Good status reflected through the distribution of seals in the Baltic Sea is based on concepts developed for the conservation of seals. The concept for defining threshold values to indicate good status is derived from the general management principle in the HELCOM Recommendation 27/28-2, which states that the distribution is to allow breeding seals to expand to suitable breeding distribution in all regions of the Baltic Sea.
Good status is achieved when the threshold values for all considered parameters are achieved. Good status is achieved when 1) the distributions of seals are close to pristine conditions (e.g. 100 years ago), 2) or where appropriate when all currently available haul-out sites are occupied (modern baseline), and 3) when no decrease in area of occupation occurs (Thresholds figure 1). Three different parameters of distribution are given for all species of seals:
Thresholds figure 1: Good status is achieved when distribution of seals is close to pristine conditions (e.g. 100 years ago), or where appropriate when all currently available haul-out sites are occupied (modern baseline), and when no decrease in area of occupation occurs.
Threshold values are defined for the exact haul-out sites for each species as shown in Results figure 6 for grey seals, and Results figure 9 for Baltic harbour seals. The haul-out sites of ringed seals are dependent on the annual sea ice extent and described in Results figure 3.
The following criteria are used to evaluate whether the threshold value is achieved or failed:
The modern baseline approach is applied when pristine conditions cannot be achieved due to irreversible long-term environmental changes (e.g. sandbanks used for haul-out have vanished), or factors such as multi-fold increased human exploitation of fish stocks that will persist for the foreseeable future. Since the environment has changed over the past century, and formerly used haul-out sites have disappeared in the Southern Baltic, current distributions are evaluated against colonization of currently available haul-out sites. This type of a modern baseline should be defined so that the species will thrive and persist in the future.
Especially in cases where a modern baseline is applied, the additional criterion for evaluating whether good status is achieved 'distributional range is not diminishing' can be applicable for populations above the limit reference level (LRL). The LRL has been agreed in HELCOM to be set at 10,000 individuals per management unit, understanding that the haul-out fraction during moult surveys is 70%.
This HELCOM core indicator is comparable to the OSPAR common indicator M-1; 'Distributional range and pattern of harbour and grey seal haul-outs and breeding colonies', which also applies a modern baseline approach. The difference between the OSPAR 'common indicator' and the HELCOM 'core indicator' is that the latter also encompasses the range of seals at sea during foraging and transport.