Additive effects of climate and fisheries drive ongoing declines in multiple albatross species

Abstract

Environmental and anthropogenic factors often drive population declines in top predators, but how their influences may combine remains unclear. Albatrosses are particularly threatened. They breed in fast-changing environments, and their extensive foraging ranges expose them to incidental mortality (bycatch) in multiple fisheries. The albatross community at South Georgia includes globally important populations of three species that have declined by 40-60% over the last 35 years. We used three steps to deeply understand the drivers of such dramatic changes: () describe fundamental demographic rates using multievent models, () determine demographic drivers of population growth using matrix models, and () identify environmental and anthropogenic drivers using ANOVAs. Each species was affected by different processes and threats in their foraging areas during the breeding and nonbreeding seasons. There was evidence for two kinds of combined environmental and anthropogenic effects. The first was sequential; in wandering and black-browed albatrosses, high levels of bycatch have reduced juvenile and adult survival, then increased temperature, reduced sea-ice cover, and stronger winds are affecting the population recovery potential. The second was additive; in gray-headed albatrosses, not only did bycatch impact adult survival but also this impact was exacerbated by lower food availability in years following El Niño events. This emphasizes the need for much improved implementation of mitigation measures in fisheries and better enforcement of compliance. We hope our results not only help focus future management actions for these populations but also demonstrate the power of the modelling approach for assessing impacts of environmental and anthropogenic drivers in wild animal populations.

Sex‐specific effects of fisheries and climate on the demography of sexually dimorphic seabirds

“…This is one of the few studies to examine sex-specific effects of environmental variation and fishing effort on survival rates in a marine vertebrate Martínez-Abraín et al, 2006;Olsson & Van der Jeugd, 2002). Although the canalization theory (Fay, Weimerskirch, Delord, & Barbraud, 2015;Gaillard & Yoccoz, 2003) predicts a stronger buffering against environmental variability in adult survival (Jenouvrier, Barbraud, Cazelles, & Weimerskirch, 2005;Pardo et al, 2017), which is the most sensitive vital rate to the population growth rate of large seabirds, we showed that the survival of giant petrels of one or both species was influenced by large-scale climatic indices, oceanographic characteristics, availability of fur seal carrion and fisheries. We found interspecific differences, and, as expected, both species showed sex-specific responses to environmental variability, highlighting the importance of considering such within-population variation.…”

“…At‐sea distributions of non‐breeding birds were mapped for each giant petrel species, based on 130 and 126 tracks of different individuals of NGP and SGP, respectively, fitted with Global Location Sensors (GLS loggers; British Antarctic Survey, Cambridge, UK) in summer 1999/2000 (Figure S2.1; based on data in González‐Solís et al, ). Subsequently, we extracted the data for the model covariates from all of the 5 × 5° cells within the 50% utilization distributions (UDs) for oceanographic characteristics (SST, NPP and wind components), as this was considered to reflect the conditions experienced in core areas, and the 90% UDs for trawl, demersal and pelagic longline fishing effort, which was considered to better reflect the potential encounters with fishing vessels (Pardo et al, ). Data on krill biomass and sea ice cover (SIC) were obtained from fixed sampling areas (see Appendix S2).…”

Flight speed and performance of the wandering albatross with respect to wind

“…In addition, recent increases in the foraging range and breeding success of wandering albatrosses are thought to have been mediated by strengthening winds in the Southern Ocean [22]. Similarly, variation in annual survival, breeding probability or breeding success of wandering albatross, black-browed Thalassarche melanophris and grey-headed albatross T. chrysostoma at South Georgia have been linked to changes in the wind regime [23], suggesting that ongoing global climate change may have major impacts on albatrosses, and pelagic seabirds in general. A necessary precursor to understanding and predicting how the wind affects the movements and, ultimately, the demography of seabirds is to quantify its effects on flight performance (i.e.…”

Fisheries Exploitation by Albatross Quantified With Lipid Analysis

“…Incidental mortality from fisheries bycatch is a principle threat to seabird biodiversity, particularly for the Procelleriformes (albatrosses and petrels) (Croxall and Gales, 1998;Tuck et al, 2001;Cherel et al, 2017;Pardo et al, 2017). Fifteen out of 22 recognized species of albatrosses are currently threatened or endangered, of which three are critically endangered (IUCN, 2017).…”