Advances in remote sensing of emperor penguins: first multi-year time series documenting trends in the global population

Abstract

Like many polar animals, emperor penguin populations are challenging to monitor because of the species' life history and remoteness. Consequently, it has been difficult to establish its global status, a subject important to resolve as polar environments change. To advance our understanding of emperor penguins, we combined remote sensing, validation surveys and using Bayesian modelling, we estimated a comprehensive population trajectory over a recent 10-year period, encompassing the entirety of the species’ range. Reported as indices of abundance, our study indicates with 81% probability that there were fewer adult emperor penguins in 2018 than in 2009, with a posterior median decrease of 9.6% (95% credible interval (CI) −26.4% to +9.4%). The global population trend was −1.3% per year over this period (95% CI = −3.3% to +1.0%) and declines probably occurred in four of eight fast ice regions, irrespective of habitat conditions. Thus far, explanations have yet to be identified regarding trends, especially as we observed an apparent population uptick toward the end of time series. Our work potentially establishes a framework for monitoring other Antarctic coastal species detectable by satellite, while promoting a need for research to better understand factors driving biotic changes in the Southern Ocean ecosystem.

Remote sensing of emperor penguin abundance and breeding success

“…While a reliable number of breeding pairs provides valuable information about the current status of the species, abundance information needs to be collected over many decades to use it as a population predictor in a long-lived species 23 . Similarly, other recent work 40 cannot clearly determine population trends from the number of breeding pairs alone, even when considering decades of satellite-based observation. This could possibly be due to the lack of a phenological correction to their data.…”