S. Beatty

Distribution and impacts of introduced freshwater fishes in Western Australia

Abstract This paper presents comprehensive distributional data, from over 1300 sites, on introduced freshwater fishes in Western Australia. Currently, there are 10 species of introduced freshwater fish established in the inland waters of Western Australia. Most of the introduced fishes found here are those that have formed feral populations elsewhere in the world, and include members of the Salmonidae, i.e., rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta); Cyprinidae, i.e., goldfish (Carassius auratus) and carp (Cyprinus carpio); Poeciliidae, i.e., mosquitofish (Gambusia holbrooki), one‐spot livebearer (Phalloceros caudi‐maculatus), guppy (Poecilia reticulata), and swordtail (Xiphophorus hellerii); Percidae, i.e., redfin perch (Perca fluviatilis), and Cichlidae, i.e., Mozambique mouthbrooder or tilapia (Oreochromis mossambicus). More recently, the eastern Australian silver perch (Bidyanus bidyanus) (Terapontidae), which was introduced for aquaculture, has been captured in the Swan River near Perth. It is not known whether this population is self‐maintaining. The majority of introduced species are confined to the south‐west, although four and one species have been recorded from the Pilbara and Kimberley, respectively. Some species are extremely common and widespread, e.g., G. holbrooki and P. fluviatilis, whereas others are far more restricted and may be confined to between one and three catchments, e.g., C. carpio, P. caudimaculatus, P. reticulata, X. hellerii, O. mossambicus, and B. bidyanus. The impact of these introduced fishes on native species varies, but ranges from predation, e.g., O. mykiss, S. trutta, G. holbrooki, and P. fluviatilis, to aggressiveness, e.g., G. holbrooki, X. hellerii, and O. mossambicus, and competition for food and habitat.

Climate change and its implications for Australia's freshwater fish

Freshwater environments and their fishes are particularly vulnerable to climate change because the persistence and quality of aquatic habitat depend heavily on climatic and hydrologic regimes. In Australia, projections indicate that the rate and magnitude of climate change will vary across the continent. We review the likely effects of these changes on Australian freshwater fishes across geographic regions encompassing a diversity of habitats and climatic variability. Commonalities in the predicted implications of climate change on fish included habitat loss and fragmentation, surpassing of physiological tolerances and spread of alien species. Existing anthropogenic stressors in more developed regions are likely to compound these impacts because of the already reduced resilience of fish assemblages. Many Australian freshwater fish species are adapted to variable or unpredictable flow conditions and, in some cases, this evolutionary history may confer resistance or resilience to the impacts of climate change. However, the rate and magnitude of projected change will outpace the adaptive capacities of many species. Climate change therefore seriously threatens the persistence of many of Australia’s freshwater fish species, especially of those with limited ranges or specific habitat requirements, or of those that are already occurring close to physiological tolerance limits. Human responses to climate change should be proactive and focus on maintaining population resilience through the protection of habitat, mitigation of current anthropogenic stressors, adequate planning and provisioning of environmental flows and the consideration of more interventionist options such as managed translocations.

Co-invaders: The effects of alien parasites on native hosts

Graphical abstract

Distribution, biology and likely impacts of the introduced redfin perch (Perca fluviatilis) (Percidae) in Western Australia

Within Western Australia, Perca fluviatilis is restricted to the south-western corner and is found in the Swan, Murray, Harvey, Collie, Capel, Carbunup, Margaret, Blackwood, Donnelly and Warren river systems. Age data suggest it was released into Big Brook Dam (Warren River) in 1992 or 1993, where it has since played a role in eliminating the native teleosts. Its success here is attributed to a young age at maturity, rapid growth (compared with populations elsewhere), predatory nature, large size (compared with native fish), broad environmental and habitat tolerances, and absence of predators. Gonadal development initiates in late summer, with peak spawning between August and September. Males and females attained maturity in their first and second years, respectively, which is earlier than reported for most Northern Hemisphere populations and can be attributed to their rapid growth here because of the warmer climate. At ages 1, 2, 3, 4 and 5, males, on average, attained 102, 159, 206, 246 and 280 mm total length (TL) and females had attained 104, 166, 228, 290 and 351 mm TL at the respective ages. Diets of fish 50–200 mm TL comprised mainly small aquatic invertebrates, whereas larger fish preyed almost exclusively on decapods, mainly marron (Cherax tenuimanus), and teleosts.

Variation in Life History of Land-Locked Lacustrine and Riverine Populations of Galaxias maculatus (Jenyns 1842) in Western Australia

Galaxias maculatus is one of the most naturally widely distributed species in the world yet there is no published literature on the biology of Western Australian populations. Galaxias maculatus in the rivers of the south coast of Western Australia inhabit an environment that is variable and at times unpredictable. By examining trends in gonadal development, lengths at first maturity, growth and appearance and persistence of larvae of G. maculatus in two saline rivers (Jerdacuttup River and Oldfield River) and one freshwater lake (Moates Lake), the life histories of populations in contrasting environments were determined. The stable conditions that prevail in the low salinity, cool waters of Moates Lake have fostered an extremely protracted breeding and larval recruitment period (year round) in comparison to limited recruitment in the riverine environments which experience less predictable flow events and water quality (salinity). An upstream migration for breeding in the Jerdacuttup and Oldfield rivers is similar to land-locked G. maculatus in south-eastern Australia and is a reversal of the downstream migration in Moates Lake or populations with marine larval dispersal, i.e. diadromous populations. Differences in population demographics existed between these habitats, with smaller maximum sizes and significantly smaller sizes at maturation occurring in the rivers compared to the lake. In Moates Lake approximately 93, 6 and 1% were 0+, 1+ and 2+, respectively; while cohort progression in the rivers suggests that most fish do not live beyond their first year. As an adaptable opportunist, G. maculatus can modify its life history strategy at a local level to persist in varied and sometimes unpredictable environments.

Ontogenetic depth partitioning by juvenile freshwater sawfish (Pristis microdon: Pristidae) in a riverine environment

The freshwater sawfish (Pristis microdon) is a critically endangered elasmobranch. Ontogenetic changes in the habitat use of juvenile P. microdon were studied using acoustic tracking in the Fitzroy River, Western Australia. Habitat partitioning was significant between 0+ (2007 year class) and larger 1+ (2006 year class) P. microdon. Smaller 0+ fish generally occupied shallower water ( 0.6 m. Significant differences in hourly depth use were also revealed. The depth that 1+ P. microdon occupied was significantly influenced by lunar phase with these animals utilising a shallower and narrower depth range during the full moon compared with the new moon. This was not observed in 0+ individuals. Habitat partitioning was likely to be related to predator avoidance, foraging behaviours, and temperature and/or light regimes. The occurrence of 1+ P. microdon in deeper water may also result from a need for greater depths in which to manoeuvre. The present study demonstrates the utility of acoustic telemetry in monitoring P. microdon in a riverine environment. These results demonstrate the need to consider the habitat requirements of different P. microdon cohorts in the strategic planning of natural resources and will aid in the development of management strategies for this species.

The diet and trophic positions of translocated, sympatric populations of Cherax destructor and Cherax cainii in the Hutt River, Western Australia: evidence of resource overlap

This study tested the hypothesis that the introduced yabbie Cherax destructor Clark, 1936 has the potential to compete with the endemic marron Cherax cainii Austin, 2002 for food resources. Multiple stable isotope analyses were conducted in the Hutt River, Western Australia, in summer (December) and winter (July), 2003. Summer samples indicated that these species occupied similar predatory trophic positions when their assimilated diet consisted of a large proportion of Gambusia holbrooki. Although C. cainii continued to assimilate mostly animal matter based on winter signatures, those of C. destructor appeared to shift towards a more herbivorous trophic position. The study suggests that C. destructor and C. cainii may be keystone species in the Hutt River, possibly altering the cycling of nutrients and structure of the aquatic food web since their introduction into this system. The ecological implications of the continued invasion of C. destructor into the aquatic systems of south-western Australia, particularly with regard to competition with the other endemic freshwater crayfishes, are discussed.

Salinity tolerances of endemic freshwater fishes of south-western Australia: implications for conservation in a biodiversity hotspot

Secondary salinisation represents an important threat to terrestrial and aquatic habitats throughout the world. In south-western Australia, widespread salinisation of waterways has caused large range reductions in the highly endemic freshwater fish fauna. We hypothesised that differences in the distributions of three fish species within the salinised Blackwood River would be related to their salinity tolerances. Galaxias occidentalis was widespread throughout the catchment, whereas Nannoperca vittata was restricted to the main channel and freshwater tributaries of the lower catchment, and Nannatherina balstoni was restricted to those tributaries and a perennial section of the main channel that received a considerable amount of fresh groundwater. Acute salinity tolerances (Effect Concentrations) of G. occidentalis and N. vittata were similar (EC50 ∼14.6gL-1), but significantly greater than that of N. balstoni (EC50 ∼8.2gL-1). The greater geographical range of G. occidentalis, compared with N. vittata, may be a consequence of the dispersal capability of the former species, and the lower salinity tolerance of N. balstoni contributes to its highly restricted range. The findings demonstrate that secondary salinisation has greatly impacted these freshwater fishes, and fresh groundwater refuges, predicted to decrease due to reduced rainfall, appear crucial in maintaining remnant populations.

Parasites of native and exotic freshwater fishes in south-western Australia

In this study, 1429 fishes of 18 different species (12 native and six exotic) were sampled from 29 localities to compare the levels of parasitism between native and exotic fish species and to examine the relationship between environmental degradation and parasite diversity. Forty-four putative species of parasites were found and most of these appear to be native parasites, which have not previously been described. Two parasite species, Lernaea cyprinacea and Ligula intestinalis, are probably introduced. Both were found on or in a range of native fish species, where they may cause severe disease. Levels of parasitism and parasite diversity were significantly greater in native fishes than in exotic species, and this may contribute to an enhanced demographic performance and competitive ability in invading exotics. Levels of parasitism and parasite diversity in native fishes were negatively related to habitat disturbance, in particular to a suite of factors that indicate increased human use of the river and surrounding environment. This was due principally to the absence in more disturbed habitats of a number of species of endoparasites with complex life cycles, involving transmission between different host species.

Life History and Reproductive Biology of the Gilgie, Cherax Quinquecarinatus, a Freshwater Crayfish Endemic to Southwestern Australia

Abstract The gilgie, Cherax quinquecarinatus, a freshwater crayfish endemic to southwestern Western Australia, occupies a wide range of permanent and temporary aquatic environments. Reproductive and population biology parameters were determined in Bull Creek, southwestern Western Australia. Crayfish were collected monthly from May 2002 to April 2003. The seasonal von Bertalanffy growth curve, fitted for the first 14 months of life for female and male C. quinquecarinatus, had respective curvature parameters (K) and asymptotic orbital carapace lengths OCL∞ (CL∞) of 0.29 and 59.6 (71.2) mm for females and 0.25 and 73.8 (87.0) mm for males, respectively. This equates to OCLs (CLs) of females and males at age 12 months of 14.7 (19.2) and 14.1 (18.4) mm, respectively. Cherax quinquecarinatus was found to mature at a relatively small size, with the length at which 50% of individuals mature L50 for females and males being 18.8 and 24.5 mm OCL (24.1 and 30.9 mm CL), respectively. The majority of C. quinquecarinatus thus first spawned at the end of their second year of life. The potential (ovarian) and pleopodal fecundities of C. quinquecarinatus were relatively low compared to other freshwater crayfish species of similar size, being 81.7 (± 5.93 S.E.) and 77.1 (± 13.76 S.E.), respectively. Cherax quinquecarinatus underwent an extended spawning period, from late winter to late summer (i.e., August to February), with three spawning events facilitated by short brood and rapid gonadal recovery periods, traits consistent with other crayfish species able to exist in temporary environments. Estimates of total mortality (Z) were relatively high at 2.34 and 1.95/year based on age-converted catch curves for females and males, respectively, with a considerable proportion of this attributed to fishing mortality (exploitation rates of 0.76 and 0.75 for females and males, respectively). Cherax quinquecarinatus underwent a life-history strategy that showed characteristics of both a summer (r- strategist) and winter (K-strategist) brooder.