Abstract
To improve ability to detect white sharks without the need for tags, or visual census, we developed a species-specific environmental DNA (eDNA) assay that targets a 163 bp fragment of the white shark (Carcharodon carcharias) mitochondrial cytochrome B gene on a digital droplet PCR (ddPCR) platform. We used this marker to detect white shark DNA in 250 ml water samples taken from across two sites in Santa Barbara, California (USA) frequented by juvenile white sharks. We did not detect white shark DNA in samples from two neighboring sites where sharks are presumably absent, suggesting that eDNA can indicate nearby white sharks. This marker development, testing, and opportunistic application in a region with known distributions of white sharks indicates that environmental DNA could be developed further to monitor white sharks, thereby informing conservation planning and public safety. With the potential increase in white shark populations due to decades of protection, there is a need for fishery independent methods for assessing white shark distributions, and eDNA may provide be an ideal, non-intrusive tool for coastal assessments.
Highlights
Carpinteria, California welcomed visitors with a billboard picturing beach goers and the claim “World’s safest beach” (Reynolds, 2017); that is until vandals defaced the scene with a spray-painted shark fin (KDL pers. obs)
Because white sharks are rarely kept in captivity (Ezcurra et al, 2017), we sought a convenient location where they were likely to be abundant based on telemetry and observations of six white sharks tagged along Padaro Lane, in Carpinteria, California (Figure 1)
The primers and probe provided speciesspecific detection for DNA from white shark but not from other elasmobranchs found in southern California (Table 1, and see Supplementary Figure 1 for alignments), including the shortfin mako and common thresher and basking shark within the same order
Summary
Carpinteria, California welcomed visitors with a billboard picturing beach goers and the claim “World’s safest beach” (Reynolds, 2017); that is until vandals defaced the scene with a spray-painted shark fin (KDL pers. obs). We sought to develop an active surveillance assay that is potentially more sensitive and is species-specific to detect white sharks from a water sample.
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