The Northwest Straits Foundation, based in Bellingham, Washington, in conjunction with Global Diving & Salvage has used a Saab Seaeye Cougar XT ROV and supporting Falcon ROV to remove derelict fishing nets from deeper waters without adversely affecting the habitat.
The Foundation has already removed over 5,600 of these derelict fishing nets from the Puget Sound by employing skilled divers whose work is restricted to shallow areas of up to 105 feet in depth.
The project involved the design and fabrication of special tooling and the development of procedures and protocols to remove the nets.
Early in 2015, Global Diving and the Foundation’s field operations manager, Natural Resource Consultants, conducted a series of trials where the Cougar, supported by the Falcon, tested various procedures and tools necessary for working in diverse habitat conditions.
They found that recovery from the seabed was fully successful, whereas disentangling nets and gear from rocks is a challenging task.
In particular it is difficult to work in a sediment-disturbed environment where visibility is poor and where there is a risk of loose strands and segments of netting getting tangled with the Cougar – although using the Falcon to observe the task helps considerably.
Whilst it is possible to remove a whole net using the Cougar to secure lifting straps and winching it up to a vessel, this technique is not favoured as the net could rip apart into multiple pieces and need extended recovery.
The best solution found was to replicate the technique successfully used by divers in shallow waters: cut or untangle the net into manageable pieces before removal to the surface.
The recovery procedure starts with topside pilots using the Cougar’s navigational software and ultra-short baseline tracking to guide the ROV to a pre-determined derelict net site where a careful survey of the area is undertaken.
Then, using the various tools designed and fabricated by Global, the recovery team manoeuvres the Cougar into a safe position to utilise the two manipulators mounted on the vehicle ready to cut or untangle the nets before attaching a surface retrieval line, one section at a time.
During the procedure the Falcon provides video coverage, giving the Cougar operator an additional vantage point and an awareness of the surroundings, and is ready to assist the Cougar during recovery as needed.
Together with Global Diving and Natural Resource Consultants, the Foundation plans more tests to evaluate the feasibility of this method and determine the best tools and method needed for the task.