Mud and silt decimate Kaipara Harbour scallop beds

The few scallops collected by NIWA were diseased.

The only scallop bed found.

The number of scallops in the Kaipara Harbour has declined to the point where there is only one scallop bed remaining in the entire harbour, and what scallops there are left are diseased and in poor health.

A decade ago, there were scallop beds found throughout the Kaipara, from south of Shelly Beach on South Head up to Tauhoa Channel, Port Albert, Tinopai and the Arapaoa River, and local residents speak of a much more widespread distribution before that. But a new survey carried out by the National Institute of Water and Atmospheric Research (NIWA) last spring found essentially only one bed left, just north of Shelly Beach.

NIWA fisheries scientist Dr James Williams, who lives at Leigh, said researchers dredged 189 sites throughout the harbour system, far more than when the last surveys were carried out in 2009 and 2007.

“In addition to the areas previously surveyed and fished, we wanted to see if there were scallops elsewhere, so we sampled the whole of the harbour anywhere the water was deeper than two metres,” he told a meeting of the Integrated Kaipara Harbour Management Group at Puatahi Marae last month. “We caught only one live scallop in the whole of the northern half of the harbour and there was nothing at all at Tinopai. We did a lot of sampling in all the places you’d expect them to be and there weren’t any.”

In the southern half of the harbour, those scallops that were caught on the one main bed north of Shelly Beach were often covered in mud and silt, there were few juveniles among them and disease testing found extreme damage to the scallops’ digestive glands.

“The scallops are not feeding properly and effectively starving to death,” Dr Williams said. MPI’s inshore fisheries manager, Steve Halley, says that the Ministry for Primary Industries is very concerned about the state of the scallops in the Kaipara Harbour, which is an important local fishery.

“Fishing is currently closed until September 1 for the normal off-season, but consideration will need to be given to future management, including whether fishing can continue given these concerning survey results, and the state of the environment in the harbour. Input from tangata whenua and consultation with the community will be very important in this process. Wider discussions, as have been promoted through the Integrated Kaipara Harbour Management Group, will also need to continue in order to address the range of activities that are impacting the environment in this very important area for fisheries”.

Tinopai resident Mikaera Miru said Tinopai used to be the biggest scallop bed in the harbour, but in the last two or three years it had completely died. He said access to the remaining scallops needed to be policed.

Dr Williams said that while harvesting did have an impact on the scallop population, the main issue affecting them was the changing habitat due to increased amounts of mud and silt in the harbour. He said young scallops needed a suitable seabed to live on, and they couldn’t settle on mud or silt.

“Our catches were all pretty muddy in the previously surveyed areas,” he said. “Even on the remaining scallop bed, there was a lot of mud and silt. In other places, it was just mud.”

Dr Williams said the survey, which was carried out in September and October last year, was simply a snapshot of what was happening in the Kaipara Harbour.

“The next step is understanding what we can actually do to actively restore valuable scallop habitat.”