Declining estuaries threaten fisheries
'There's potential fisheries may collapse'TERRI RUSSELL
Some fisheries in Southland could collapse if the region's estuaries continue to decline, experts say.
The estuaries, which act as a nursery habitat for fish, are being overloaded with nutrients and sediments.
Food sources for fish and birds, such as marine worms, find it difficult to survive within the oxygen-starved heavy sediment.
Environment Southland coastal scientist Nick Ward said it could lead to the collapse of some fisheries in Southland.
"There's a potential that some fisheries may collapse if the estuaries do continue to rapidly decline," he said.
The biodiversity in some estuaries had already decreased by significant amounts, he said.
Worst affected are the Waihopai arm of the New River estuary, Bushy Point, Daffodil Bay, Jacobs River estuary and the Waiau Lagoon. The source of the nutrients and sediment was unknown but runoff from farms could be contributing, he said.
"The end point is that it could strip away their [fish] food source and cause collapse of the fish we are catching.
"It is a worry because it looks like there is a deterioration, and continued deterioration, and where is the end point of that?"
There had been a "fairly big" decline in the number of pipis in the New River estuary, he said.
Mr Ward said the safety of food sourced from estuaries for human consumption was also an issue.
Environment Southland councillor and Southland Fish and Game manager Maurice Rodway said some birds were also under threat.
Birds such as stilts and godwits would be forced to find food elsewhere, he said. The birds fed on marine worms, that would find it difficult to survive in sediment.
Fish such as flounder, trout and juvenile red cod would be affected, Mr Rodway said.
This week, Mr Rodway asked Environment Southland councillors to take part in a field day to the New River estuary with other stakeholders after the local body elections.
The aim of the field day would be to find the source of the sediment and look at ways to reduce it.
The sediment was likely to be from an intensification of agriculture, particularly winter grazing practices, and possibly development in urban areas, Mr Rodway said.
Maori resource management of Te Ao Marama Dean Whaanga said he was concerned that food in the estuaries such as cockles, pipis and flounder were not edible due to pollution from run-off.
"I wouldn't recommend our people get them from some sites.
"There's continuing signs of the estuary continuing to decline. We're keen to see if the food is consumable," he said.
A report on the New River and Jacobs River estuaries, prepared by coastal specialists Wriggle Coastal Management, will be released next month.
Another report looking at the source of sediment compiled by Environment Southland, NIWA and GNS science is expected to be released in coming months.
- © Fairfax NZ News
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