Guidelines for monitoring seabirds at sea.

Abstract

The efforts of HELCOM to conserve the Baltic Sea environment are aggregated in its Baltic Sea Action Plan. Measures to guarantee the environmental integrity of the Baltic Sea need to be backed by science-based environmental data. To get this information, HELCOM is conducting holistic assessments, which include various components of the Baltic Sea ecosystem. Seabirds (marine birds including coastal waterbirds) are substantial components at various levels of the food web and serve as herbivores of littoral vegetation and predators of macroinvertebrates, fish, other birds, carcasses and fishery discard in the Baltic marine environment. While breeding seabirds are concentrated along and around their breeding sites at the coast or on islands, non-breeding seabirds are distributed across the entire marine area of the Baltic Sea. In the second holistic assessment of the Baltic Sea (HOLAS II), the abundance of wintering seabirds was assessed by the HELCOM Core Indicator “Abundance of waterbirds in the wintering season” (HELCOM 2018). In HOLAS II, the assessment of wintering seabirds relied on coastal (land-based) counts only, thus any conclusions were restricted to the coastal waters. In order to expand the validity of the indicator to the entire marine area of the Baltic Sea, the indicator needs to include assessments of birds wintering off the coast. This expansion needs surveys and monitoring at sea, and these guidelines describe the designing and methodology of such surveys.