David Morgan

Remote underwater video, established in marine ecosystems, has infiltrated the toolbox of researchers in estuarine and freshwater systems more recently. Arguably, the greatest limiting factor in the application of underwater video for surveying many freshwater and estuarine ecosystems is water clarity. Indeed some systems are perpetually turbid while others are intermittently turbid in response to flow events or tidal fluctuations. We used Baited Remote Underwater Video Stations (BRUVS) to survey the fish assemblage in a turbid tropical estuary on Cape York in northern Australia. Poor water clarity in the upper estuary prevented the identification of fishes that were not close to the baits. In an attempt to address this issue, we tested the attractiveness of two bait types and unbaited camera controls and employed Underwater Dark Channel Prior (UDCP) to enhance image quality and enable more accurate identification of species with a greater degree of certainty. In addition we present the outcomes of deploying a camera within the immediate area of interest of a large estuarine reptile.

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.

Temperature affects most physiological processes which in turn impact animal behaviour and ecology. In ectotherms, both short- and long-term variations in temperature impact physiological (i.e. locomotor and metabolic capacity) and ecological (i.e. body condition and growth) performance and thus affect survival. It is therefore critical to understand the mechanisms driving these relationships. Here, we investigated the impact of seasonally changing temperature on the ecological and physiological performance of juvenile free-ranging largetooth sawfish (Pristis pristis) in its riverine nursery in North Western Australia. Animal-attached accelerometers, revealed that despite a 10°C increase in temperature, sawfish were active and displayed substantial burst-swimming capacity. Physiological performance, as ascertained by locomotory capacity, increased in the warmer late dry season conditions, whereas timing and duration of activity did not. Contrary to the physiological performance, late season sawfish were poorer condition that those in the early season. Activity was primarily crepuscular, irrespective of the season. This suggests that even though locomotory performance of juvenile sawfish increased at greater temperature, foraging activity and thus energy intake was not sufficient to maintain body condition, resulting in declining growth. Contrary to popular belief, seeking warmer temperatures can represent a disadvantage for juveniles under certain scenarios. Especially for individuals that are intake limited, greater temperatures and associated metabolic rates are disadvantageous and can result in lower growth rates and potentially starvation. Physiological and ecological performances may thus respond differently to warming temperatures, emphasizing that ‘optimal’ temperatures may be highly context dependent. Ecological scenarios responsible for mediating growth performance are discussed and integrated into a classic bio-energetics framework.