all the TMG surveys of lakes in Victoria. The presence of finclipped trout has enabled the growth rates to be monitored more accurately (Fig. 2). The best growth rates in recent years were achieved by the 1989 and 1991 liberations.
Figure 2: Growth rates of known age brown trout caught in gill netting surveys in Toolondo Reservoir 1988-'94
Condition Factor - K
The Condition Factor is calculated using the following formula:
K = 105 x W
L3
where W is the weight in grams and L the length to the caudal fork in mm.
The average Condition Factor for the brown trout caught in the surveys is given in Fig. 3
Figure 3: Average Condition Factor for brown trout caught in Toolondo Reservoir, 1980-'94.
Catch Per Unit Effort (CPUE)
The reservoir was surveyed, in most instances, during the cooler winter months. By standardising the time of the survey, the gear used, the locations the nets were set and using the same personnel, the CPUE can be used as a relative measure of abundance. The unit of effort used is the net-hour. One net hour is equal to one standard 23 metre long net being set for a period of one hour. CPUE can be calculated for the number of trout caught per net hour or the weight of trout caught per net hour. The calculations for brown trout taken from Toolondo Reservoir are shown in Fig. 4 and 5.
Figure 4: Number/100 net hour CPUE for brown trout caught in Toolondo Reservoir between 1980 and 1994
| | Figure 5: Weight (g)/ net hour CPUE for brown trout caught in Toolondo Reservoir between 1980 and 1994
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Discussion
The continual decline in the condition of the brown trout, growth rates and CPUE between 1986 and 1990 caused some concern and recommendations were made in 1990 to reduce the stocking rate, if the reservoir was to be managed as a trophy fishery. There was also a corresponding decline in the average size of redfin taken during the same period (Fig. 5). The data collected in the CERP, particularly the Condition Factor, indicated that the fishery was in worse condition than indicated by the netting survey data.
Figure 6 Mean weight of redfin taken in surveys of Toolondo Reservoir where the sample size exceeded 10.
The very low mean weight in 1981 was due to the fact that 50 to 75mm size mesh nets were used compared to the normal 89 to 114mm nets in latter surveys. (Gill nets can be very size selective in what they catch).
In the early 1990's, there was a marked improvement in the fishery but this appears to have been short-lived. A number of theories have been proposed, initially for the decline (e.g. stocking of rainbow trout, low water levels), and then for the apparent improvement but the data suggests that it was probably due to very poor recruitment to the fishery from the 1990 liberation.
In 1990, 50% of the 35,000 brown trout released into Toolondo Reservoir were finclipped (right ventral). Only one right ventral finclipped trout was taken in the post 1990 surveys (Fig. 2). A Catch and Effort Return Program (CERP) was run with the assistance of local anglers from July 1989 to December 1991. Between July 1990 and December 1991, 127 brown trout were entered in the CERP and not one had a right ventral finclip which supports the poor recruitment hypothesis.
Poor recruitment equates to a reduced stocking, i.e. there are fewer fish. The best growth rates in recent years were observed in the 1989 and 1991 releases (Fig. 2). This is to be expected because of the reduced competition resulting from poor recruitment in 1990. In 1993, two 5 year old brown trout were taken which is the first confirmed record of a finclipped 5 year old brown trout caught in any of the waters stocked by the Department in recent years. The reduced competition may have been responsible for this. The condition of the trout taken by anglers involved in the CERP also improved in the Spring of 1991 compared with 1990.
In 1994, the growth rates were again declining, the average condition of the brown trout was almost at its lowest recorded level and the CPUE was as its lowest level since the brown trout fishery became established in the mid 1980's. These facts led to the recommendation that , if the brown trout fishery in Toolondo Reservoir was to be managed as a trophy fishery, then the stocking rate should be reduced.
A reduction in the stocking rate of brown trout from 35,000 to 20,000 was agreed to at the 1996 Consultation Meeting between Victorian Fisheries and the South-West Region of the Department. The decision was not supported by delegates from the Victorian Recreational Fishing Peak Body. Five thousand rainbow trout will also be stocked. The impact of the reduced stocking rate will be monitored by regular netting surveys. It is hoped that this adaptive approach to stocking will result in clear improvements in the Toolondo Reservoir brown trout fishery.
References
Baxter, A. F. The Recreational Trout Fishery in Toolondo Reservoir and Recommendations on Future Trout Stockings. Fisheries Management Report No. 43. Fisheries Branch, NRE.
This publication may be of assistance to you but the State of Victoria and its officers do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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