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Combined seabird indices show lagged relationships between environmental conditions and breeding activity
Zador, S., Hunt, G.L.Jr., TenBrink, T. & Aydin, K. (2013) Mar Ecol Prog Ser 485:245-258
Ecosystem managers and policy-makers need ecological indicators that have a sound scientific basis and that can inform them about the ecological state of the marine environment. In this study, we integrate existing data on seabird reproductive performance into 2 simplified indices in the eastern Bering Sea and use these indices to test hypotheses concerning the effects of environmental conditions on this suite of predators. We used principal components analysis to integrate 17 data sets on the reproductive effort of common murres Uria aalge, thick-billed murres U. lomvia, black-legged kittiwakes Rissa tridactyla, red-legged kittiwakes R. brevirostris, and red-faced cormorants Phalacrocorax urile. Two strong patterns were evident in the leading principal components (PC). In general, PC1 represented the hatch timing and reproductive success of diving foragers; PC2 represented kittiwake reproductive success trends. Together, PC1 and PC2 accounted for 65.2% of the variability in the seabird reproductive performance data. Time series analysis of these indices against selected environmental variables showed significant, but in most cases, lagged relationships. Warmer bottom and surface temperatures, greater wind mixing, and higher stratification correlated with delayed and lower productivity for most seabirds up to 2 yr later. Later ice retreat was correlated with lower kittiwake productivity 2 yr later, whereas higher local abundances of age-1 walleye pollock Theragra chalcogramma were linked to higher kittiwake productivity the following year. Since the observable impacts of environmental forcing on seabirds may be delayed, oceanographic and prey variables may serve as leading indicators of seabird breeding activity in the eastern Bering Sea.

Keywords: Eastern Bering Sea, Pribilof Islands, Principal components analysis, Ecosystem indicators, Common murre, Thick-billed murre, Black-legged kittiwake, Red-legged kittiwake


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