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Seal population on the rise in Baltic Sea

The grey seal population has grown by an average of five percent annually since the turn of the millennium.

A grey seal in the Gulf of Finland. Image: AOP

More than 38,000 grey seals have been observed in the Baltic Sea this year, the Natural Resources Institute Finland (Luke) said on Tuesday. Previous counts have suggested that the number has levelled off at around 30,000 in recent years. Less than half of the animals, some 14,200, are in Finnish territorial waters.

Grey seals (Halichoerus grypus) can typically be seen on remote rock skerries in late May and early June, when they shed part of their winter fur. At this point most of them can be photographed from the air. In Finland the species is primarily seen in late spring on the outer islets of the southwestern Archipelago, around the same time as in maritime areas off central Sweden and western Estonia.

The Baltic Sea's grey seal population has grown by an average of about five percent annually since the early 2000s. In recent years the growth has been most brisk in the southern Baltic, mostly due to seals moving there from other areas. Biologists note that the larger number of seals counted last spring may be partly due to better-than-usual conditions during the census period.

Fluctuations linked to ice conditions

The number of Baltic ringed seals (Pusa hispida botnica) counted in the Bothnian Bay has fluctuated in recent years.

This year 12,800 Baltic ringed seals were detected in the Bothnian Bay, up from about 9,900 last year. In 2017 though the number was 13,600.

Luke researchers say that these differences are attributable to ice conditions, which have varied sharply over the past six years. Larger groups of ringed seals are seen in years when the ice has begun to break up before the census. In these years the overall count is significantly higher than when the ice is still intact at census time.

There are at least five subspecies of ringed seals, including the Baltic ringed seal, classified as a vulnerable species, and the endangered Saimaa ringed seal (Pusa hispida saimensis), which is endemic to eastern Finland's lake district. The latter population recently surpassed 400, but its future still remains in doubt.