The Swedish Museum of Natural History is currently carrying out studies on the health, susceptibility to pollution, and genetics of the endangered species.
“To get two reports from the central Baltic in such a short space of time is fantastic,” said museum researcher Anna Roos in a statement.
“We generally just get the occasional report per year form the Baltic Sea and we now encourage anybody who spends time around the Baltic Sea area to keep an eye out for porpoises and report observations to us via our website,” she added.
The museum said the first of the two recent sightings was recorded south-east of Stora Fjärdholmen in the Stockholm archipelago. The second came a week later when a group of five to ten porpoises was spotted between the Söderarm and Tjärven lighthouses north-east of Norrtälje.
Porpoises are small-toothed whales and are related to dolphins. But, unlike dolphins, they can be hard to spot as they are quite shy and rarely leap out above the water’s surface.
Baltic Sea porpoises often die after becoming entangled in fishing nets and are listed as Critically Endangered.