Warm-water abalone offers rich harvest to Irish fish farmers

A mollusc renowned for its promiscuity in warmer waters is adapting well to the Irish marine environment. Research into farming abalone has produced some very successful results.

In fact, the progress is such that two commercial hatcheries here have produced 500,000 juvenile abalone; "quite a breakthrough", according to Mr Declan Clarke, aquaculture technical specialist with Bord Iascaigh Mhara.

The hatcheries at Streamstown Bay in Clifden, Co Galway, and Bere Island, Co Cork, have been assisted by BIM.

Characterised by a single, whorled pearly shell, and a muscle or foot which can be sliced and broiled as "abalone steak", the mollusc favours warmer climes such as the Australian and South African coasts.

The largest species, red abalone (H. rufescens), is taken commercially along the western coast of North America, but is now threatened by growing numbers of sea otters. In Europe, given water temperatures, Jersey has been the most northerly limit for the wild fishery.

The development of artificial feed and settlement techniques in aquaculture has encouraged fish farmers to try their hand.

Thus the hatcheries in production here are breaking new ground in this part of the world, according to Mr Clarke.

The biggest challenge in research and development has been the weaning stage, but this has been cracked, he said.

Since the beginning of the year, Chinese techniques have been on trial in Bere Island and in Clew Bay, while Australian methods are also being tested.

The Chinese techniques involve "lanterns" or cages at sea, and undulated plastic plates in tanks on land.

Undulations in the plates provide ample surface area for settlement and also for a source of food for the abalone - diatoms - which grow on this surface.

However, as researcher Ms Emma Couderc noted in a recent contribution to BIM's Aquaculture Newsletter, it is difficult to maintain the diatom coat on the plates once the animals have been grazing for some time, and they then have to be fed by diatoms regularly introduced to the tanks.

The Chinese "lanterns" are cages made of drilled plastic plates linked by ropes and surrounded by an elastic plastic mesh. The average density of the abalone is 50 per plate, with about 300 in each cage.

The method allows for animals of 20 millimetres or under to grow to a commercial size of 70 millimetres. The cages are then attached to long lines, five metres deep, in sheltered water and with some light.

The diet is seaweed every second week during summer, and once a month in winter.

The advantage of a sea site is less cleaning for the farmer, but the obvious disadvantage is the hostile nature of the Irish marine environment in winter.

Either way, farmers can break even without having to produce a very large tonnage, according to Mr Clarke.

Large abalone can fetch astronomical prices on the Asian market, where they are a delicacy. Farmed crop is worth about £30,000 a tonne, compared to £1,000 a tonne for oysters and £3,000 for clams.

The average land-based system will be doing well at a production of 20 tonnes a year, and the main market here and in Britain is the ethnic restaurant trade.

The high prices won for the abalone compensate for the relatively slow growth of the animals and the labour-intensive nature of the activity.

As for the abalone's sexually adventurous nature, that has been confirmed by biologists in California who have identified the reason for the mollusc's "loose habits".

Eggs that flirt with deviant sperm contribute to evolution, they say - as if telling us something new!