Genetics: a vital tool for understanding connectivity and the ability of a threatened marine species (Maugean skate (Zearaja maugeana)) to withstand future challenges

The Maugean skate (Zearaja maugeana) has been classified as Endangered by the IUCN and the Australian EPBC Act, based on its low estimated population size and restricted range in one estuarine embayment in western Tasmania, Macquarie Harbour (MH). Given Z.maugeana’s highly restricted distribution, this species is vulnerable to environmental changes caused by natural and anthropogenic forces present in MH. With no knowledge existing on population characteristics of Z.maugeana, population genetics was used to investigate habitat use, population connectivity, population structure, genetic diversity and effective population size (Ne) of Z.maugeana in MH. Mitochondrial DNA (mtDNA) results showed no significant variation for 16 individuals for four gene regions, with a haplotype diversity (h) and nucleotide diversity (π) of zero within each region. Genotyping results of 195 individuals using 8 microsatellites suggest the population in MH is one large, interbreeding population with very low genetic diversity (Fst=0.35±0.2). Low genetic diversity in mtDNA and microsatellites could indicate a genome wide lack of genetic diversity, which may reduce the ability of Z.maugeana to withstand future environmental changes. Environmental DNA (eDNA) was investigated as an additional genetic tool for determining habitat use and connectivity of endangered elasmobranchs in the wild. Zearaja maugeana eDNA was successfully amplified from as little as 1L of marine water collected at depth in MH. Exponential decay models revealed that Z.maugeana eDNA persists 6.4 days in MH water, before dropping below detectable limits of the assay. These results may be incorporated into the development of future eDNA assays for the detection and management of threatened elasmobranchs. Overall, genetics is an important tool for investigating habitat use and connectivity of populations of threatened marine species, providing vital information for conservation and management at appropriate scales. With recent molecular technological advances, genetics can be incorporated into all population studies on threatened marine species, without requiring extensive genetic expertise.