Kerrylyn Johnston,1,2,† Belinda J. roBson 3,4 and Christopher M. austin 5
Population Structure and Life History Characteristics of the Freshwater Crayfish Gramastacus insolitus and Geocharax falcata (Parastacidae) in the Grampians
National Park, Australia
INTRODUCTION
Relatively few comprehensive studies have been conducted on the population structure or life histories of wild freshwater crayfish populations worldwide, despite them being the largest invertebrates in many freshwater systems (Horwitz 1990). Freshwater crayfish are important components of freshwater ecosystems (Lorman and Magnuson 1978; Lodge et al. 1994; Momot 1995; Nyström et al. 1996; Statzner et al. 2003) because they are key energy transformers between trophic levels (Momot et al. 1978). Understanding the population biology of crayfish species is important as life history strategies and mechanisms controlling population size and structure need to be adequately understood to ensure successful conservation management. In Australia, detailed studies of freshwater crayfish have been largely restricted to species of significant recreational fisheries importance and those having commercial culture potential (Merrick and Lambert 1991). As such, knowledge of the population biology of wild species (> 150 species) is limited, but includes: studies of the life histories of two Tasmanian species (Hamr and Richardson 1994; Hamr 1996), the life history and reproductive biology of
Cherax quinquecarinatus (Grey) in Western Australia (Beatty et al. 2005b), the life history of invasive Cherax destructor Clark in Western Australia (Beatty et al. 2005a) and the life history of C. destructor and Euastacus bispinosus Clark in western Victoria (Johnston et al. 2008).
Life history strategies of freshwater crayfish are often classified as either winter or summer brooders. Summer brooders can colonise a range of habitats, have the life history characteristics of generalist crayfish species, and generally have an asynchronous spawning regime during the short summer breeding period that may include multiple spawning events, short life spans, rapid growth, high fecundities and small eggs (Honan and Mitchell 1995). In contrast, winter brooders have life history traits characteristic of specialist crayfish species, including a long life span, relatively large size at sexual maturity, low fecundity and large eggs (Honan and Mitchell 1995). Therefore, it may be expected that crayfish species usually found in seasonally inundated habitats such as those that predominate in semi-arid areas, would breed in early summer, before these habitats dry out, and show the characteristics of generalist species.
Abstract.— Means by which freshwater crayfish persist in seasonally-dry wetlands are poorly understood, but this information is important for their management and conservation. This study examined the population structure, reproductive timing, and life history strategies of two Australian freshwater crayfish species that have a commensal relationship, through seasonal surveys conducted once in each season over 24 months. Gramastacus insolitus is able to achieve large population densities in ephemeral waterbodies but lacks the capacity to burrow, while Geocharax falcata can burrow to survive annual drying. Higher abundances were generally recorded in spring and summer than other times of year for both species. Sex ratios in G. insolitus almost always favoured females, sexually mature females were 7.2 mm OCL or larger and gravid females were captured in the highest abundances in spring. Preparatory moulting, spawning, brooding of eggs and release of juveniles occurs in both species over the period of late winter to late summer. Both species have the life history characteristics of summer brooders such as: potentially asynchronous spawning regimes, short breeding periods, relatively short life spans, and the ability to grow rapidly. These traits demonstrate the flexibility required by freshwater crayfish to enable them to inhabit seasonally-dry wetlands where the timing and duration of inundation of these habitats is unpredictable. [Keywords.— life history, population structure, reproductive timing, sex ratios].
1 School of Life and Environmental Sciences, Deakin University, PO Box 423, Warrnambool, Vic. 3280, Australia 2 School of Geography, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, United Kingdom
† Corresponding Author — [email protected] School of Life and Environmental Sciences, Deakin University, PO Box 423, Warrnambool, Vic. 3280, Australia
4 School of Sustainability, Murdoch University, South Street, Murdoch 6150, Western Australia, [email protected]
5 School of Science and Primary Industries, Charles Darwin University, Darwin, Australia [email protected]
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Recent work has shown that the non-burrowing crayfish Gramastacus insolitus Riek survives dry periods by occupying the upper parts of the burrows of a larger crayfish species, Geocharax falcata Clark (Johnston and Robson 2009a). This appears to be an adaptation to survive wetland drying, but as there are few examples of commensalisms among crayfish and few studies of freshwater crayfish population biology in seasonally-dry habitats, little is known of how crayfish life histories accommodate annual drying. Therefore, the aim of this study was to investigate and describe the population structure, life history and reproductive timing of G. insolitus and G. falcata across four different habitat types in the semi-arid Grampians National Park in south-west Victoria, Australia and classify their life history strategies.
MATERIALS AND METHODS
Study Species
Species of the freshwater crayfish genus Geocharax occur only in the Bass Strait Basin of south-eastern Australia (Riek 1972) and have previously been found to inhabit wetlands, small streams, marshes, hilltop areas and drains (Riek 1972; Zeidler 1982). Geocharax falcata is a medium-sized crayfish (≤ 80 mm total length (TL) and adults have moderate burrowing ability (Riek 1972; Zeidler 1982)). Only three previous studies have included G. falcata, with the first investigating its physiology (Mills et al. 1976), the second its commensalism with G. insolitus (Johnston and
Robson 2009a) and the third its habitat use (Johnston and Robson 2009b). To date, the population structure, life history, reproductive timing and general behavior of G. falcata remain unknown.
Gramastacus insolitus is a small freshwater crayfish (up to 40 mm TL) endemic to southwest Victoria and southeast South Australia (Riek 1972), with a distribution restricted to areas of shallow wetlands, the marginal zones of small streams and drains connected to these water bodies (Riek 1972; Zeidler 1982; Zeidler and Adams 1989). Gramastacus insolitus has no ability to burrow, females have been reported gravid at 20 – 30 mm TL, and breeding between October and December (Zeidler and Adams 1989). It can occur in sympatry with G. falcata, Engaeus lyelli (Clark) and C. destructor (Zeidler 1982), and depends on the presence of a burrowing crayfish species to survive wetland drying (Johnston and Robson 2009a).
Study Site
The Grampians National Park is located in central western Victoria, Australia at the southwestern end of the Great Dividing Range (Figure 1). The majority of the area’s annual rainfall occurs in winter, with July and August being the wettest and coolest months, while January to March are the driest and hottest (Calder 1987). The study sites were distributed across three catchments; the Wannon River catchment, the Scrubby Creek catchment and the Glenelg River catchment (Figure 1), in order to ensure that the results were comparable to other crayfish studies. Within these three catchments, duplicate sites of each of four common habitat types were sampled. The habitat types common to all catchments were stream channels, fire dams, floodplain wetlands, and flooded vegetation. These habitats are undisturbed by agricultural activities, with channels (generally lotic) and fire dams (lentic) being permanent habitats that contain water all year round, but fluctuate depending on the season. Both floodplain wetland and flooded vegetation habitat types are temporary in nature, with the former inundated with water from winter to late summer, and the later potentially inundated with water from winter to late summer, but likely only inundated for weeks depending on habitat size.
Seasonal Crayfish Surveys
Eight seasonal surveys were conducted in each season over 24 months from spring 2003 to winter 2005. Different sampling techniques were employed for day and night sampling. Day sampling used multiple random 30 sec dip-net (250 μm mesh) sweeps of a 25 m2 area of lentic habitats (or the littoral zone of fire dams), or a series of sweeps of a 50 m length of channel habitats over a period of one hour. Night sampling used three standard box traps (5 cm apertures) baited with beef liver, placed randomly at each site sampled that day, traps were left in place overnight and collected the next morning. Marked crayfish were rarely recaptured (Johnston 2008). Samples were sorted on trays and crayfish placed in holding containers until site sampling was complete. Crayfish were identified to species (Riek 1972), their occipital-carapace length (OCL) measured with vernier calipers to the nearest 0.05 mm, sex and the presence of external eggs on females was recorded. In addition, during spring 2004, the colour of eggs and the dimensions of three eggs from all captured gravid females were recorded. The moult status of all individuals was
Figure 1. Location of the Grampians National Park in Victoria and the Wannon River, Glenelg River and Scrubby Creek catchments within the National Park.
2010 Johnston et al. — population Biology of two freshwater Crayfish 247
recorded as either hard, soft (carapace flexes between fingers) and very soft (carapace jelly-like). Due to time constraints secondary sexual characteristics were not recorded. The data obtained from day and night sampling were pooled, as were the duplicate sites for each habitat type.
RESULTS
Geocharax falcata
Abundance and sex ratios
In total, 288 G. falcata were captured during the day and 287 at night. On average smaller G. falcata (average OCL 11 mm) were captured during the day, than at night (average OCL 26 mm). This result is not surprising as the limitations of using baited traps are well documented (Hazlett et al. 1974; Brown and Brewis 1978; Rabeni et al. 1997) and favour the collection of larger males in a population, while smaller crayfish are thought not to be as readily attracted to baited traps and may be excluded by the presence and dominance of larger individuals. Geocharax falcata occurred in all three catchments and all habitat types, however there were differing abundances between the various habitat types and catchments. Typically the highest abundances were recorded in flooded vegetation and floodplain wetlands, followed by the channel habitat (Glenelg catchment) (Figures 2 and 3). It occurred least frequently in fire dams in the Glenelg River catchment and Scrubby Creek floodplain wetland habitats and in consistently lower abundances compared to other sites. Abundances were generally higher in spring and summer than other times of year (Figures 2 and 3). However in some flooded vegetation and channel habitats very high abundances were recorded in winter, including the highest abundance of the study, which was recorded in winter 2004. With the exception of the Glenelg River channel habitat, G. falcata abundances in all catchments and habitats were low, or
zero in autumn of both years, which coincides with the driest time of year in the study area (Figures 2 and 3). Male G. falcata were almost always substantially more abundant than females (M:F ratio range: 1:2 through 15:2) in all catchments, habitat types, and seasons, however, this bias was not so evident during spring.
Population size structure
The population size structure of G. falcata varied between habitats, catchments and seasons (Figure 3), however, a number of broad patterns were evident. Large G. falcata (> 20 mm OCL) were generally captured more frequently in winter and spring, fewer were captured in summer, and very few or none were captured in autumn. Typically the medium-sized (10 – 19.9 mm OCL) G. falcata were captured more frequently in spring and summer, fewer in winter, and very few or none in autumn. With the exception of spring 2003 and summer 2005 the smallest size-class of G. falcata (< 10 mm OCL) were captured year-round (albeit sometimes in very low numbers), beyond that there were no consistent patterns evident in the capture data (Figure 3). There were appreciable differences in numbers of small crayfish captured between habitat types (both within and between catchments), between catchments, and seasons between years.
Reproduction and moulting
A single gravid G. falcata female (15.6 mm OCL) was captured in flooded vegetation habitat (Wannon River). Soft-shelled individuals were captured frequently year-round, although much less frequently in autumn (when the species was rarely captured anyway), suggesting that this species moults at any, or all times of the year. In summer 2005 a number of very soft-shelled individuals were captured in the Glenelg and Wannon river catchments (channel and flooded vegetation habitats respectively), suggesting some form of “peak moult” event in these two areas.
Figure 2. Total abundance of Geocharax falcata in the Wannon River catchment fire dam (WF), flooded vegetation (WFV), and floodplain wetland (WFW), Scrubby Creek catchment flooded vegetation (SFV) and floodplain wetland (SFW), and the Glenelg River catchment fire dam (GF), channel (GC) and floodplain wetland (GFW) in the Grampians National Park, for each season.
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Figure 3. Total frequencies of Geocharax falcata in each size class for Wannon River catchment fire dams (WF), flooded vegetation (WFV) and floodplain wetlands (WFW); Scrubby Creek catchment flooded vegetation (SFV), channel (SC) and floodplain wetlands (SFW); and Glenelg River catchment channel (GC) and floodplain wetland (GFW).
2010 Johnston et al. — population Biology of two freshwater Crayfish 249
Gramastacus insolitus
Abundance and sex ratios
In total, 1239 G. insolitus were captured during the day and 9 at night. Gramastacus insolitus occurred in all three catchments, mainly in flooded vegetation habitat in the Glenelg catchment, and very few were captured in the fire dams (Figure 4). Abundance was the highest in summer, then spring, and while low abundances were typical in winter, moderate numbers were recorded during winter of both years in the Glenelg catchment channel habitat. No G. insolitus were captured in autumn of either year (Figure 4 and 5). Sex ratios generally favored females however some differences between habitat types, catchments, and seasons were evident.
Population size structure
The population size structure of G. insolitus varied between habitats, catchments, seasons and years (Figures 5 and 6), there were however a number of broad patterns. Small G. insolitus (< 3.5 mm OCL) were found in summer of both years and in Glenelg River channel habitat in winter 2004. In spring of both years, large G. insolitus (7.5 – 13.5 mm OCL) were more frequent than in winter or summer. During summer, small and medium (3.5 – 7.5 mm OCL) sized G. insolitus were, in general, more frequently recorded than for the same habitats in spring and winter of both years. In the Glenelg River catchment channel habitat, small G. insolitus were present in winter 2004, while medium individuals were more frequent at this time than in summer 2004. Gramastacus insolitus from the Glenelg River flooded vegetation habitat were recorded in spring 2004 only, and were medium and
large sized. No small G. insolitus were found in fire dams in the Wannon River catchment but medium sized G. insolitus were found in winter and spring.
Reproduction and moulting
With the exception of a single female G. insolitus captured carrying eggs in winter 2005, all egg carrying females were captured in spring of both years (19 in total), or summer 2004 (one female), with a single female G. insolitus carrying young captured in spring 2003. Gravid female G. insolitus ranged in size from 7.2 to 11.5 mm OCL, therefore, for the purposes of this study, females 7.2 mm OCL or larger were considered sexually mature. Gravid females were found in all habitats, except the flooded vegetation habitat in the Glenelg catchment.
Soft-shelled individuals were captured year-round (bar autumn, when the species was not captured at all), with the exception of autumn, this species moults at all other times of the year. Very soft-shelled individuals were only captured in spring 2004 and winter 2005. The majority of soft-shelled and very soft-shelled individuals recorded were female.
Egg data
Gramastacus insolitus eggs are oval in shape and vary widely in colour from mustard, light olive green, olive green, to olive green with dark green at one end. Eggs dimensions ranged from 1.2 mm x 0.9 mm to 1.6 mm x 1.0 mm. The number of eggs carried by a female ranged from 42 to 77, the G. insolitus captured displayed high fecundity and large eggs relative to body size.
Figure 4. Total abundance of Gramastacus insolitus in the Wannon River catchment flooded vegetation (WFV), fire dam (WF) and floodplain wetland (WFW), the Scrubby Creek catchment flooded vegetation habitat (SFV), and the Glenelg River catchment flooded vegetation habitat (GFV), channel (GC) and floodplain wetlands (GFW) in the Grampians National Park for each season.
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DISCUSSION
Highest abundances of G. falcata were typically recorded in those habitat types featuring semi-permanent water. A notable exception to this was the fire dams in the Glenelg catchment, and this might be attributable to the presence of the introduced C. destructor (Johnston et al. 2008), and the fact that fire dams typically have low habitat complexity, are steep sided and clay lined. Abundances were generally higher in spring and summer, when surface waters had been present for around three months and the aquatic food webs were reestablished, thereby providing abundant food and mating opportunities for G. falcata emerging from their burrows after the dry period.
Male G. falcata were almost always substantially more abundant than females across all catchments and habitat types, however, this trend was not as strong during spring.
The greater presence of females in spring coincided with the time of year when juveniles were recruited into the population, therefore, this trend likely reflects the reproductive cycle of this species. In contrast, sex ratios of another species of Geocharax have been found not to differ significantly from a 1:1 male to female ratio (Lake and Sokol, 1986).
Differences in population structure and abundance of G. falcata between habitat types and catchments are almost certainly driven by the presence of water and the length of its duration (with crayfish species responding opportunistically to both) more than any other factor. For example, in the Wannon River and Scrubby Creek catchments, winter and spring are likely the times of year when juveniles are recruited into the population after being released. In contrast, channel habitat in the Glenelg River catchment yielded small G. falcata in all seasons, except spring 2003 and summer 2004. Juveniles found in this catchment in autumn can be attributed to one of the channel sites being perennial. The extended duration of time over which they were recorded, indicates that this species has an opportunistic reproductive strategy and is able to take advantage of a longer than usual presence of water. An early release of juveniles into populations at flooded vegetation sites in the Wannon River catchment is inferred from observations of cohorts of juveniles growing through the size classes during spring 2004 and summer 2005, demonstrating considerable flexibility in the timing of recruitment among both habitat types and different catchments.
The lower female abundances, and single gravid female, captured in this study may be explained by the brooding behaviour
Figure 5. Total frequencies of Gramastacus insolitus in each size class for day sampling in the Wannon River catchment fire dams (WF) and floodplain wetland habitat (WFW), the Scrubby Creek catchment flooded vegetation habitat (SFV), and the Glenelg River catchment flooded vegetation (GFV), channel (GC) and floodplain wetland habitat (GFW). No G. insolitus were captured in autumn 2004.
Figure 6. Total frequencies of Gramastacus insolitus in each size class for day sampling in the Wannon River catchment fire dams (WF) and floodplain wetland habitat (WFW), the Scrubby Creek catchment flooded vegetation habitat (SFV), and Glenelg River catchment flooded vegetation (GFV), channel (GC) and floodplain wetland habitat (GFW). No G. insolitus were captured in autumn 2005.
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of females, probably retreating into burrows (to brood eggs) and not emerging until juveniles are released. Studies of crayfish in seasonally flooded wetlands in Louisiana (USA) reported reproductive activities coinciding with the dry period, so that young were released when the wetlands flooded (Lindqvist et al. 1998). These brooding female crayfish were able to survive the dry period (6 – 8 months) and reproduce on energy stored in the hepatopancreas (Lindqvist et al. 1998). This strategy would enable gravid females to avoid any aggressive encounters, predation and ensure the maximum survival of their young to the juvenile stage. Lake and Sokol (1986) also found relatively few gravid females in a study of two Victorian populations of C. destructor and attributed this to berried females remaining concealed in burrows or under cover, thereby avoiding capture. Woodland (1967) also commented that berried C. destructor females were almost untrappable because they avoided encounters with large individuals or crowding.
Although G. falcata reached sexual maturity at a relatively small size in this study, it likely takes two years to attain this size given the relatively small size of juveniles captured. Therefore, juveniles released in a particular year must construct their own burrows upon the drying of waterbodies in order to survive to reproduce in the following year when surface waters reappear. Unlike some species of Engaeus that live in family groups in complex burrows, with juveniles leaving the parent burrow upon reaching sexual maturity at the end of their second year (Riek 1969), juvenile G. falcata do not share the burrows of their parents (Johnston and Robson 2009a).
Since only a single gravid G. falcata female was captured, the fecundity, size of eggs, exact longevity and size at sexual reproduction for this species could not be determined. However, the observed seasonal size distributions suggests that G. falcata has an asynchronous spawning regime, a short to moderate life span and the ability to grow rapidly, and therefore has the life history characteristics of a summer brooder, suited to life in habitats that dry annually or for extended periods of time. Geocharax falcata breeding occurs over an extended period of time, and this trait has probably arisen as an opportunistic response to take advantage of the inundation of temporary habitats and presents an interesting compromise between specialist and generalist life-history strategies.
Gramastacus insolitus occurred in all three catchments and almost exclusively in floodplain wetland and flooded vegetation habitats. Exceptions were channel habitat in the Glenelg River catchment and fire dams in the Wannon River catchment, which upon closer examination were found to share several physical characteristics with the aforementioned habitats, including reduced permanency (channel habitat), the presence of the aquatic plants Myriophyllum verrucosum Lindl. and Triglochin sp., soft organic sediment and the presence of C. destructor and/or G. falcata. Low numbers of G. insolitus captured at night suggest that baited traps are not a suitable method for capturing this species. No G. insolitus were captured in autumn of either year because the temporary habitats where this species occurs were dry and individuals had probably retreated to the burrows of larger, co-occurring crayfish species (Johnston and Robson 2009a).
Uneven sex ratios favoring females were found in all three catchments and at all habitat types, except one, in spring of both years. Most freshwater crayfish populations have an approximately even sex ratio, so ratios favouring females are rare (Reynolds 2002), but have been documented previously (Lake and Newcombe 1975; Westman and Pursiainen 1982; Hamr and Richardson 1994; Honan and Mitchell 1995). However, none of these records show sex ratios favouring either sex on the order of two to five times, as found here. In the freshwater crayfish Parastacoides tasmanicus tasmanicus (Erichson), sex ratios favouring females have been attributed to its biennial breeding strategy, with the suggestion that a greater proportion of females may be advantageous in ensuring a greater number of females breeding in a given season (Hamr and Richardson 1994). However, if G. insolitus is short lived, it will not be able to exhibit a biennial reproductive strategy. Sex ratios can be obscured by seasonal differences in activity and catchability and most studies have shown a reduced proportion of female catches in the breeding season (Reynolds 2002), however, E. bispinosus reportedly has an overall sex ratio in favour of females during the brooding season (Honan and Mitchell 1995). Similar results were recorded for an E. bispinosus population occurring in channel habitat in the Grampians National Park (Johnston et al. 2008).
Sex ratios favoring females would seem sensible in an opportunistic and short-lived species that relies on the appearance of surface waters to find mates and breed. Fewer males (than seen in a 1:1 male to female ratio) are probably required to fertilize the eggs of a larger female population in a temporary habitat within a relatively small period of time. A large female population would ensure that enough young are released for a proportion of them to find their way into the burrows of G. falcata and C. destructor to aestivate during the dry season, subsequently reemerging when their temporary habitats are inundated again.
Large G. insolitus were more frequently caught in Spring than other times of the year, suggesting that by this time, the habitats had been inundated for a sufficient duration for those large G. insolitus which had aestivated over the dry months to reemerge into the surface waters to breed. Small G. insolitus were found in summer of both years, suggesting that by this time, the large individuals present in spring had spawned, brooded and released juveniles into the population. Minimum size at sexual maturity, as determined by gravid females, was 7.2 mm OCL in this study, which corresponds to 20 – 30 mm TL previously reported for gravid female G. insolitus (Zeidler and Adams 1989).
These results suggest that preparatory moulting, spawning and the brooding of eggs and juveniles (probably only lasting 2 – 3 months) of G. insolitus probably occurs sometime during the period of late winter to late summer, with the exact duration of this period determined by the duration of the presence of surface waters. Zeidler and Adams (1989) reported G. insolitus to breed between October and December (mid spring to summer), supporting the findings of the current study. Although most G. insolitus individuals probably only live for one year (due to the seasonality of the habitats they occur in), some survive for at least two by aestivating in the burrows of G. falcata and/or C. destructor (Johnston and Robson 2009a), thus surviving to reproduce and
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ensure the continued survival of the populations at the sites at which they occur.
Honan and Mitchell (1995) suggested that the life histories of all freshwater crayfish species could be separated into two main groups. While the life history strategy employed by G. insolitus allows it to survive from one season to another in temporary habitats is a new discovery, both G. insolitus and G. falcata can be included in group one of Honan and Mitchell’s (1995) classification of freshwater crayfish based on life-cycle characteristics. That is, they are summer brooders, with a short breeding season, a potentially asynchronous spawning regime, a short life span, an ability to grow rapidly and high fecundity compared to body size. These traits show flexibility suited to life in seasonal waters. However, G. insolitus also displays some traits that are characteristic of a winter brooder, including large eggs relative to body size and breeding predominantly in spring as opposed to summer. Of course, this is because the temporary habitats in which they occur fill with water in later winter to early spring, making spring the optimum time to reproduce. While the traits of summer brooders have been associated with generalist life history strategies, G. insolitus cannot be regarded as a generalist species because its occurrence is restricted to a few habitat types.
Implications for Conservation
Our results suggest that spring is the ideal time for population assessments to be made for both species. Assessments of G. falcata populations will need to involve both day and night sampling in order to obtain representative results while the assessment of G. insolitus populations need only involve day sampling by dip-net, since bait trapping was not effective. For the threatened G. insolitus, relatively few populations are known so further work identifying major populations of this species throughout its range are needed.
Habitat modification and disturbance arising from park management activities may affect crayfish populations. For example, the construction or upgrading of roads, fire dams and visitor facilities and fuel reduction burning of wetland vegetation. In particular, burning should be avoided in autumn when water tables are lowest and the crayfish present in burrows are most vulnerable to the radiant heat resulting from fires burning across the dry seasonal habitats. Instead, fires for management should occur during the wettest time of year (late winter and spring), when crayfish are protected by surface waters. It is possible that climate change will increase the frequency and duration of drought and the frequency and intensity of wildfires in western Victoria. Both of these changes are likely to have negative impacts on crayfish and active management may be required to minimize their effects. In particular, prolonged drying of seasonal wetlands will increase the duration of time spent over-summering in burrows for both species, lengthening the period of exposure to fire impacts and potentially reducing the time available for surface feeding and reproduction.
ACKNOWLEDGMENTS
The authors wish to thank Lyn Johnston, Travis Howson, Sally-Anne Williamson and Andrew McIntyre for assistance in the field. Thank you also to Tom McRae for providing comments
on the manuscript and to Parks Victoria for permission to work in the Grampians National Park and for providing fieldtrip accommodation. We also thank three anonymous reviewers for helpful comments and suggestions on a previous draft.
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