Photo: Adobe Stock.
A harmful algal bloom is moving westwards along Norway’s southern coastline, raising concerns for fish farmers as concentrations increase in key aquaculture areas.
According to Norway's Institute of Marine Research (Havforskningsinstituttet), the algae Pseudochattonella has now been detected stretching from as far as the Swedish west coast to Øygarden, near Bergen.
Levels are considered particularly high in Production Area 1, Norway's southernmost aquaculture region which encompasses waters from the Swedish border to Jæren in Rogaland county, where some aquaculture operators have already reported increased mortality.
Further north, in Production Areas 2 and 3, concentrations remain lower, and the risk to fish stocks is currently assessed as limited, the Institute indicated.
Researchers said recent sampling along the Skagerrak coast shows especially high concentrations in waters off Arendal and further south. The Institute’s modelling suggests the bloom is likely to move south and west from Kristiansand before reaching coastal areas between Egersund and Flekkefjord. In the coming days, it may then drift northwards towards Stavanger.
Unlike a similar harmful algal bloom last year, which reportedly killed up to 1 million salmon, this bloom has developed closer to shore and inside fjords, which the institute said could increase the likelihood of harm to aquaculture operations.
The algae is known to affect farmed fish when present in high densities. “In recent days, we have registered a marked change in the density of Pseudochattonella on the Skagerrak coast. The densities are now above the threshold values that lead to mortality in farmed fish,” said marine scientist Lars-Johan Naustvoll, in a news update published on the Havforskningsinstituttet website.
Water samples collected on 17 March showed concentrations high enough to trigger behavioural changes or death in farmed fish, and reports from the industry point to rising mortality along the coast.
Dispersion modelling carried out by the institute suggests the algae will continue to spread close to land and into fjords.
“With the weather conditions that are forecast for the future, we assume that the algae will reach the outer parts of Boknafjorden during the coming week. Low densities have already been observed in this area as well,” Naustvoll said.
Fish farmers in affected areas are being urged to remain vigilant and to report any unusual fish behaviour or losses. “We ask that any behavioral changes or increased mortality in farmed fish be reported to the Institute of Marine Research,” Naustvoll added.