Where to Forage in the Absence of Sea Ice? Bathymetry As a Key Factor for an Arctic Seabird

The earth is warming at an alarming rate, especially in the Arctic, where a marked decline in sea ice cover may have far-ranging consequences for endemic species. Little auks, endemic Arctic seabirds, are key bioindicators as they forage in the marginal ice zone and feed preferentially on lipid-rich Arctic copepods and ice-associated amphipods sensitive to the consequences of global warming. We tested how little auks cope with an ice-free foraging environment during the breeding season. To this end, we took advantage of natural variation in sea ice concentration along the east coast of Greenland. We compared foraging and diving behaviour, chick diet and growth and adult body condition between two years, in the presence versus nearby absence of sea ice in the vicinity of their breeding site. Moreover, we sampled zooplankton at sea when sea ice was absent to evaluate prey location and little auk dietary preferences. Little auks foraged in the same areas both years, irrespective of sea ice presence/concentration, and targeted the shelf break and the continental shelf. We confirmed that breeding little auks showed a clear preference for larger copepod species to feed their chick, but caught smaller copepods and nearly no ice-associated amphipod when sea ice was absent. Nevertheless, these dietary changes had no impact on chick growth and adult body condition. Our findings demonstrate the importance of bathymetry for profitable little auk foraging, whatever the sea-ice conditions. Our investigations, along with recent studies, also confirm more flexibility than previously predicted for this key species in a warming Arctic.

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S1 Fig. GPS tracks of 3 little auks in 2011 and sea ice extent.
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S2 Fig. Chick Growth curves for 2012 (black, n = 24 chicks) and 2014 (red, n = 29 chicks).
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S3 Fig. Adult body condition index (mean±SE) in 2012 (black, n = 65) and 2014 (red, n = 120) calculated following [42].
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S1 Table. Model selection using Akaike’s information criterion (AIC) to test the effects of age and year on chick body mass (51 chicks, 256 observations).
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S2 Table. Parameter estimation of model 1 testing the effects of age on chick body mass.
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How to cite
Amelineau Francoise, Gremillet David, Bonnet Delphine, Le Bot Tangi, Fort Jerme (2016). Where to Forage in the Absence of Sea Ice? Bathymetry As a Key Factor for an Arctic Seabird. Plos One. 11 (7). e0157764. (19p.). https://doi.org/10.1371/journal.pone.0157764, https://archimer.ifremer.fr/doc/00626/73762/

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