Not all seabird species can overcome marine threats when predator removal at their colonies is prioritised

Abstract

Seabirds are globally threatened. In the face of multiple threats, it is critical to understand how conservation strategies that mitigate one threat intersect with others to impact population viability. Marine threats, including pollution, climate change, and fisheries could derail gains to seabird populations resulting from arduous predator eradication efforts. However, this potentially negative effect is yet to be evaluated. We test whether mortality from marine threats can subvert the on-going recovery of 17 seabird species from 37 colonies on islands worldwide where predators were removed. We use demographic modelling to estimate potential adult mortality from fisheries, plastic ingestion, and climate change. For 82% of the species we examine, marine threats do not impede recovery following predator eradication. However, for six colonies of three species, Calonectris diomedea, C. borealis, and Ardenna carneipes, mortality from multiple marine threats may interrupt their recovery. Combining our demographic approach with comparative phylogenetic methods, we explore whether foraging niche, range, and morphometric traits inform the vulnerability to marine threats using an expanded dataset of 81 seabird species. Our analyses reveal surface filtering and pursuit diving species, and species with smaller at-sea distributions to be most vulnerable to declines due to multiple threats. However, these traits do not necessarily predict species vulnerability to marine threats in the absence of predators at nesting colonies, suggesting that shared traits may not be useful to infer vulnerability to multiple marine threats. Post-eradication monitoring to determine whether species require additional conservation management following predator eradication are essential in the face of intensifying pressures in the marine environment.