Trawling for More

A while back AccuPixel director Simon Brown had a letter published in the weekend supplement of the Financial Times. The magazine had published a piece about a fishing practice known as damage bottom trawling and the damage it was doing to the seabed in Orkney and this triggered the letter – Simon has first-hand experience of trawl damage and the sonar surveys conducted by Grahame Knott bear witness to what goes on out of sight on the seabed.

A few folks have been in touch asking for more details…so here goes…with a look at the background before looking at a few examples of aircraft crash sites.

Bottom Trawling

Bottom trawling involves a fishing boat dragging a net across the seabed. The lower half of the net is weighted to hold it down and is often fitted with a set of steel rakes to cut into the seabed. The net tapers back and is fully enclosed, holding whatever is caught.

The method is both indiscriminate – catching everything in the path – and is sufficient to leave near-permanent scars in the seabed.

These scars are deep enough to be visible on side scan sonar…and the marks are clear track lines in the seabed.

Screenshot from sonar the lines left by bottom trawling. The curving lines are gouges in the seabed created by bottom trawl fishing gear. Image courtesy Grahame Knott

Large steel wrecks will present a significant obstacle and risk of lost fishing gear. Most are known and marked on the charts and fishing boats will avoid them.

But low lying ship wrecks, typically the older wooden ships now little more than a pile of ballast, cargo or armaments, will be unknown and unmarked. Their charted position just does not exist and trawlers will be unaware of their presence.

The Vulnerable

Most vulnerable are aircraft crash sites. Most will date from the Second World War but the Cold War recorded a few losses and even as recently as 2019 the tragedy of Emiliano Sala’s last flight saw another aircraft crash in the Channel.

Compared to a cargo ship or submarine an aircraft is exceptionally fragile. Only heavier items such as main landing gear, engines and weapons will typically remain intact after impact but occasionally aircraft ditch and are intact. However, a trawl running into an aircraft crash site will cause no end of damage and the wreck of Wildcat JV751 bears witness to this.

JV751 was located by Kevin Heath of Sula Diving and you can read more about the story of this aircraft here.

The irony is the presence of JV751 in Scapa Flow was raised when a fishing boat landed a small section of airframe it had snagged in its net…the part number was linked to a Grumman Wildcat. In the case of the Wildcat we have substantial remains; engine, oil cooler, fuel tank, landing gear, wings and machine guns…but the rear section of the airframe and tail is missing.

The trawl has gone through the aft section of the aircraft. Where it lies now is anyone’s guess.

It’s often a fishing snag that reminds us of the potential of what is out there. Here’s another example, this time of a propeller landed at Weymouth harbour:

The impact of trawling is not to be underestimated. The recovery of the aircraft carrying Sala was thwarted by the aircraft remains being dragged away from its recorded crash position and this occurred within a matter of weeks from discovery to disturbance.

The thing is…fishermen have no desire or intention to snag cultural history. Snagged, lost or damaged fishing gear costs time and money and it’s not what commercial fishing is about. And it can be more serious than a loss of catch or gear. We know of at least one fishing vessel lost with all hands when its nets snagged what is believed to be the remains of an aircraft.

Knowing where the history lies, and sharing the position, would be the perfect way to help fishermen avoid damage and loss of earnings…but as Grahame and Simon both know, no one is willing to cover the costs of a sonar and investigative survey to figure out what is on the seabed and record it.

Digital Preservation

If there was ever a tool for recording submerged sites then photogrammetry is *the* tool and applications like 3DF Zephyr deliver amazing results. For underwater sites, the power to record to very high levels of detail – 1mm per pixel – delivers a fantastic visual record and very powerful tool for explanation and interpretation for non-divers.

A good example is the P47-D crash site in Weymouth Bay. It has taken 20 years but we have identified the names of two possible pilots – you can read the full story here.

This site has fishing gear snags. A lobster pot is caught on a section of airframe and long length of rope is wrapped around one of the main landing gear legs. Both are visible in the orthomosaic:

We have no idea what is already lost. Submerged history is out of sight and only the dedicated maritime archaeologists, divers and fishermen will have an idea.

It’s being lost faster than it can be found, let alone recorded. Grahame and Simon continue to do what they can…mostly for the personal satisfaction of adventure, to satisfy the incurable curiosity and discovery.

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