MEPS 201:301-309 (2000)  -  doi:10.3354/meps201301

Influence of annual variation in food supply on abundance of wintering common eiders Somateria mollissima

Jesper K. Larsen*, Magella Guillemette**

National Environmental Research Institute, Department of Coastal Zone Ecology, Kalø, Grenåvej 12, 8410 Rønde, Denmark
Present addresses: *Carl Bro as, Nordlandsvej 60, 8240 Risskov, Denmark. E-mail: **Département de biologie et sciences de la santé, Université du Québec à Rimouski, 300 allée des Ursulines, Rimouski, Québec, Canada

ABSTRACT: We investigated how the annual variation in the abundance of wintering common eiders Somateria mollissima was related to the abundance of benthos over 4 yr. The study was conducted at 2 sites, Tunø Knob and Ringebjerg Sand, Denmark, from 1994 to 1998. Benthos was sampled along permanent transects in November, and common eiders counted and localized from observation towers during the winter. The benthic community was dominated by the blue mussel Mytilus edulis, with sizes varying with depth. Small and intermediary-sized individuals were primarily found in 0 to 6 m depth, and large individuals exclusively in 6 to 12 m depth. The pattern of variation in abundance of common eiders matched that of the benthos in 0 to 6 m depth, where they were mostly found, but not in 6 to 12 m depth. Based on a bioenergetic model of food consumption, we estimated that common eiders during the 3rd and 4th years exploited between 22 and 64% of the entire benthic community biomass in 0 to 6 m depth, compared to ≤3% in 6 to 12 m depth. We conclude that common eiders tracked annual variation in food abundance, primarily related to the presence of small and intermediary-sized blue mussels.

KEY WORDS: Common eider · Abundance · Annual variation · Benthic biomass · Mytilus edulis · Food consumption · Prey size

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