Out of 10 pens that had contained 550,700 salmon, six were found to be structurally sound with fish in good condition and are now secured back in their original position.
Mowi said the remaining four pens were structurally compromised (two of which experienced torn netting), and the salmon contained within the four pens have now either been harvested (125,900), removed as mortality (30,616), or escaped (48,834).
The company said that following a thorough inspection by dive teams, the cause of the incident appeared to be breakage of mooring ropes that attach to the main system seabed anchors.
The rope type is marine grade, 4.8cm in diameter with a break strength of 89.5 ton – roughly twice the maximum strength required for its application (ranging from 33t to 51t). The rope has been sent to third-party testing facilities in Aberdeen, with further investigation to follow.
The farm was installed five years ago according to the Marine Scotland’s Technical Standard for Scottish Finfish Aquaculture, and the infrastructure inspected three months ago.
Mowi said that following the incident it immediately informed Marine Scotland of the event and the potential for fish escape. Key stakeholders and media were informed of the event within 12 hours.
The company’s immediate priority was to secure the fish pens in place until Storm Ellen subsided, and to safeguard staff, contractors and fish stock – this was achieved by August 22.
The farm was secured back in its proper location by today and all 10 pens either visually inspected for integrity and/or inventoried. The recovery operation was completed by teams of trained staff and service contractors without injury or incident.
Caught by anglers
Mowi said there had been local reports of the salmon being predated upon by seals and other wildlife, and being caught by anglers. The salmon raised at the Carradale North farm are healthy, with some having already been processed for market.
The company “continues to engage with local and national wild fisheries groups to monitor and assess the presence or absence of salmonid genetic introgression”.