I have always adored seafood. I’ll eat it in all forms- fish, shellfish, crustaceans, raw, boiled, baked, I don’t care, as long as it gets in my belly. As I near the end of my undergraduate degree I’ve found myself following my appetite passion and beginning to focus on following a career in fisheries and aquaculture science. Being able to support sustainable practices is something I value highly as I want future generations to also enjoy the oceans delicious bounty. One of the most exciting papers I have taken this semester has been solely focussed on fisheries and aquaculture and I’m thoroughly enjoying the breadth of topics covered.

One lecture was spent analysing green-lipped mussel farming in New Zealand. Green-lipped mussels, Perna canaliculus, are endemic to New Zealand and are most commonly found in the North Island and top of the South Island. They are a very tolerant species, hardy in a range of conditions and reach maturity in a year- traits that ensure the species can flourish in the wild and when farmed. Their gem-like green colour provides a significant economical edge as all other mussels on the international market are blue or black shelled. Greenshell mussels are currently sold in 15 countries around the world, USA and the EU taking around 30% of exports each with the remainder going mainly to Asian nations and Australia. In 2018 total exports of Greenshell mussels were worth over $260 million NZD, domestic sales were more than $50 million and approximately $60 million was generated from pet food revenue.

Greenshell mussels were first turned into pet food when the Chinese market dipped and we were left with an excess of supply. Mussels were turned into dried powder and as they are full of natural anti-inflammatories, vitamins, Omega-3, nutrients and amino acids are great at relieving symptoms of arthritis in dogs and cats (and humans).

What is now one of the world’s most successfully farmed mussels did however have very humble beginnings. First dredged in New Zealand in 1927 in the Hauraki Gulf and Firth of Thames the fleet gradually increased to between six and ten boats by 1960 and in 1961 reached its peak landings with 40,910 sacks of mussels (around 1000 tonnes). After this, the beds began to thin out and inspired by the Spanish mussel-farming industry, people turned to aquaculture. McFarlane’s Fisheries Ltd first mussel raft was built in 1965 with 230 bundles of manuka brush suspended below.

Harvesting mussels in the early days was back-breaking work. Hauling the ropes up by hand took 3 to 4 men who then had to sort them one by one.

By 1973 it was apparent the raft method wasn’t working- the concrete structures initially stuck well above the surface of the water (to allow for the inevitable descent once the mussels grew), and many were being destroyed in storms and washing ashore. Before long the industry turned to a longline method, with big floats holding up a backbone line with the dropper lines full of mussels hanging 5-10m long below.

There were many instances of Kiwi ingenuity in the early days. As glass milk bottles were being phased out there were thousands of free excess milk bottles waiting to be repurposed and it was discovered they could be filled with concrete to use as anchor weights on the mussel farms.

Ninety Mile Beach is the source of most mussel juveniles (spat) for the New Zealand green-lipped mussel industry. The spat can be tiny, smaller than the size of a match head, clinging to seaweed before it migrates to adult mussel beds. Storms and disturbance events dislodge the seaweed bringing it and the mussel spat to shore, creating a frenzy of harvesters driving up and down the beach collecting the seaweed for aquaculture farms.  

Sadly, many early mussel farmers had a great deal of trouble keeping the mussel spat attached to their ropes and experimented with the best possible fibres to encourage a strong hold. The aim was for a biodegradable material to hold them on until they were securely fastened to the main rope. Dissolve too fast and you lose your crop, dissolve too slow and the fibres would have to be cut away from the ropes, catching and clogging the equipment. People tried Spanish lace, plastic mesh and some even tried a completely different approach, sacrificing their bathtubs or guttering to soak the ropes and encourage mussel spat migration. A breakthrough was inspired by the daughter of a Christchurch-based rope sales representative. Her Knit Magic toy knitted circular cotton stockings which could be modified to make dolls clothes and also, as it turns out, mussel socks. A drill was attached to the Knit Magic with a thermostat taken from an electric blanket wired in. They initially made a hundred metres which was enthusiastically received and met with a request for a thousand metres.

While mussel aquaculture continues to grow and succeed in our waters  the group Revive our Gulf is working with mussels in a different way, hoping to restore the mussel beds in the Hauraki to what they once were. Mussels provide an important ecosystem service, filtering up to 350 litres of water a day removing particles and cleaning the water. In their prime the seabed mussels could’ve filtered the entire Firth of Thames daily and bringing them back would be a massive win for water quality and underwater life.

If you want to get involved with helping the project, please visit their website.

Georgia Third

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