Grieg Seafood ASA (OSE: GSF): Abnormal mortality in September impacts harvest volume and farming cost guidance for full year 2026

From a strong biology at sea throughout August, Grieg Seafood experienced a negative development at one site, causing elevated mortality during September 2026. The mortality is due to an unexpected algae event causing gill damage.

Mortality rose gradually throughout September. The Company closely monitored the situation and is implementing measures to mitigate the impact, including temporary suspension of harvest which is reflected in the new guidance below.

The company has now determined that the cumulative impact has reached the threshold for formal disclosure.

Based on the information currently available, the total biomass loss associated with the event is estimated at approximately 1,000 tonnes.

The increased mortality is expected to impact both harvest volume and farming cost for the full year 2026. As a result, Grieg Seafood revises its full year guidance as follows:

* Harvest volume: Revised from 31,000 tonnes to 29,000 tonnes

* Farming cost: Revised from 67.5 NOK/kg to 71.0 NOK/kg

The increase in farming cost primarily reflects the reduced harvest volume and the financial impact associated with the mortality event. The mortality event will not impact the production for 2027.

Grieg Seafood continues to assess the operational and financial consequences of the event and will provide further information in connection with its ordinary financial reporting

For further enquiries, please contact:

Nina W. Grieg, Chief Executive Officer +47 953 39 161 Magnus Johannesen, Chief Financial Officer +47 959 13 243

About Grieg Seafood ASA Grieg Seafood ASA is one of the world's leading salmon farmers. Our farms are located in Rogaland in Norway with our headquarter in Bergen, Norway. Grieg Seafood ASA was listed at the Oslo Stock Exchange in June 2007. Sustainable farming practices are the foundation of Grieg Seafood's operations. The lowest possible environmental impact and the best possible fish welfare is both an ethical responsibility and drive economic profitability.

To learn more, please visit www.griegseafood.com.

The information included in this announcement is publicly disclosed in accordance with section 5-12 of the Norwegian Securities Trading Act.

This stock exchange announcement was published by Trude Østvedt, CAO, Grieg Seafood ASA, on 2 Ocotober 2026 at 17.30 CEST.