Where do mussels come from?

Where do mussels come from?

In a former life, I had a lot to do with Greenshell mussels.  There’s a large export industry based upon farming these shellfish, which are found only in New Zealand. Not only do they taste good, but they are also good for your health.  (I managed to get off anti-inflammatory drugs for about seven years by including Greenshell mussels in my regular diet, but that’s another story.)

But this multimillion dollar industry recruits its juvenile mussels in a very strange way. It goes like this: like many other shellfish, Greenshell mussels have a reproductive strategy that is a bit of a numbers game.  The female releases many millions of eggs into the water,  which prompts the males to do likewise with their sperm.  After fertilisation, tiny larvae are formed complete with swimming organs. These eventually settle onto some object or surface, the swimming gear is discarded and the shell starts to grow.  At this stage, they look like this:

Juvenile Greenshell Mussels
baby Greenshell mussels, about 0.2mm long

In the early days, mussel farmers collected these babies, called spat, by hanging especially designed “fuzzy” ropes in the water at the appropriate times.  This was often rather hit or miss.  Nowadays, around 80% or more of the juveniles come from one location: from spat which has settled upon seaweed which then washes up on the shores of 90 Mile Beach, in the far north of New Zealand.

As soon as the seaweed is spotted, harvesters swoop on the spot, load up the baby mussels, seaweed and all, onto trucks which transport it up and down the country.  The system works extremely well.  Very sophisticated methods and machinery have been developed to relocate these tiny creatures, perhaps less than half a millimetre long, from the beaches of Northland to their new home attached to a longline in a marine farm in the Marlborough Sounds, Akaroa Harbour or Stewart Island.

Mussel farm
Mussel farm

Most years, the babies arrive on time.  Occasionally there has been a nervous wait, and the whole system was threatened a few years back when a toxic algae bloom on the west coast of the North Island stopped transport of spat to the South Island.  But on the whole, the system works very well and provides a low-cost source of juveniles.

But there are some hidden costs. Imagine if New Zealand’s  wool industry was based upon the same principles. For example, if all of New Zealand’s lambs came from one of a number of caves which magically opened up in ravines, deep in the Southern Alps. Spotters on ridges armed with binoculars and mobile phones would then call up the sheep trucks to distribute the lambs around the country.  And they would be feral lambs: all shapes, sizes and colours.  No such thing as Merinos, Romneys or Southdowns.  Sounds silly? Well, that’s essentially what the mussel industry does.

Is there a better way?  Too right!  But that’s probably a topic for another chapter.

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