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Assessing the Status of a Disjunct Population of the Endangered Crayfish Euastacus Bispinosus in a Karst Rising-Spring Habitat in Southern Australia

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Assessing the Status of a Disjunct Population of the Endangered Crayfish Euastacus Bispinosus in a Karst Rising-Spring Habitat in Southern Australia AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS Aquatic Conserv: Mar. Freshw. Ecosyst. 25: 599–608 (2015) Published online 19 June 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/aqc.2478 Assessing the status of a disjunct population of the endangered crayfish Euastacus bispinosus in a karst rising-spring habitat in southern Australia NICK S. WHITERODa,*, OISÍN F. SWEENEYb,c, and MICHAEL P. HAMMERa,d, aAquasave - Nature Glenelg Trust, Goolwa Beach, SA, Australia bSouth Australian Department of Environment, Water and Natural Resources, Mount Gambier, SA, Australia cRed Branch Ecology, Old Erowal Bay, NSW, Australia dMuseum and Art Gallery of the Northern Territory, Darwin, NT, Australia ABSTRACT 1. Many species of freshwater crayfish of the endemic Australian genus Euastacus are threatened with extinction. Routine monitoring of most Euastacus species is minimal, and a subsequent lack of information has hampered prioritization of conservation and management efforts. 2. The present study investigated population parameters and temporal changes in abundance in a disjunct population of Euastacus bispinosus. This occurs at the western extent of the range of the species in the state of South Australia (SA) and inhabits a groundwater-dependent karst habitat distinct from the larger population in the Victorian Glenelg basin. 3. Euastacus bispinosus was recorded at sites within seven karst rising-springs as well as two isolated locations (sinkhole and cave), which expanded the extent of occurrence of the species in SA, but the area of occupancy remains limited. Most subpopulations contained low numbers, had little or no signs of recruitment, were dominated by large crayfish, and demonstrated a high incidence of gonopore aberrations. Declines in abundance were observed across these subpopulations between 2006 and 2011, although these declines were not statistically significant. 4. Of critical importance to the conservation of the species in SA is ensuring that groundwater discharge is maintained in karst rising-springs, hydrological connectivity is enhanced between subpopulations and degradation within habitats is reversed. Further monitoring and research is necessary to gain a clear understanding of the status of subpopulations of the species over time. Copyright # 2014 John Wiley & Sons, Ltd. Received 13 January 2014; Revised 26 March 2014; Accepted 11 May 2014 KEY WORDS: groundwater-dependent ecosystems; freshwater crayfish; endangered species; conservation evaluation; population fragmentation *Correspondence to: Nick S. Whiterod, Aquasave – Nature Glenelg Trust, 7 Kemp St, Goolwa Beach, South Australia, 5214, Australia. E-mail: [email protected] Copyright # 2014 John Wiley & Sons, Ltd. 600 N. S. WHITEROD ET AL. INTRODUCTION (hereafter KRS) has recently been adopted by Keith Freshwater crayfish are a diverse group, with et al. (2013) to describe this habitat. currently more than 640 species described The endemic Australian genus Euastacus provides worldwide, distributed across all continents except a prime example of the threats posed to freshwater fi Antarctica and occupying wide-ranging habitats cray sh, with 40 of the 50 species considered (Crandall and Buhay, 2008). In these habitats they threatened according to IUCN Red List criteria are valuable indicators of environmental change (Furse and Coughran, 2011b; Coughran and Furse, and form important links in the transformation of 2012). This is true of Euastacus bispinosus Clark, energy through aquatic foodwebs (Reynolds and 1941, which is a slow-growing and long-lived Souty-Grosset, 2011). However, at least one-third (~26 years: Honan and Mitchell, 1995a) species of all freshwater crayfish species are threatened with endemic to the Glenelg River Basin in south-west extinction with the two major common threats Victoria and KRS in coastal drainages of south-east being over-exploitation by humans and degradation South Australia (Figure 1) (Zeidler, 1982; Morgan, of habitat (Collen et al., 2014). Freshwater crayfish 1986). Across its range, E. bispinosus has undergone inhabiting groundwater-dependent karst systems reductions in distribution and abundance owing to appear particularly at risk because of localized over-fishing, hydrological alteration and habitat impacts but also broader groundwater extraction degradation, which has triggered the closure of the (Walsh, 2000; Boulton et al., 2003; Taylor et al., recreational fishery (TSSC, 2011). A recent 2007). For instance, almost all North American conservation assessment has escalated the conservation crayfish species associated with karst caves are status to endangered under Federal environmental considered threatened (Culver et al., 2000). In legislation (the EPBC Act 1999: TSSC, 2011) and south-east South Australia, karst systems discharge vulnerable globally (under the IUCN Red List: groundwater under pressure to form surface water Coughran and Furse, 2010). The distribution of bodies resembling small lakes and streams (Allison the species is now considered to be heavily and Harvey, 1983). The term ‘karst rising-spring’ fragmented and it persists as discrete populations Figure 1. Approximate distribution of Euastacus bispinosus in south-west Victoria and south-east South Australia (red polygon). Surveys focused on the narrow section of coastal drainages between the SA border and Port MacDonnell as well as two isolated locations (red dots). National parks and state forests are shown by green polygons, and the larger waterways of the Glenelg Basin in Victoria are shown in dark blue. Copyright # 2014 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 25: 599–608 (2015) EUASTACUS BISPINOSUS IN KARST RISING-SPRING HABITAT 601 across much of its range (Honan, 2004; Hammer become locally extinct, while knowledge of the and Roberts, 2008). The most westerly population reproductive characteristics of a species allows of the species (hereafter referred to as the South managers to identify potential hindrances to Australian (SA) population), is of particular population growth. This study sought to: conservation concern as it has an extremely small extent of occurrence (24 km2) that is disjunct from 1. resurvey known subpopulations of the species nearby populations in the Glenelg River Basin and detect new populations; (minimum 9 km away) owing to changes in 2. document information on population parameters hydrology in the region (Boutakoff, 1963; Hammer (sex ratio, size distribution, frequency of gonopore aberrations), including those relating to and Roberts, 2008; Miller et al., 2013, in press). reproduction (presence of berried females, size The SA population is largely restricted to KRS at onset of reproduction) and recruitment habitat that occurs along a narrow (3 km) section of (presence of juveniles); and coastal drainages (Zeidler, 1982; Hammer and 3. investigate changes in the abundance of Roberts, 2008). These KRS were once hydrologically subpopulations between 2006 and 2011 so as to linked through the seasonal inundation of the elucidate population trends. surrounding peat swamp (Eardley, 1943; Stephens, 1943). Extensive drainage and native vegetation clearance from the 1840s to the present day for METHODS agriculture (SEWCDB, 1993) has disrupted Study region connectivity and, as a result, individual KRS and their associated flora and fauna are now largely The study focused on KRS scattered throughout a isolated within an intensively irrigated agricultural narrow section of coastal drainages between the landscape. This has contributed to the recent SA–Victoria border and Port MacDonnell assessment of KRS as a critically endangered (Figure 1, Table 1). In these habitats, clear (little ecological community (Keith et al., 2013). The SA or no suspended solids), fresh (typically population of E. bispinosus persists as discrete <1000 μScm-1) and cool (approximately 13–17°C subpopulations (i.e. populations hydrologically year-round) groundwater is discharged from the isolated from other nearby populations) (Hammer bottom of pools (pool sites) 1–10 m deep, from and Roberts, 2008), with females maturing at which water flows along creeks, modified to act as considerably smaller sizes and aberrant crayfish drainage channels (hereafter creek sites), to the (those possessing both male and female gonopores) ocean (Allison and Harvey, 1983). Hammer and much more common than in Victorian populations Roberts (2008) recorded E. bispinosus from 13 of 17 (Honan and Mitchell, 1995b). Genetic analyses have surveyed sites within KRS from 5–16 December revealed very little differentiation between these 2006 (austral summer). In the present study, subpopulations, although this is likely to be due to a sites were re-surveyed where E. bispinosus had founder effect and subsequent genetic drift rather previously been recorded as well as new than high gene flow (Miller et al., in press). locations thought suitable for the species in an Despite their conservation status, ecological attempt to identify new populations. The 13 importance and charismatic nature, knowledge gaps known sites were re-surveyed during the austral in our understanding of population parameters and winter (21–27 August 2011) and summer (5–10 threatening processes exist for most Euastacus December 2011) to explore seasonal differences, species (Furse and Coughran, 2011a, c). Evaluation with the comparison between years (2006, 2011) of population trends and information on life-history achieved for summer only. There were 16 new characteristics is required
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