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Finding ghost gear with 3D sonar

At the weekend, our team comprising volunteers from Fathoms Free and Sea Shepherd UK were busy surveying two locations in Falmouth Bay, Cornwall.

The plan was for the two teams to each carry out two dives on two different marks (sites) to assess their condition and whether or not we should return with a larger team and additional boat for a large coordinated clean up of the area.

Due to the single RIB full of divers, two sets of cylinders, and lonesome skipper, we wouldn't be lifting anything unless it posed an immediate danger to life.

After the first dive, both teams reported that there were various amounts of trawl net tangled into wreckage that should be revisited and cleared, and that we should move onto the second to see what was there.

During the surface interval, we slowly scanned the sea floor between and around the two marks to see if we picked up anything interesting on the sounder. Not far from the second planned dive site, we spotted something "interesting" on the scanner at a depth of 26m and decided that we should take a look.

Within 10 minutes of the teams entering the water, a lift bag appeared just a few metres from the shotline!

It turned out we had found a tangled mass of ghost monofilament gill net suspended in the water column! The deadly net was snagged on the sea floor and was stretching a few metres upwards on its floats. After the first tangled mass was sent up on a lift bag, the remaining was brought up by divers in manageable lumps.

This is the first time we've ever located a ghost net this way. Although a bit of a fluke as we didn't know what it was, we'll definitely be repeating the exercise during future surface intervals.

Sorry for the lack of surface photos, but our skipper only managed one whilst catching his breath halfway through dragging the net over the side of the RIB and another quickly whilst a diver dealt with another clump brought to the surface by the last team.

Thanks again to our supporters for enabling us to continue our work and for Sea Shepherd UK loaning us the RIB equipped with such a great piece of equipment that allowed us to "see" what was hidden deep beneath the surface.

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