Kattegat

After several weeks at anchor in the Kattegat strait between Sweden and Denmark, the Chinese tanker was eventually boarded by authorities from Sweden, Denmark, Germany and Finland, but then set sail last week.

The ship has been in the Kattegat strait - a passage between Sweden and Denmark that connects the Baltic Sea to the North Sea - since 19 November and is being monitored by the Danish navy.

For many years researchers thought that the harbor porpoises in Kattegat were fine.

At least that is the case for the population living in Kattegat.

The porpoises in the Kattegat hunt fish in shallow waters, but that is also where most of the recreational motor boats are.