Results and Confidence

Grey seal 

The grey seal did not achieve good status in the Baltic Sea with regard to reproductive status during 2011-2016 (Results figure 1). The reproductive rate (the proportion of pregnant females and females having postpartum pregnancy signs) reached the threshold value in the 2013, 2014 and in 2016 but on average across the current assessment period the threshold value of 90%, which is representative of a healthy increasing population, was not achieved. The inferred birth rate parameter achieved the threshold in 2014 and 2015, though failed the threshold value on average for the current assessment period (Results table 1 and Results figure 2). Combining these two parameters into a single status assessment indicated that the aggregated threshold value (see assessment protocol below) was achieved in 2013 and 2014, however the overall average for the assessment period 2011-2016 field the threshold (Results table 1). These assessment results must be treated with caution since the sample size (165 for whole assessment period) is small in relation to the population size, and this factor is reflected in the confidence assigned to the indicator assessment. Current pooled data from Finland and Sweden show that pregnancy rate is 82% (SD = 13%) in 6–24 year-old females referring to the period 2011–2016. It is however important to note that there do appear to be improvements with pooled values for the period 2014-2016 indicating the threshold would be achieved (91 %) and the aggregated assessment value for this shorter more recent period being 1 which would also indicate that the indicator may be on the borders of achieving the threshold values in recent years.

 

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Results figure 1. Baltic grey seals is not in good status with regard to reproductive rate. Click here to access interactive maps at the HELCOM Map and Data Service: reproductive status of seals.

 

Results table 1. Data and aggregated results for the reproductive status of the grey seal. The numbers in parentheses indicate the number of samples in the parameter. In the three last columns, 1.0 represents the threshold value for which and ratio values is compared, with values at or above 1 indicating good status. 

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Results Figure 2.  Temporal change in the parameters used to evaluate the reproductive status of seals. The squares represent the reproductive rate (pregnancy rate) based on Swedish data. The diamonds represent reproductive rate (inferred birth rate) based on Finnish data. These two parameters are shown on the % scale (left vertical axis). The filled black circles and trend line represent the combined indicator value (aggregated ratio, see Results table 1) which is used to assess the overall status against the threshold value (1, green line), as shown on the right vertical axis.

 

Ringed seal

The provisional assessment indicates that the threshold value of 90% is not met for ringed seals. The pregnancy rate of >5-year-old females was 71% (SD = 46.2, n = 34, 95% Cl = 54.5–86.7) in 2001–2015. The corresponding figure before 2001 was 41% (SD = 49.7, n = 46), suggesting that the reproductive rate has improved during the 2000s (Results figure 3). Pregnancy rates of females > 4 years of age was 70% (SD = 48.3, 95% Cl = 35.4–1.05) during the 2000s but the sample size is very small (n = 10). Combined it is not possible to assess the reproductive status of ringed seals because the sample size is too small.

 

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Results Figure 3. Reproductive rate of ringed seals 1986–2015 from Finnish and Swedish data.

 

Harbour seal

The threshold value is set at 90% also for harbour seals, but no assessment could be conducted at this time due to data constraints, and an assessment will be developed in the future.

 

Confidence of the indicator status evaluation

Overall, the confidence for the assessment is low due to small sample size in relation to the population sizes, and due to the current limited spatial sampling. Furthermore, in future assessments of reproductive status it will be important to review if the seal populations have reached carrying capacity or not, as this can markedly influence the threshold values applied.

In addition to wider data coverage additional data should be gathered where possible for grey seals in Finland and Sweden so the confidence of the indicator status evaluation for this species in the central and northern part of the Baltic Sea can be improved. Currently the samples used in this assessment are dominantly from the northern Baltic Sea regions, though they also include Swedish data from the southern Baltic Sea. However, it would be desirable to include samples from Denmark, Germany and Poland. An improved reporting and data collating system for this indicator would facilitate progress, for example annual reporting of relevant data from all countries.

The confidence of the evaluation for ringed seals is low due to insufficient data for evaluating the reproductive rate against the threshold. The difference between birth rate and pregnancy rate would give us valuable data of fetal mortality, if the data for pregnancy rate were larger.

High confidence will be achieved for harbour seals in the Kattegat for the phase of exponential growth. Material is collected annually, but remains to be compiled and analysed. However, threshold values remain to be elaborated for the carrying capacity scenario as well.