How mussels are farmed in New Zealand
Green-lipped mussels are New Zealand’s major aquaculture species. In this interactive, Professor Andrew Jeffs (Leigh Marine Laboratory) describes the key stages in farming green-lipped mussels.
See our related interactive, in which Andrew explains some of the challenges faced by New Zealand’s mussel farmers.
Transcript
Harvesting spat from 90 Mile Beach
Professor Andrew Jeffs (Leigh Marine Laboratory) explains that Ninety Mile Beach is the source of most juvenile mussels (spat) for New Zealand’s green-lipped mussel industry.
Transcript
Professor Andrew Jeffs
Mussel spat is a funny word used to describe baby mussels. So they’re tiny mussels that are usually the size of a match head or even smaller. They’re collected from two places. One is Ninety Mile Beach.
Ninety Mile Beach has a really unusual situation where there must be some very large adult populations of mussels there that produce lots of young, and those young settle on what must be large populations of seaweed in that area. And there must be storms that detach the seaweed from the seafloor, and the baby mussels together with the seaweed then wash up on the beach. So there’s spat harvesters who drive up and down the beach every day waiting for that material to wash ashore on the beach, and then they gather it up with pitchforks and put it in trailers and then they truck it off to be put out on mussel farms where it’s grown to mussels.
ACKNOWLEDGEMENTS Professor Andrew Jeffs – Leigh Marine Laboratory, Auckland University. NASA. Coromandel Mussel Kitchen. Sheree Wagener. Certain photos in this video are the copyrighted property of 123RF Limited, their contributors or licensed partners and are being used with permission under licence. These images and/or photos may not be copied or downloaded without permission from 123RF Limited.
Growing spat on ropes
Professor Andrew Jeffs (Leigh Marine Laboratory) explains what Christmas tree rope is and how it is used to collect mussel spat.
Transcript
Voiceover
One alternative to harvesting spat from 90 Mile Beach is to dangle hairy rope – called Christmas tree rope – in the water near mussel farms.
Professor Andrew Jeffs
They’re called Christmas tree ropes because they look a bit like Christmas tree tinsel. They have a central thread with lots of hairy fibres hanging off them, and the mussel seed which is floating in the water finds it and thinks it’s a piece of hairy seaweed and settles in it and attaches to it and sets up home there. That Christmas tree rope is then harvested and hung out on a mussel farm, and the mussels then grow up from there.
ACKNOWLEDGEMENTS Professor Andrew Jeffs, Oliver Trottier – Leigh Marine Laboratory, Auckland University. Just the Job, Dave Mason Productions. www.careers.govt.nz/resources/tools-and-activities/just-the-job
Growing spat in hatcheries
Professor Andrew Jeffs (Leigh Marine Laboratory) explains that some mussel spat is sourced from hatcheries.
Transcript
Professor Andrew Jeffs
The other source of mussel spat is in a hatchery, so a hatchery is a human-made system where mussels are bred, a mum and dad mussel produce egg and sperm and then the larvae, which are a little swimming seed, is raised and fed on floating plants again, until it gets to the point where its ready to settle on a piece of seaweed, and then they use Christmas tree rope in the tanks. And the baby mussels settle on that rope and then the rope’s moved out and hung out on a farm.
That’s quite an expensive process to do compared to just going and picking seaweed up off the beach which is covered in millions and millions of mussel spat.
ACKNOWLEDGEMENTS SpatNZ. Mass Audubon Joppa Flats Education Center, Massachusetts – www.massaudubon.org/joppaflats Professor Andrew Jeffs – Leigh Marine Laboratory, Auckland University.
Seeding spat
Professor Andrew Jeffs (Leigh Marine Laboratory) describes how spat are attached to mussock – a biodegradable cotton stocking – for growth on mussel farms.
Transcript
Professor Andrew Jeffs
Once the spat is collected off the beach, it’s normally chilled and put in bags and then put in a chilled truck like an ice-cream truck and taken to the farm usually within 24 hours. It’s put on a mussel barge which goes out onto the farm, and the seaweed, which is covered in spat, is forced down a tube with a rope going down it and into some cotton stocking, which is called mussock.
And that stocking holds the seaweed with the mussel spat on it against the rope and then that’s hung on floats on the surface and the mussel attaches to the rope, and the stocking’s made of cotton so it rots in the sea over a couple of weeks. And so you’re left with a rope that’s completely coated with baby mussels.
ACKNOWLEDGEMENTS Professor Andrew Jeffs – Leigh Marine Laboratory, Auckland University. Sheree Wagener. Just the Job, Dave Mason Productions. www.careers.govt.nz/resources/tools-and-activities/just-the-job
Reseeding juvenile mussels
Professor Andrew Jeffs (Leigh Marine Laboratory) explains why juvenile mussels must be reseeded onto new rope after approximately 6 months’ growth.
Transcript
Professor Andrew Jeffs
The spat spends about 6–8 months on the nursery line, and by that time, there’s just so many mussels on that line and they’re getting bigger and bigger and growing very, very quickly at that age.
And the more they grow, they start pushing each other off the line and they start dropping off the line. So the mussel farmer will take those lines out of the water and drag them through a steel ring which pulls the mussels off the rope and then will seed those mussels back onto another rope but at lower numbers, so to space them out a bit more, so the mussels are reseeded to give them enough space to grow up to a bigger size.
ACKNOWLEDGEMENTS Professor Andrew Jeffs, Oliver Trottier – Leigh Marine Laboratory, Auckland University. Just the Job, Dave Mason Productions. www.careers.govt.nz/resources/tools-and-activities/just-the-job
Growing mussels on longlines
Professor Andrew Jeffs (Leigh Marine Laboratory) describes the Japanese longline system, which is used to farm virtually all of New Zealand’s green-lipped mussels.
Transcript
Professor Andrew Jeffs
The Japanese longline system for farming mussels involves a series of large plastic floats on the surface, with two lines running between them joining them up, in a line along the surface of the water, with an anchor on either end.
The mussel lines then are suspended from the ropes that run along the surface between the floats and so they hang down in the water column, so it gives a huge length of rope going up and down covered in mussels growing underneath the farm. One of the issues for a mussel farmer is making sure that they have enough floats, so as the mussels grow, the farmers often have to add more floats to keep the weight of mussels held up in the water column.
ACKNOWLEDGEMENTS Professor Andrew Jeffs, Oliver Trottier – Leigh Marine Laboratory, Auckland University. Just the Job, Dave Mason Productions. www.careers.govt.nz/resources/tools-and-activities/just-the-job
Monitoring for toxins
Professor Andrew Jeffs (Leigh Marine Laboratory) describes how mussels and the water they grow in are rigorously tested before harvest for toxins and algal bloom, respectively.
Transcript
Professor Andrew Jeffs
To ensure that mussels don’t contain toxins there’s an incredibly strict monitoring programme in place that took a number of years to develop. There’s a number of aspects to it. One is those tiny floating plants in the water that produce toxins. We know what they are, so you can sample the water and have a look for those to see whether they’re present.
There’s also a rigorous testing programme with the mussels themselves. Before they can be sent off to market, they have to be tested to make sure they don’t contain any of the toxins.
So it’s a two-part process – one gives you an early warning sign, the other one guarantees human food safety that mussels that are going to cause human health issues aren’t being sent to market, and that’s absolutely critical in terms of having an industry that people can trust.
ACKNOWLEDGEMENTS Paul McNabb, Cawthron Institute. NASA. Professor Andrew Jeffs – Leigh Marine Laboratory, Auckland University.
Harvesting
Professor Andrew Jeffs (Leigh Marine Laboratory) explains how green-lipped mussels are harvested.
Transcript
Professor Andrew Jeffs
Mussels are harvested from a farm by pulling a barge up alongside the farm. The ropes are cut off from the lines holding them in the water, and they’re pulled through a steel ring, and the mussels let go.
They’re tumbled and washed at the same time to get some of that fouling material out, to get some of the accumulated silt that often accumulates on the mussels. And then they’re put on a conveyor belt and then dropped into a bag, and that bag is then ready to be handled by a crane off onto the wharf once the barge gets back to the wharf.
ACKNOWLEDGEMENTS Professor Andrew Jeffs – Leigh Marine Laboratory, Auckland University.
Processing
Professor Andrew Jeffs (Leigh Marine Laboratory) describes the key steps in post-harvest processing of green-lipped mussels.
Transcript
Professor Andrew Jeffs
Most processing factories for mussels in New Zealand, the mussels are brought in, they’re inspected to make sure they’re clean. Any broken mussels get removed, and only the clean good-quality mussels are then sent through to processing.
Normally, they’re lightly cooked usually with a steaming, and that’s just enough open up the mussels so that one of the shells can be removed. They are then put through what’s called a de-bearder. Mussels extrude threads which they use to cling onto ropes or onto the rocks in the wild, and the de-bearder just basically removes those threads because they’re not very nice to eat, in fact, you can’t eat them. The mussels are then sent through a freezing plant where they are snap frozen quickly to preserve the goodness and to make sure they’re good quality.
So typically in a mussel plant, there’s testing along the way to make sure that the quality standards are maintained.
ACKNOWLEDGEMENTS Professor Andrew Jeffs, Oliver Trottier – Leigh Marine Laboratory, Auckland University. NIWA. Just the Job, Dave Mason Productions. www.careers.govt.nz/resources/tools-and-activities/just-the-job
