Using genetic and chemical techniques to aid elasmobranch conservation

Tiktak, Guuske Paulien (2025) Using genetic and chemical techniques to aid elasmobranch conservation. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Elasmobranchs encompass some of the most threatened species on our planet, with their biggest threat being overfishing, either when they are targeted as a group themselves (i.e., for fins and meat) or when they are incidentally caught as bycatch. Elasmobranch products are sold and consumed all over the world, with threatened and CITES-listed species dominating the trade. Conservation and management of elasmobranch populations requires a multidisciplinary approach and to address some of these conservation issues, this thesis uses genetic and chemical techniques to aid elasmobranch conservation. In Chapter 2 a total of 85 studies were included in a systematic review, which found that 11.3% of samples were mislabelled and 10.1% labelled using umbrella terms. Species listed as threatened made up 48.7% of mislabelled elasmobranchs and 53.7% of species labelled using umbrella terms. In Chapter 3, I developed a paper-based Lab-on-a-Chip (LOC) for the identification of three threatened and CITES-listed sharks (bigeye thresher, pelagic thresher and shortfin mako shark) that incorporated DNA amplification and visualisation using Loop Mediated Isothermal Amplification (LAMP). I was able to successfully identify the three sharks, where when target species where present there was a simple colour change from pink to yellow. In Chapter 4, a total of 176 studies were included in a systematic review of pollutants in elasmobranchs. The highest concentrations of pollutants were found in sharks occupying top trophic levels (Carcharhiniformes and Lamniformes). A human health risk assessment carried out in both Chapter 4 and 5 identified that humans consuming shark as little as once a week are exposed to more mercury than is recommended by the US EPA. This not only poses a risk to local fishing communities and international consumers of shark-based products but also those subject to the widespread mislabelling of elasmobranch products. Overall, this thesis has helped to address a significant gap in our understanding of mislabelling and pollutant levels in elasmobranchs. Additionally, the LOC for identifying CITES-listed sharks has promising implications for shark conservation efforts as it has the potential to enhance the monitoring of trade in protected and threatened shark species. Key words: Elasmobranchs; Conservation; Genetics; Pollutants; Lab-on-a-Chip (LOC); Threatened