Stephen Beatty

Temperate wetlands and estuaries are widely regarded as the most degraded of all aquatic ecosystems, largely due to their exposure to a range of deleterious anthropogenic influences. In the case of the Vasse-Wonnerup Wetland System (VWWS) near Busselton, such impacts have included, land clearing for agriculture and associated severe eutrophication, the diversion of river flow and the construction of barriers (floodgates) to prevent the intrusion of saltwater into the wetland. Although the prevention of flooding and maintenance of surrounding pastoral land has been achieved, the VWWS has also suffered from numerous fish kill events and algal blooms. Current managers are thus faced with the problem of managing the legacy of historical management decisions, while also being under community and political pressure to introduce additional (but non-compromising) measures to reduce the frequency and severity of fish kills and algal blooms. This presentation details the anthropogenic changes that have occurred in the VWWS over the last 200 years and describe the resultant changes in environmental conditions, particularly salinity. The implications of these changes are then explored by comparing the fish and macroinvertebrate communities within different parts of the wetland in different seasons and also to those fauna recorded in other local systems. These analyses show that while the invertebrate fauna comprises wetland/freshwater species, the fish fauna of the VWWS is typical for an estuary. The compositions of both faunas undergo marked seasonal and regional changes in response to changes in salinity. The preliminary results of an acoustic tracking study demonstrate that, by understanding the movements of selected fish throughout the VWWS, management strategies could be refined to mitigate the effects of poor water quality and prevent or reduce the severity of fish kills.

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.

Estuaries are widely regarded as the most degraded of all aquatic ecosystems, largely due to their exposure to a range of deleterious anthropogenic influences. In the case of the Vasse-Wonnerup, such impacts have included, land clearing for agriculture and associated severe eutrophication, the diversion of river flow and the construction of barriers (floodgates) to prevent the intrusion of saltwater into the estuary. Although the prevention of flooding and maintenance of surrounding pastoral land has been achieved, the Vasse-Wonnerup now suffers from regular fish kills and algal blooms. Current managers are thus faced with the problem of managing the legacy of historical decisions, while also being under community and political pressure to introduce additional (but noncompromising) measures to reduce the frequency and severity of deleterious events. This poster details the anthropogenic changes that have occurred in the Vasse-Wonnerup over the last 120 years and describe the resultant changes in environmental conditions and how these influence the fish community. For example, fish faunal composition undergoes marked seasonal and regional changes in response to changes in dramatic changes in water quality and there is the seasonal expatriation of fish from particular regions of the estuary at times during the year. Moreover, growth rates and condition of the key recreational species Black Bream Acanthopagrus butcheri are poor in comparison to nearby systems. Ways to ensure the maintenance of a viable fish population in this estuary are discussed.