7 EXISTING CONDITIONS IN THE PROJECT AREA
7.10 Marine mammals
7.10.2.4 Echolocation and hearing
Harbour porpoises have good underwater hearing and use sound actively for navigation and prey capture (echolocation). Harbour porpoises produce short ultrasonic clicks (130 kHz peak frequency, 50-100 μs duration; /208//209/) and are able to orient and find prey in complete darkness. Data from porpoises tagged with acoustic data loggers indicate that they use their echolocation almost continuously /210//211/. Their hearing sensitivity is extremely high and covers a vast frequency
range (see Figure 7-40, /212//213//214//215/). The audiogram (see Figure 7-40) shows the hear-ing threshold; porpoises can only hear sound above the threshold for each frequency. The best ability to detect sound is at frequencies with the lowest threshold (the highest sensitivity).
Mammals do not hear equally well over their entire range of hearing. For sound intensities close to the hearing threshold, the audiogram is a good approximation of the perceived sound levels (the loudness of the sound). In marine mammals, there is a great difference in sensitivity between the frequencies of best hearing and those close to the cut-off frequencies.
Figure 7-40 Audiograms for harbour porpoises modified from /215/ (green), /212/ (blue) and /213/
(red). The audiogram also shows the frequency range of harbour porpoise vocalisation (yellow).
7.10.2.5 Biodiversity status
In 2017, HELCOM assessed the integrated biodiversity status of the Baltic Sea /104/. Harbour porpoise is not assessed in this report.
7.10.2.6 Protection
A number of international treaties, agreements and laws have been enacted in order to protect the harbour porpoise. In northern European waters, the species has been listed in Annex II and IV of the Habitats Directive 92/43/EEC, Annex II of the Bern Convention, Annex II of the Bonn Convention and Annex II of the Washington Convention. Furthermore, the harbour porpoise is covered by the terms of ASCOBANS, a regional agreement under the Bonn Convention and HELCOM. In Denmark, the species is furthermore protected under Administrative Order 867 of 27/06/2016 /216/.
In the regional assessment for Europe, the harbour porpoise is listed as “Vulnerable”, while the sub-population of Baltic Sea harbour porpoise is listed as “Critically Endangered” on the IUCN Red List.
Protected areas for marine mammals are described in section 10.
Harbour seal
This section presents the Baltic Sea population of harbour seal, with information on population structure and size, distribution, behaviour, reproduction, hearing, and protection.
7.10.3.1 Population structure and size
Based on genetic data and satellite telemetry, harbour seals in the Baltic Sea region have been split
(along the southern Danish and Swedish coasts) and (3) the Kattegat /217//218/. The Kalmarsund population comprises approximately 1,000 individuals /219/, the south-western Baltic population comprises approximately 1,500 individuals, and the Kattegat population comprises approximately 7,800 individuals /220/. The proposed NSP2 route is located in the transition zone between the Kalmarsund population and the south-western Baltic population.
7.10.3.2 Distribution
Harbour seals are found in temperate and arctic waters of the Northern Hemisphere. Haul-out sites (also called colonies) are land localities occupied by seals during periods of mating, giving birth and moulting. Haul-out sites for harbour seals are well-known and do not change between years. Annual counts are made during the moult in August. Knowledge of seal abundance and density is extensive with respect to the locations of the haul-out sites, which are shown in Figure 7-41. A tagging study showed that 10 tagged harbour seals travelled with a mean travel range of below 25 km /222/ and the zone of regular occurrence is taken as the maximum distance from the tagging site.
In the Baltic Sea, harbour seals are only found in Kalmarsund between Öland and the mainland of Sweden and in the south-western Baltic Sea, concentrated around the Rødsand sandbar (7 km west of Gedser in Denmark) and Falsterbo and Saltholm in the Sound.
The Danish section of the proposed NSP2 route does not cross any areas with colonies or regular occurrence of harbour seals. However, foraging harbour seals may potentially be present at all depths within their range in the areas surrounding the proposed NSP2 route.
Figure 7-41 Haul-out sites (colonies) in the Baltic Sea used by harbour seals for resting, breeding and moulting. Global positioning system (GPS) tracking of harbour seals in the Danish sector is indicated by blue dots. No satellite tracking has been undertaken in the Swedish colonies. Source: HELCOM Seal Data-base /223/.
7.10.3.3 Behaviour and reproduction
The harbour seal is a relatively small seal with an adult weight of approximately 65-140 kg. Harbour seals are opportunistic predators. They feed mainly on benthic fish but can catch and eat all fish species. Moulting occurs in August, when seals spend more time on land to develop their new fur.
Females are believed to give birth once a year on land between May and June, with a gestation period of 11 months. The pup suckles for about three to four weeks, after which it is left to feed on its own. Harbour seal pups shed their embryonic fur (lanugo) before birth and are thus born with adult fur. Pups are able to swim and dive just after birth. Mating occurs immediately after the end of suckling and takes place in the water. Little is known on the exact circumstances surrounding mating; however, as noted above, mating and periods of birthing are focused on haul-out sites/col-onies (as shown in Figure 7-41).
7.10.3.4 Hearing
Seals have ears that are well-adapted to an aquatic life. These adaptations include cavernous tissue in the middle ear, which allows for balancing the increased pressure on the eardrum when the animal dives /224/.
Figure 7-42 shows an audiogram of harbour seals, demonstrating that they have good underwater hearing in the range from a few hundred Hz to approximately 50 kHz.
Figure 7-42 Audiograms of three harbour seals, showing the threshold of hearing under quiet conditions at frequencies in the range from 80 Hz to 150 kHz. The legend Møhl, Terhune and Kastak refers to results from references /225/, /226/and /227/, respectively.
7.10.3.5 Biodiversity status
In 2017, HELCOM assessed the integrated biodiversity status of the Baltic Sea /104/. The proposed NSP2 route is located in the zone between the Kalmarsund population and the south-western Baltic population. Under the most recent assessment of biodiversity under HELCOM, the Kalmarsund pop-ulation falls below the threshold for ‘Good Status’, based on the low abundance, while the growth rate of the stock is satisfactory. The southwestern population falls below the threshold based on a positive growth rate lower than the threshold.
Audiogram
7.10.3.6 Protection
Harbour seals are protected under the EU Habitats Directive and the Convention for the Protection of Migratory Species (Bonn Convention). In addition, they are fully protected under national legis-lation. Furthermore, the Kalmarsund population is listed as endangered by the IUCN. The harbour seal is listed on the EU Habitats Directive Annex II, which means that it should be protected via the designation of special areas of conservation. For seals, these areas are primarily placed in connec-tion with important haul-out sites on land. In Denmark, the species is furthermore protected under Administrative Order 867 of 27 June 2016 /216/.
Protected areas for marine mammals are described in section 10.
Grey seal
This section presents the Baltic Sea population of grey seal, with information on population struc-ture and size, distribution, behaviour, reproduction and protection.
7.10.4.1 Population structure and size
There are three separate populations of grey seal in the world. One of them is the Baltic grey seal, which is found in the Baltic Proper, in the Bothnian Sea and in the Gulf of Finland; the other two populations live in the north-east and north-west Atlantic Ocean, respectively.
One hundred years ago, the grey seal population in the Baltic Sea comprised 80,000-100,000 indi-viduals, but by the 1970s it had decreased to approximately 4,000 due to hunting and reproductive disorders that were connected to pollution by organochlorides /228/. Abundance based on photo-identification in 2000 revealed an estimate of 15,600 individuals, while an aerial survey in 2004 observed 17,640 grey seals on land /229/. Studies have counted 30,000 grey seals in the Baltic Sea /219/, and it is estimated that the total population in the Baltic Sea was up to 40,000.
7.10.4.2 Distribution
Baltic grey seals are distributed from the northernmost part of the Bothnian Bay to the south-western waters of the Baltic Proper (see Figure 7-43). Generally, during the breeding period, the seals dwell on drift ice in the Gulf of Riga, the Gulf of Finland, the northern Baltic Proper and the Bothnian Bay or on the rocks in the north-western Baltic Sea. As was the case with harbour seals, haul-out sites/colonies are land localities occupied by grey seals. The locations of these sites are shown in Figure 7-43.
Satellite tracking of grey seals has shown that this species moves over several hundreds of kilome-tres in the Baltic Sea. There are indications that seasonal migrations are closely related to the species requirements for feeding and suitable breeding habitats /222/. Typically, however, the an-imals feed locally, foraging just offshore and adopting a regular pattern of travelling between local feeding sites and preferred haul-out sites /230//231/.
Figure 7-43 Haul-out sites (colonies) used by grey seals for resting, breeding and moulting. Global posi-tioning system (GPS) tracking of grey seals is indicated by blue dots. Source: HELCOM Seal Database /223/.
In the Danish part of the Baltic Sea, the number of grey seals has increased drastically over the last decade (see Figure 7-44). The grey seal colony in closest vicinity to the proposed NSP2 route is at Christiansø (part of Ertholmene), north-east of Bornholm, approximately 22 km from the pro-posed NSP2 route. This colony is, at present, the largest Danish grey seal colony, and in 2011-2014, 33-99% of all observed grey seals in Danish waters were detected here /220/. The colony at Ertholmene is at present the largest of the Danish grey seal colonies and up to 600 grey seals have been counted here. In recent years, grey seals have also been observed at the colony of Rødsand, south of Zealand (not on map).
Figure 7-44 Number of grey seals counted during their moulting period (May-June) in the Danish part of the Baltic Sea in the years 2002-2016 /221/.
7.10.4.3 Behaviour and reproduction
Grey seals feed on many species of fish in cold, open waters and breed in a variety of habitats where disturbance is minimal, such as rocky shores, sandbars, sea ice and islands /232/. Birth takes place on pack ice between February and March. Some grey seals, however, also pup at uninhabited islets, most notably in Estonia and in the Stockholm Archipelago as well as in Denmark (Rødsand sandbar). Males follow the female closely after she has given birth, in order to mate with her as soon as nursing has ended. Pups are born in autumn. Within a month or so they shed the pup fur, grow dense, waterproof adult fur and leave for the sea /233//234/.
Grey seals are gregarious and gather for breeding, moulting and hauling out. They primarily haul out in coastal areas, in winter on drift ice close to open water and in summer preferably on unin-habited islands, outer islets and rocks. During the moulting period, they dwell on rocks and islets and sometimes on the last drift ice in the Bothnian Bay /233/.
7.10.4.4 Biodiversity status
In 2017, HELCOM assessed the integrated biodiversity status of the Baltic Sea /104/. The Baltic grey seal population falls below the threshold for ‘Good Status’, based on inadequate reproductive and nutritional status, while the abundance and population growth rate are above the evaluation thresholds.
7.10.4.5 Protection
The grey seal is a protected species listed in Annex II and Annex V of the EU Habitats Directive and Annex III of the Bonn Convention. The Baltic population of the grey seal is also listed as endangered by the IUCN.
In Denmark, the species is furthermore protected under Administrative Order 867 of 27 June 2016 /216/. However, Denmark has recently opened small quotas for hunting grey seal in order to protect fisheries /235/.
Protected areas for marine mammals are described in section 10.
Overview of critical periods for Baltic Sea mammals
The most vulnerable periods for seals in the Baltic Sea are during their moulting, breeding and lactation periods. Harbour porpoises are also vulnerable during the breeding period, but the calves may be vulnerable throughout the first year and especially in the first period after leaving their mothers. Table 7-19 summarises the most critical periods for Baltic Sea marine mammals.
Table 7-19 Critical periods for marine mammals and countries around the Baltic Sea. Countries are defined as “countries in which the species distribution overlaps with the proposed NSP2 route and potential impact area” /194/.
Species Period Country
Breeding and lactation Moulting Harbour porpoise All year (nursing persists
through-out the following year) - Sweden, Denmark, Germany, Fin-land, Poland
Harbour seal May-July August Sweden
Grey seal February-March/April May-June Finland, Estonia, Sweden, Den-mark, Poland, Russia, Germany
7.11 Seabirds
Seabirds are an important component of the marine food chain and of the ecosystem in the Baltic Sea. Furthermore, a number of seabird species have protected status under national/international legislation and seabirds are therefore considered an important receptor.
Seabirds in the Baltic Sea
The Baltic Sea is an important area for numerous seabird species, especially staging seabirds. Sea-bird species encompass many different feeding types. Many are predators of fish, mussels and shellfish, but other types include scavengers and grazers of coastal vegetation. Whereas some spe-cies occur all over the Baltic Sea region, such as breeding common terns and wintering long-tailed ducks, others are restricted to smaller parts of the Baltic Sea or only selected sites.
Seabirds comprise both pelagic species (e.g. gulls (Laridae) and auks (Alcidae)) and benthic feeders (e.g. dabbling ducks, sea ducks, mergansers (Anatidae) and coots (Rallidae)) /236//238/. In 2006, the total number of waterbirds in the Baltic Sea was 10.2 million during winter, 9.8 million during spring, 3.9 million during summer and 5.8 million during autumn /236/. Thus, in terms of numbers, the Baltic Sea is relatively important as a wintering and staging area for seabirds and as a migration route, especially for waterfowl, geese and waders nesting in the Arctic tundra. In spring and au-tumn, the birds use the coastal areas in the Baltic Sea for resting and staging on their migration to and from their nesting grounds. During late summer and early autumn, many seabirds congregate for moulting in particular areas with easy access to optimal feeding grounds. During this moulting period, the birds are generally unable to fly /238/.
Concerning wintering and staging seabirds, the majority of the species are associated with relatively shallow water (<30 m) including lower sub-littoral areas, offshore banks and lagoons. The deeper part of the littoral zone is less important to seabirds. The distribution of seabirds is also affected by proximity to human activities in the shallow areas. A lower number of birds forages in the more open and deeper parts of the Baltic Sea. These feeding grounds are mainly used by pelagic-feeding species such as razorbill (Alca torda), guillemot (Uria aalge), herring gull (Larus argentatus), com-mon gull (Larus canus) and great black-backed gull (Larus marinus) /236//238/.
Seabird populations in Danish marine areas
The Danish marine areas are of international importance for seabirds, and hold significant numbers of birds during all times of the year, with the highest numbers being found during winter and mi-gration periods. Danish marine areas lie at the heart of the major flyway for migratory birds, com-prising some of the most important staging and wintering areas for many species, especially divers, seaducks and alcids. The shallow marine areas are of particular importance to a number of diving
A 2011 report provided national abundance estimates and modelled the distributions of selected species of waterbirds in Danish waters on the basis of aerial surveys /237/. These estimates are presented in Table 7-20. The estimates cover all Danish waters, i.e. the Baltic Sea, the North Sea and inner Danish waters.
Table 7-20 National abundance estimates or guesstimates for six waterbird species/types in Danish waters during winter, spring and summer based on surveys in the summer of 2006, the winter of 2008 and the spring of 2008 and 2009 /237/. “-“ indicates no estimate is available.
Bird species/type Winter Spring Summer
Divers 10-15,000 20,000 -
Common eider 503,000 - -
Common scoter 600,000 - 55,000
Long-tailed duck 28,000 - 0
Red-breasted merganser 55,000 - -
Razorbill / guillemot 76,00 - -
Seabirds in the Danish section of the Baltic Sea
Ertholmene, located north-east of Bornholm, holds one of the largest breeding populations of com-mon eider (Somateria mollissima) and herring gull in Denmark, while the shallow areas of Rønne Banke west of Bornholm provide foraging habitat for the birds, and higher densities are thus found here.
Based on a census of seabirds and knowledge of their biology and ecology, wintering grounds have been identified /238/. These wintering grounds are shown in Figure 7-45.
Figure 7-45 Wintering grounds for seabirds /238/.
Based on the census of the wintering waterbird population covering the Baltic Sea in 2007-2009, a total of 14 species were observed within the Danish EEZ (at Rønne Banke and near the coasts of Bornholm) /238/. The abundance of all species observed in the Danish EEZ represented less than 1% of the Baltic Sea populations. The most abundant species by far was the long-tailed duck (Clangula hyemalis), observed mainly at Rønne Banke. Information on observed species, abundance and conservation status is presented in Table 7-21 /238/.
Table 7-21 Abundance of seabirds observed in the Danish sector during winter surveys in 2007-2009 /238/.
Species Average number of
winter-ing birds 2007-2009* Relative proportion of the Baltic Sea population (%)
Long-tailed duck (Clangula hyemalis) 12,000 0.81
Red-throated diver (Gavia stellata) and
black-throated diver (Gavia arctica) 50 0.58
Great cormorant (Phalacrocorax carbo) 138 0.26
Mute swan (Cygnus olor) 70 0.05
Mallard (Anas platyrhynchos) 2,472 0.97
Common pochard (Aythya ferina) 42 0.14
Tufted duck (Aythya fuligula) 1,334 0.28
Greater scaup (Aythya marila) 3 0.00
Common goldeneye (Bucephala clangula) 73 0.04
Smew (Mergus albellus) 2 0.02
Red breasted merganser (Mergus serrator) 21 0.13
Goosander (Mergus merganser) 24 0.04
Common coot (Fulica atra) 241 0.01
* Wintering birds include staging and migrating (passage) birds.
It should be noted that not all of the seabird species present in the Danish part of the project area are included in the study summarised in Table 7-21 /238/. Only birds observed at the defined transects for surveys are included.
Other species are presented in the following sections, based on information from the IBAs, and species designated as protected under Natura 2000 are presented in section 10.
Seabird studies from NSP
During NSP, surveys of seabirds were undertaken in Danish and German waters. Transect studies were undertaken at Ertholmene in 2008, and at Rønne Banke and Oder Bank in 2006-2007. Fur-thermore, studies were undertaken in the German part of Rønne Banke in 2010-2012.