The rapid and distressing disappearance of our once abundant scallop beds has been blamed on a few environmental factors. But increasingly, experts point the finger at one clear cause of the decline: dredging.

Today, September 1, is the first day of scallop harvesting season. But New Zealanders feasting on fresh scallops this season will probably be eating them from one of only two main beds left open on mainland New Zealand, in Auckland’s Hauraki Gulf.

Forty years ago it was different. My family would go scalloping with our cousins in our favourite spots around the Kaipara Harbour in Northland. Dad and his brothers would dive for abundant scallops while we kids played in the pōhutukawa and chased crabs. Afterwards we’d sit on the beach in our 70s towelling shorts, next to a driftwood fire with a battered frying pan sizzling, and we’d eat fried fresh scallops with white bread and sand.

In 2018, the entire Kaipara Harbour finally closed for the taking of scallops after researchers found just one healthy bed left, following dredge harvesting used in the area since about 1960.

For decades now, New Zealand’s scallop beds have been closing due to depleted stocks, two more in March this year, leaving just those two critical beds in the Hauraki Gulf. This is the first commercial quota species to be so comprehensively brought to the edge of being wiped out.

As the philosopher Milton Friedman said: Only a crisis – actual or perceived– produces real change. It is hard to argue that this taonga, our scallop species, is not in crisis. It’s time to change the way we safeguard them.

Primarily, we need to ask questions about the role of dredging in the species’ decline.

Dredging is a harvesting method that started commercially in most areas of New Zealand in the middle of last century, with the use of a bottom contact device called a Victorian box dredge. There are a variety of scallop dredges, and in different areas of New Zealand different kinds are used based on the type of seafloor. A dredge can weigh up to 200kg, with a toothed bar attached to the bottom so it can scrape 5cm deep into the seafloor.

Internationally, it is estimated one in five scallops die during the dredging and harvesting process. It has been banned in parts of Wales and Scotland. But in New Zealand dredging for scallops is still legal. 

There is more than one species of scallop in New Zealand waters, but the one we all know and love to eat is called the New Zealand scallop, or Pecten novaezelandiae. They are fast-growing, with high mortality rates related to the amount of stress they’re subjected to – whether that be environmental stressors such as temperature or water flow, resource availability, predation, or human-induced stressors such as dredging.

The end of a traditional summer delicacy

The beginning of the end arrived long before March this year when the last remaining mainland beds were closed. Major problems were surfacing as far back as 1980 off the Marlborough region’s coasts. 

A report on fishing and aquaculture, produced for the Ministry of Primary Industries, outlines how that year for the first time in New Zealand, a scallop population in the Marlborough region totally collapsed and had to be closed. 

Not long before that year, scallops had been plentiful, with a fleet of 216 licensed boats dredging up 1,244 tonnes in 1976. 

Fishers were cautious when the region reopened in 1982 and, this time, only 48 licences were issued. The region’s Challenger Scallop Enhancement Company also put in place a programme to reseed beds in Tasman and Golden Bay and a rotational harvesting approach was introduced with each bed only harvested once in three years.

This approach seemed to offset the species decline initially. Millions of dollars were poured into the scheme, dredging continued and a decade later the fishery seemed to be booming. Harvests bounced back as high as 800 tonnes in 1995. However, after that, annual catches dropped away. The last good year was 2002, when 700 tonnes were harvested.

By then, commercial fishers were no longer keeping to their rotational harvesting agreement, and the seeding programme had essentially failed. The fishery finally shut in 2016, with only about 20 tonnes able to be harvested. It has never reopened.

It would appear a tipping point was reached but, despite scientific reports blaming dredging, other potential causes of the decline were highlighted.

In 2009, Challenger operations manager Mitch Campbell told the Nelson Mail that the company had extensively researched the cause of the decline, to no avail. That same year former Challenger Scallop Enhancement Company chairman Buzz Falconer blamed the toxic residues from a former fruit-growing chemical factory by the shores of Tasman Bay for the scallop decline. In another interview, he suggested a massive flood in 2011, which pumped a great deal of sediment into the sea, had caused the loss of Golden Bay’s scallop harvest.

In 2016 Cawthron Institute marine scientist Paul Gillespie also blamed sedimentation for the closure, saying a slow build up over hundreds of years had finally hit home. 

In contrast, scientist Chris Cornelison, also of the Cawthron Institute, raised concerns last year about dredging, the only way scallops are commercially harvested in NZ.

Cornelison told Stuff the sea bottom was so degraded in parts of the Tasman Bay that it was impossible for sediment to settle in rough weather. The bottom, he said, had been dredged to uniformity, ironing out natural roughness and making sediment resuspend in waves above one metre. Scallops could not survive in this environment. 

A Fisheries Department study also pointed the finger at fish trawling for the failure of the reseeding program. Trawling uses a net with heavy weights which is towed across the sea floor. The study suggested scallop spat survival (spat are very young scallops which float in the water) was higher in areas that had not been trawled. This study also noted scallops survived underneath mussel farms, where there was no trawling.

In retrospect, the region was the canary in the coal mine, heralding what was to come for other areas. The same fate has befallen almost every scallop bed in New Zealand, including both locations where sedimentation is a problem and locations such as off shore islands where it’s not.

From Marlborough to the Kaipara Harbour, the Coromandel and the Far North, there’s a common theme: overharvesting and destructive harvesting methods that make it impossible for scallop spat to survive.

Communities fight back

For locals of Whitianga and the upper eastern coast, scallops are not only a delicacy, they’re the source of much tourist activity and income. Scallop beds were once so abundant that tourists would come from all over to harvest during the open season, an annual scallop festival was held, and the scallop shell stands proud on many a logo. The commercial industry was thriving, and some seafood shops exclusively sold scallops.

Ngāti Hei kaumātua Joe Davis says Ngāti Hei has relied on shellfish species as a core part of their diet and trade for generations. Their rohe was abundant with shellfish, so much so that their main method of gathering scallops was to await a wash-up on the beach, regarded as a gift from Māori god of the sea Tangaroa.

When Davis was a boy he saw thousands of scallops wash up along the shores after big storms. “This gift allowed us to hand gather scallops off beaches, as well as providing food for seabirds.” 

Such bounty was once a common sight around the eastern Coromandel coast. But Davis’s local Kūaotunu beach has not experienced a wash-up for at least 10 years. He says that for years, until 2021, Fisheries New Zealand, the government department that has responsibility for New Zealand’s commercial fisheries, ignored Coromandel communities who pleaded with politicians and officials to take action and protect their local scallop beds. 

By then, the east Coromandel scallop fishery’s once-thriving commercial fleet had decreased from a peak of 23 boats, down to only four. “The government was doing nothing. So we took it into our own hands,” says Davis.

Ngati Hei joined with LegaSea, a non-profit that works to restore New Zealand’s marine environments (and for which this writer works), to conduct a dive survey of scallops beds. In an area of 25 metres squared, they found only one legally-sized scallop.

Linda Bird, owner of Dive Zone Whitianga and organiser of the Whitianga Oceans Festival, also became involved. “Being owners of the local dive shop, our customers were reporting poor catch opportunities when trying to harvest at both Opito and Home Bay. At first there was the hope that the beds were just shifting. But gradually, we came to the realisation that some of the lesser known beds had disappeared altogether.  Gone were the days of in, under and back in 10 to 15 mins.”

The dive shop volunteered its boats and divers for the survey, and Bird remembers feeling relief when the group’s combined efforts with a community campaign resulted in a rāhui. In September 2021, after more than 2,000 submissions, the rāhui was finally officially ratified by the government and the area’s once-famous scallop beds finally lay at rest.

“It was evident that the beds wouldn’t have survived another season,” says Bird.

In response, the Whitianga Scallop Festival, a longstanding iconic occasion with economic benefit to the community of $3.5 million, pivoted to become the Whitianga Oceans Festival.

The new-look festival is one that promotes awareness of sustainability in the marine environment.

Hope for the future

Lucas Evans loves all things Coromandel, including scallops. As wild scallops have declined, his job has been to find alternative ways to grow them.

“We’ve been trialing the process of collecting spat and growing it up through the various nets that they traditionally use in Japan, to try and get them to a mature stage.”

Because New Zealand lacks an existing scallop infrastructure, scallops are being grown using net “lanterns” hanging off mussel farming lines hung between floats. “We generally go out once a once a month for rotating the scallops through the various nets, putting them into clean nets, and assessing their health, measuring and those sorts of things.”

Evans sees the process as an essential alternative to what has gone before. “Dredging for scallops is just a blanket sort of way of collecting the scallops and involves the big solid metal dredge being dragged over the sea floor,” he says. “On top of being labour intensive, hit-and-miss, and unpredictable, it also disrupts the seabed and upsets substrates that are reef systems and seaweed beds. It’s indiscriminate. “

LegaSea fisheries management advocate Trish Rea, who’s been gathering scallops and witnessing their decline throughout her adult life, says one thing is clear. “We cannot go back to managing our scallops in the same way and expecting a different outcome.”

Dredging, as the common link between every region’s scallop decline, must be banned, she says. “When the scallop populations recover we endorse the use of low impact, innovative harvest techniques… Our focus should be on not just rebuilding scallop populations, but a new approach that will prevent this ever happening again.”