Wayne M. Koster

Catadromous migrations by female tupong (Pseudaphritis urvillii) in coastal streams in Victoria, Australia

Understanding migratory requirements is critical for the conservation of diadromous fishes. Tupong (Pseudaphritis urvillii) are diadromous fishes found in freshwater and estuarine regions of south-eastern Australia. Previous studies have hypothesised that mature female tupong undertake downstream spawning migrations from freshwater to the estuary or sea, with a compensatory return of juveniles, and possibly spent fish, back upstream. We applied acoustic telemetry to test this hypothesis. We tagged 55 female tupong in two river systems in Victoria, Australia, and tracked movements for 4- to 6-month periods over 2 years. Thirty-one fish undertook rapid downstream migrations and then appeared to move through the estuary and out to sea between May and August in each year. Migration was associated with relatively high river discharges, and movement from the estuary to the sea tended to occur most frequently during intermediate moon phases. Low rates of movement between September and April suggested that tupong inhabited restricted home ranges outside of the spawning season. The apparently disparate migratory patterns of female (catadromous) and male (non-diadromous) tupong are rare amongst fishes globally. Differential exertion of a range of selective pressures may have resulted in the evolution of sexual differences in migratory modes in this species.

Provision of environmental flows promotes spawning of a nationally threatened diadromous fish

Detailed understanding of flow-ecology requirements for aquatic biota underpins the use of environmental flows as an effective restoration tool in regulated rivers. However, flow recommendations are often overly simplistic and insufficient to provide the necessary environmental requirements for these biota. This is often due to failure to gain and integrate information on individual species ecology and, by using coarse generalisations, about flow-ecology responses. To inform more effective delivery of environmental flows, we investigated spawning responses of the threatened Australian grayling (Prototroctes maraena) to environmental flows over 2 years in three coastal rivers. Spawning activity was highest during within-channel flow pulses, especially during periods of environmental flow delivery. Peak spawning occurred in late autumn and was positively related to flow duration. This result has important implications for environmental flows management in regions where water is scarce and there is potential conflict among multiple users because, for Australian grayling, it is not necessarily the volume of water released that is important, but how the flow is delivered. Our study demonstrated the importance of quantifying flow-ecology relationships via targeted monitoring and research so as to develop appropriate flow regimes, and should encourage managers to examine more critically the logic behind generalised environmental flow objectives.

Influence of streamflow on spawning-related movements of golden perch Macquaria ambigua in south-eastern Australia

In this study, linkages were examined between movement and spawning behaviour for golden perch Macquaria ambigua in a lowland river by integrating acoustic telemetry and egg and larval drift sampling over 4 years. Movement was strongly seasonal, being most prevalent during the spawning season (spring to early summer), and occurred primarily downstream into the lower river reaches during elevated flows. A very strong association was found between the occurrence of spawning and long-distance M. ambigua movement. The results also revealed that targeted environmental water allocation can promote movement and spawning of this species. By integrating multiple analytical approaches and focusing on key life-history events, this study provides an improved picture of the life history and flow requirements of M. ambigua. The findings can help guide the development of effective environmental flow recommendations.

Make the Most of the Data You’ve Got: Bayesian Models and a Surrogate Species Approach to Assessing Benefits of Upstream Migration Flows for the Endangered Australian Grayling

Environmental water managers must make best use of allocations, and adaptive management is one means of improving effectiveness of environmental water delivery. Adaptive management relies on generation of new knowledge from monitoring and evaluation, but it is often difficult to make clear inferences from available monitoring data. Alternative approaches to assessment of flow benefits may offer an improved pathway to adaptive management. We developed Bayesian statistical models to inform adaptive management of the threatened Australian grayling (Prototroctes maraena) in the coastal Thomson River, South-East Victoria Australia. The models assessed the importance of flows in spring and early summer (migration flows) for upstream dispersal and colonization of juveniles of this diadromous species. However, Australian grayling young-of-year were recorded in low numbers, and models provided no indication of the benefit of migration flows. To overcome this limitation, we applied the same models to young-of-year of a surrogate species (tupong—Pseudaphritis urvilli)—a more common diadromous species expected to respond to flow similarly to Australian grayling—and found strong positive responses to migration flows. Our results suggest two complementary approaches to supporting adaptive management of Australian grayling. First, refine monitoring approaches to allow direct measurement of effects of migration flows, a process currently under way. Second, while waiting for improved data, further investigate the use of tupong as a surrogate species. More generally, alternative approaches to assessment can improve knowledge to inform adaptive management, and this can occur while monitoring is being revised to directly target environmental responses of interest.

Threatened Fishes of the World: Galaxiella pusilla (Mack 1936) (Galaxiidae)

Common name: Dwarf galaxias, eastern little galaxias. Conservation status: Vulnerable (Commonwealth Environment Protection and Biodiversity Conservation Act 1999, IUCN 2002), Threatened (Victorian Flora and Fauna Guarantee Act 1988), Rare (Tasmanian Threatened Species Protection Act 1995). Identification: D 6–9, A 8–11, P 10–14, V 4–6, C 12–14, gill rakers 12–17, vertebrae 36–40 (McDowall & Frankenberg 1981). A scaleless freshwater fish with a fusiform body. Maximum TL ca. 48 mm, commonly to 30 mm. Dorsal fin origin behind anal fin origin. Caudal fin rounded (McDowall & Frankenberg 1981). Colour typically translucent olive-brown dorsally and laterally. Three black lateral stripes on trunk. Ventral surface silvery-white. Sexually dimorphic: males smaller than females, with orange lateral stripe extending through eye, most prominent during breeding season (iridescent purple in females) (Backhouse & Vanner 1978). Illustration by David Crook. Distribution: South-eastern Australia, between Salt Creek (South Australia) and Bairnsdale (Victoria), southward to Flinders Island and northeast and northwest Tasmania (139◦40′–148◦20′ E, 36◦07′–41◦05′ S) (Cadwallader & Backhouse 1983, Chilcott & Humphries 1996, M. Hammer, pers. comm.). Abundance: Patchy distribution although can be locally abundant (Cadwallader & Backhouse 1983, Chilcott & Humphries 1996, Koster 1997). Habitat and ecology: Still or slow-flowing permanent or ephemeral waterbodies, often amongst dense aquatic vegetation (Backhouse & Vanner 1978). May be able to survive dry conditions by taking refuge in crayfish burrows or by aestivating (Humphries 1983, Beck 1985). A sedentary non-migratory species (Andrews 1976). Generalist carnivore feeding mainly on zooplankton (Humphries 1983). Reproduction: Multiple spawner, breeding between winter and spring, adhesive eggs (0.6–1.3 mm) laid individually on aquatic vegetation (Backhouse & Vanner 1978, Humphries 1983). Fecundity 66–247 eggs per female (Humphries 1983). Described as an annual species in the wild, with adults dying soon after spawning (Humphries 1983), although lifespan of at least 2 years observed in aquaria. Threats: Drainage of wetlands, water abstraction, stock damage and water pollution has reduced available habitat and fragmented populations. Interactions with alien fishes, especially eastern gambusia, Gambusia holbrooki, are considered a threat. Conservation actions: Protected under legislation described above. Conservation strategies for Victorian and Tasmanian populations in development. Translocation to several wetlands near Melbourne to establish new populations. Protection and rehabilitation of existing populated habitats. Unsuccessful attempt to eradicate G. holbrooki from a wetland containing Galaxiella pusilla near Melbourne. Conservation recommendations: Protection of remaining habitats and monitoring of populations. Incorporation of G. pusilla habitat requirements into land management strategies. Research to improve understanding of species longevity, aestivation capabilities, species boundaries, population genetics and key habitat requirements. Translocation of G. pusilla, particularly where populations are under threat, may be valuable once a spatial genetic framework is established. Alien fishes should be removed, and stocking prevented where G. pusilla may occur.

Using telemetry data to develop conceptual models of movement to support the management of riverine fishes

As human demands for freshwater resources increase, there is growing concern for the long-term viability of native fish populations globally. Understanding the movements of fish, and how these are influenced by or respond to environmental changes, is a critical knowledge requirement for effective management; however, limited information on the ecological requirements of many fish species currently hinders our ability to sustainably manage fish populations. In this paper, we use four native Australian fish species with contrasting life histories as case studies to demonstrate how data derived from acoustic and radiotelemetry studies can be synthesised into conceptual diagrams to help scientists and managers develop targeted and effective conservation management strategies. Commonalities in the observed movement patterns were observed among the species despite their contrasting life histories, but there were also important differences that need to be recognised in the development of species-specific conservation management strategies. We conclude by discussing how such information has been or could be incorporated into conservation management actions, including the implementation of environmental flow releases and the identification of critical habitats.

Temporal change in fish assemblages in the lower Goulburn River, south-eastern Australia: comment on Pollino et al. (2004)

A recent analysis of fish assemblages in the Goulburn River, south-eastern Australia, used fish survey data collected between 1970 and 2002 to examine spatial patterns in the compositions and relative abundances of fish assemblages in the catchment. Based on this analysis, it was concluded that the native fish fauna of the Goulburn River is in a stressed condition and that introduced species dominate the fish assemblages. Fish survey data collected in 1982–1983 are compared with data collected in 2003–2004 to examine whether fish assemblages in the lower Goulburn River were stable at the temporal scale at which the data were aggregated in the previous analysis. The results show significant differences in fish assemblage composition between the two surveys, suggesting that fish assemblage structure in the lower Goulburn River did not remain stable between 1982–1983 and 2003–2004. The aggregation of data collected over several decades has the potential to confound analysis of spatial variations in fish assemblages and is unlikely to provide a reliable means of assessing their current condition.

Habitat use and movements of Australian grayling (Prototroctes maraena) in a Victorian coastal stream

Riverine fishes are among the most imperilled fauna in the world; however, for many species, there is little or no understanding of their ecological requirements. The Australian grayling (Prototroctes maraena) is a small diadromous fish endemic to rivers in south-eastern Australia that has declined considerably in range and abundance and is listed as threatened nationally. To improve understanding of the species’ movement ecology and to inform the development of conservation management actions, we examined the day-to-day movements and habitat use of Australian grayling (n=7) over 8 weeks by using radio-telemetry. Tagged individuals of Australian grayling typically occupied restricted (i.e. tens to hundreds of metres) reaches of stream, and were mostly located in moderate- to fast-flowing habitats (i.e. glide or run), although, at night, use of slower-flowing habitats (i.e. pools) increased. They also undertook longer-distance downstream movements during a period of increased streamflow. Incorporation of such information into management strategies has the potential to improve our capacity to maintain or re-instate the conditions required to conserve and restore Australian grayling populations.

Deficiencies in our understanding of the hydro-ecology of several native Australian fish: a rapid evidence synthesis

Environmental flows aim to mitigate the impacts of modification of riverine flow regimes by restoring components of the natural flow regime. Explicit evidence-based cause–effect relationships between flow regimes and fish responses are required for defensible flow recommendations. However, flow recommendations are typically based on expert opinion rather than a rigorous test of the available evidence. We used rapid evidence synthesis to systematically review the literature on responses of several native Australian fish to flow-related and other important environmental variables, and tested 13 explicit hypotheses. The hypotheses were related to the condition, reproduction and survival of pygmy perches, carp gudgeons, blackfish and flat-headed gudgeons. The evidence was insufficient to reach strong conclusions for all but three of our hypotheses. Late-spring high flows are associated with increased survival of pygmy perches and carp gudgeons, and exotic fish are associated with decreased survival of these fishes. The evidence that warmer spring water temperatures enhance their reproduction was inconsistent. The dearth of evidence to support or refute most hypotheses points to substantial gaps in our understanding of hydro-ecology of these native Australian fish, highlighting the need for targeted monitoring and research to further understand key flow relationships for these fish species.