Halichoerus grypus, Grey Seal (Phocidae)

Compiled by: Dieter Boedeker & Wolfgang Dinter, Germany

1. Description of the habitat/autecology of the species

Grey seals are found on both sides of the North-Atlantic in temperate and sub-Arctic waters. The actual Baltic Sea population is distinct from the eastern North-Atlantic population. Grey seals are gregarious and gather together for breeding, moulting and hauling out at exposed areas. The main breeding season in the Baltic Sea is from February to March. Pupping in the Baltic Sea takes place mostly on drift ice although in some areas seals also give birth on land. The pup is nursed for about 15-18 days. Grey seals moult on ice and haul-out sites from April-June. In the Baltic, they grow to an average length of 1.65 – 2.1 meters and a mass of 100 – 180 kg for females and > 300 kg for males. They can reach an age of 25 (males) – 35 (females) years[1]. Females become sexually mature between 3 and 5 years. The pup is born with a creamy-white woolly lanugo coat, which it will moult after 2-4 weeks for a shorter adult-like coat[2]. Grey seals are sexually dimorphic, e.g. distinct larger sized males with a more convex muzzle, although grey seals in the Baltic do not exhibit the degree of sexual dimorphism generally ascribed to this species (Karlsson 2003). They feed on a wide variety of fish. The diet varies with location, season and prey availability (Stenman & Pöyhönen 2005, Lundström et al. 2007). Fasting occurs during the breeding and moulting seasons[3]. Juveniles in particular are known to travel over long distances (Sjöberg et al.).

2. Distribution (past and present)

Today (2008), the grey seal population is growing fast (up to 10 % per year) in the Baltic Sea (see Halkka et al. 2005, Stenman et al. 2005, Harding et al. 2007). Grey seals are mainly distributed north of latitude 58^o N, whereas in the beginning of the 20th century the species was frequently abundant over the entire marine area.  The number of grey seals counted in 2007 was about 22,000 individuals (it should be noted that census numbers are always smaller than the real population size). However, the results of annual censuses demonstrate a clear increasing trend in Baltic grey seal numbers. A model calculation has estimated that in the beginning of the 20^th century, the estimated population size was in the range of tens of thousands up to 100,000 (Kokko et al. 1999, Harding and Härkönen 1999), but only 2,000 in the late 1970s (Boedeker et al. 2002).

3. Importance (sub-regional, Baltic-wide, global)

The Baltic Sea area population is considered to be of Baltic-wide importance in the HELCOM area. In EU waters, this species is protected by the Habitats Directive and listed in its Annexes II and V.

4. Status of threat/decline

Although the population size is steadily increasing since the end of the 1970s, the former distribution area south of latitude 58^o N is being recolonised only very slowly. In Germany, for example, its status is assessed as “critical” for the Baltic Sea (Merck & von Nordheim 1996). According to the EU Habitats Directive Art. 17 reporting, the conservation status in Finland is assessed as favourable.

5. Threat/decline factors

By the 1970s, hunting and pollution had reduced the total population drastically. Current threats include habitat loss due to coastal development, and entanglement of young seals in fishing gear.

6. Options for improvement

National seal conservation and management plans should be developed in order to ensure proper conservation and management of the populations. These should include continuation of long-term monitoring and research programmes, the restoration of suitable habitats where appropriate, as well as the establishment and proper management of seal sanctuaries. Further, the responsible national authorities should coordinate their management and monitoring strategies regarding shared seal populations with neighbouring countries.

7. References

Boedeker D., Benke H., Norden Andersen O., Strempel R. 2002. Marine Mammals. Environment of the Baltic Sea Area 1994-98). BSEP 82b: 171-173.

Halkka, A., Helle, E., Helander, B., Jussi, I., Karlsson, O., Soikkeli, M., Stenman, M. & Verevkin, M. 2005. Numbers of grey seals counted in the Baltic Sea, 2000–2004. International conference on Baltic seals, 15–18 February Helsinki, Finland.

Harding, C.K., Härkönen, T, Helander, B. and O. Karlsson 2007. Status of Baltic grey seals: Population assessment and extinction risk. NAMMCO Sci. Publ. 6:33-56

Harding, K.C., and Härkönen, T.J. 1999. Developments in the Baltic grey seal (Halichoerus grypus) and ringed seal (Phoca hispida) populations during the 20th century. Ambio, 28(7): 619-627.

ICES 2005. Advice to HELCOM on seal and harbour porpoise populations in the Baltic marine area.

Karlsson, O. 2003. Population structure, movements and site fidelity of grey seals in the Baltic Sea. Ph.D thesis, University of Stockholm.

Kokko,H, E Helle, J Lindström, E Ranta, T Sipilä, F Courchamp, 1999, Backcasting population sizes of ringed and grey seals in the Baltic and Lake Saimaa during the 20th century: Annales Zoologici Fennici, v. 36, p. 65–73.

Lundström, K., Hjerne, O., Alexanderson, A., & O., Karlsson 2007. Estimation of grey seal (Halichoerus grypus) diet composition in the Baltic Sea. NAMMCO Sci. Publ. 6:177-196

Merck T., von Nordheim H. 1996. Rote Listen und Artenlisten der Tiere und Pflanzen des deutschen Meeres- und Küstenbereichs der Ostsee. Schriftenr. f. Landschaftspfl. u. Naturschutz Heft 48: 108 pp.

Stenman O., Pöyhönen O. 2005. Food remains in the alimentary tracts of Baltic grey and ringed seals. Symposium on Biology and management of seals in the Baltic area, 15-18 February 2005 Helsinki, Riista- ja kalatalouden tutkimuslaitos 51-53.

Stenman O, Verevkin M, Dmitrieva L, Sagitov R (2005) Numbers and occurrence of ringed seals in the Gulf of Finland in the years 1997-2004". "Symposium on Biology and Management of Seals in the Baltic area, 15 –18 February 2005 Helsinki, Riistaja kalataloudentutkimuslaitos: 55-57.

[1] http://www.chelonia.demon.co.uk/GREYSEAL.html

[2] http://www.pinnipeds.org/species/grey.htm

[3] http://www.pagophilus.org/grey.html