Pinpointing Drivers of Extirpation in Sea Snakes: A Synthesis of Evidence From Ashmore Reef

Ruchira Somaweera,Michelle Glover,Vinay Udyawer,Mathew Hourston,Bruce L Webber,John Keesing,Arne Redsted Rasmussen,Rohan H Clarke,Damian P Thomson,Michael L Guinea,Kate Sanders,Richard Shine,Daniela M Ceccarelli

doi:10.3389/fmars.2021.658756

Abstract

Over the past decade, vertebrate populations globally have experienced significant declines in distribution and abundance. Understanding the reasons behind these population declines is the first step in implementing appropriate management responses to improve conservation outcomes. Uncovering drivers of extirpation events after the fact, however, requires a careful forensic approach to prevent similar declines elsewhere. The once abundant and species-rich sea snake fauna of Ashmore Reef Marine Park, in the Timor Sea, collapsed dramatically in the early 2000s. No such decline has occurred on surrounding reefs. We synthesise the evidence for this collapse and the subsequent slow recovery and evaluate the plausibility of potential drivers for the declines, as well as provide evidence against certain explanations that have been proposed in the past. Our systematic review shows that of seven possible hypotheses considered, at least three are credible and require additional information: (1) stochastic environmental events may have increased the snakes’ susceptibility to pathogens, (2) a resurgence in the abundance of top predators may have induced a localised change in trophic structure, and (3) an acute increase in local boat traffic may have had negative physical impacts. One or more of these factors, possibly acting in combination with as yet other unidentified factors, is the most plausible explanation for the precipitous decline in sea snake populations observed. Based on this position, we identify future research directions with a focus on addressing critical gaps in knowledge to inform and prioritise future management actions.

Highlights

Vertebrate populations across terrestrial, fresh water and marine environments are experiencing precipitous declines in distribution and abundance (Butchart et al, 2010; Hoffmann et al, 2010; Rodrigues et al, 2014; Ceballosa et al, 2017; Sánchez-Bayoa and Wyckhuysb, 2019), such that many species are being pushed toward both local extirpation and global extinction (Wake and Vredenburg, 2008)
Management policies designed without a good understanding of key drivers of population declines may result in significant investment of time and money into conservation efforts that do not provide recovery outcomes for populations (Campbell et al, 2020)
Coral bleaching events at Ashmore were not identified as a likely driver of declines due to mismatch in timing, the strong associations between many species within the sea snake group (e.g., Aipysurus spp.) and coral reefs ecosystems means that populations are likely to be highly sensitive to large-scale and long-term coral mortality

Summary

Introduction

Vertebrate populations across terrestrial, fresh water and marine environments are experiencing precipitous declines in distribution and abundance (Butchart et al, 2010; Hoffmann et al, 2010; Rodrigues et al, 2014; Ceballosa et al, 2017; Sánchez-Bayoa and Wyckhuysb, 2019), such that many species are being pushed toward both local extirpation and global extinction (Wake and Vredenburg, 2008). Coral bleaching events at Ashmore were not identified as a likely driver of declines due to mismatch in timing, the strong associations between many species within the sea snake group (e.g., Aipysurus spp.) and coral reefs ecosystems means that populations are likely to be highly sensitive to large-scale and long-term coral mortality.

Results

Conclusion