Assessing the effect of temperate MPAs on elasmobranch communities

Abstract

Global chondrichthyan (sharks, skates, rays and chimaeras) populations are experiencing alarming declines, driven by intense targeted and incidental extraction. Marine Protected Areas (MPAs) represent one potential solution, which has gained traction in recent years. When implemented effectively, MPAs demonstrate potential to rebuild populations and enable ecosystem recovery. However, their value as an elasmobranch conservation tool remains contested, particularly in temperate waters such as the UK. One essential component of MPA efficacy is the implementation of robust ecological monitoring regimes that allow species trajectories to be characterised and responded to, in real-time. However, several challenges, inherent to both elasmobranchs and temperate marine environments, currently impede adequate elasmobranch surveillance inside MPAs. This thesis addressed these two interlinked components of elasmobranch conservation by 1) exploring the drivers of temperate MPA success and 2) investigating opportunities for elasmobranch monitoring advancements. A literature review was conducted to explore the determinants of MPA success for temperate elasmobranch conservation. Meanwhile, novel monitoring opportunities presented by technological developments were explored, in relation to current method limitations. This was aided by an in-depth field study exploring the impact of Lyme Bay MPA on the elasmobranch community, using a 12-year BRUV dataset. Finally, a drifting pelagic BRUV was developed to address specific difficulties associated with surveying pelagic sharks and their wider food webs. This thesis found that MPAs exhibit potential to benefit temperate elasmobranchs, but their success varies vastly between contexts depending on a variety of social and biophysical factors. Furthermore, studying Lyme Bay MPA identified minimal robust evidence of benefits on the elasmobranch community, and these were mainly afforded to a small-bodied, fast-growing shark (Scyliorhinus canicula). Finally, the pelagic drifting BRUV failed to detect pelagic sharks, but demonstrated value for characterising spatial variation in the wider pelagic food web. Overall, this work indicates that temperate elasmobranch MPAs can represent an effective elasmobranch conservation tool when the necessary guardrails are in place. Furthermore, to guarantee comprehensive elasmobranch protection, MPA establishment should be supported by robust ecological monitoring and a wider network of target and limit-based conservation strategies.