New Zealand's largest salmon farmer New Zealand King Salmon is warning investors that it is currently experiencing higher than expected mortalities thanks to "particularly warm" sea water temperatures.

The situation, which is particularly impacting the company's farms in the Pelorus Sound, continues to unfold. Workers are deploying measures to counter the heat and other contributing stressors.

To minimize the impact, the company is evaluating options to accelerate its existing harvest schedule, starting in the first week of February.

"This outcome is particularly disappointing for our dedicated teams who closely monitor and care for our fish because our improved farming model was showing good results," said NZKS CEO Grant Rosewarne.