Alan Lymbery

Findings from my Honours research were presented at the ASFB Conference in Sydney 2015. The presentation begins by briefly introducing the definition behind aestivation, before touching on the climate change that has occurred within the south-west of Western Australia. Following this, the two model species, salamanderfish and black-stripe minnow were introduced, before aims of research, methods and results were discussed. Finally, I concluded the talk with the significance of the findings including potential increases in listing for both species, the potential for creating artificial refuge pools to help increase the resilience of each species, and finally areas of future research. Acknowledgements for co-authors, and collaborators are listed at the end, and my sincere apologies if I have left anyone from this. This presentation provides bullet points on each slide, and is best viewed accompanying the full thesis paper

Goldfish Carassius auratus has been widely introduced across the globe and feral populations are known to have considerable ecological impacts within the receiving environments. Despite centuries of domestication and its current widespread distribution, there is a dearth of information on the spatial and temporal movement patterns of this species, which limits the understanding of the impacts of introduced populations and hampers the development of effective control measures. The current study examined the movement patterns of an introduced population of C. auratus in a regulated south-western Australian river using passive acoustic telemetry. The species had a high residency index within the array (mean 0.64 ±0.06 S.E.). Mobility was high, with the mean minimum distance travelled within the array for individuals over the study period equalling 81.5 rkm (linear river kilometres, which was the sum of the distances of all movements between receivers and an underestimation of actual distances travelled); with one fish moving 231.3 km (including 5.4 km in a 24 hour period). Importantly, C. auratus displayed notable seasonal movement patterns including a clear shift to certain habitats during its breeding period; with most individuals being detected in an off channel wetland during that time. The results of this study have considerable implications for developing control programs for the species, such as targeting connections to off-channel lentic systems during the breeding period. Finally, the presentation will touch on the subsequent study that tracked the movements of Black Bream in the heavily modified estuary habitat downstream of the Goldfish acoustic array that aimed to refine the operation of floodgate barriers.

Among the many environmental conditions that structure estuarine fish assemblages, salinity is perhaps the most influential. While most estuaries have a positive salinity gradient, where salinity declines in an upstream direction, and several exhibit the reverse pattern, very few experience both salinity regimes within a typical year. One estuary that does, however, is the shallow Vasse- Wonnerup Estuary, which receives no freshwater discharge during summer. In this system, salinity ranges from 0 (upstream) to 15 (mouth) during winter and 130 (upstream) to 35 (mouth) in summer. The fish faunas of the shallow and deeper waters were sampled on a seasonal basis for two years. The nearshore fish fauna was dominated by atherinids and gobies, which complete their life cycle within the estuary and are highly euryhaline, but also included 18 species of marinespawning fish that utilise the system as a nursery area. Species richness and density decreased with increasing distance from the ocean and faunal composition changed markedly seasonally, in response to massive changes in salinity. The fish of the deeper waters comprised predominantly marine-spawning species, with the notable exception of Black Bream, which is solely estuarine. This species, together with two mugillids, largely dominated these deeper waters and their abundances remained relatively consistent. However, the prevalence of other species varied with changes in salinity and/or the frequency and duration of bar openings. This estuary is used as model for predicting the impact of climate change on seasonally-open estuaries in southern Australia, which will become more saline in the future.

The Goldfish (Carassius auratus) is arguably the most popular and well known ornamental fish species and this popularity has been responsible for feral populations of Goldfish being recorded from almost every Australian state and indeed throughout much of the world. While generally regarded as a freshwater fish, a preliminary study of the fish faunas of the Vasse-Wonnerup by the authors recorded Goldfish in the system during a time when the estuary was salty (~17 ppt, i.e. half full strength seawater). A population of Goldfish has been known to occur in the Vasse River since the early 1990s, however, it was incorrectly thought that the Goldfish could not penetrate into the Ramsar listed Vasse-Wonnerup wetland, as, at certain parts of the year, the system became salty. Worringly, in Europe, research has shown that several introduced freshwater fish (e.g. the Zander; Stizostedion lucioperca) have been able to survive in estuarine waters for long enough to use these systems as a ‘salt bridge’ to invade other, previously uncolonised, freshwater environments. As Goldfish are known to resuspend nutrients and increase turbidity during their foraging, exacerbate algal blooms, decrease aquatic vegetation and predate on and compete with native species, they could pose a major threat to health of the Vasse-Wonnerup wetland and its other tributaries. This poster and presentation document (i) the abundance of goldfish in seven regions of the Vasse-Wonnerup wetland and in each of its four tributary rivers, including the Vasse River, which has an abundant Goldfish population, seasonally over 18 months; (ii) the results of a set of laboratory experiments to test the acute and gradual salinity tolerances of Goldfish from the Vasse River and (iii) a comparison of these tolerances with those obtained from Goldfish bought from a pet store. The management implications of these findings are then discussed.

The Vasse-Wonnerup wetland is an ecologically important area for birds and is listed as a 'Wetland of International Importance' by the Ramsar Convention. However, despite extreme eutrophication, regular algal blooms and large fish kills, most recently in April 2013, almost no faunal research has been undertaken. This poster and presentation details the spatial characteristics of the fish fauna of seven regions of the estuary, each of which differ in their environmental characteristics and illustrates how they change through the year as salinity changes. For example, the Lower Vasse River Wetland (LVRW) remains entirely freshwater all year, while the Vasse and Wonnerup Estuaries fluctuate seasonally from freshwater (~0) to markedly hypersaline (~80) and the Deadwater and Wonnerup Inlet remain marine. Species richness and fish density were the highest in the marine areas (Deadwater and Wonnerup Inlet) and lowest in the LVRW during all seasons. No species were recorded in the upper Vasse and Wonnerup estuaries in summer and autumn due to the very high salinities and shallow waters. The fish fauna differed markedly among most regions, with the biggest differences occurring between the marine areas and the LVRW. The fish in the former regions were dominated by estuarine species, i.e. the Elongate Hardyhead (Atherinosoma elongata), Black Bream (Acanthopagrus butcheri) and Southern Longfin Goby (Favonigobius lateralis), while species with preference for oligohaline/freshwaters i.e. the Western Hardyhead (Leptatherina wallacei) and Swan River Goby (Pseudogobius olorum) dominated the LVRW. Two introduced species, namely the Goldfish (Carassius auratus) and Eastern Gambusia (Gambusia holbrooki), were also captured. The trends in fish composition are then correlated to changes in salinity to demonstrate the effect that the massive fluctuations in this variable have on the fish fauna and show the impact that particular management decisions have on the fish community of the Vasse-Wonnerup.