Assessment Protocol

This core indicator uses three different parameters for evaluating the distribution of the three species of seal that occur in the Baltic Sea. These parameters are:

  1. distribution during breeding
  2. distribution during moulting, which occurs on land or ice,  where data is achieved by surveys from land and air in both cases
  3. area of occupancy, which is the area used for foraging and transport. Data is given by satellite- and GSM tagging data

All three components are evaluated for each species in the applicable areas. Good status is achieved if a species in a given area achieves the threshold values for all three parameters. If one parameter does not achieve the threshold value, then the result for the evaluation for the given species and area is not good status i.e. the One-Out-All-Out (OOAO) approach.


Assessment units and management units

This core indicator evaluates the distribution of Baltic Sea seal species using HELCOM assessment unit scale 2 (division of the Baltic Sea into 17 sub-basins). The assessment units are defined in the HELCOM Monitoring and Assessment Strategy Annex 4.

The existing management plans for seals operate according to management units that are based on the distribution of seal populations. The management units typically encompass a handful of HELCOM scale 2 assessment units. Evaluations are therefore done by grouping HELCOM assessment units to align with the management units defined for each seal population.

  • The assessment of grey seals is carried out using grouping of scale 2 HELCOM assessment units Data is available both from land-based surveys starting in the mid-1970s and later aerial surveys.
  • The Baltic ringed seal is distributed in the Gulf of Bothnia (northern management area) on the one hand and Southwestern Archipelago Sea, Gulf of Finland and Gulf of Riga on the other (most southerly management area), and is represented by two different management units. This sub-division is justified by ecological data that indicate separate dynamics of the stocks. Since ringed seals from both areas show a high degree of site fidelity, as seen in satellite telemetry data (Härkönen et al. 2008), it is unlikely that extensive migrations occur at current low population numbers, although some individuals can show more extensive movements (Oksanen et al. 2015)
  • Harbour seals in the Kalmarsund, Sweden, constitute a separate management unit and is the genetically most divergent of all harbour seal populations in Europe (Goodman 1998). It was founded about 8,000 years ago, and was close to extinction in the 1970s as a consequence of intensive hunting, and possibly also impaired reproduction (Härkönen et al. 2005). The genetic diversity is substantially reduced compared with other harbour seal populations
  • Harbour seals in the southwestern Baltic (Danish Straits, Danish, German, Polish Baltic and the Öresund region including Skåne county in Sweden) as well as the Kattegat are genetically connected, and should be managed as a metapopulation, where sub-populations may have different growth and vital rates. Management actions should take special care dealing with small sub-populations, ensuring that anthropogenic activities do not jeopardise future persistence of such sub-populations.
  • Harbour seals in the Limfjord form a separate management unit and are genetically distinct from the Kattegat harbour seals (Olsen et al. 2014).