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North de Kort
editor online
The explosions in gas pipelines Nord Stream 1 and 2 last September probably caused cod, porpoises and seals in the area to die or go deaf. This is the conclusion of Danish, German and Polish researchers.
It is good that attention is being paid to the effects of explosions on marine animals, says marine ecologist Geert Aarts of Wageningen University & Research and the Royal Netherlands Institute for Sea Research (NIOZ). “Because this also happens in the Netherlands.”
He is talking about controlled explosions of bombs from the First and Second World War, which lie on the bottom of the Dutch North Sea. In World War II, English pilots often dropped bombs they had not dropped in Germany into the North Sea to save fuel.
“Defence clears those bombs,” says Aarts. In 2021 there were 52 pieces. In the event of an explosion, porpoises and seals in the immediate vicinity can die, and further away from the blow they become completely or partially deaf, says Aarts.
No more catching fish
At the beginning of last year, a lot of commotion arose when the Defense Explosive Ordnance Disposal Service (EOD) cleared a bomb from World War II off the coast of Zandvoort. That explosion was comparable to the explosions at the Nord Stream, says Aarts. The bang and vibrations could be heard and felt miles away and raised questions about the impact on marine mammals.
“Normally, if it’s further from the coast, it doesn’t matter,” says Aarts. “While it can have quite serious consequences.”
The shock waves from the explosions in Nord Stream 1 and 2 immediately killed all harbor porpoises within a radius of 4 kilometers, the researchers estimate in the recent report. Because the population in the Baltic Sea is relatively small at 500 animals, the loss of a few animals is already a threat to survival, they say.
Porpoises may also have become deaf within a radius of 50 kilometers. And that is problematic, says Aarts. “Porpoises send clicks in the water, and with the help of reflection – just like bats – they know where a fish is swimming and how big it is. If a porpoise has severe hearing damage, it can no longer catch a fish, and the chances of survival are slim. “
Population under pressure
In the North Sea, the population of porpoises is much larger: 350,000 animals, of which 30,000 to 80,000 in Dutch waters. But here too, according to Aarts, the population is under pressure from, among other things, shipping, bycatch, and therefore also explosions.
A 2016 study showed that explosions in the North Sea probably cause permanent hearing damage to more than 1,000 harbor porpoises each year, and temporary hearing damage to 15,000 to 25,000.
In 2015, the Ministry of Defense commissioned research into how far porpoises can hear the sound of the explosion, and at what distances permanent or temporary hearing loss can occur:
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NOSThe impact of an explosion in the North Sea on harbor porpoises near the seabed -
NOSThe impact of an explosion in the North Sea on harbor porpoises at the sea surface
Since 2015, Defense has been disposing of more and more bombs in the North Sea, according to figures from Rijkswaterstaat. In 2015 there were 26, in 2021 there were 52 cleared bombs. The increase is partly due to the construction of wind farms at sea, says Frans-Peter Lam of the TNO research institute. “People don’t want accidents, so an area where such a wind farm will be built will be thoroughly searched for bombs.”
When clearing explosives, the Ministry of Defense looks in advance at what measures are possible to reduce the risks for marine animals, says spokesman Alex Kranenburg. For example, by leaving an explosive lying around or detonating it elsewhere in the sea or on land.
But that is not always possible, which is why mine hunters have been using an Acoustic Deterrent Device (ADD) since 2018. “By emitting a certain sound underwater, it scares away porpoises and seals before we detonate explosives in a controlled manner.”
Those devices don’t help against everything, says Aarts. “If you detonate a bomb, it always has an impact. The sound goes much further than that device can scare away animals.”
Thousands more bombs
The Ministry of Defense has conducted research into other methods of detonating explosives that have less impact on marine animals. “But they are not always successful and in certain cases entail other problems,” says Kranenburg. More research is needed, he says.
But he also points out that it is “tremendously important that explosives are cleared at sea”. It is estimated that there are still thousands of bombs on the bottom of the North Sea. “When a fishing or merchant ship sails on an explosive device, the environmental damage is much greater and less easy to oversee.”
- Rare large number of sea mines cleared in the North Sea
- Helderse fishermen bring up a huge depth mine
- Rare mass stranding of harbor porpoises on Wadden Sea, and more to come
