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Wednesday, 19 March 2014

Increase in Adelie penguin breeding population in Ross Sea over last 10 years: PLoS ONE; March 2014

Title
Trends in the Breeding Population of Adélie Penguins in the Ross Sea, 1981–2012: A Coincidence of Climate and Resource Extraction Effects

Citation
PLoS ONE 9(3): e91188. doi:10.1371/journal.pone.0091188
LINK

Authors
Phil O’B. Lyver, Mandy Barron, Stephen McNeill
Landcare Research, Lincoln, New Zealand
Kerry J. Barton
Bartonk Solutions, Nelson, New Zealand
David G. Ainley, Annie Pollard
H. T. Harvey & Associates Ecological Consultants, Los Gatos, California, United States of America
Shulamit Gordon
Antarctica New Zealand, Christchurch, New Zealand
Grant Ballard
Point Blue Conservation Science, Petaluma, California, United States of America
Peter R. Wilson

Auckland, New Zealand

Abstract
Measurements of the size of Adélie penguin (Pygoscelis adeliae) colonies of the southern Ross Sea are among the longest biologic time series in the Antarctic. We present an assessment of recent annual variation and trends in abundance and growth rates of these colonies, adding to the published record not updated for more than two decades. High angle oblique aerial photographic surveys of colonies were acquired and penguins counted for the breeding seasons 1981–2012. In the last four years the numbers of Adélie penguins in the Ross and Beaufort Island colonies (southern Ross Sea metapopulation) reached their highest levels since aerial counts began in 1981. Results indicated that 855,625 pairs of Adélie penguins established breeding territories in the western Ross Sea, with just over a quarter (28%) of those in the southern portion, constituting a semi-isolated metapopulation (three colonies on Ross Island, one on nearby Beaufort Island). The southern population had a negative per capita growth rate of −0.019 during 1981–2000, followed by a positive per capita growth rate of 0.067 for 2001–2012. Colony growth rates for this metapopulation showed striking synchrony through time, indicating that large-scale factors influenced their annual growth. In contrast to the increased colony sizes in the southern population, the patterns of change among colonies of the northern Ross Sea were difficult to characterize. Trends were similar to southern colonies until the mid-1990s, after which the signal was lost owing to significantly reduced frequency of surveys. Both climate factors and recovery of whale populations likely played roles in the trends among southern colonies until 2000, after which depletion of another trophic competitor, the Antarctic toothfish (Dissostichus mawsoni), may explain the sharp increasing trend evident since then.

Figure 2. 
Time-series plots of the logged Adélie penguin colony counts at Cape Royds, Cape Bird, Cape Crozier and Beaufort Island, Antarctica from 1981 to 2012.

The linear regression trend lines are for the period 1981–2000.



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