The status of biodiversity is assessed using several core indicators. Each indicator focuses on one important aspect of the complex issue. In addition to providing an indicator-based evaluation of the abundance of waterbirds in the breeding season, this indicator contributes to the overall biodiversity assessment along with the other biodiversity core indicators.
The indicator on abundance of waterbirds in the breeding season addresses the Baltic Sea Action Plan (BSAP) Biodiversity and nature conservation segment's ecological objectives 'Thriving and balanced communities of plants and animals' and 'Viable populations of species' as well as the eutrophication segment's ecological objective 'Natural distribution and occurrence of plants and animals'.
The core indicator is relevant to the following action of the 2013 HELCOM Ministerial Declaration:
The core indicator also addresses the following qualitative descriptors of the MSFD for determining good environmental status (European Commission 2008):
Descriptor 1: 'Biological diversity is maintained. The quality and occurrence of habitats and the distribution and abundance of species are in line with prevailing physiographic, geographic and climatic conditions';
Descriptor 4: 'All elements of the marine food webs, to the extent that they are known, occur at normal abundance and diversity and levels capable of ensuring the long-term abundance of the species and the retention of their full reproductive capacity'.
and the following criteria of the Commission Decision (European Commission 2017):
The EU Birds Directive (a) lists in Annex 1 barnacle goose, pied avocet, dunlin (Baltic subspecies Calidris alpina schinzii), Caspian tern, sandwich tern, common tern, Arctic tern and little tern as subject of special conservation measures and (b) generally covers all migratory species and they have to be reported (European Commission 2010). Thus, all species included in the concept of the indicator are also covered by the EU Birds Directive, which requires conservation of habitats in a way that allows birds to breed, moult, stage during migration and spend the winter.
Furthermore, the Baltic Sea is located in the agreement area of the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA). Contracting Parties (all HELCOM member countries except Poland and Russia) are obliged to undertake measures warranting the conservation of migratory waterbirds and their habitats.
The goals of the BSAP, EU MSFD, AEWA and EU Birds Directive are largely overlapping and the data needed for the indicator are roughly the same as needed for reporting within the framework of the EU Birds Directive.
In order to protect migrating birds in the Baltic Sea region, HELCOM has adopted the Recommendation 34/E-1 'Safeguarding important bird habitats and migration routes in the Baltic Sea from negative effects of wind and wave energy production at sea'. Since some species included in the concept of the indicator are vulnerable to habitat loss caused by wind farms and access to feeding areas of breeding birds may be blocked by wind farms, while others are prone to collisions (e.g. Masden et al. 2010, Furness et al. 2013, Bradbury et al. 2014), the indicator is linked to the intentions of the recommendation.
Waterbirds are an integral part of the Baltic marine ecosystem. They are predators of fish and macroinvertebrates, scavengers of carcasses and fishery discards and herbivores of littoral vegetation. They can be assigned to functional species groups, meaning that different prey types are taken from different compartments of the marine environment. Most species are specialized in certain species and/or size classes of prey. As they cannot survive without a sufficient food supply, changes in the number of waterbirds reflect conditions in the food web of the Baltic Sea. A high number of breeding waterbirds may not automatically indicate a good environmental status, because for instance piscivorous species benefit from a high availability of small fish, which in turn may points to a disorder of the food web owing to overfishing of large fish species.
As they are predators at or close to the top of the food web, waterbirds accumulate contaminants and their numbers, and even more their breeding success, may indicate the degree of contamination. Moreover, several waterbird species are predated by white-tailed sea eagles, transferring the loads of contaminants to a higher level in the food web.
Some waterbird species are not only breeding, but also wintering in the Baltic Sea region. For several reasons, those species are potentially included in the concepts of both the breeding and wintering waterbird abundance indicators. The intention of the indicators is to support the assessment of environmental status of marine areas rather than the state of bird populations per se. This is most obvious in species that have differing distribution patterns between breeding and wintering seasons (e.g. alcids). In general, the explanatory power of the indicator is constrained by factors acting on the waterbirds in the non-breeding season, either in the Baltic Sea or in staging and wintering areas along the flyways to southern Europe and Africa or even Australia and Antarctica, depending on the migration routes of the respective species.
Pressures by substances, litter and energy
in addition to those mentioned above:
Pressures by substances, litter and energy:
The abundance of breeding waterbirds in the Baltic Sea is strongly influenced by a variety of human activities, both directly and indirectly. The effects are cumulative, because pressures exist in the breeding season, during migration and in winter.
In general, waterbirds strongly respond to food availability. Therefore, human activities influencing the food supply of waterbirds are reflected in bird numbers. For fish-eating birds, direct human pressure is posed by the extraction of fish, while physical damage of the seafloor directly affects benthic feeders. On the other hand, overfishing of large predatory fish species increases the abundance of smaller species and thereby improves the food supply for birds. Indirect effects can also occur via human induced eutrophication: in the oligotrophic end of the eutrophication status, the bird populations are limited by the availability of food sources, whereas towards eutrophic conditions plant and zoobenthos biomass increases, which first benefits waterbird populations, but in the extreme end will cause a decrease in food availability.
As their reproduction takes place on land, even waterbirds that live at sea during all other times are prone to predation by non-indigenous mammals such as American mink and raccoon dog, which have been introduced by humans and therefore have to be treated as a human pressure. While many breeding colonies are well protected nowadays, some breeding sites are still under pressure from direct human disturbance, for example from tourism and recreational boating, but also from habitat loss due to changes in land use and agriculture..
Bird losses from drowning in fishing gear, hunting and plumage oiling as well as habitat loss from offshore wind farming, aggregate extraction and shipping are pressures mostly acting in the non-breeding season. At least in those species that both breed and spend the winter in the Baltic Sea, also these human pressures affect the numbers of breeding birds – not only by the elimination of birds from the population, but also in terms of carry-over effects by reducing body condition with effects on survival and reproductive success. Negative impacts on body condition are also obtained year-round from the accumulation of contaminants ingested via the food web.