KEY POINTS:
Mark Richards is fascinated by the scallops in Manukau Harbour.
"At low tide you see them spitting jets of water out to swim along fast. It's really quite amazing," said Mr Richards, who lives at Clarks Beach.
During last week's extremely low tides he saw "a couple of
hundred" people a day scooping up the delicious shellfish from tidal flats.
"You can get well over 1000 people here when the low tides make the scallop beds accessible - it's something where people can come and experience something different.
"This year, like last year, the scallop fishing is looking good ... walking only 30m up and down I got my legal limit of 20 and didn't even get my feet wet."
But Mr Richards recalled a scallop feast and famine during his 11 years running the Clarks Beach Holiday Park.
"For the first two years the fishing was awesome and then for three years it went downhill and got to the stage where I didn't bother. But the last couple of seasons have been good despite how many people go out there."
Ministry of Fisheries district compliance manager Ian Bright said it was disappointing that officers found 90 per cent of weekend gatherers at Clarks Beach had undersized scallops.
With instant fines of $250 for scallops under the legal size of 100mm being introduced in 2001, Mr Bright said the message should have got through.
"But maybe we have people new to the fishery and they do not take enough care to properly measure that the catch is legal size."
Further up the west coast, the vast Kaipara Harbour's scallop beds have been closed for harvesting since 2005.
In September, Fisheries Minister Jim Anderton extended the temporary closure of the beds for a further year to help rebuild the fishery.
This was at the request of the Kaipara Harbour Sustainable Fisheries Management Study Group.
"People recall two decades ago walking out with a kite and gathering off the hard substrate," said a member of that group, Juliane Chetham, who is manager of Te Uri o Hau's Environs Holdings. "But more people came and in boats and that led to the demise of a enormous scallop bed there in northern Kaipara.
"The scallop was of great importance and now if you go to marae for hui or tangi you will be fed oysters."
Ms Chetham said the group suspected other factors caused the stock's decline, such as poorer water quality due to run off from septic tanks, dairy farms, and land clearances for forestry and subdivision.
The group, backed by local authorities, requested the ministry to undertake a scientific survey to see whether stocks were improving to the stage where the rahui or ban could be lifted next season.
Preliminary results showed low scallop numbers in most of the harbour and though recruitment of juveniles was up, the adult scallops were thin and did not reach their potential condition.
Fisheries Ministry fishery manager Sarah Omundsen said the specific cause of the Kaipara beds decline was unknown.
"A lot of people are scratching their heads over that," she said. "It's not necessarily over harvesting. Clarks Beach is heavily utilised every year but Clarks comes back, because the size limit protects the fishery - the scallop matures at 60mm which gives them time to spawn a couple of times before they are of legal harvesting size."
The ministry has increased the number of scallops that can be taken from the Coromandel fishery this season for commercial, Maori and recreational fishers - though the recreational daily bag limit stays at 20 scallops per person. The annual total allowable catch for the recreational sector has been increased from 7.5 tonnes to 10 tonnes meat weight.
Mr Anderton said given the ministry's survey results showing an abundance of scallops, he believed it was still a cautious harvest level.
Northland's recreational catch is unchanged this season but the ministry says hunters and their prey will benefit by its delaying the season from a July opening to September 1 for the whole east coast from Cape Reinga to Cape Runaway. The ministry says this recognises that scallops are not in a good condition in July and August and allows early season scallops to improve in condition and spawn before dredging.
Niwa research scientist Keith Michael said scallop populations worldwide are characterised by cycles of boom and bust.
"They disappear for a few years and then come back," said Mr Michael.
"Scallops are ... incredibly productive but also if we knew how to predict the productivity based on larger factors of weather and climate then it would make management of this fishery a little easier.
"There's so much uncertainty and variability that it's always a challenge to keep ahead of what's happening."
SCALLOPS: BOOM AND BUST
* Larvae drift in currents for three weeks and can be transported far away.
* Scallops reach legal size of 100mm in 18 months to three years and can spawn at 60mm.
* Older scallops up to five years release 40 million sperm and eggs in one spawning.
* Growth and reproduction rates depend on availability of phytoplankton - food which they filter out from the water.
* Threats: sediment-laden water, hungry snapper, disease, being cast ashore in rough weather, toxic algae.
* Legal season: For west coast: July 14 to February 14; east coast: September 1 to March 31. Legal limit: 20 scallops of at least 100mm size per person.