Marine farmers keep eye on sea temperature
Marine farmers are ‘‘at the mercy of mother nature’’ as a looming heatwave threatens.
National Institute of Water and Atmospheric Research (Niwa) experts expect temperatures to rise across the country next week, with an impact on seasurface temperatures.
The warning comes after New Zealand King Salmon lost more than 1600 tonnes of fish after they overheated in warmer-thanusual Marlborough Sounds farms last year.
Marine Farm Association president Jonathan Large said farmers would be keeping an eye on the weather as it warmed up over the next few weeks.
‘‘It’s obviously nothing that we can control. We’re at the mercy of mother nature and what she dishes up each year,’’ he said.
Niwa meteorologist Ben Noll said the country was facing what could be the warmest week of the season.
‘‘I would expect to see a return to those warm conditions that we were seeing a little bit earlier in the month of January.
‘‘With that will come lighter winds, which is one of those things we look for, for those really warm seas.
‘‘We have the recipe for warming oceans in the short term here as we go into the next week,’’ he said.
Southerly winds had churned up the Cook Strait and northeast Marlborough, temporarily cooling sea temperatures.
But stocks could be affected again temperatures continue to rise.
Earlier this month, Niwa confirmed marine heatwave conditions in parts of the Tasman Sea and seas east of the country, for the second consecutive summer.
Over a two-week spell in early January, sea-surface temperatures in Marlborough peaked at 19 degrees Celsius, sitting 3 degrees above the long-term average.
King Salmon chief executive Grant Rosewarne branded 2018 as an ‘‘absolute outlier, the worst ever’’ in 30 years of temperature tracking.
But he said temperatures so far this year were closer to average.
‘‘They [water temperatures] are normal or slightly elevated . . . but way down on what they were last year,’’ Rosewarne said.
Last year, 20 per cent of King Salmon’s
‘‘We’re at the mercy of mother nature and what she dishes up each year.’’ Jonathan Large
if stock did not survive, Rosewarne said. ‘‘In our best year, that would be more like 5 per cent.’’
To put the loss in perspective, in the wild, it’s generally 1 or 2 per cent that would survive, he said.
The water temperature was satisfactory for the salmon up to 17C. ‘‘In excess of 17 degrees, there’s some level of stress involved.’’
Temperatures at the King Salmon farm in Pelorus were recorded at 17.7C on Thursday and 17.1C in Queen Charlotte Sounds on January 11. The Tory Channelbased farm was sitting at a cooler 14.2C on Thursday.
Due to algal bloom in 2018, which is partly caused by the warm water, seafood business Sandford deferred the harvest of about 2500 tonnes of mussels.
Sandford general manager aquaculture Ted Culley said water temperatures were approaching similar levels to last year.
‘‘However, this year we didn’t get the big spike that we got in December last year.
‘‘That’s put us in a pretty good place going forward.’’
Large said he didn’t see the current water temperatures as being a ‘‘critical thing’’ for mussel farming.
‘‘Mussels are a bit more hardy, they can cope with waters up to 24 degrees.’’
It would be in the later part of the summer when they would potentially experience warmer waters, he said.