Table of Contents

  • This report outlines the results of the coordinated census of wintering waterbirds in the Baltic Sea 2007–2009 undertaken under the SOWBAS project (Status of wintering Waterbird populations in the Baltic Sea). The international co-ordination and analyses of the waterbird census was funded by a grant from the Nordic Council of Ministers, and the surveys were funded by the regional and national authorities and organised by the involved governmental agencies, universities, NGOs and private consulting companies.

  • The international co-ordination and analyses of the waterbird census was funded by a grant from the Nordic Council of Ministers. At the national level, the surveys were funded by the regional and national authorities and organised by the governmental agencies as part of their monitoring programmes or as targeted surveys.

  • This report outlines the results of the coordinated census of wintering waterbirds in the Baltic Sea 2007–2009 undertaken under the SOWBAS project (Status of wintering Waterbird populations in the Baltic Sea).

  • The Baltic Sea is a brackish non-tidal sea covering about 415,000 km2 (including the Kattegat, the Danish straits, the Bothnian Bay, the Bothnian Sea andthe Gulf of Finland). The Baltic Sea was created after the lce Age. 10,000 years ago, a milder climate caused the ice in Sweden to melt, and the Baltic Ice Lake found an outlet to the ocean over central Sweden. Subsequently, this outlet was blocked due to the progressing uplift of mainland Sweden. As a result, the Baltic Sea basin became again an isolated lake. Because the land uplift was greater in the north than in the south, the floor of the Baltic Sea basin slowly tilted. About 7,500 years ago, a new contact with the ocean was established through the Danish sounds and straits. Since then, this outlet has been the only connection between the Baltic Sea and the North Atlantic.

  • The present atlas includes the entire ice-free areas of the Baltic Sea during the winters of 2007, 2008 and 2009, and is bounded by the coastlines of Sweden, Finland, Estonia, Latvia, Lithuania, Russia (Kaliningrad), Poland, Germany and Denmark (Map 1). It includes all coastal, territorial and EEZ waters, as well as all bays and semi-enclosed brackish-water lagoons and fjords along the Baltic coasts. Limfjorden (Denmark) is not included in the present atlas.

  • The north-west European winter population of Red-throated Divers is estimated at 150,000-450,000 birds, while the population of Black-throated Divers is estimated at 250,000-500,000 birds (Delany & Scott 2006). The results of the present study indicate a massive decline from 56,500 birds in the Baltic Sea during 1988–1993 to 8,575 in 2007–2009, equivalent of 84.1%. As the estimated sizes of the total populations of both species of divers have been completely revised since the 1994 status report it is not possible to assess whether the decline in the Baltic winter population is a reflection a large-scale or just regional population declines. Assuming that the estimates in Delany & Scott (2006) are correct the current status indicates that between 0.9% and 2.1% of the north-west European winter populations of both species winter in the Baltic Sea. The range of the proportion of birds wintering in the Baltic Sea is caused by uncertainties regarding the sizes of recruiting populations in Russia (Delany & Scott 2006).

  • On the following pages the results of the analysis of trends in the numbers of wintering waterbirds in selected regions with comparable yearly coverage between 1987 and 2008 are presented species by species. The purpose of the trend analyses has mainly been to allow for an interpretation of the differences observed in the distribution and abundance of several species between 1992–1993 and 2007–2009. To that end, the trends in the waterbirds would also allow us to link numbers of individual species per region with trends in the selected pressures. With the exception of the trends which have been established for the Long-tailed Ducks on Hoburgs Bank the trend data stem from counts in coastal areas. These coastal counts have to a large degree been undertaken as part of the Wetlands International Midwinter Census.

  • In table 27 an overview is given of the population estimates for all wintering waterbirds covered by this status report. In addition to listing the estimated totals for the surveys during the two periods 2007–2009 and 1992–1993 the table also gives proportions of the total bio-geographic populations wintering in the Baltic Sea during these two periods. Of the 20 species of waterbirds covered the total population size has decreased between the two periods for 11 species; 7 of which have declined seriously by more than 30% in 16 years.

  • As reported in Chapter 6 and 7 large-scale declines (> 30%) are documented for 7 out of 20 species of waterbirds since 1993. Moderate declines are documented for three species, stable populations are documented for two species, moderate increases for three species and large-scale increases for four species. Thus, the overall picture which has emerged from SOWBAS is that the majority of the wintering waterbird species currently show decreasing trends. A range of potential pressures behind these declines has been suggested, including climate change, oil pollution and incidental bycatch (Rönkä et al. 2005, Skov 2007, Lehikoinen et al. 2008, Nilsson 2008, Hario et al. 2009a, Zydelis et al. 2009). In the following, the available information on relevant regional pressures in relation to wintering waterbirds in the Baltic Sea will be reviewed. The reviews are presented pressure by pressure and focus on recent (after 2000) data and references, and include trends for selected pressures to ease comparisons with the trends in waterbird numbers. At the end of the chapter results of correlations between trends in selected pressures and numbers of wintering waterbirds are presented, and key pressures are identified for the main ecological guilds present in the wintering waterbird community.

  • In chapter 8, a qualitative and quantitative assessment was made of the impact of the different anthropogenic pressures on current population numbers of waterbirds in the Baltic Sea. In this chapter, an attempt will be made to synthesize the results of the individual assessments into recommendations for indicators. Indicators are here interpreted as both priority species for conservation and species which may be used as performance indicators in relation to the international and national actions taken to reduce the anthropogenic pressures in the Baltic Sea. As documented in chapter 8, multiple pressures can be identified as playing an important (either negative or positive) role in the development of populations and distributions of most species of waterbirds. Teasing out the relative influence of each pressure on the health and conservation status of each species will require more detailed statistical analyses, which are outside the scope of this report. Thus, the suggested indicators should be seen as a first step in the direction of including targets and indicators for wintering waterbirds into the Baltic Sea Action Plan (BSAP). The goal of BSAP is to restore good ecological status of the Baltic marine environment by 2021, i.e. the Baltic Sea should be unaffected by eutrophication, life in the sea should be undisturbed by hazardous substances, maritime activities in the Baltic Sea should be carried out in an environmentally friendly way and the Baltic Sea biodiversity should have a favourable conservation status.

  • Approximate significance of smooth terms (Chi square and F values) of variables in the distribution model for Red-throated Diver/Black-throated Diver. Values for both model parts are presented on separate panels. The model was evaluated by fitting the model on 70% of the data set and testing the model on 30%. Evaluation results are presented as area under the receiver operator characteristic curve (AUC) for the presence/absence part and Spearman’s correlation coefficient for the combined model. Deviance explained for both model parts are shown. The presence-absence part was fitted by a binomial distribution, and the positive part by a gamma distribution.