Abstract
Environmental DNA (eDNA) is a relatively new tool for the detection of rare, threatened and invasive species in water bodies. In this study we investigated the utility of an eDNA approach in detecting the Critically Endangered largetooth sawfish Pristis pristis in freshwater habitats in northern Australia. Water samples were collected from large aquaria mesocosms containing largetooth sawfish and other aquatic species, and floodplain waterholes and the main river channel of the Daly River, Northern Territory. Water samples were filtered using a 20 mu m nylon filter. DNA was extracted from filters and analysed with PCR using species-specific mitochondrial cytochrome c oxidase subunit I (COI) primers designed to amplify only largetooth sawfish DNA. PCR products were cleaned and the COI gene sequenced to confirm the species identity. Using 3 aquaria, with one containing a largetooth sawfish, this method positively identified sawfish only in the correct aquarium. In the field water samples, 7 of 8 floodplain waterholes produced a sawfish eDNA PCR product, while eDNA was not detected in the main river channel. Based on gillnet sampling and traditional ecological knowledge, largetooth sawfish were known to occur at half of the waterhole and floodplain sites that tested positive for sawfish eDNA. These results demonstrated that an eDNA approach to detecting largetooth sawfish can produce reliable outcomes and can be used as a survey tool to help with conservation efforts for this and other threatened elasmobranchs.
Highlights
Sawfishes (Family Pristidae) are the most threatened family of elasmobranch (Dulvy et al 2014), with all 5 species listed on the IUCN Red List of Threatened Species as either Critically Endangered or Endangered (IUCN 2015)
DNA was successfully PCR amplified using the species-specific c oxidase subunit I (COI) primers from all aquaria water samples containing the largetooth sawfish specimen
This confirmed that the Environmental DNA (eDNA) COI marker was specific for largetooth sawfish and could be used to detect eDNA from the species in a complex and mixed DNA template sample
Summary
Sawfishes (Family Pristidae) are the most threatened family of elasmobranch (sharks and rays) (Dulvy et al 2014), with all 5 species listed on the IUCN Red List of Threatened Species as either Critically Endangered or Endangered (IUCN 2015). Public encounter data have been used to determine the distribution and habitat associations of smalltooth sawfish Pristis pectinata in Florida (Poulakis & Seitz 2004, Wiley & Simpfendorfer 2010, Waters et al 2014) This approach is less expensive, but relies on the distribution of observational effort, considerable outreach, the ability of the public to identify species correctly and their willingness to report encounters ( given the apprehension over reporting the capture of a listed protected species) to gather sufficient data (Wiley & Simpfendorfer 2010). Targeted interviews with fishers have been used to examine sawfish distribution and abundance (Leeney & Poncelet 2015, Leeney & Downing 2016) These types of survey have proved useful in determining the changes in the distribution and abundance of sawfishes over time and can be carried out with limited resources. To enhance the availability of information on the distribution of sawfishes, further detection techniques that are reliable, relatively inexpensive and easy to implement need to be developed and tested
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