There are several important European trade links between the North Sea and the Baltic Sea.

Maritime traffic between the Baltic Sea and the North Sea is linked via the Sound, Kattegat and Skagerack.

There is today a depth restriction in the entry and exit from the Baltic Sea between Sweden and Denmark, which affects the passability of the largest freight and oil tankers.

The large ships can therefore not pass between the seas.

The problem has been solved with so-called STS operations or "ship to ship" as it is also called.

(See video and fact box.)

The Danish-owned towing operator Svitzer has been responsible for STS operations in the area for many years.

These operations have been carried out almost exclusively in the area between Skagen and Fredrikshamn.

But now this has changed.

Just over a week ago, Svitzer announced that it was no longer conducting STS operations due to the current situation in Ukraine.

This has led other players to choose to carry out these operations instead.

Svitzer writes to SVT that since March 3, all STS activities that can be linked to Russian gas and oil trade have been suspended.

Others took over

Since March 3, only one registered STS operation has taken place in the area.

It took place on March 13 and involved a ship carrying oil from St. Petersburg.

The salvage boats that towed the vessels were at that time registered with Norwegian Bukser & Bering and German Fairplay Towage Group.

Vetle Svedrup, CEO of Bukser & Bering, tells SVT that at the time of the towing, they did not know that the ship was transporting oil from Russia.

On the question of whether there may be problems in such an operation at present, Vetle Sverdrup chooses not to comment.

Shortly afterwards, the telephone call is interrupted.

Thorsten Schieferstein, freight manager at Fairplay Towage Group, announces that the towing operator follows all European rules and agreements and therefore does not make any mistakes in substance.

STS operations are common in marine transport and something that happens all over the world where shallow water meets deep.

Implementing an STS makes it easier for ships to transport goods when access is limited.

Something several players currently want to avoid when it comes to Russian ships and Russian cargo.