Disentangling the Influence of Three Major Threats on the Demography of an Albatross Community

Clive R Mcmahon,Geoffrey N Tuck,Jaimie B Cleeland,Rachael Alderman,Richard A Phillips,Ben Raymond,Deborah Pardo,Mary-Anne Lea,Mark A Hindell

doi:10.3389/fmars.2021.578144

Abstract

Climate change, fisheries and invasive species represent three pervasive threats to seabirds, globally. Understanding the relative influence and compounding nature of marine and terrestrial threats on the demography of seabird communities is vital for evidence-based conservation. Using 20 years of capture-mark-recapture data from four sympatric species of albatross (black-browedThalassarche melanophris, gray-headedT. chrysostoma, light-mantledPhoebetria palpebrataand wanderingDiomedea exulans) at subantarctic Macquarie Island, we quantified the temporal variability in survival, breeding probability and success. In three species (excluding the wandering albatross because of their small population), we also assessed the influence of fisheries, oceanographic and terrestrial change on these rates. The Southern Annular Mode (SAM) explained 20.87–29.38% of the temporal variability in survival in all three species and 22.72–28.60% in breeding success for black-browed and gray-headed albatross, with positive SAM events related to higher success. The El Niño Southern Oscillation (ENSO) Index explained 21.14–44.04% of the variability in survival, with higher survival rates following La Niña events. For black-browed albatrosses, effort in south-west Atlantic longline fisheries had a negative relationship with survival and explained 22.75–32.21% of the variability. Whereas increased effort in New Zealand trawl fisheries were related to increases in survival, explaining 21.26–28.29 % of variability. The inclusion of terrestrial covariates, reflecting extreme rainfall events and rabbit-driven habitat degradation, explained greater variability in trends breeding probability than oceanographic or fisheries covariates for all three species. These results indicate managing drivers of demographic trends that are most easily controlled, such as fisheries and habitat degradation, will be a viable option for some species (e.g., black-browed albatross) but less effective for others (e.g., light-mantled albatross). Our results illustrate the need to integrate fisheries, oceanographic and terrestrial processes when assessing demographic variability and formulating the appropriate management response.

Highlights

Climate-driven changes in the marine ecosystem affect animal populations in complex ways (Constable et al, 2014), yet understanding how populations respond to environmental change is vital for predicting their viability (Vargas et al, 2007)
Large-scale climate cycles such as the Southern Annular Mode (SAM) and the El Niño Southern Oscillation (SOI) are influenced by climate change, with demographic consequences predicted for multiple species (Forcada and Trathan, 2009)
Understanding the extrinsic drivers of demographic variability is critical to assess population viability, in small populations where small decreases in vital rates can have a considerable impact on the population

Summary

Introduction

Climate-driven changes in the marine ecosystem affect animal populations in complex ways (Constable et al, 2014), yet understanding how populations respond to environmental change is vital for predicting their viability (Vargas et al, 2007). Changes in physical oceanographic and atmospheric conditions may influence individual foraging efficiency by affecting the accessibility and predictability of prey (Lea et al, 2006), or the energetic cost of reaching foraging areas (Weimerskirch et al, 2012). These changes are occurring simultaneously with fisheries that overlap with the foraging habitat of numerous seabird species (Tuck et al, 2003). Simultaneous negative effects on both survival and reproductive output can drive rapid declines and lead to extirpation (Weller et al, 2014)

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Conclusion