A survey of the fish fauna of the Roper River near Jude’s Photograph: P. Cowan Crossing in the late dry season 2013 Report number 02/2014D www.nt.gov.au/lrm This report can be cited as: Dostine, P.L. (2014). A survey of the fish fauna of the Roper River near Jude’s Crossing in the late dry season 2013. Department of Land Resource Management. Report number 02/2014D. Palmerston, Northern Territory. © Northern Territory of Australia, 2014 ISBN 978-1-74350-053-8 Freshwater fish fauna of the Roper River ii Executive summary Ground and surface water extraction during the dry season will reduce dry season flows in the Roper River and may impact ecological processes within the river. This report describes preliminary studies of the fish fauna of the Roper River, along a reach of the Roper River near Jude’s Crossing (14° 49’ S 134° 02’ E) on Flying Fox Station. The site is located in the middle reaches of the Roper River downstream of potential ground and surface water extractions for irrigation and mining use. The objective of the study was to assess appropriate sampling methods for quantitative description of fish communities within different stream habitats. Trials were conducted of the efficacy of bankside observation, gill-netting, and baited underwater video stations. The work is a precursor to the establishment of an environmental monitoring program linked to potential reductions in dry season flow. The fish fauna of the middle reaches of the Roper River includes at least 35 species from 21 families. The families Ariidae (fork-tailed catfishes), Plotosidae (eel-tail catfishes) and Terapontidae (grunters) are each represented by at least 4 species. A field survey of the Roper River in the vicinity of Jude’s Crossing in late 2013 identified 23 species of fish. Twenty of these species were identified by direct observation, the remaining three (all ariid catfish) were collected by gill-netting in a main channel pool. Eighteen species were recorded during standardised bankside observations of fish at 24 sites during day-time and night-time censuses. Species richness per site ranged from 4 to 12 species. Two species were ubiquitous (Melanotaenia splendida inornata) or nearly ubiquitous (Craterocephalus stercusmuscarum). Some species were more likely to be detected during day-time censuses (principally terapontid species); conversely some species were more likely to be detected during night-time censuses (principally small-bodied, sit-and-wait ambush predators). Results suggest that surveys based on direct observation can yield a high proportion of species present in the littoral zone, but that surveys need to include both day and night-time observations at individual sites. Multi-panel gill-nets were used to capture seven fish species, including three species not recorded during bankside observations. Baited remote underwater video stations (BRUVS) were deployed in the same habitat as gill-nets and recorded at least five species of fish and two turtle species. Three of these fish species were not captured by gill-netting. Large numbers of sooty grunter Hephaestus fuliginosus were attracted to BRUVS; their numerical dominance will present difficulties quantifying relative abundance. Further studies are needed to standardise sampling methods to derive a robust monitoring program for fish communities in the Roper River. Freshwater fish fauna of the Roper River iii Contents 1. Introduction .................................................................................................................... 2 2. Methods .......................................................................................................................... 3 2.1 Fish fauna of the Roper River ................................................................................... 3 2.2 Bankside observations ............................................................................................. 3 2.3 Multi-panel gill-nets .................................................................................................. 4 2.4 Baited underwater video stations .............................................................................. 4 2.5 Environmental measurements .................................................................................. 5 3. Results ........................................................................................................................... 8 3.1 Fish fauna of the Roper River ................................................................................... 8 3.2 Bankside observations ............................................................................................. 8 3.2.1 Patterns of species richness ........................................................................ 12 3.2.2 Factors influencing probability of detection .................................................. 12 3.3 Multi-panel gill-nets ................................................................................................ 14 3.4 Baited underwater video stations ............................................................................ 14 3.5 Environmental measurements ................................................................................ 16 4. Discussion ................................................................................................................... 17 5. Acknowledgements ......................................................................................................... 18 6. References ................................................................................................................... 18 7. Appendices .................................................................................................................. 19 Freshwater fish fauna of the Roper River 1 1. Introduction The Roper River system is one of the largest river systems in northern Australia, with a catchment of over 80,000 km2 (Faulks 2001). Dry season flows within the main stem of the Roper are maintained by discharge from ground water aquifers in the upper reaches of the catchment. The extraction of water for mining operations and agriculture will diminish flow during the dry season, and potentially place stresses on the ecological processes of the river. Consequently there is a need to undertake research on the composition and dynamics of the biota of the river, and to develop monitoring approaches to guide and inform management. Previous studies of the fish fauna of the Roper system include Midgley (1979), Dally and Larson (2008), and Hammer et al. (2012). Dally and Larson (2008) recorded 18 species from a survey of a large waterhole on the Roper River bordering Elsey and Moroak stations in late September 2008. Hammer et al. (2012) recorded 27 species from a survey of 28 sites on a tributary of the Roper River on Wongalara Station, and listed an additional five species which are expected to occur, based on occurrence on adjoining properties. This report describes preliminary studies of the fish fauna of the Roper River, along a reach of the Roper River near Jude’s Crossing (14° 49’ S 134° 02’ E) on Flying Fox Station. The site is located downstream of potential mining operations which may require extraction of river water, and irrigated agriculture in the Mataranka area. The objective of the study was to assess appropriate sampling methods for quantitative description of fish communities within different stream habitats. Trials were conducted of the efficacy of bankside observation, gill- netting, and baited underwater video stations. Freshwater fish fauna of the Roper River 2 2. Methods Studies were conducted along a reach of the main channel Roper River near Jude’s Crossing (14° 49’ S 134° 02’ E) and a northern anabranch (14° 49’ S 134° 01’ E) on Flying Fox Station (Figure 1). Field trips were conducted in the late dry season of 2013. Flow in the Roper River at Jude’s Crossing was not measured; the anabranch ceased to flow late in the dry season after the field survey. However, flow in the main channel is likely to be equivalent to flow downstream at Red Rock (G9030250). Flow at Red Rock was estimated to be 2.51 m3/s on 25/10/13 (Wagenaar and Tickell 2013). 2.1 Fish fauna of the Roper River Records of fish species present in the middle section of the Roper River were compiled from previous surveys conducted by staff of NT Museum (Dally and Larson 2008) and Hammer et al. (2012), and from records of specimens of freshwater fish held by the NT Museum. Figure 1. Satellite image of the eastern Top End of the Northern Territory showing boundary of Roper River catchment, Roper River drainage system, and location of study area. 2.2 Bankside observations Detection/non-detection data on fish species were collected by bankside observation within marked 15 m transects at 24 sites during two field trips from 28-29th August and 9-13th September 2013. Photographs of each site are shown in Figures 2 and 3; the locations of individual sites are given in Appendix 1. Censuses of ten minutes duration were conducted at each site on four occasions, two during daylight hours, mostly from 10:00 to 14:00; and two at night, mostly from 20:00 hours. Daytime observers were aided by Spotter polaroid sunglasses; night-time observations were aided by LED Lenser headlights. All fish species detected during each census were recorded. The identity of some specimens was confirmed Freshwater fish fauna of the Roper River 3 by capture at the site during the survey using a hand net. There were ninety six individual site visits,