Algal bloom hits mussel farms
It has caught the industry by surprise, but a large-scale closure of mussel farms to combat toxic algal blooms in the Marlborough Sounds won’t sink this year’s harvest, say those affected.
More than 100 mussel farms in the Kenepuru Sound and inner Pelorus Sound have closed after the toxic algal bloom Alexandrium catenella ripped through the area earlier this month.
With 122 farms closed and another 128 voluntarily ceasing their harvest while the toxins clear up, the closures are believed to be the largest number since 1993.
On May 11, the Ministry for Primary Industries (MPI) issued a public health warning against collecting shellfish in the area, extending outward to Tawero Point and Opani-aputa Point.
Routine tests on shellfish samples taken from this region showed levels of paralytic shellfish poisoning (PSP) toxins above the safe limit of 0.8 mg/kg set by MPI.
Anyone eating shellfish from this area is potentially at risk of serious illness.
Similar warnings have been issued in Hawke’s Bay and the Bay of Islands.
However it was not known why the algal bloom had manifested at this time of the year.
Despite the closures, the industry has been able to meet demand by sourcing mussels from other non-affected areas.
It is understood the algal bloom will filter out in two to three weeks time, ready for harvesting.
While 60 of its farms were affected by temporary closure, aquaculture company Sanford’s general manager of aquaculture, Ted Culley, said staff were continuing to harvest at other unaffected locations around the outer Sounds area. ‘‘We work in a natural environment and these things happen.’’
Culley said a good chain of communication in relation to the blooms emergence had enabled Sanford and other farmers to act quickly. ‘‘We have a really good system to alert industry around potential toxin blooms to make sure our customers are safe and we don’t produce any mussels that go to market with toxins in them.’’
Based on previous experience, Culley estimated it would be 20-30 days before the mussels would be ready to harvest, depending on the level of PSP found.
‘‘Once the algal bloom dissipates, the toxins are processed out of the mussels – [mussels] quite like the algal blooms because they get nice and fat and in good condition and we’ll harvest them when they’re clear of toxins.’’
A farmer with close to 50 years of experience in marine farming, John Young, said the algal bloom regularly occurred in the Queen Charlotte and Tory Channels, but had not been an issue in local mussel growing areas recently. ‘‘It’s quite unusual to see it this time of year but then look at the year we’ve had – a heatwave in summer and a lot of the nutrients are there to make it grow and it’s sort of caught us by surprise.
‘‘We farm with all the vagaries of the weather cycles.’’