Abstract
AbstractThe number of human–shark interactions has increased worldwide during the past decade resulting in injuries and fatalities. In Australia, the white shark (Carcharodon carcharias), tiger shark (Galeocerdo cuvier), and bull shark (Carcharhinus leucas) are responsible for the majority of fatal incidents. On the southeast coast of Australia, monitoring programs currently rely on SMART (Shark‐Management‐Alert‐in‐Real‐Time) drumlines and mesh nets to catch, tag, and monitor shark movement. However, these methods are laborious, costly, and involve the capture of only a fraction of the total shark population. Here, we develop a multiplex environmental DNA assay capable of detecting all three shark species simultaneously from water samples by targeting conserved but specific mitochondrial sequences that are characteristic of each species. The specificity of the assay was validated by testing for cross‐amplification across a range of non‐target but co‐occurring shark species from eastern Australia. We test the sensitivity of the assay on water samples collected from shark capture events and sites where these shark species are known to frequent, and undertake DNA sequencing on positive samples to confirm species haplotype authenticity. Samples collected from one of these sites also demonstrate that eDNA detections are dependent on shark activity in the area. This assay will allow for rapid detection of DNA from each shark species in water samples, providing a cost‐effective alternative for monitoring sharks along the east coast of Australia and potentially elsewhere.
Highlights
Sharks are critical apex predators, which underpin the trophic structure and functionality of marine ecosystems, yet many shark species globally have suffered major declines in recent decades due to human activities
The most problematic shark species include the white shark (Carcharodon carcharias Linnaeus 1758), tiger shark (Galeocerdo cuvier Péron & Lesueur 1822), and bull shark (Carcharhinus leucas Müller & Henle 1839), which are responsible for ~56% of all bites and ~98% of all fatalities over the last three decades globally (McPhee, 2014)
The most successful non-lethal monitoring program to date has been the Shark Management Strategy (SMS), which currently operates in eastern Australia and is one of the shark mitigation programs run by the New South Wales Government
Summary
Sharks are critical apex predators, which underpin the trophic structure and functionality of marine ecosystems, yet many shark species globally have suffered major declines in recent decades due to human activities. While the size of resident C. leucas and G. cuvier populations remain uncertain, it has been estimated that approximately 2500–6750 C. carcharias persist on the Australian east coast (Hillary et al, 2018) These figures suggest the number of SMS program tagged sharks represent only a fraction of the total population, highlighting the need for more innovative and cost-effective methods for the detection and monitoring of problem shark species in eastern Australia. In regions where there is sympatric occurrence of multiple target shark species, careful consideration needs to be given to the specificity of eDNA assays in order to reliably discriminate between co-occurring species This is pertinent in eastern Australia where there is significant overlap in seasonality and habitat use of C. carcharias, G. cuvier, and C. leucas (Espinoza et al, 2016; Holmes et al, 2014; Lee et al, 2019; Lipscombe et al, 2020; Spaet et al, 2020a, 2020b). We expect the application of the assay could help reduce risks of shark attack and allow further insights into patterns of species movement, near-shore visitation, and habitat use for informing future conservation management
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