What scuba divers would be used to seeing in the waters of the Flensburg Fjord - in the westernmost part of the Baltic Sea near the northern German town of Flensburg on the Danish border - can be summed up in two very short words: Not much. But over the past couple of months, divers and boaters have been astonished to find themselves accompanied on occasion by a couple of playful bottlenose dolphins.

On Thursday this week (18.02.2016), a kayaker and a diver spent some quality time with "Selfie" and "Delfie," as the dolphins have come to be called. Last summer, the pair played in the bow-wake of a tourist boat off the south coast of Sweden (picture at top). Their maneuvers have become a local sensation.

"They're uncannily fast, they circle around you and then suddenly emerge from the water," said Stephan Thomsen, a professional diver for the Flensburg fire department. He'd spotted the dolphins four times in the space of this week already. "It's great how close they come up to you."

Ever a wild rover

Bottlenose dolphins can be found in tropical and temperate waters around the world - but not usually in the Baltic Sea, which is only connected to the rest of the global ocean through a pair of narrow channels on either side of the island of Sjaelland (Zealand).

The island on which Copenhagen sits is poised like a cork in a bottle between peninsular mainland Denmark to the west, and the southern tip of Sweden to the east. It's through one of the channels bordering Sjaelland that the bottlenoses swam into the Baltic Sea.

"It's pretty special having this dolphin species here," said Harald Benke, director of the German Ocean Museum Stralsund, who wrote his PhD about whales and dolphins. Common dolphins or white-beaked dolphins have occasionally been seen in Baltic waters, according to Benke - but bottlenose dolphins, almost never.

Since record-keeping began, there have been only three previous sightings of bottlenoses, the marine biologist said: A dead bottlenose was found floating in the waters near Stralsund in 1842, and another near Lübeck in 1882.

In 1852, a pod of bottlenoses was seen swimming in the shallow waters near Greifswald. Other than those three incidents, all has been quiet on the bottlenose-dophin-spotting front in the Baltic Sea over the past couple of centuries.

The two bottlenoses now cruising the Baltic must have entered from the Atlantic nearly a year ago. They spent the summer off Kalmar in southern Swedish waters, where they were also a hit with tourists.

Clever, friendly, wild predators

"Dolphins are highly intelligent animals," Benke said. "They have tight-knit social groups and they're very playful." The two Bottlenoses have been demonstrating their playfulness by approaching divers and sea kayakers, circling and leaping, and playing in the bow-waves of boats.

However, people should keep in mind that the animals are wild predators, Benke warned. They're fine "as long as they're not tormented or irritated." But it would be a mistake to get too close to their mouths, grab at them, or chase them in the water.

Stephan Thomsen, the fire department diver, returned three more times after first spotting the dolphins over the course of the past week, to take photographs and shoot video footage. "They don't like flash photographs," he said. "If you use a flash, they turn around and swim away."

"The dolphins seems to feel good about being here," Benke said. The chances for their survival in the Baltic Sea, in his view, are good.

Given how sociable the creatures are, however, the absence of any other members of their species in Baltic waters could leave them feeling a bit lonely. It's good they have each other.

nz/sd (DPA)