ESTIMATING THE IMPACT OF MARINE THREATS TO SEABIRD RECOVERY AFTER PREDATOR ERADICATION

Pelagic seabirds are one of the most threatened taxa due to sustained and intensifying threats at their breeding sites on land and when foraging at sea. Predator eradication at seabird breeding sites has become a key strategy for the long-term conservation and viability of seabird populations. However, the extent to which increasing marine threats (i.e., those causing excess mortality such as fisheries bycatch, plastic ingestion, climate change/prey depletion) impact recovery remains poorly understood. We used computer simulations to model demographic data obtained from a review of existing databases to explore the impact of direct marine threats to seabird recovery following land-based predator eradication. Using the resulting parameters, we explored the impact of multiple marine threats to the population growth rates of 16 seabird species from 36 colonies worldwide. Next, we tested whether and which seabirds’ phylogenetically conserved traits could predict risk to multiple marine threats. The majority (88%) of examined colonies are projected to recover despite multiple marine threats, in the absence of invasive predators. We suggest that phylogenetically conserved traits (e.g., body mass) and species’ ecological descriptors (e.g., foraging strategy) are not good predictors of how interacting marine threats may affect population recovery. In the absence of robust at-sea mortality data or reliable predictors of risk from several at-sea sources of mortality, monitoring population recovery for seabirds is a critical element of seabird island restoration projects. Our conclusions can shape how managers implement additional conservation actions for species that fail to recover following predator eradication.