Mowi Scotland's new wellboat will have knock-on benefits for Ireland

The arrival of Scotland’s largest wellboat later this year will benefit salmon farmer Mowi’s operations in Ireland as well as Scotland, says Ben Hadfield, who is chief operating officer for both regions.

The Inter Alba, which has a well capacity of 6,500 cubic metres and a reverse osmosis (RO) system capable of producing 15,000m³ of fresh water every 24 hours, will free up one of the wellboats currently being used in Scotland for use in Ireland, where Mowi’s fish face challenges from amoebic gill disease (AGD) and salmon rickettsial septicaemia (SRS).

“Some of the best farmers we've got are in Ireland but we need them because it's a tough environment,” says Hadfield.

“One of the main things that we will be doing when the new vessel arrives in Scotland is putting a larger vessel for freshwater treatments in Ireland, and I think that will make a big difference for them.”

All three of the wellboats in service for Mowi Scotland - Inter Atlantic, Inter Scotia, and Ronja Skye – have high-capacity RO systems that can generate around 5,000m³ of freshwater in 24 hours. Mowi uses the freshwater to bathe its fish for around four hours, which tackles both lice infestations and AGD, which can in turn limit SRS.

“When you see the SRS come on to the fish, both in Scotland and Ireland, it's at the end of the season, at high temperatures when the gills are damaged, so the obvious factors there are temperature, environment, and [infection] coming to the fish through damaged gills. So, keeping the gills in good condition is our priority," explains Hadfield.

Freshwater treatments

Freshwater production capacity is a crucial asset of the Inter Alba, along with having the well capacity to load a full 160-metre pen of fish at one time, and the ability to strip carbon dioxide (CO₂) from the water in the wells, adds the Mowi Scotland boss.

“The RO production capacity is most important, so we can produce the volume that we need to do a treatment refresh every 10 hours, which is key to water quality and then fish welfare,” he tells Fish Farming Expert. “The CO₂ stripping system on the vessel is massive, as we know from experience that the bigger you make that, and the more redundancy you build into it, the better.

We can produce the volume that we need to do a treatment refresh every 10 hours, which is key to water quality and then fish welfare

Ben Hadfield

“If you can strip off all the CO₂ and you can chill the water, then you can hold the fish indefinitely in theory - not that we do that, but you want to be able to do that if you’re moving fish or on closed valve or you're holding fish for longer for whatever reason.

“The Alba has three wells so that we can control the load and have quite a good speed on the load.”

Wrasse also treated 

Another advantage of the new vessel is that it is equipped with the latest grading and treatment system for ballan wrasse, which Mowi Scotland uses as a natural lice control in salmon pens.

“We have it on the other vessels, but this has been improved over time, so we're quite confident that we will be able to grade off all the wrasse, take them separately within the vessel to another small tank where they can be treated for AGD, and then they go straight back into the pen because there’s no point in treating salmon to get them clean and then putting the cleaner fish back if they've got AGD.”

'Pared back' from 8,000m³

Inter Alba, built at the Sefine Shipyard in Turkey, is 92.66 metres long, with a beam of 22.4m and a draft of 8m. It is owned by Trident Aqua Services, which owns aquaculture marine services firms Intership, Aquaship, and FVS, and was built to meet Mowi Scotland’s requirements.

“When we started the process we looked at between six and eight thousand cubic metres. Obviously 8,000m³ is massive and that’s a challenge for some locations and some farm structures, so we pared it back from 8,000 to 6,500m³ so that it would take 600 tonnes of fish, which is one full 160-metre pen,” explains Hadfield.

“Even when we have 200-metre pens, we stock them as a 160. So, the most we have in any pen is 600 tonnes, and more often than not it’s operating around the 450-tonne mark. Towards the end of the cycle, if we were going towards our maximum biomass of 17 kilos per cubic metre then you could have towards 600 tonnes in it.”