The Maugean Skate has been recorded in only two isolated estuaries: Bathurst Harbour and Macquarie Harbour in south-western/western Tasmania. This constitutes one of the most limited distributions of any known extant elasmobranch. As a result, the species is listed as Endangered under Tasmania’s Threatened Species Protection Act and the Commonwealth Environmental Protection and Biodiversity Conservation Act 1999.
Even though it was first discovered in Bathurst Harbour, most knowledge of the species stems from the Macquarie Harbour population. In fact, only four individuals have been reported in Bathurst Harbour, with the last reported sighting in 1992. Environmental conditions in Macquarie Harbour have changed markedly in recent times, due to anthropogenic activities in and around the estuary. These activities include historical mining, hydro-electric generation and alteration of natural river flows, and marine fish farming.
Previous research has shown clear signs of population stress and evidence of detrimental impacts of degraded environmental conditions on the Maugean Skate in Macquarie Harbour. There is a critical need to elucidate the status of the Maugean Skate in Bathurst Harbour to strengthen the evidence base for effective conservation plans and specific recovery actions.
A better understanding of the status of the Maugean Skate in Bathurst Harbour will assist in determining conservation actions and future research to ensure the persistence of this unique species.
Approach and findings
This project collected environmental DNA to determine the presence of the Maugean Skate in Bathurst Harbour. Sampling in Bathurst Harbour occurred across two surveys in November 2021 and February 2022 and positive eDNA controls were collected in Macquarie Harbour in December 2021.
Water within one metre of the seafloor was collected at various sites in Bathurst Harbour and filtered using a self-preserving eDNA sampling system. Following each survey, DNA from the samples was extracted and analysed through qPCR amplification. Mitochondrial primer pairs from two gene regions were used to detect the presence of Maugean Skate DNA in the samples. Where possible, positive detections were sequenced, and their identity verified.project collected environmental DNA to determine the presence of the Maugean Skate in Bathurst Harbour. Sampling in Bathurst Harbour occurred across two surveys in November 2021 and February 2022 and positive eDNA controls were collected in Macquarie Harbour in December 2021.
Maugean Skate DNA was successfully extracted and amplified. Detection from environmental samples in Macquarie Harbour confirms that eDNA assays and field sampling protocols as employed here can be used as a tool to monitor the presence of rare and cryptic elasmobranchs in remote or challenging environments.
Sufficient concentrations of Maugean skate DNA were not found anywhere in Bathurst Harbour to allow positive identification based on eDNA alone. There were multiple putative detections in the second survey, but only four of these yielded sufficient material to allow sequencing. Sequencing confirmed that these four samples were extremely low quantity Maugean Skate DNA detections. The total number of DNA copies per qPCR reaction in the Bathurst Harbour samples (4-6) was two orders of magnitude lower than concentrations in environmental samples from Table Head in Macquarie Harbour (approximately 2000 copies of DNA per reaction).
Possible explanations for the extremely low traces of Maugean Skate DNA seen in Bathurst Harbour are:
- Only very few individuals exist in Bathurst Harbour.
- Latent DNA left over in the sediments from biological material, such as egg cases, was released due to the unusual environmental conditions in Bathurst Harbour during the summer of 2022.
- Maugean skate are rare and transient within the system, although this scenario does not align with their known adaptability, resilience, and preference for estuarine environments.
Regardless of which of the scenarios presented above is correct, it is now clear that the vast majority, if not all, of the remaining Maugean skate live in Macquarie Harbour.
Outcomes
The findings of this study document the vulnerability of the Maugean skate and the need for urgent conservation action and continued research focused on the Macquarie Harbour population to ensure the persistence of this unique species. A follow-up Marine and Coastal Project is using next generation genetic sequencing and novel imaging survey tools to delineate and estimate the size of the Macquarie Harbour Maugean Skate population.
Project location
Bathurst Harbour and Macquarie Harbour, Tasmania
Project leader
Research partners
University of Tasmania
CSIRO
Research users
Department of Climate Change, Energy, the Environment and Water
Tasmanian Government