Seal monitoring methods

Today, the estimates about seal populations in Finland are based on aerial surveys. Until the middle of the 1970's the estimates of seal numbers were mainly based on calculations in which hunting statistics played a major part.

Aerial surveys are the most effective and fastest way to estimate the number of seals. Grey seal numbers are obtained by counting them during their moulting period, towards the end of May and in the beginning of June, on the islets of the outer archipelago. The counts, which take two weeks, are carried out at the same time in Finland, Sweden, Estonia and Russia. The census period is short to minimize multiple counts of the same individuals who may move from one place to another.

Grey seals are social animals. During moulting in May-June, grey seals gather in great colonies consisting of over a thousand individuals on the islets of the outer archipelago. Photo: Mervi Kunnasranta

The count of ringed seals takes place during the moulting period in April on the last remaining ice floats. In the ringed seal count the result is a sample-based estimate (the counting lines cover only a part of the total area of the ice), in the grey seal count the result is an accurate, counted value of the minimum number of individuals.

The count results are less than the true size of the population, since some seals are always in the water out of reach of the count, no matter what the weather conditions may be. The counts nevertheless take into account a large proportion of the population, and as the counts are repeated at the same time year after year, the results give a good idea of the seal population trends.

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