title: Trends in the breeding population of Adélie penguins in the Ross Sea, 1981-2012: a coincidence of climate and resource extraction effects.
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.
authors.affiliation: Landcare Research, Lincoln, New Zealand.
authors.forename: Phil O'B
authors.initials: PO
authors.lastname: Lyver
authors.affiliation: Landcare Research, Lincoln, New Zealand.
authors.forename: Mandy
authors.initials: M
authors.lastname: Barron
authors.affiliation: Bartonk Solutions, Nelson, New Zealand.
authors.forename: Kerry J
authors.initials: KJ
authors.lastname: Barton
authors.affiliation: H. T. Harvey & Associates Ecological Consultants, Los Gatos, California, United States of America.
authors.forename: David G
authors.initials: DG
authors.lastname: Ainley
authors.affiliation: H. T. Harvey & Associates Ecological Consultants, Los Gatos, California, United States of America.
authors.forename: Annie
authors.initials: A
authors.lastname: Pollard
authors.affiliation: Antarctica New Zealand, Christchurch, New Zealand.
authors.forename: Shulamit
authors.initials: S
authors.lastname: Gordon
authors.affiliation: Landcare Research, Lincoln, New Zealand.
authors.forename: Stephen
authors.initials: S
authors.lastname: McNeill
authors.affiliation: Point Blue Conservation Science, Petaluma, California, United States of America.
authors.forename: Grant
authors.initials: G
authors.lastname: Ballard
authors.affiliation: Auckland, New Zealand.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Wilson
mesh_terms: D000818:Animals; D000864:Antarctic Regions; D061006:Bays; D001947:Breeding; D002980:Climate; D011156:Population Density; D046429:Spheniscidae; D013997:Time Factors