Decline of an arctic top predator: synchrony in colony size fluctuations, risk of extinction and the subpolar gyre
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Analysis of synchrony in population fluctuations is a central topic in ecology. It can help identify factors that regulate populations, and also the scales at which these factors exert their influence. Using long-term data from seven Brünnich’s guillemot colonies in Svalbard, Norway, we determined that year to year population fluctuations were synchronized in six of the seven colonies. The seventh colony was located farther away and in a different oceanographic system. Moreover, all seven colonies have declined significantly since the late 1990s following a very similar pattern. If the rate of population decline does not change, Brünnich’s guillemots in Svalbard have a high probability of becoming quasi-extinct within the next 50 years. The high synchrony between the different colonies could further increase this risk of extinction. Our results indicate that environmental forcing plays a role in the colony size fluctuation of Brünnich’s guillemot (i.e., a Moran effect). These fluctuations are well explained by changes in the subpolar gyre in the region where Brünnich’s guillemots overwinter. This subpolar gyre weakened in the mid-1990s, leading to a warming of the North Atlantic. Our study indicates that this basin-scale shift in the subpolar gyre is closely related to the decline in Brünnich’s guillemot in Svalbard. Our results suggest that the causal mechanism linking changes in oceanographic conditions in the North Atlantic and Brünnich’s guillemot population dynamics are likely mediated, at least partly, by changes in recruitment.
KeywordsMoran effect Regime shift Svalbard Subpolar gyre Synchrony Uria lomvia
This study was funded by programs MOSJ (http://mosj.npolar.no/) and SEAPOP (http://seapop.no/). We are indebted to Fridtjof Mehlum and Vidar Bakken, who established the monitoring program in Svalbard, to all summer field assistants who participated to the study and counted Brünnich’s guillemots in Svalbard since 1988, to Anders Skoglund for making maps and to Kjell-Einar Erikstad, Christopher Johnson and two anonymous referees for very useful comments on a first version. Thanks to Peter and Marie Fast for English editing and to Helge Drange for providing and explaining the subpolar gyre data.
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