New source of mussel spat?

Press, Volume CXV, Issue 33933, 28 August 1975, Page 9

New source of mussel spat?

C.V Z Press Assoctatieni WELLINGTON. The development of mussel farming in New Zealand might benefit from the chance find of a Ministry of Agriculture and Fisheries’ scientist — spat-encrus-ted seaweed.

Difficulty in obtaining suitable supplies of mussel spat has been hindering the growth of the musselfarming industry, according to Mr R. W. Hickman, of the Ministry’s Fisheries Research Division, whose views are reported in its information service. However, an alternative to the traditional method of dangling ropes in the water and hoping spat would settle on them might already exist, he said. On a routine sampling trip to experimental mussel farms in Northland last year, he happened on a very recent heavy stranding of seaweed on Ninety Mile Beach, and on examining it found the weed heavily encursted with minute green mussels (Perna canaliculus), Imm to 3mm long. In places, dense spat settlement completely obscured the weed. One 12cm-long seaweed

segment, weighing only l seven grams, contained 3000 seed mussels. Even if the density averaged only half this, there was still a tremendous potential for seaweed as a source of mussel spat, Mr Hickman said. On this basis, seven kilograms of weed (roughly the content of a five-gallon bucket) would support Um seed mussels.

Allowing for an 80 per cent loss during tansfer of seed to a suitable growing site, and for 50 per cent mortality during the first

two years growth to 120 mm (40 grams meat weight), a five-gallon bucket of seed-mussel-encrusted seaweed could, in theory, produce 6000 kilograms of mussel meat.

Problems such as the risk of spreading disease and parasites, connected with the transfer of shellfish from one area to another, were minimised by the use of mussels of this very small size.

However, if the material was to be used, it had to be collected immediately after stranding, as seed mussels overheat and die in direct sunlight. If kept damp and cool, they will survive out of water for several days. The Fisheries Research Division has experimented with various methods of attaching seed mussels taken from seaweed on ropes. Techniques include tying the weed directly to the rope, binding the weed in plastic netting, and putting the weed in plastic cones and trays on the rope. All seemed to have considerable disadvantages, Mr Hickman said. Further investigations by the Ministry and commercial mussel farmers were required.

The seed mussels according to Mr Hickman, probably come from offshore green-mussel beds known to

exist in deep water on both the west and east coasts of the North Island. “As these beds cannot be worked by conventional dredging, harvesting their seed would offer an efficient use for an otherwise wasted resource,” he said. “A quick examination of seaweed will show whether seed mussels are present. Miniature mussels, Imm to smm long, with a reddish, zig-zag pattern on a palegreen background, are immediately obvious,” he said.