Population assessment of Trout Cod and sympatric fish species within the closed section of Seven Creeks during 1997. S.R.Saddlier and D.J.Harrington December 1997 Marine and Freshwater Resources Institute 123 Brown St. Heidelberg, 3084 TABLE OF CONTENTS page no. List of Figures ii List of Tables iii Summary iv Introduction 1 Methods Sampling sites Sampling methods 4 4 4 Results 5 Total Numbers of Fish Captured 5 Native Freshwater Fish Trout Cod Freshwater Blackfish Macquarie Perch Mountain Galaxias Australian Smelt Southern Pigmy Perch 7 7 7 8 8 8 8 Decapod Crustacea Spiny Freshwater Crayfish Yabby 9 9 9 Introduced Freshwater Fish Brown Trout English Perch Carp Mosquitofish 9 9 10 10 10 Trout Cod length-frequency distribution (sites combined) Trout Cod length-frequency distribution at individual sites 15 15 Discussion Current survey results Comparison with 1991 data 20 20 23 Acknowledgements 24 References 25 i LIST OF FIGURES page no. Figure 1. Map of the Goulburn River system, with Seven Creeks highlighted in yellow (map taken from Tunbridge and Glenane, 1994). 2 Figure 2. Upper section of Seven Creeks, showing associated tributaries and sections where fish surveys were conducted between 28 April and 18 June 1997 3 Figure 3. Total numbers of each fish species captured from Seven Creeks during 1997. 6 Figure 4. Total numbers of Trout Cod captured from each site within Seven Creeks during 1997. 6 Figure 5. Density of each fish species (fish per 100m) captured from sites C&D during 1997. 11 Figure 6. Density of each fish species (fish per 100m) captured from site E during 1997. 11 Figure 7. Density of each fish species (fish per 100m) captured from site F during 1997. 11 Figure 8. Density of each fish species (fish per 100m) captured from site G during 1997. 12 Figure 9. Density of each fish species (fish per 100m) captured from site H during 1997. 12 Figure 10. Density of each fish species (fish per 100m) captured from site I during 1997. 12 Figure 11. Density of each fish species (fish per 100m) captured from site J during 1997. 13 Figure 12. Density of each fish species (fish per 100m) captured from site K during 1997. 13 Figure 13. Density of each fish species (fish per 100m) captured from site L during 1997. 13 Figure 14. Density of each fish species (fish per 100m) captured from site M during 1997. 14 Figure 15. Length-frequency of Trout Cod captured from all sections (combined data) 16 Figure 16. Length-frequency of Trout Cod captured from site H 17 Figure 17. Length-frequency of Trout Cod captured from site I 17 Figure 18. Length-frequency of Trout Cod captured from site J 17 Figure 19. Length-frequency of Trout Cod captured from site K 18 Figure 20. Length-frequency of Trout Cod captured from site L 18 Figure 21. Length-frequency of Trout Cod captured from site M 18 Figure 22. Estimated Trout Cod density (fish/100m) calculated at each site for 1991 and 1997. 19 ii LIST OF TABLES page no. Table 1. Presence ( ) or absence (-) of fish species captured at each of the 10 sites surveyed in Seven Creeks during 1997 (shading indicates native fish species) iii 5 SUMMARY A total of 12 species of freshwater fish were captured from the 10 sections surveyed within Seven Creeks, including six species of native freshwater fish, two species of native decapod crustacea and four species of introduced freshwater fish. Of the native fish, Trout cod Maccullochella macquariensis represented the most abundant species with a total of 412 fish captured from all sites, followed (in decreasing abundance) by Freshwater blackfish Gadopsis marmoratus (231 fish), Macquarie perch Macquaria australasica (103 fish), Southern pygmy perch Nannoperca australis (17 fish), Mountain galaxias Galaxias olidus (12 fish) and Australian smelt Retropinna semoni (1 fish). Two species of decapod crustaceans were also captured, including a total of 50 Spiny freshwater crayfish Euastacus armartus and 13 specimens of the Yabby Cherax destructor. Four species of introduced freshwater fish were also captured, including Carp Cyprinus carpio (75 fish), Brown trout Salmo trutta (69 fish), English perch Perca fluviatilis, (56 fish) and one specimen of the Mosquitofish Gambusia holbrookii. Distribution of Trout Cod varied significantly over the length of the survey area. No Trout cod were captured from the upper reaches of the study site (sections C, D, E, F and G), while progressively higher densities of Trout cod were observed further downstream of these sites, ranging from 1.1 fish per 100 metre section at site H to the highest density of 22.1 fish per 100 metre section at site L. A strong correlation was observed between increasing Trout cod density and progressive distance downstream from site H. However, this correlation does not apply to the lowest site (site M) where Trout cod density decreases from 22.1 fish/100m to 3.8 fish/100m. Trout cod length-frequency distribution data indicate that very strong recruitment occurred in the 1996 spawning season, with fish within the 50 - 80mm length class comprising 48% of the total numbers of Trout cod captured. Length-frequency data also suggests that recruitment over the past three spawning seasons has been consistent, as indicated by a broad distribution of fish ranging from 100 - 200 mm in length. Although age-length data is not available for Trout cod collected from Seven iv Creeks, year classes (determined from length-frequency graphs) appear to indicate that fish ranging from 100 - 200 mm in length correspond to 1+ to 2+ age classes. Information collected from Seven Creeks during the current survey indicate that of all the trout cod captured, those which are presumed to be of a sexually mature length constitute only 9% of the entire catch and represent a total of 35 fish. Assuming a sex ratio within the population of 1:1, a total of 35 mature size fish corresponds to approximately 17 potential spawning pairs captured. This number of mature size fish is in contrast to that of a survey conducted in 1991 where a total of 42 fish were of a mature size, representing 25% of the entire Trout cod population captured. v INTRODUCTION The headwaters of Seven Creeks originate in the Strathbogie Ranges approximately 130 km NNE of Melbourne, initially flowing South-West through predominantly granitic country for a distance of approximately 35 km before heading NNW through the township of Euroa to meet with the Goulburn River approximately 5 km upstream of the township of Shepparton (Figure 1). The upper reaches of Seven Creeks supports the only viable Victorian population of the nationally endangered Trout Cod Maccullochella macquariensis which was translocated from the Goulburn river in 1921-22 (DCNR 1995). This population is restricted to a relatively small section of Seven Creeks which extends between Polly McQuinns Weir, downstream to the crossing of Galls Gap Road below Watchbox Creek, covering a distance of approximately 11 kilometers (Figure 2). The majority of this section of Seven Creeks has a riparian zone which is fenced off to cattle access, or is protected within the Gooram Falls Reserve apart from a section extending approximately 2 kilometers downstream from Polly McQuinns Weir. As one of the actions recommended by the National Trout Cod Recovery Team, a fish population survey was conducted in this section of Seven Creeks between 28 April and 18 June 1997 to determine the current population status of this species, as well as the status of other fish species present in this section of Seven Creeks. 1 Figure 1. Map of the Goulburn River system, with Seven Creeks highlighted in yellow (map taken from Tunbridge and Glenane, 1994). 2 Figure 2. Upper section of Seven Creeks, showing associated tributaries and sections where fish surveys were conducted between 28 April and 18 June 1997 3 METHODS Sampling sites A total of ten sampling sites were surveyed within Seven Creeks following nomenclature used by Anderson (1991). The study area extends between Polly McQuinns Weir, downstream to the crossing of Galls Gap Road below Watchbox Creek, covering a distance of approximately 11 kilometers (Figures 1 and 2). Sampling methods The fish fauna of Seven Creeks was assessed using two fish sampling techniques. At shallow sites which were easily wadeable, fish were sampled using a fully portable Smith-Root Model 12 backpack electrofisher. Electrofishing was the preferred sampling technique due to its relative lack of species selectivity. Sites F, H and I contained waters which (due to depth) could not be electrofished effectively. At these sites, single wing fyke nets were used. Fyke nets are more selective for benthic species which move around the margins of waters where they are likely to be captured. Because of this requirement, catch results from fyke nets may not accurately reflect actual ratios of all species within a given area and must be interpreted with caution. 4 RESULTS Total numbers of fish captured A total of six species of native freshwater fish were captured from Seven Creeks during this survey (table 1). These species include Trout cod Maccullochella macquariensis which represent the most abundant species with a total of 412 captured from all sites (Figure 3). Freshwater blackfish Gadopsis marmoratus (231 fish) were the next most abundant species, followed by Macquarie perch Macquaria australasica (103 fish). The remaining three species of native freshwater fish were represented by low numbers of fish, with 17 specimens of Southern pygmy perch Nannoperca australis, 12 specimens of Mountain galaxias Galaxias olidus and a single specimen of Australian smelt Retropinna semoni captured. Two species of decapod crustaceans were also captured, including a total of 50 Spiny freshwater crayfish Euastacus armartus and 13 specimens of the Yabby Cherax destructor. Four species of introduced freshwater fish were also recorded, including Carp Cyprinus carpio (75 fish), Brown trout Salmo trutta (69 fish), English perch Perca fluviatilis, (56 fish) and one Mosquitofish Gambusia holbrookii. SPECIES C/D E F G Trout cod - - - - Site H I J K L M Macquarie perch Freshwater blackfish - Mountain galaxias - - - - Australian smelt - - - - - - - - Southern pygmy perch - - - - - - - - - - - - Spiny freshwater crayfish - - - - Yabby - - - - - - - - Brown trout - - English perch - - - - - - - - Carp - - - - - - - - - Mosquito fish - - - - - - - - - Upstream------------------------------------Downstream Table 1. Presence ( ) or absence (-) of fish species captured at each of the 10 sites surveyed in Seven Creeks during 1997(shading indicates native fish species) 5 6 Native Freshwater Fish The density (represented as number of fish per 100 metre section of stream) of individual fish species captured at each site is presented in Figures 5 - 14. Trout Cod A comparison of Trout cod density at each site indicates a surprising lack of fish in the upper reaches of Seven Creeks. Trout cod were not recorded at sites C/D, E, F or G. Site H (immediately downstream of site G) supports low numbers of Trout cod (1.1 fish/100m) while 10.3 fish/100m were captured from site I (figure 4). This progressive increase in density continues in a downstream direction until a maximum density of 22.1 fish/100m was observed at site L. The lowest site (site M) support far lower densities of Trout cod with 3.8 fish/100m being captured. This site is unique within the study area in supporting moderate densities of Carp (2.74 fish/100m) which were not recorded from any other sites within the survey. A comparison of the habitat at sites throughout the study area indicates that this lowest site is in a more degraded condition compared to sites upstream, with large amounts of sand being present and subsequently less variation in instream habitat. Freshwater Blackfish Freshwater blackfish were captured from all sites apart from site J. The lowest three sites (sites K, L and M) support similar densities of this species with 3.6, 3.1 and 3.5 fish/100m respectively, while sites further upstream (G, H, and I) possess lower densities of blackfish (0.44, 1.67 and 2.0 fish/100m). The three sites situated highest in the study area (C/D, E and F) were surveyed predominantly using fyke nets, combined with a low level of electrofishing where possible. Fyke nets are particularly effective for benthic species such as blackfish and consequently results may reflect higher densities of this species at 5.3, 6 and 4.4 fish/100m at sites C/D, E and F respectively. 7 Macquarie Perch Macquarie perch were also distributed throughout the study area, being captured at densities ranging from 0.17 fish/100m at site I to 6.2 fish/100m at site F. Generally, the density of Macquarie perch was high in the lower reaches of the survey area (sites M, L and K) with 1.0, 2.1 and 1.7 fish/100m being captured, dropping in the mid reaches (sites J, I, H and G) to 0.7, 0.2 and 0.3 fish/100m respectively. The upper sites (sites C/D, E and F) provided relatively high catch levels of 2.7, 3.2 and 6.2 fish/100m, although, as was the case for Freshwater blackfish, the predominant use of fyke nets may be the reason for recording higher densities. Mountain Galaxias Very low numbers of Mountain galaxias were recorded at only four of the ten sites surveyed, including the lowest sites, L and M where densities of only 1.3 and 0.2 fish/100m were observed(figures 13 and 14). One specimen was captured at site H and site I, corresponding to densities of 0.04 and 0.2 fish/100m respectively (figures 9 and 10). Australian Smelt One Australian smelt was captured at the lowest site (site M), corresponding to a density of 0.04 fish/100m. Southern Pygmy Perch Southern pygmy perch were restricted to the upper two sites, where a total of 15 fish were captured from site E (a density of 6.0 fish/100m) and a further 2 fish were captured from the highest site surveyed (site C/D), at a density of 1.33 fish/100m. 8 DECAPOD CRUSTACEA Spiny Freshwater Crayfish Spiny freshwater crayfish Euastacus armartus were captured from sites H, K, L and M. Densities varied significantly across the survey area, with low numbers being captured from the lowest sites within Seven Creeks (sites K, L and M) where 0.4, 1.0 and 0.1 fish/100m were captured, compared to the higher density (1.8 fish/100m), observed at site H. Yabby The Yabby Cherax destructor was only captured from the lowest site (site M), at a density of 0.5 fish/100m. Introduced Freshwater Fish Brown Trout Brown trout were ubiquitous throughout the survey area, apart from site F where none were captured. Densities were highest at those sites situated furthest downstream where 1.0, 2.3 and 0.4 fish/100m were captured from sites M, L and K respectively, and from those sites situated furthest upstream (sites C/D and E), where 10 and 1.6 fish/100m were captured. Far lower densities of brown trout were observed in the mid reaches of the survey area (G, H, I and J) where 0.2, 0.2, 0.5 and 0.3 fish/100m were captured respectively. 9 English Perch The distribution of English perch is restricted to below Gooram Falls (sites L and M), with high numbers of this species being captured from the lowest site (site M) at a density of 1.9 fish/100m. Site L supports lower numbers of this species, being captured at a density of 0.8 fish/100m. Carp Site M was the only site in which Carp were captured during this current survey. As with English perch, it appears Gooram Falls may present a barrier to the upstream movement of this species. The slower moving waters found in site M also appear to be more suitable to this species which tends to prefer pools and deeper slow moving waters which are found at site M. Mosquito Fish Only one specimen of Mosquito fish was recorded in this survey at site H. 10 11 12 13 14 Trout Cod Length-Frequency Distribution (sites combined) The length-frequency distribution of Trout cod (all sites combined) is presented in Figure 15. High numbers of Trout cod from the smallest length class were observed, with fish within the 50 - 80 mm length class comprising 48% of the total number of Trout cod captured (192 fish). Fish within this first year class (representing ages of approximately 6 - 7 months), average a length of approximately 64 mm and are quite distinctly separated from the following year class of fish which are approximately 18 months of age. Fish within this 1+ age class range from a length of 103 mm to approximately 160 mm, although a small number of larger individuals from this group appear to merge with smaller individuals of the next (2+) year class. Trout cod from larger length classes (3+ and greater) are less distinct again and no conclusion can be drawn from the population structure in the absence of verified age data. Trout Cod Length-Frequency at Individual Sites The length-frequency distribution of Trout cod at individual sites are presented in Figures 16 - 21. Results indicate that 0+ Trout cod constitute the greatest proportion of the total captured populations at sites H, I, J and K, comprising 88%, 58%, 59% and 81% of total Trout cod numbers at each site respectively. Sections downstream of site K (sites L and M) exhibit decreasing proportions of this length class, with 0+ fish comprising 35% of the entire population sampled at site L and 13% at site M. The distribution of 1+ Trout cod within Seven Creek exhibits very different characteristics to that of 0+ fish. Very low proportions of 1+ fish were present within the mid-sections of the study area. The proportion of 1+ fish at sites H, I, J and K were 8%, 9%, 6% and 9% respectively, whereas at sites L and M, this proportion increased to 19% and 29%. 15 Trout cod which fell into the size range of 100 mm - 250 mm (i.e. those individuals which were at least 2+ years of age but which are presumed to be sexually immature) were absent from catch results obtained from the highest site supporting a population of Trout cod (site H). This size class was represented at sites I and J by 22% and 31% respectively, before dropping to only 7% at site K. Higher proportions of these immature size fish were present at sites L and M where they comprise 32% and 45% of the entire Trout cod population captured. The remaining fish (representing size ranges of 251 - 590 mm) captured at each site are presumed to be sexually mature (Cadwallader, 1977). These fish comprise a very small proportion of the entire Trout cod population at each site, including 4% at site H, 11% at site I and 3% at sites J and K. Slightly higher proportions were observed at site L and site M where 14% and 13% were captured respectively. 16 17 18 19 DISCUSSION Current survey results There was a clear increase in the density of Trout cod moving downstream from site H to site L (1.1 to 22.1 fish/100m), however at the lowest site (site M), a density of only 3.8 fish/100m was recorded. No fish were captured above site H. Habitat within the section of Seven Creeks above Gooram Falls (above site H) is predominantly characterised by large pools, which are either sand based where water velocities are low, or granite based where velocities are high. These pools are most often linked by either rock (granite) chutes and falls, or by riffle sections possessing a boulder/cobble base. This substrate variation provides extensive habitat diversity for aquatic fauna within this section of Seven Creeks. This habitat diversity does not exist within the study area below Gooram Falls (site M), where due to a combination of reduced stream fall and poor land management practices (which have recently been addressed by local LandCare groups), high levels of sand have entered the system, filling pools and generally covering the substrate. Presumably this lack of habitat diversity affects the distribution of trout cod, a species which establish well defined territories (Cadwallader and Gooley, 1984) and appears to be highly dependant upon adequate habitat availability in Seven Creeks. Drifting Trout cod larvae were first observed in Seven Creeks on 14th December 1995 (S. Saddlier, pers. obs. 1995) which indicates spawning may have occurred from late November to early December. Assuming that the time of spawning does not vary dramatically from year to year, young of the year Trout cod (having an average length of 64 mm) captured between 28 April and 18 June would therefore represent fish of approximately 5 - 6.5 months of age. This approximate age for length information varies slightly in comparison to data collected on the age of juvenile Trout cod from the Murray River (assessed at the National Ageing Facility at Queenscliff), which calculates juveniles of the same length (64mm) at 121 days (approximately 4 months). 20 This size for age contrast may indicate a variation in growth rates between the two sites, or may indicate that the time of spawning at Seven Creeks varies substantially from year to year. Further conclusions may be drawn from information which is currently being produced at the National Ageing Facility at Queenscliff, where specimens of juvenile Trout Cod captured from Seven Creeks during this survey are being aged. Although very little age-length data is available for Trout cod collected from Seven Creeks, year classes (determined from length-frequency graphs) appear to indicate that the high proportion of fish within the entire population from this smallest length class (50 - 80 mm) reflect strong recruitment in the 1996 spawning season. This length- frequency data also suggests that recruitment over the past three spawning seasons has been consistent, as indicated by the broad distribution of fish ranging from 110 - 260 mm in length. Little information is available on the size of trout cod at maturity, particularly for fish in the wild. However Trout cod captured from the Murray River at Yarrawonga during 1949-50 were in spawning condition at 254 mm in length (Cadwallader, 1977). During the current survey in Seven Creeks of the total numbers of trout cod captured, those which are greater than 254 mm in total length constitued only 9% of the entire catch and represented a total of 35 fish. Assuming a sex ratio within the population of 1:1, a total of 35 mature size fish corresponds to approximately 17 potential spawning pairs captured. This number of mature size fish suggests a very small breeding population of Trout cod is present, particularly considering that this population is distributed over a stretch of approximately six km of Seven Creeks and is to a large extent “compartmentalised” as a result of the presence of natural instream barriers which prevent the upstream movement of this species. The distribution of other fish species varied markedly throughout the study area. Other native species include Macquarie perch and Freshwater blackfish which were ubiquetous in catch results, although higher densities were observed in the higher sections surveyed. 21 These higher densities may in-part be attributed to the use of fyke nets as the dominant sampling technique, as this method is particularly effective for catching both Macquarie perch and Freshwater blackfish. Fyke nets were used in these sections due to a general change in habitat conditions, with an increase in larger, deeper pools, making electrofishing very difficult and relatively inneficient. This habitat is favourable to species such as Freshwater blackfish (Jackson, 1978) and Macquarie perch (Cadwallader, 1981), giving rise to the increased abundance of these species in catch results from the higher sections surveyed. However, without standardised sampling throughout the sections, quantitative assessments of the densities of these two species should be interpreted with caution. Introduced species also show marked variation in densities, with English perch and Carp only recorded below Gooram Falls. Gooram Falls represents a barrier to the upstream movement of these species, effectively isolating them from waters above the falls area. 22 Comparison with 1991 data A survey of the fish fauna of the upper Seven Creeks area was conducted during 1991 by staff of the Kaiela Fisheries Research Station (Anderson, J.R. 1991). This survey was conducted as part of an ongoing monitoring program, as well as an attempt to determine the impact which bush fires (which occurred during late December 1990) may have had on the instream fauna of Seven Creeks. Although it is difficult to draw conclusions based on a comparison of the total numbers of each fish species captured during the two sampling events due to variations in electrofishing and netting efficiencies, useful comparisons can be made on the relative proportions of fish species captured from each section and in particular on the relative proportions of each length class of Trout cod captured throughout the survey. Preliminary comparisons indicate that while Trout cod densities were similar at sites G - J during both surveys (Figure 22), sites situated further downstream (sites K, L and M) exhibited marked variation. Highest Trout cod densities were observed at site J during the 1991 survey, progressively decreasing with increasing distance downstream, while in the 1997 survey, densities progressively increased to a maximum at site L, before decreasing dramatically at the lowest site (site M). This trend appears to reflect a downstream movement of the Trout cod population, with the highest densities currently being observed at sites which in 1991 supported relatively low proportions of Trout cod. 23 ACKNOWLEDGEMENTS Assistance in the field was provided by P. Fairbrother, T. Glenane, J. Lieschke, J. Mahoney and D. O’Mahony. Thanks also to Bill O’Connor and Pam Clunie for their valuable comments on the report. 24 REFERENCES Anderson, J.R. 1991 (Draft Report) Status of the protected population of Trout Cod (Maccullochella macquariensis) and other native fish in the upper reaches of Seven Creeks, Victoria, in 1991. Kaiela Fisheries Research Station, Flora and Fauna Division, Dept. of Conservation and Environment, Victoria. Cadwallader, P.L. (1977) J. O. Langtry’s 1949-50 Murray River Investigations. Fisheries and Wldlife Paper, Victoria. No. 13, 70pp. Cadwallader, P.L. (1981) Past and present distributions and translocations of Macquarie perch Macquaria australasica (Pisces : Percichthidae), with particular reference to Victoria. Proceedings of the Royal Society of Victoria. 93: 23-30. Cadwallader, P.L. and Gooley, G.J. (1984). Past and present distributions and translocations of Murray Cod Macculochella peeli and Trout Cod Macculochella macquariensis (Pisces : Percichthyidae) in Victoria. Proc.R.Soc. Vic. 96 : 33-43. Department of Conservation and Natural Resources Maccullochella macquariensis. Action Statement No. 38. (1995). Trout Cod Jackson, P. D. (1978) Benthic invertebrate fauna and feeding relationships of brown trout Salmo trutta Linnaeus, and river blackfish Gadopsis Marmoratus Richardson, in the Aberfeldy River, Victoria. Australian Journal of Marine and Freshwater Research. 29: 725-742. Tunbridge , B.R and Glenane, T.G. (1982) Fisheries Value and Classification of Fresh and Estuarine Waters in Victoria. Fisheries and Wildlife Division, Ministry For Conservation, Arthur Rylah Institute for Environmental Research. 25