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Saturday, 29 October 2016

Toxic risk from sunken ships off the Swedish coast

Both media and research focus has been put on the risk posed by sunken ships off the Swedish coast. One especially media friendly collection of wrecks are the wrecks on the Swedish Exclusive Economic Zone (EEZ) off the island and lighthouse Måseskär (west of Orust on the Swedish west coast). After World War II German ships were sunk there by the allies, the ships were filled with German ammunition and chemical weapons. The number of ships, the amount of ammunition, what type of chemical weapons and so on is unclear. After reading reports from the latest investigations on site (Swedish Maritime Administration, 2015) it is clear that it is bad. However, the claims made over the last 20-30 years by journalists about the number of ships and amount of mustard gas is most probably exaggerated and a result of unreliable secondary sources. But let us not focus on those issues because the problems are real no matter what.
The work localizing and learning more about the wrecks off Sweden is an intriguing  mix of diving, ROVs, archive searches, risk analysis and classic detective work. It thus includes an important, challenging and close cooperation between researchers and practitioners. It is from 2016 decided that the (new) agency Swedish Agency for Marine and Water Management (SwAM or HaV in Swedish) is responsible for the coordination of the work and late 2016 the first wrecks will be investigated for oil and emptied if oil is found. The first wreck to be drilled for oil is the Thetis in the Skagerrak. The SwAM is also aiming for IMO to ban fishing around the ammunition  ships off Måseskär on the Swedish EEZ.
The list of the most prioritized wrecks (the emergency to-do list) also include ships in other positions than off the Swedish west coast. One is just of my home island where I and many others often passes over it on the fairway to and from Stockholm. It is the cargo ship Harburg, she collided February 16, 1957 with the tanker Tinny. Harburg sank fast and 10 men were killed. Tinny of 16450 DWT, loaded with gasoline, was on her way to Stockholm and hit Harburg amidships and probably caused the boiler to explode and tare the ship up from inside. The collision pushed Harburg down under Tinnys keel. Harburg sits on approximately 30-37 m depth about 180 meters from shore. The ship is broken just in front of the first cargo hold with the bow lying flat on the ground and the aft part of the angle from the bottom. Harburg has previously leaked oil.

An interesting side story to this investigation is that neither fishermen nor fish are stupid ;-)

While on site the Swedish Maritime Administration used both side scan sonars and ROVs to investigate the wrecks. What was evident from the sonar data was that the waters are often used as fishing ground for bottom trawling. From the tracks it is clear that the fishermen knows the positions of all the wrecks and to a good job dragging the trawl in-between as shown on the picture below.
Tracks from bottom trawling. (C) the Swedish Maritime Administration, 2015.
However, also the fish seems to have grasped the important aspects of the situation and spend their time cramped together just around the wrecks. This is evident from the ROV reports as there was problems getting any shots of the wrecks and cargo onboard as a result of all the fish. (Sadly the Swedish Maritime Administration does not publish the pictures with the fish, the focus on the wreck. However, you can find fish also on those pictures as shown below.) I suspect that the fish has analyzed the fishermen's activity and now make sure to spend their time where they are out of reach for the trawlers...
ROV and side scan sonar pictures. Note the weapons on the ROV pictures and around the ships on the sonar picture, but also the fish on the top left picture. (C) the Swedish Maritime Administration, 2015.
Swedish Maritime Administration, 2015. Miljörisker sjunkna vrak II, Undersökningsmetoder och miljöaspekter [Environmental risks from sunken wrecks II, Investigation and environmental aspects]. Dnr: 1399-14-01942-15. Swedish Maritime Administration