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Seismic surveys do not significantly harm Calanus finmarchicus

Field experiments show that seismic activity does not harm this important species of zooplankton: not at all when the air guns are over ten metres away, and with a maximum of 30% higher mortality than controls even in close proximity.

As the favourite food of several important fish stocks, Calanus finmarchicus is a species of zooplankton that plays a key role in the ecosystem in the Norwegian Sea.

Seismic surveys are also carried out in the Norwegian Sea.

Seismic surveys involve firing many air guns simultaneously in order to produce powerful, low-frequency sound waves. 

By analysing their echoes, geologists form a picture of the composition of the sea bottom and of whether there are any oil and gas deposits in the area.

Seismic activity often takes place in important fishing grounds

“Seismic surveys are often performed in areas that are important to large, commercial fisheries, and often in key grazing areas”, says Nils Olav Handegard, a scientist at the Institute of Marine Research (IMR).

“We are studying how seismic activity may affect marine life. Since Calanus finmarchicus plays such an important role in the ecosystem, we wanted to see whether it could be killed by sound waves from seismic surveys.”

Low mortality rates at distances of over 10 metres

To investigate this, the researchers did a field survey at the Austevoll archipelago in Hordaland.

They fired air guns at varying distances from the zooplankton, ranging from right beside them to 25 metres away. They also had a control group of zooplankton away from the area where seismic activity was taking place.

“At distances of 0-5 metres, the mortality rate was a maximum of 30% higher than in the control group”, says Handegard.

“One week after the seismic activity, the mortality rate of the plankton ten metres away from the air guns was also nine percent higher than in the control group.

But the group exposed to seismic activity at a distance of twenty metres showed no difference from Calanus finmarchicus that hadn’t been exposed to seismic activity at all.”

No change in escape response

As well as studying the mortality rate of Calanus finmarchicus, the researchers also looked at whether its ability to escape from danger was affected.

Calanus finmarchicus has ‘antennae’ that enable it to ‘feel’ any predators and hence to flee danger. We wondered whether this response would be affected, for example through damage to the antennae”, explains Nils Olav Handegard.

However, they didn’t see any signs of this.

“The escape response of Calanus finmarchicus was not affected, regardless of their distance from the air guns”, says the IMR researcher.

Few negative impacts on Calanus finmarchicus

The field experiments did not identify any major negative impacts of seismic activity on Calanus finmarchicus.

“Our results suggest that seismic surveys have little impact on Calanus finmarchicus, provided that the plankton are over ten metres away from the air guns and limited effects even in close proximity.”, concludes Nils Olav Handegard.

The research project and the resulting scientific paper are collaborations between the Institute of Marine Research and Bigelow Laboratory for Ocean Sciences, US.