Record salmon deaths in hot summer

Salmon are dying at a faster rate than ever in the Marlborough Sounds, after warmer sea temperatures fuelled by a long, hot summer led to record numbers of deaths.

Environmental watchdog group Guardians of the Sounds has obtained figures showing New Zealand King Salmon dumped close to 1300 tonnes of fish waste in landfill over the past three months.

Between December and February, trucks from Havelock and Picton made 160 trips to the Bluegums Landfill in Blenheim, dumping 1269 tonnes of dead fish and waste from New Zealand King Salmon farms.

NZ King Salmon chief executive Grant Rosewarne said the losses were disappointing.

"We put an amazing effort in preparing for the summer because we always know it's going to be a difficult time for our fish and there's a range of things we can do to try and improve the situation," Rosewarne said. "We were thought we were on top of it and indeed we were, but unfortunately it was a particularly hot summer that started quite early and has continued on."

Records show 243 tonnes of fish and fish waste were dumped in December, 394.7 tonnes in January, and 632 tonnes in February.

Rosewarne said several factors led to fish dying in high numbers, but the strongest correlation with fish mortality was high temperatures.

"Salmon are a cold-water species and the ideal temperature is around 15C or 16C but, when it gets to 18C, and it's sustained there for weeks, that's when the problems really start."

The salmon producer now expected its underlying profit for the current financial year to be between $6.5 million and $7.5m, down from $10.5m and $12.5m.

Rosewarne said it was one of the reasons the company had applied to establish a farm in the cooler, deeper and faster current conditions of the Cook Strait.

The resource consent application for the Blue Endeavour project, off Cape Lambert was lodged in October 2019, with a decision expected by mid-year.

Conditions in the Marlborough Sounds were perfect for salmon nine months of the year but, during summer, the sea temperature - particularly in Pelorus Sound, was too warm, he said.

Clare Pinder of environmental watchdog group Guardians of the Sounds said the amount of dead fish being dumped was appalling.

"Something is seriously going wrong at King Salmon's farms, it might be yet another unusual heatwave, it could be poor husbandry, it could be overstocking, it could be disease, but it's a huge proportion of their harvest that have died this year."

Monitoring of sea temperatures near the proposed Blue Endeavour site showed it was too warm to successfully farm salmon but the company was pinning its hopes on the expectation it would be successful in the cooler waters of the Cook Strait, Pinder said.

"The problem is it's not cooler, there have been temperatures in the range of 18C to 19C this summer, well above the optimum range of 12C to 16C." According to Marlborough District Council landfill data going back five years, there had never been as many dead salmon dumped in such a short time, she said.

"If we were driving through the countryside and we saw dead sheep or dead pigs or dead horses in the paddock, they'd be an outcry. So why is there not an outcry on king salmon trying to grow fish when the environmental conditions are not suitable for them?"

MPI said it was aware of the higher-than-usual death rates at King Salmon's farms this summer.

Biosecurity NZ aquatic and environment health team manager Dr Michael Taylor said it was investigating the deaths, but warmer water temperatures are likely to be a contributing factor. There had been no signs of exotic bacterial or viral disease infection but Biosecurity NZ was awaiting further test results.¦ -RNZ