Elasmobranch (sharks and rays) interaction with plastic pollution from global and local perspectives, via entanglement within anthropogenic debris and synthetic fibre ingestion

Abstract

Plastic pollution is a known threat to a host of marine organisms across the world. Research in recent years has exposed numerous negative impacts on some of the world’s most threatened marine species, including turtles, cetaceans and pinnipeds. The impact of plastic pollution on elasmobranchs, however, has been relatively understudied. Sharks and rays are widely accepted to be two of the most threatened marine species in the oceans, most notably due to anthropogenic impacts including direct fisheries and bycatch. Their relationship with plastic pollution is only now being investigated in further detail. Previous studies have alluded to damaging effects on sharks and rays as a result of plastic pollution but have lacked in wide synthesis of existing information and empirical evidence. In this thesis, the impact of entanglement within and ingestion of plastic is highlighted for sharks and rays both globally and locally in the North-East Atlantic. Chapter one aimed to collect existing information on the occurrence and distribution of elasmobranch entanglement events, using a systematic literature review and novel data collection from social media site “Twitter”. Our results highlighted ghost fishing gear to be the most common entangling material for sharks and rays globally, consistent with previous studies on other marine species. The review also highlighted the lack of standardised reporting for elasmobranch entanglement and therefore resulted in the creation of an online entanglement report form for sharks and rays (ShaREN), allowing citizen scientists across the world to report entanglement incidents quickly and efficiently. Chapter two investigated the presence of microplastics and synthetic contaminant particles in four species of demersal shark found in the North-East Atlantic. Almost 70% of sharks analysed contained at least one contaminant particle, 2 however no significant relationship between size/weight and number of contaminants was identified, although further analysis was recommended. The study highlighted the ubiquity of synthetic fibres such as rayon and viscose, commonly found in clothing items, as contaminants in the marine environment. Chapter two presents the first empirical evidence of microplastic ingestion by UK shark species and highlights the pervasive nature of microplastic pollution off the English coast. While these two threats are unlikely to have significant population impacts on sharks and rays globally, similar to that of direct fisheries and bycatch, they are identified to be of clear animal welfare concern for these species. Entanglement within and ingestion of plastic is symptomatic of a degraded marine environment and highlights the need for policy-makers, scientists and stakeholders to work together to mitigate this issue for all marine species.