Phoca vitulina vitulina (LINNAEUS 1758), Common (harbour) seal (Phocidae)

Compiled by: Dieter Boedeker & Wolfgang Dinter, Germany

1. Description of the habitat/autecology of the species

Common seals occur in all moderately temperate seas of the northern hemisphere. They grow to an average length of 1.4 – 1.7 metres and a mass of up to 100 kilograms, and they can reach a maximum age of 36 years  (Härkönen and Heide-Jörgensen 1990). Generally the species is gregarious, hauling out in small to large scattered groups to breed, moult and rest. Some colonies in protected bays and estuaries can number over 1,000 individuals[1]. Females become sexually mature between 3 and 6 years and they then normally generate one pup every year. The pups are usually born on sheltered beaches, rocks or littoral sandbanks, from where they can follow the mother into the water immediately after birth. Common seals feed on a great number of fish species (Härkönen 1987 a, b, 1988). They tend to stay within 25 km from shore but individuals are occasionally found 100 km or more offshore.

2. Distribution (past and present)

With a population of about 15,000 in 2007 (Härkönen et al. 2008), common seals are very abundant in the Skagerrak, Kattegat and the Belt Sea area, whereas further east (east of 13^o E) they are restricted to only three small breeding colonies with the Kalmarsund as their easternmost breeding area. The Kalmarsund population differs genetically from the current Skagerrak/Kattegat and Southwest Baltic common seal populations (Stanely et al. 1996).

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

The Baltic Sea area populations of the common seal are considered to be of sub-regional 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

In the beginning of the 20^th century the population in the Skagerrak, Kattegatt and the Danish Straits exceeded 17000 but declined to some 2500 in the 1930s as a consequence of hunting (Heide-Jörgensen and Härkönen 1988). In times from the 19^th to the 20^th century the population in the western Baltic Proper was about 5,000 compared to ca. 1000 in 2007 (Karlsson et al. 2008). The Skagerrak/Kattegat population has ben hit by three massmortalities. The two first, in 1988 and 2002 were caused by  PDV virus and killed half the population on both occasions. The third epidemic in 2007 killed some 3000 seals was caused by an unknown pathogen. The recovery rate in the Kattegat is low ever since the 2002 epidemic[2].

5. Threat/decline factors

The common seal populations were severely depleted by hunting, by-catch in fisheries, and later by diseases related to effects of pollution and the PDV virus. Other threats include habitat loss due to coastal development. A low rate of population increase in the Kattegat area, compared to the Skagerrak prior to the 2002 epizootic, may be an indication of reduced reproductive capacity (ICES 2005).

6. Options for improvement

National seal conservation and management plans should be developed in order to ensure conservation 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 conservation and monitoring strategies regarding shared seal populations with neighbouring countries.

7.  References

Härkönen, T. and M.-P. Heide-Jørgensen 1990. Comparative life histories of East Atlantic and other harbour seal populations. Ophelia 32 (3): 211-235.

Härkönen, T. J. 1987. Seasonal and regional variations in the feeding habits of harbour seals Phoca vitulina in the Kattegat and the Skagerrak. J. Zool. Lond. 213: 535-543.

Härkönen, T. J. 1987. Feeding ecology and population dynamics of the harbour seal (Phoca vitulina) in Kattegat-Skagerrak. Ph. D. Thesis. University of Göteborg.

Härkönen, T. J. 1988. Food-habitat relationship of harbour seals and black cormorants in Skagerrak and Kattegat. J. Zool. Lond. 214: 673-681.

Harkonen, T., Bäcklin, B-M., Barrett, T., Anders Bergman, A., Corteyn, M., Dietz, R., Harding, K., Malmsten, J., Roos, A., Teilmann, T. (2008). Mass mortality in harbour seals and harbour porpoises caused by an unknown pathogen. The Veterinary Record, 162: 555-556.

Härkönen, T., R. Dietz, P. Reijnders, J. Teilmann, K. Harding, A. Hall, S. Brasseur, U. Siebert, S. Goodman, P. Jepson, T. Dau Rasmussen, P. Thompson (2006). A review of the 1988 and 2002 phocine distemper virus epidemics in European harbour seals. Diseases of Aquatic Organisms, 68: 115-130.

Heide-Jørgensen, M.-P. and T. Härkönen. 1988. Rebuilding seal stocks in the Kattegat-Skagerrak. Marine Mammal Science. 4(3):231-246.

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

Stanley, H. F., Casey S., Carhahan, J. M., Goodman, S., Harwood J. & Wayne R. K. 1996. Worldwide patterns of mitochondrial DNA differentiation in the harbour seal (Phoca vitulina). Mol. Biol. Evol. 13: 368-382.

^[1] http://www.pinnipeds.org/species/harbour.htm

[2] Interestingly, the distinct Kalmarsund population was not affected by the PDV virus epidemics in 1988 and 2002.

Last updated: 9.6.2008