Thresholds and Status evaluation

Good status is achieved when the aggregated ratio for annual pregnancy rate and inferred birth rate achieve the threshold value (of 1). The initial assessment addressed the annual pregnancy rate and the inferred birth rate to determine if each parameter meets the level of at least 90% in an increasing population - for five years and older harbour seals and six years and older grey and ringed seals (see assessment protocol, below).

The concept for defining threshold values for reproductive rates of seals is derived from the general management principle in the HELCOM Recommendation 27/28-2, which states that the population size is to be managed with the long-term objective of allowing seal populations to recover towards carrying capacity levels. The Recommendation further states that the long-term goal is to reach a health status that ensures the future persistence of marine mammals in the Baltic.  Reproductive rate is an important aspect of population status, affecting population growth rate.  

A modern baseline approach is applied for establishing the threshold value for all species of seals, since pristine conditions are unknown. The modern baseline is based on the first available data, and data on reproductive rates from populations with minimal impacts from human activities are used in this indicator. 

 

Thresholds table 1. Species specific threshold values for seal species showing increasing populations (i.e. not currently at carrying capacity) in the Baltic Sea, as agreed by HELCOM HOD 48-2015 (outcome para 3.63, Annex 4).

 
 Species
Threshold value
Age class [year]  
Threshold value
Pregnancy rate
Grey seal
≥6
90%
Ringed seal (tentative)
≥6
90%
Harbour seal
≥5
90%

 

The modern baseline approach (using 1992 data as a baseline) is also applied in OSPAR (Commission for the Protection of the Marine Environment of the North-East Atlantic).  The reproductive rate would appear to be similar as the OSPAR common indicator M5: 'Grey seal pup production', but pup production is only used for estimating total population size by multiplying numbers of counted pups with a factor between 4 and 5 in HELCOM. For these indicators there is no comparability between HELCOM and OSPAR.