Cover Story
Manihiki Pearls
Lessons learnt from disaster.
Manihiki produces about 90 percent of Cook Islands pearl output. It is beginning to recover from a bad experience.
A disease, which hit its oyster stock, is expected to cost more than NZ$30 million in lost production. But perhaps the experience has been a blessing since it underlines the perils attached to unwise (farming), says Kori Ramea, formerly the Cook Islands Minister of Marine Resources, but now acquaculture adviser with the Pacific Community.
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Manihiki had another bad experience in 1997 when a hurricane cut the number of pearl farms in the atoll's lagoon from 164 to 111 farms with 690 culture lines and 424 spat collection lines. Prior to a disease outbreak last November, the lagoon had an estimated 1.8 million adult cultivated oysters.
Farms cover 30 percent of the depth strata in which pearl farming is feasible, which is 10 to 30 metres If managed correctly, available space should support 2 million oysters without the risk of degrading the lagoon environment.
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Growth trends suggest that by 2003 that limit will be reached for the production of NZ$18 million worth of pearls.
The ecological sustainability of the industry has good prospects provided the whole lagoon is managed as one unit, since degradation by one farm will later affect all others.
A bacterial disease problem was caused by a combination of factors. Overcrowded pearl farms were producing unhealthy pearl oysters.
Unusually still and hot weather caused the lagoon waters to become poorly flushed and warmer.
This probably triggered the poor water quality in which bacterial loads became highly concentrated. Bacteria infected the pearl oysters causing the disease outbreak.
The Manihiki disease was similar to outbreaks in French Polynesia. About 300,000 adult and about 900,000 juvenile oysters died. Wild pearl oysters were also affected. Shells recently "seeded" (implanted with the bead that is the nucleus of the cultured pearl), were badly affected since the open wounds caused by seeding surgery enable bacteria to kill the oyster.
Some farms reported about 80 percent loss of their seeded shells. Farms with healthy oysters fared better. The juvenile oysters were highly susceptible, with losses of up to 90 percent.
The disease set Manihiki's industry back by several years, Ramea says. "Over the next five years pearl production is expected to be reduced by NZ$34 million."
To contain the disease, oysters were lowered to deeper and cooler waters, dead and such sick oysters were removed and activity as seeding and cleaning was suspended.
In November/December last year about 75% of the oysters were still infected. Since then oysters have been showing signs of recuperation and by February the percentage of infected shell was down to no more then 25%. An assessment of the lagoon will be made prior to resuming farming activities.
The long-term solution to the disease problem is the adoption of management practices to ensure that farms are not overcrowded and that good husbandry practices are adhered to by everybody. The Ministry of Marine Resources is working with regional organisations to arrange for long-term monitoring of water quality.
"Many in the industry view this disease outbreak as some kind of a blessing-in-disguise because it is a wake-up call for environmentally sustainable practices," Ramea says.
