North wind gives Mowi hope of salvaging crop after Bantry Bay die-off

Around 500,000 fish with an average weight of 3kg were in the pens at the sites and Mowi feared losing them all when the bloom of toxic dinoflagellates was carried into the farms in the middle of last week.

But northerly winds this week appear to have pushed the bloom away, giving the company hope that the surviving fish can be left in the pens and grown on to harvest size.

Emergency harvest

“We’re much more hopeful today than we were a week ago,” said a Mowi Ireland spokesperson, adding that prior to the event the fish had been healthy and thriving.

“We took an emergency harvest out on Wednesday, but we’ve stopped that because the signs are looking good for the remaining stock. We’re trying to assess what we have left.

“We are dealing with an acute event, and it’s very hard to count accurately until you start to do grading. The priority in an event like this is to get the dead fish out very quickly, for fish health and environmental reasons.”

Red tides

Mowi is working with Ireland’s Marine Institute and other scientific institutions to identify the organism that caused the fish kill.

“The south-west of Ireland has a history of ‘red tides’ from long before fish farming was established in the area,” said the spokesperson.

“We’re working with all the various state agencies and scientists to get the exact identification of the species. It’s a very small dinoflagellate that had a big impact on the fish.

“We think the situation has settled at the moment. We had northerly winds earlier this week that appear to have pushed the bloom away. Evidence of this organism has been found further south, around the coast. These blooms normally occur offshore, and with downwelling systems that happen in Bantry in autumn, they can be brought in that way.

“On top of that we’ve had a very mild autumn with higher-than-normal sea temperatures for this time of year.”

Stopped eating

Mowi said the problem was not caused by a large, obvious plankton bloom. Staff first noticed something was wrong in the middle of last week, when the fish stopped eating.

“We are not talking about a deoxygenation event here,” said the spokesperson. “In some blooms we have massive numbers, you can see them and the water’s discoloured and at night-time you get a collapse of oxygen. That’s not the case here, it was like a toxic bloom. There are several known species where it takes relatively low numbers, compared to other bloom species, to cause problems.”

Knowing what organism caused the die-off won’t help mitigate the current problem but will add to existing knowledge of harmful algal blooms.

Bantry Bay is the location of Mowi Ireland’s planned Shot Head farm, which will be around three or four kilometres east of the Ahabeg and Roancarrig sites. The site, which will have a maximum permitted biomass of 2,800 tonnes, will be the first new salmon farm in Ireland for 17 years.