Evaluation of Past and New Stocking Practices for Recreational Fisheries in the Kerang Lakes

Recreational Fishing Grants Program Research Report
Project number: R06/07/01
December 2011

Contents

• Executive summary
• Introduction
  Purpose of this report
• Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• References
• Appendix 1. Does stocking make a significant contribution to fish numbers in the Kerang Lakes?
  • Methods
  • Results
  • Discussion
• Appendix 2 Does stocking make a significant contribution to angler success in the Kerang Lakes?
  • Methods
  • Results
  • Discussion
• Appendix 3
• Appendix 4

Table of Tables

• Table 1. Stocking densities of tagged and chemically marked golden perch and Murray cod for the Kerang Lakes. ARS = Alizarin Red S.
• Table 2. Stocking contributions of chemically marked golden perch in Reedy Lake, Kangaroo Lake, and Lake Charm.
• Table 3. Angler satisfaction of fishing activity in the Kerang Lakes during the survey by year.
• Table 4. Percentage of anglers targeting fishing in the Kerang Lakes.
• Table 5. Description of factors that reduce the quality of the fishing experience at the Kerang Lakes.

Table of Figures

• Figure 1. The Kerang Lakes of north western Victoria. The four lakes (in black) indicate research locations.
• Figure 2. Catch rates (number caught / hour) of golden perch and Murray cod from Kangaroo Lake, Lake Charm, Reedy Lake, and Kow Swamp.
• Figure 3. Numbers of fish caught (as a percentage) at Kangaroo Lake, Kow Swamp, Lake Charm, and Reedy Lake by recreational anglers (survey years combined).
• Figure 4. Percentage of fish released after capture by year of survey (Lakes combined).
• Figure 5. Distribution of where anglers fishing the Kerang Lakes reside.

Executive summary

Murray cod and golden perch are targeted by recreational anglers and contribute to recreational fisheries in inland water-bodies across south eastern Australia. Many inland Victorian freshwater water-bodies support Murray cod and golden perch populations. The abundance of these species in some water-bodies is restricted by low natural recruitment. As a consequence, the fisheries in these water-bodies do not satisfy angler expectations.

In order to enhance these fisheries, Fisheries Victoria stocks selected rivers and lakes with hatchery-reared Murray cod and golden perch. Despite widespread stocking of golden perch and Murray cod, the contribution that stocked fish make to existing populations, anglers' catch and angler attitude has not been investigated.

This study aimed to determine the contribution stocking makes to:

• Fish abundance
• Angler catch and perceptions.

The study was conducted in the Kerang Lakes, where hatchery-reared juvenile Murray cod and golden perch were released into Reedy Lake, Kangaroo Lake, Lake Charm and Kow Swamp. These fish were chemically marked and identified by an external tag.

The contribution these fish made to the existing populations and to anglers catch was determined using netting surveys and angler creel surveys.

The stocking program for golden perch in the Kerang Lakes resulted in:

• An increase in abundance
• An increase in anglers' catch (number and quality)
• An increase in angler satisfaction.

Results of the Murray cod stocking program were inconclusive as few fish were caught in the netting surveys. Only in Kangaroo Lake did hatchery-reared Murray cod make a significant contribution to the population. Of the 13 fish caught from Kangaroo Lake, 62% were hatchery-reared. Too few Murray cod were caught by anglers to determine the contribution the stocking program made to anglers' catch of this species.

The success of the stocking program for golden perch in the Kerang Lakes positively influenced anglers' perceptions of this fishery.

Introduction

Golden perch (Macquaria ambigua) and Murray cod (Maccullochella peeli) are native freshwater fish found throughout south eastern Australia.

It isestimated that the size of the Murray cod population has declined substantially over the past 30 years (conservatively estimated to be at least 30%) due to habitat degradation (McKelleher 2005).The Native Fish Strategy (NFS) for the Murray-Darling Basin 2003–2013 considers that overall, native fish numbers in the basin are presently at 10% of pre-European settlement levels. Under the provisions of the Environmental Protection and Biodiversity Conservation Act 1999, Murray cod is listed as vulnerable. A draft recovery plan has been developed to return populations to 60% of pre-European settlement levels (MDBC 2004).

Golden perch is found throughout the Murray-Darling Basin and was once very common. Golden perch is considered rare within much of its original range, although it is still present in large numbers in some locations (North Central CMA 2011). Its decline is due to negative effects on recruitment of juveniles into existing populations. This has occurred as a result of river management and construction of weirs and dams which have altered natural flow regimes, caused temperature stratification, and impeded migration. Golden perch has recently been listed as part of a threatened fish community in the lower Murray River (North Central CMA 2011). As declines were observed in the range and abundance of golden perch (Cadwallader 1978; Cadwallader et al. 1984), Victorian and New South Wales fisheries agencies initiated stocking programs in the 1970s to re-establish populations (Brumley 1987; Rowland 1983).

Both golden perch and Murray cod are highly valued by recreational anglers for their eating and sporting qualities. Both species are important components of the recreational fishery in inland waters (Rowland 1996).

To ensure that both conservation and fisheries management objectives are achieved, stocking programs for both species must result in an increase in the abundance of fish. Despite widespread stocking of golden perch and Murray cod, the contribution of stocked fish to existing populations has not been investigated.

Fisheries Victoria undertook a program to improve the native recreational fishery in Kerang Lakes through stocking both golden perch and Murray cod.

The Kerang Lakes is an inter-connected wetland located in northwest Victoria, Australia (Figure 1) covering an area of 9,419 ha. First Reedy Lake, Kangaroo Lake, Lake Charm, and Kow Swamp are the largest water-bodies within the system. The Kerang Lakes is a shallow, permanent and open freshwater system used to store water for irrigation (Ho et al. 2006). It is unlikely that Murray cod and golden perch reproduce within the Kerang Lakes, but rather wild fish immigrate into the Lakes from interconnected rivers.

The Recreational Fishing Grant Scheme funded a research project to determine the contribution that the stocking program for Murray cod and golden perch in the Kerang Lakes made to:

• The abundance of both species within the Lakes
• The catch of recreational anglers fishing in the Lakes.

Purpose of this report

This report describes the contribution stocking programs:

• Made to the abundance of golden perch and Murray cod in the Kerang Lakes
• Made to angler catch of golden perch and Murray cod in the Kerang Lakes and angler satisfaction of this fishery.

Methods

Detailed methods are presented in Appendices 1 and 2.

Survey design

From 2003 to 2008 Fisheries Victoria released chemically marked and tagged hatchery-reared golden perch and Murray cod into the Kerang Lakes.

To determine the contribution the stocking program:

• Netting surveys were undertaken in 2008 and 2009 to quantify the contribution released fish made to the native fish populations
• Angler interviews were undertaken from 2008/09 to 2010/11 to quantify the contribution released fish made to recreational anglers' catch and attitudes to the fishery.

Figure 1. The Kerang Lakes of north western Victoria. The four lakes (in black) indicate research locations.

Results

Discussion

Does stocking make a significant contribution to fish numbers?

GOLDEN PERCH

Stocked fish contributed substantially to the adult populations of golden perch at all three lakes surveyed.

Of the 212 golden perch caught (all lakes combined) during the 2008 and 2009 survey, 102 were reared in the hatchery and released into the Lakes.

The contribution of stocked golden perch to the population was:

• 47 ±9% (mean ± SE) at Reedy Lake
• 55 ±6% at Kangaroo Lake
• 90 ± 5% at Lake Charm.

The percent contribution of stocked golden perch varied with year class at each lake.

Growth (length- and weight-at-age) of golden perch did not differ significantly between stocked and wild fish suggesting that survey gear susceptibility was similar for stocked and wild fish.

The contribution stocking made to golden perch populations had an inverse relationship with the degree of connectedness to a source of a wild population:

• Reedy Lake is connected all year to the Loddon River and yielded the lowest stocking contribution (47%)
• Kangaroo Lake yielded a stocking contribution of 55%; although it is also connected to the Loddon River all year round, it is located further along irrigation channels than Reedy Lake.
• Lake Charm connects to the Loddon River for only a few days each year, yielded the highest stocking contribution (90%).

MURRAY COD

Only a relatively small number of Murray cod were caught at Kangaroo Lake during 2009 (13 fish). Of these fish 62% had been reared in the hatchery and released into the Lakes.

Does stocking make a significant contribution to angler success?

SURVEY DATA

A total of 637 interviews were conducted at the Kerang Lakes from December 2008 to April 2011:

• 192 interviews were conducted in Kangaroo Lake
• 143 in Kow Swamp
• 192 in Lake Charm
• 110 in Reedy Lake.

Species targeted (combined years) by anglers in the Kerang Lakes include redfin (36%), golden perch (25%), carp (14%), and Murray cod (13%).

Catch rate

GOLDEN PERCH

Catch rates (numbers caught / hour of fishing) of golden perch across all the Kerang Lakes surveys increased over the survey period.

Anglers' perception of fishing activity in the Kerang Lakes increased between 2008/09 and 2010/11:

• In 2008/09 anglers indicated that fishing was "OK" or "Slow"
• In 2009/10 satisfaction increased to being mostly "OK"
• In 2010/11 angler satisfaction was the highest recorded, where 47% of anglers indicated fishing activity as "Fast" or the "Best Ever".

MURRAY COD

No increase in catch rate was evident for Murray cod due to the relatively low numbers caught.

Release rate

The number of golden perch caught and released by anglers decreased from 84% to 27% between 2008/09 and 2010/11. Golden perch were released if they were either undersized (84%) or if they were caught and released for sport (16%). Similarly the vast majority of Murray cod were released because they were undersize (77%) or caught and released for sport (17%).

Angler Attitude

The majority (99%) of anglers surveyed support the stocking of native fish into Kerang Lakes believing that it is required to maintain and improve the chance of catching a native fish species.

Discussion

The stocking of hatchery-reared golden perch into the Kerang Lakes system made a significant contribution to existing populations, substantially increasing catch rate and the quality of fishing.

Changes in the hydrology of many of the inland rivers and lake systems mean that the natural recruitment of golden perch will continue to be restricted. Stocking, therefore, may become increasingly important in the suite of ecosystem restoration and management tools available to managers to sustain and improve golden perch populations and fisheries.

This study showed, for the first time, that lake populations of golden perch having naturally low recruitment can be effectively augmented by stocking.

The degree of connectedness of the stocked water-body to other waterways determines the level of augmentation the stocked fish provide to the fishery. Increasing connectedness reduces the returns from the stocking.

Connection between waterways where wild fish are found can influence stocking contribution percentages for golden perch. Our results support a decline in stocking contribution with increased lake connectedness to a wild source population. A reasonable explanation for this trend is that lakes that are highly connected to rivers experience higher natural recruitment from wild fish coming into the lake, higher emigration of stocked fish from the lake, or both. Both explanations can result in lower stocking contributions. In turn, lakes that were less connected to rivers would experience less natural recruitment of wild fish and emigration of stocked fish, which would result in higher stocking contributions. This finding suggests that further examination into a relationship between stocking contribution and lake connectedness is required to determine whether the connectedness of a lake is an important consideration when planning stocking programs for golden perch.

Stocking programs for golden perch are more likely to be effective when undertaken in:

• Water-bodies where the natural recruitment of native fish is limited
  These are usually heavily regulated waterways such as isolated impoundments
• Water-bodies isolated from other systems and sources of wild fish.

This approach will maximise the fisheries benefits of stocking while minimising the potential negative impacts of stocking such as replacing wild fish with hatchery fish and reducing or changing the genetic diversity of natural populations (Lorenzen 2005).

The success of the stocking program for golden perch to the Kerang Lakes changed angers perceptions of the success and quality of this fishery (Appendix 4). Greater numbers of fish within the system attracted fishers from all over Victoria (and NSW) to target golden perch.This study has also shown that not all stocking programs have equal success. The benefits derived from stocking hatchery-reared Murray cod into the Kerang Lakes were inconclusive. Only in one lake, Kangaroo Lake, was there some evidence of a boost to the population of this species. Across the other lakes in the system, Murray cod abundance remained low and insufficient fish were caught (across all lakes) to determine if stocking boosted the angler catch of Murray cod.

Conclusions

The stocking program for hatchery-reared golden perch into the Kerang Lakes boosted:

• The abundance of the existing population of this species
• The success and quality of the anglers fishing experience.

The connectedness of a stocked water-body with sources of wild fish determines the level of augmentation the stocked fish provide to the fishery.

• Increasing connectedness reduces the returns from the stocking.

Stocking hatchery-reared Murray cod into the Kerang lakes boosted existing populations only in Kangaroo Lake.

Acknowledgements

Research funding for this project was provided by the Recreational Fishing Licence Trust Fund (RFL Grant R/06/07/1) and conducted under the Victorian Department of Economic Development, Jobs, Transport and Resources (former) Department of Primary Industries, Animal Ethics Committee project number Fish Aug07 0029.

The authors are grateful to Wayne Fulton, John Douglas, Robert Gibb, and Marc Ainsworth for establishing the pr Rogers, Nathanoject; Dan Steel, Cameron McGregor, Mark O'Mahony, and Gary Hodges for technical assistance; Dan Gwinn for statistical analysis assistance. Leanne Gunthorpe and James Andrews, provided comments on the report.

Thanks to the creel clerks Matt Bayley, Nick Taylor, and Peter Mahy who conducted angler interviews. Fish Ageing Services for provided age estimates and determined the presence / absence of otolith dye.

Greatest thanks go to fisheries officers, fishing clubs, and the many anglers who fished the Kerang Lakes that willingly shared information with creel-clerks. Without their involvement this project would not have succeeded.

References

Anderson JR (1991) The implications of salinity, and salinity management initiatives, on fish and fish habitat in the Kerang Lakes management area. Arthur Rylah Institute for Environmental Research, Shepparton, Australia.

Brumley AR (1987) Past and present distributions of golden perch Macquaria ambigua (Pisces: Percichthyidae) in Victoria, with reference to releases of hatchery-produced fry). Proceedings - Royal Society of Victoria 99, 111-116.

Brumley AR, Morison AK, Anderson JR (1987) Revision of the conservation status of several species of warmwater native fish after surveys of selected sites in northern Victoria (1982-1984). . Arthur Rylah Institute for Environmental Research, Shepparton, Australia.

Cadwallader PL (1978) Some causes of the decline in range and abundance of native fish in the Murray-Darling river system. . Proceedings of the Royal Society of Victoria 90 211-224.

Cadwallader PL, Backhouse GN, Beumer JP, Jackson PD (1984) The conservation status of the native freshwater fish of Victoria. . Victorian Naturalist 101, 112-114.

Crook DA, O'Mahoney D, Gillanders BM, Munro AR, Sanger AC (2007) Production of external fluorescent marks on golden perch fingerlings through osmotic induction marking with alizarin red s. North American Journal of Fisheries Management 27, 670-675.

Ho S, Roberts J, Cheers G, Suitor L (2006) Development and application of an ecological monitoring and mapping program for targeted Kerang lakes. Report prepared by the Murray-Darling Freshwater Research centre, Mildura for the North Central Catchment Management Authority.

McKelleher R (2005) An outline of the threatened species listing process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). . Murray-Darling Basin Cimmission and the Cooperative Research Centre for Freshwater Ecology, Canberra.

MDBC (2004) Native Fish Strategy for the Murray-Darling Basin 2003-2013. MDBC Publication No. 25/04.

Morison AK, Robertson SG, Smith DC (1998) An integrated system for production fish ageing: Image analysis and quality assurance. . North American Journal of Fisheries Management 18, 587–598.

Rowland SJ (1983) The hormone-induced ovulation and spawning of the Australian freshwater fish golden perch, Macquaria ambigua (Richardson) (Percichthyidae). Aquaculture 35, 221-238.

Rowland SJ (1996) Development of techniques for the large-scale rearing of the larvae of the Australian freshwater fish golden perch, Macquaria ambigua (Richardson, 1845). Marine and Freshwater Research 47, 233-242.

Appendix 1. Does stocking make a significant contribution to fish numbers in the Kerang Lakes?

Hunt, T.L., Allen, M.S., Douglas, J., Gason, A. (2010) Evaluation of a Sport Fish Stocking Program in Lakes of the Southern Murray–Darling Basin, Australia. North American Journal of Fisheries Management 30:805–811

Methods

Hatchery-reared golden perch and Murray cod were stocked by Fisheries Victoria at various densities into Reedy Lake, Kangaroo Lake, and Lake Charm annually from 2003 to 2008 (Table 1). Golden perch were chemically marked with alizarin red S (ARS), which is a fluorescent dye that marks calcified structures such as otoliths (Crook et al. 2007). Golden perch fingerlings were immersed for 24 hours in a 0.025 mg L-1 solution of ARS, which was buffered to a pH of above 9 with sodium bicarbonate. Murray cod were marked using dart tags. The dart tagging protocol used was to immerse yearlings in a freshwater AQUIS solution until anaesthetised then use a syringe applicator to insert a 50 mm dart tag into the fish's left shoulder. The fish was then returned to freshwater to recover and then immersed in a salt bath solution overnight to sterilise the dart tag entry point. During 2004, 2006 and 2007 yearling Murray cod were in short supply from commercial aquaculture farms, therefore fingerling Murray cod were sourced and chemically marked with ARS to compensate for low numbers. All Murray cod and Golden perch were transported and released into the Kerang Lakes the day after marking procedures were completed.

Two private stocking events of unmarked golden perch have also occurred in Kangaroo Lake. The Mystic Park Angling Association stocked 4,000 fingerling golden perch in Autumn 1996 and Steve Hounsell (ex-commercial fisherman) stocked 15,000 fingerling golden perch in April 1997.

FIELD SURVEYS AND LABORATORY ANALYSIS

Based on the effectiveness of the pilot surveys, it was concluded that mesh netting was the most appropriate technique for surveying golden perch and Murray cod in all lakes. Sampling locations within each lake were randomly selected prior to the sampling event by dividing each lake into segments and using a random number generator to select which segment to sample. Each sampling event used four 'fleets' of four 25 x 1.8 metre gill nets in sizes of 76, 102, 127 and 152 mm (stretch gill mesh). The nets were set in the afternoon, left overnight and retrieved the following morning. Sampling was undertaken in each lake in July and August 2008 and twice (two weeks apart) in February 2009. Each fleet sample was treated as a replicate to assess relative abundance of Murray cod and golden perch. Catch per unit effort (CPUE) and associated confidence intervals was defined as the number of each fish species captured per net hour of sampling per hectare of water (number of fish/net hour/ha).
All fish caught were measured, weighted and the mesh size from which they were taken recorded. Two sagittal otoliths were extracted from each fish for processing. One otolith from each pair was embedded, transversely sectioned and mounted (Morison et al. 1998). Annuli were identified using a Leica MZ80 stereo dissecting microscope. To examine the sections for the presence of ARS, samples were viewed using a Leica Diaplan epi-fluorescence microscope. The wavelengths used for the examination were 515–560 nm excitation filter, 580 nm dichroic mirror and 580 nm barrier filter (Leica N2.1 filter block). The transverse sections were examined at 100x using a PL / Fl 10 x objective with a high numerical aperture for increased sensitivity to fluorescent marks.

ANALYSES

To determine the contribution of the stocked fish to the lake populations, only golden perch larger than 300 mm total length (TL) were included in the analysis. The Victorian legal minimum length (LML) for taking golden perch at the time of this study was 300 mm, thus fish of this size or greater were considered to have recruited to the recreational fishery. The standard error (SE) around each lake contribution percentage was estimated by treating overnight net fleet percentage contributions as replicates.
To investigate the consistency of contributions to lake populations from stocking, a contribution analysis was undertaken for each cohort in each lake over the six years of the stocking program. Due to the large variation in contribution percentages, we provided the range of values around each age cohort contribution.

To investigate any potential differences in vulnerability to sampling between stocked and wild fish, growth rates were compared with linear regression. Length at age exhibited a linear relationship due to the low number of ages in our samples. We used an analysis of covariance to test the difference between length-age and weight-age slopes of stocked and natural fish at each lake. Linear models were deemed more suitable for growth analyses because they fitted the data more closely than non-linear models. The model for comparing length-age slopes was:

L = lake + age + lake X age + e
W = lake + age + lake X age + e
where, L = Length, W = weight, age is a covariate, lake is a categorical variable and e = error.

We evaluated the potential for stocking to increase adult golden perch abundance by qualitatively comparing our gill-net CPUE data with data from previous surveys at the lakes before stocking (Anderson 1991; Brumley et al. 1987). The previous surveys used bar gill mesh sizes of a larger range than ours (38–254 mm versus 76–152 mm in this study), indicating that equal or higher CPUE values in our study would provide evidence for increased adult abundance after stocking.

RESULTS

Stocked fish contributed substantially to the adult population of golden perch at all three lakes. The contribution of stocked fingerling golden perch was 47 ± 9% (mean ± SE) at Reedy Lake, 55 ± 9% at Kangaroo Lake, and 90 ± 5% at Lake Charm. The percent contribution of stocked golden perch varied with year class at each lake. The contributions from each stocked age-cohort ranged between 33% and 63% at Reedy Lake, the age-6 fish yielding the highest contribution percentage (Table 2). At Kangaroo Lake the contributions from each stocked age-cohort ranged between 0% and 86%, the age-2 fish yielding the highest contribution percentage. The contribution at Lake Charm ranged between 50% and 100%, the fish at ages 1, 4, and 5 all yielding the highest contribution percentage (Table 2). The percent contribution of stocked golden perch varied widely across individual fleet catches at each lake, ranging between 0 and 100% (Table 2).

Murray cod were excluded from analyses as relatively small numbers were caught at Kangaroo Lake during 2009 (13 fish); however, 62% of these Murray cod were tagged.
Growth did not differ significantly between stocked and wild fish. There was no significant length–age growth difference between stocked and wild fish at Reedy Lake (F1, 50 = 1.94, P = 0.17, R2 = 0.59), Kangaroo Lake (F1, 92=0.60, P=0.44, R2=0.35), and Lake Charm (F1, 32 = 0.65, P = 0.42, R2 = 0.71). Similarly, there was no significant weight–age growth difference between stocked and wild fish at Reedy Lake (F1, 89 = 1.97, P = 0.16, R2 = 0.26), and Lake Charm (F1, 32 = 0.17, P = 0.69, R2 = 0.53). These results suggest that gear susceptibility was similar for stocked and wild fish.

Comparing our results with those of previous gill-net surveys made before stocking commenced, suggests that lake populations have been enhanced from the stocking. Brumley et al. (1987) surveyed the Kerang Lakes between 1980 and 1984, and Anderson (1991) surveyed Reedy Lake in 1987. Brumley et al. (1987) found that Reedy Lake yielded four golden perch from 14 nets (0.0089 fish/net-hour), Kangaroo Lake yielded one golden perch from 42 nets (0.0013 fish/net-hour), and Lake Charm yielded zero golden perch from 31 nets. Anderson (1991) found that Reedy Lake yielded six golden perch from 10 nets (approximately 0.011 fish/net-hour). Although the survey methods in these studies were not wholly consistent with the sampling method in this study, their catch rates of golden perch were considerably lower than the present study, even though they used a larger range of mesh sizes. We caught 78 golden perch from 60 nets in Reedy Lake (0.053–0.11 fish/net-hour), 133 golden perch from 60 nets in Kangaroo Lake (0.048–0.316 fish/net-hour), and 33 fish in 60 nets in Lake Charm (0.016–0.045 fish/net-hour). On the basis of this comparison, we think it likely that stocking fingerlings increased the abundance of golden perch at all three lakes.

Stocking contribution percentages declined with the degree of connectedness to a source of a wild population. Reedy Lake is connected all year to the Loddon River and yielded the lowest stocking contribution (47%). Kangaroo Lake yielded a stocking contribution of 55%; although it is also connected to the Loddon River all year round, it is located further along irrigation channels than Reedy Lake is. Lake Charm, connected to the Loddon River for only a few days each year, yielded the highest stocking contribution (90%).

Discussion

Stock enhancement with hatchery-produced fry has generally had limited success (Molony et al. 2003; Lorenzen 2005); the present study, however, adds to the growing body of literature that suggests stock enhancement can make significant contributions to populations where natural recruitment is low.

Australian fisheries agencies have long suspected significant contributions to golden perch populations from stocking in impoundments and lakes, but this is the first study to quantify those contributions. Despite the relatively low numbers of Murray cod caught during the survey, they did contribute to the success of the fishery.

Replacement of wild fish by stocked fish is always a concern in stocking programs (Hilborn 1999), and our findings suggest that stocked fish did increase the absolute abundance of golden perch at the Kerang Lakes. Although unstocked reference sites were not available for comparison with stocked sites, the pre-stocking gill-net surveys indicated substantially lower CPUE of golden perch before stocking. In the interim period after stocking (2003–2009), no large floods or other flow events occurred that would be expected to substantially increase immigration of wild golden perch into these systems.

Hatchery fish represented a substantial percentage of the adult golden perch and this, combined with the gill net CPUE surveys, provided strong evidence that stocking added to the total golden perch populations at the lakes. Future stocking evaluations should explore both percent contribution and abundance measures to search for additive effects of stocking programs.

Connection between waterways where wild fish are found can influence stocking contribution percentages for golden perch. Our results support a decline in stocking contribution with increased lake connectedness to a wild source population. A reasonable explanation for this trend is that lakes that are highly connected to rivers experience higher natural recruitment from wild fish coming into the lake, higher emigration of stocked fish from the lake, or both. Both explanations can result in lower stocking contributions. In turn, lakes that were less connected to rivers would experience less natural recruitment of wild fish and emigration of stocked fish, which would result in higher stocking contributions. This finding suggests that further examination into a relationship between stocking contribution and lake connectedness is required to determine whether the connectedness of a lake is an important consideration when planning stocking programs for golden perch.

Despite our data supporting the study hypothesis, other factors that may have affected our findings include commercial fishing up until 2002, hydrologic-environmental changes, or low abundances of golden perch in surveys conducted by Anderson (1991) and Brumley (1987). Similarly, native fish could have immigrated in to the Kerang Lakes from fish originally stocked in the Loddon River (5,000 / year since 1996).

Appendix 2 Does stocking make a significant contribution to angler success in the Kerang Lakes?

Methods

A targeted creel survey was undertaken to determine angler attitudes and perceptions of the success that stocking golden perch and Murray cod into Kerang Lakes has on the recreational fishery.

Creel-clerks surveyed anglers fishing in Kangaroo Lake, Reedy Lake, Kow swamp, and Lake Charm.

Interviews were conducted on weekends and public holidays from December to May in 2008/09, 2009/10, and 2010/11.

Interview questions (Appendix 3) were created to obtain information on the fishery and its anglers and included questions on:

• Species targeted
• Species caught
• Fishing method
• Fishing location
• Satisfaction of the Kerang Lakes fishery
• Fishing quality
• Improvements to the fishery.

Angler success was defined by two categories:

• Angler perception
• Catch rate.

Data were analysed and presented using descriptive statistics such as percentages, charts and tables.

Results

Survey results

A total of 637 interviews were conducted at the Kerang Lakes from December 2008 to April 2011

• 192 interviews were conducted in Kangaroo Lake
• 143 in Kow Swamp
• 192 in Lake Charm
• 110 in Reedy Lake.

Catch rate

GOLDEN PERCH

Catch rate (numbers caught / hour of fishing) of golden perch across all the Kerang lakes increased over the study period.

The catch rate of golden perch:

• Was the highest for each lake in 2010/11
• Was the highest recorded during 2010/11 in Reedy Lake (Figure 2).

MURRAY COD

No increase in catch rate was evident for Murray cod due to the relatively low numbers of caught.

Catch rates for Murray cod were highest in Kangaroo Lake and peaked in 2009/10 (Figure 2). Catches of Murray cod were negligible in the other lakes surveyed.

Anglers' perceptions

Anglers' perception of fishing activity in the Kerang Lakes increased between 2008/09 and 2010/11:

• In 2008/09 anglers indicated that fishing was OK or Slow
• In 2009/10 satisfaction increased to being mostly OK
• In 2010/11 angler satisfaction was the highest recorded, where 47% of anglers indicated fishing activity as Fast or the Best Ever (Table 3).

Since 2003:

• 32% of anglers indicated that fishing had improved
• 15% indicated that it remained the same
• 18% indicated that it has declined
• 35% were unsure.

The majority of anglers indicated that they were either very satisfied (8%) or quite satisfied (60%) with the quality of fishing during the survey.

Targeting preference

Species targeted (over all the years of the study ) by anglers in the Kerang Lakes include:

• Redfin (36%)
• Golden perch 25%
• Carp (14%)
• Murray cod (13%).

From 2008/09 anglers targeting preference changed over the course of the study. Anglers:

• Increased targeting of golden perch
• Decreased targeting redfin (Table 4).

Catch composition

In Kangaroo Lake successful anglers had a 25% chance of catching a golden perch and a 9% chance of catching a Murray cod (Figure 3).

Although golden perch and Murray cod were caught in all of the lakes surveyed, angler catches were dominated by carp and redfin.

In Lake Charm 92% of all fish caught were carp and redfin. Up to 2 to 3 times more redfin were caught from Lake Charm than from the other lakes.

Both carp and redfin dominated the catch in Kow Swamp. The highest percentage (23%) of silver perch caught from the Kerang Lakes was caught from Kow Swamp.

Release rates

The number of golden perch caught and released by anglers decreased from 84% to 27% between 2008/09 and 2010/11 (Figure 4).

Release rates and the reason for release varied with species:

• Golden perch were released because they were undersized (84%) or were caught and released for sport (16%)
• Similarly Murray cod were released because they were undersized (77%) or caught and released for sport (17%)
• The majority of redfin caught were retained
• Release rate of silver perch increased from 13 to 90% over the study.

Attitudes to stocking

The majority (99%) of anglers surveyed support the stocking of native fishing into Kerang Lakes, believing that it is required to maintain and improve the chance of catching a native fish species.

Anglers who do not support stocking the Kerang Lakes indicated that they would prefer stocking to be undertaken in rivers to keep the lakes as a redfin fishery.

Angler avidity

The majority (66%) of anglers who fish in the Kerang Lakes did so between 1 and 5 times annually:

• 22% fished 6–10 times per year
• 6% fished 11 –20 times a year
• 4% fished 21 – 50 times a year.

Angler profiles

Anglers fishing in the Kerang Lakes fish from:

• The lake shore (85%)
• A boat (12%)
• Both shore and boat (2%).

Anglers targeting fish use:

• Bait (88%)
• Lure (5%)
• Both bait and lure (7%).

Most anglers (58%) were 36 to 50 years of age. Although avid anglers fishing the Kerang Lakes are predominantly local, many anglers come from around Victoria (Figure 5).

Angler attitudes

Interviews from 338 anglers provided information on factors that reduce the quality of their fishing experience in the Kerang Lakes (Table 5);

• 22% indicated that nothing lessens the quality of their fishing
• 20% indicated that ski boats and jet skis show a lack of respect of other users (anglers) and a disregard for regulations.

Other significant factors cited that reduce the quality of an angler's fishing experience were:

• The number of dead carp (caught and discarded) rotting on the banks
• A lack of facilities that included
• Toilets
• BBQ's
• Camping facilities
• Rubbish bins for litter and for the disposal of dead carp.

Figure 2. Catch rates (number caught / hour) of golden perch and Murray cod from Kangaroo Lake, Lake Charm, Reedy Lake, and Kow Swamp.

Figure 3. Numbers of fish caught (as a percentage) at Kangaroo Lake, Kow Swamp, Lake Charm, and Reedy Lake by recreational anglers (survey years combined).

Figure 4. Percentage of fish released after capture by year of survey (Lakes combined).

Figure 5. Distribution of where anglers fishing the Kerang Lakes reside.

Discussion

The stocking program for hatchery-reared golden perch in the Kerang Lakes increased angler catch rate and improved anglers' perceptions of the fishery.

The highest catch rates of golden perch occurred during 2010/11 and this was attributed to stocked golden perch recruiting to the fishery. Increasing catch rates improved anglers' perception of the fishery as many indicated that fishing success was better in 2011 than in 2003.

Numbers of golden perch released by anglers decreased annually over the survey period indicating that perch were growing beyond the legal minimum length. Lower release rates also contribute to increased angler satisfaction rates.

The redfin fishery in the Kerang Lakes is larger than that of either golden perch or Murray cod. This fishery has relatively low release rates.

Although redfin are a valued component of this fishery, over the course of the study, targeting preference moved from redfin to golden perch. This trend indicates that anglers prefer to catch golden perch compared with redfin despite a greater chance of catching the latter.

Anglers' believed that the stocking program was a success despite the low numbers of Murray cod caught. Almost all anglers support ongoing stocking programs for Murray cod and golden perch in the Kerang Lakes.

Although anglers can see the benefits of the Kerang Lakes as a fishing and holiday destination, the quality of their experience is reduced by the number or dead carp along the banks, limited facilities, and a minority of boat users showing little respect for regulations and other users.

Appendix 3

Appendix 4

• Herald Sun - March 10 2011
• Sunraysia Daily - March 10 2011
• Swan Hill Guardian - March 11 2011
• Bendigo Advertiser - March 11 2011
• Northern Times - March 11 2011
• Weekly Times - April 07 2010
• DPI Media Release - June 30 2008
• Northern Times - July 04 2008
• Riverine Herald - July 07 2008
• Northern Times - September 02 2008
• Bendigo Advertiser - March 25 2009
• Riverine Herald - March 25 2009
• Bendigo Advertiser - June 03 2009
• Weekly Times - July 16 2008
• Northern Times - June 05 2009
• Swan Hill Guardian - April 14 2010
• Northern Times - April 13 2010
• DPI Media Release - June 02 2009
• DPI Media Release - August 25 2008
• DPI Media Release - March 13 2009