Distribution and numbers of wintering sea ducks in Swedish offshore waters

Leif Nilsson

doi:10.34080/os.v22.22595

Abstract

The first survey of seaducks covering the offshore waters of the entire Baltic was undertaken in 1992/1993, when, however, the Swedish waters were covered with relatively few ship surveys. The second all Baltic survey 2007–2011 included extensive aerial surveys of all Swedish offshore waters. This paper presents the Swedish data from these two surveys, supplemented with data from several other but partial surveys back to the early 1970s. The most numerous wintering seaduck in the Swedish waters was the Long-tailed Duck Clangula hyemalis with an estimated population of 1.41 million in 1992/1993, decreasing with 69% to 0.44 million in 2007–2009. Hoburg bank south of Gotland and the two Midsjö banks accounted for the vast majority of these ducks. In 2009–2011 only small numbers of scoters Melanitta fusca and M. nigra were found in Swedish Baltic waters. The totals for the Eider Somateria molissima and Red-breasted Merganser Mergus serrator were estimated at 20,000 and 8,000, respectively. Larger numbers of Eiders (50,000) and scoters (20,000) were found on the west coast.

Highlights

Annual counts of wintering waterbirds have been undertaken in Sweden since 1967 as a part of the International Midwinter Counts organized by what is Wetlands International
Long-tailed Duck Clangula hyemalis The Long-tailed Duck is mainly restricted to the Baltic during the winter and only very small numbers are found on the west coast
From the data presented here and in comparison with the estimates from the total surveys of wintering seabirds in the Baltic (Durinck et al 1994, Skov et al 2011; see Delany & Scott 2006 for the entire NW Europe) it is clear that the Swedish offshore areas in the Baltic are of very large international importance for wintering seaducks, especially for the Long-tailed Duck and for the Red-breasted Merganser (Nilsson 2008) whereas the two scoter species are more sparse

Summary

Introduction

Annual counts of wintering waterbirds have been undertaken in Sweden since 1967 as a part of the International Midwinter Counts organized by what is Wetlands International (see Nilsson 2008 for a review of the Swedish studies and references to the international work). These surveys are a part of the Swedish Bird Monitoring Program organized by The Swedish Environmental Protection Agency (SEPA, Naturvårdsverket). Some offshore aerial surveys were performed during this period

Methods

Results

Conclusion