Suchergebnisse

Context
Mass strandings of cetaceans occur frequently in Tasmania, Australia, with efforts made by authorities to rescue stranded animals when possible. Determining the fate of rescued cetaceans following a stranding event is essential to assess individual survival and the effectiveness of rescue procedures; however, few studies have monitored animals post-release and their fate remains largely unknown. Satellite telemetry of released cetaceans provides a means of assessing the short- to medium-term success of stranding management techniques.


Aims
To examine the short- to medium-term survival and at-sea movement and behaviour of long-finned pilot whales (Globicephala melas) on their release following a mass-stranding event.


Methods
We deployed satellite transmitters on 5 of 11 long-finned pilot whales returned to sea after a mass-stranding event in Tasmania in November 2008. The transmitters, incorporating a corrosive link, were attached to the dorsal fin of two adult and three subadult whales before release. The resulting telemetry data were examined to infer behaviour of the tagged individuals post-release, including swim speeds and how individuals moved in relation to each other over time.


Key results
Tracking data established the success of the rescue attempt and confirmed survival of stranded individuals in the short term (12–32 days) following release. Although conditions required whales to be released individually, data showed the tracked whales re-united immediately after release. A subsequent aerial survey revealed that they had formed a larger group with six additional whales which then separated and reformed.


Conclusions
Short-term survival of long-finned pilot whales following mass stranding and rescue was confirmed and behaviour was consistent with known behavioural information for this species. Importantly, the present study demonstrated physical recovery from a traumatic event in spite of delayed rescue and that individuals successfully re-united following individual release.


Implications
The present study confirmed that the rescue procedures employed were successful in the management and release of mass-stranded long-finned pilot whales, at least in the short term. It also provided some insight into the at-sea behaviour of this highly social and gregarious species and supported the theory behind stranding management techniques and the considerable resources and effort required for rescue of stranded cetaceans.

Context Good body condition in juvenile marine mammals is crucial for survival and, therefore, population demography. Australian fur seals, endemic to Australia, recently established a breeding colony at the southern edge of their range, at The Needles, a small group of islands in south-west Tasmania (43.6614°S) and a significant distance from their core breeding range in Bass Strait. Aims We aimed to compare pup body condition at two breeding colonies, distinct in time since establishment and latitude. Specific aims were to: (1) establish the timing of peak pupping, to compare condition of known-age pups, and determine a baseline at The Needles; (2) investigate pup body condition over time at an established colony; and (3) gain insight into the effects of environmental conditions on pup body condition. Methods We conducted a colony comparison of pup body condition using condition indices at The Needles and an established breeding colony in Bass Strait, Tenth Island, for the 2019/20 and 2020/21 breeding seasons. Pup body condition was quantified at Tenth Island over 18 years (2003–2020) using a long-term morphometric dataset. To establish breeding phenology at these two colonies, we determined peak pupping date for the 2019/20 breeding season using daily pup counts. We assessed the effect of environmental parameters on body condition for the long-term dataset. Key results Pups from The Needles displayed significantly higher body condition than those from Tenth Island, despite similar peak pupping date. Breeding phenology was consistent with published timing for Australian fur seals. Pup body condition at Tenth Island over the 2-year colony comparison was comparable to the historical average. Environmental drivers that affect maternal foraging efficiency are linked to pup body condition. Conclusions Higher pup body condition at The Needles is likely underpinned by better foraging conditions resulting in increased pup provisioning levels. Our results indicate that south-west Tasmania is a region of foraging and emerging breeding importance for Australian fur seals. Implications Future research to monitor pup body condition, maternal foraging behaviour and ecosystem productivity at The Needles will help to provide greater understanding of likely population trajectories at this southernmost breeding site for Australian fur seals.

Context Artificial intelligence algorithms are beneficial for automating the monitoring of threatened species. Devil facial tumour disease (DFTD) is an endemic disease threatening Australia's Tasmanian devil. The disease is a cancer that can be transmitted from one devil to another during social interactions. Cameras and trapping techniques have been employed to monitor the spread of the disease in the wild. The use of cameras allows for more frequent monitoring of devils than does trapping, but differentiating wounds from tumours in images is challenging, and this requires time and expertise. Aim The purpose of this work is to develop a computer vision system to assist in the monitoring of DFTD spread. Method We propose a system that involves image segmentation, feature extraction, and classification steps. U-net architecture, global average pooling layer of pre-trained Resnet-18, and support vector machine (SVM) classifiers were employed for these purposes, respectively. In total, 1250 images of 961 healthy and 289 diseased (DFTD) devils were separated into training, validation, and testing sets. Results The proposed algorithm achieved 92.4% classification accuracy for the differentiation of healthy devils from those with DFTD. Conclusion The high classification accuracy means that our method can help field workers with monitoring devils. Implications The proposed approach will allow for more frequent analysis of devils while reducing the workload of field staff. Ultimately, this automation could be expanded to other species for simultaneous monitoring at shorter intervals to facilitate broadened ecological assessments.