Scallop fishery may not recover

DWINDLING: Nelson scallops at Guyton's fresh fish shop.
DWINDLING: Nelson scallops at Guyton's fresh fish shop.

A seabed layer of thick murk means that the return of good scallop numbers in Tasman and Golden bays will take years and might never happen, industry figures and shellfish experts say.

Hailed as a great success story for nearly two decades after being brought back from collapse by a spat-seeding programme and a new management regime, the scallop fishery in the two bays is virtually gone.

Lucrative harvests of more than 400 meatweight tonnes were taken nine times in the years between 1991 and 2002, with the worst season in that period, 1996, contributing 231 tonnes, and the better ones generating $25 million or more.

Since then it has been a steady downward progression. This year's projected 53 tonnes, likely to be all taken by the end of next week, is coming mainly from two beds in the Marlborough Sounds. Since 2005 there has been no commercial dredging in Tasman Bay, scene of a scallop "gold rush" in the 1970s. Golden Bay, still producing commercial harvests until last year, is now also virtually devoid of mature scallops.

Amateur scallopers, meanwhile, are concentrating on Squally Cove outside Okiwi Bay, and Ketu Bay in Pelorus Sound, putting pressure on the healthy scallop beds there.

There has been considerable speculation about the cause of the decline, with chemical pollution and nutrient loading from the land, the effects of flooding and heavy rain, dredging and shifting weather patterns all debated.

While further scientific investigation takes place, there is agreement that there are probably many factors working in combination to make conditions unsuitable for scallops to live and grow.

But a range of people with a connection to the industry - fishermen, scientists, divers and representatives of the Challenger Scallop Enhancement Company - agree that a murky slurry just above the seabed in both bays is what's wiping out both the naturally occurring and commercially seeded spat at the moment.

Tasman Bay was hit first and hardest. It has more fine sediment and has to absorb the plume from the Motueka River, which contributes 41 per cent of the annual suspended sediment load to both Tasman and Golden bays, with the Waimea, Aorere, Wainui and Takaka catchments providing most of the balance.

The scallop company, which runs the top of the south fishery under an agreement with the Primary Industries Ministry, is carefully managing the residual populations in the Sounds.

The catch is determined in advance after biomass surveys and the boats, mainly fishing for Talley's, are closely monitored using satellite technology, which pinpoints their location and speed. There are meticulous records of where the scallops are taken.

The company was conservatively operating its rotational fishing plan, chairman Buzz Falconer said, because it wanted to ensure that catches could be maintained in future years.

But the fishery was "like a three-legged race", he said, comprising Tasman Bay, Golden Bay and the Sounds.

"If one of those legs fails, you put pressure on the others." Tasman Bay has been ruled out since 2005. "It's only with careful management that we've been able to save Golden Bay, we've had it down and it's come back up. Unfortunately it's down now, and it's staying down. Because, we believe, of the sedimentation problem."

Operations manager Mitch Campbell said the company has had excellent success in catching the drifting scallop spat since 2005, but there's very poor survival once the tiny scallops are released to the seabed.

"I put it down to the fact the seafloor within 25 metres of shore in Tasman Bay and 18m in Golden Bay now comprises very fine silt and this makes filter-feeding for bivalves impossible. The bays once had structure to them, but now as many divers will attest, it is thick, black anoxic sludge - worse near the river-mouths."

No-one was prepared to guess when the scallop numbers might bounce back. The consensus: it won't be soon, and without the cooperation of nature and some changes in land and sea-based activities, maybe not at all.

The Nelson Mail