An adverse effect on marine ecology from the disposal of large volumes of spoil could not be avoided by Port Otago's proposed channel deepening and widening project, aquatic ecologist Dr Mark James says.
Significant short- to medium-term effects at the disposal site were expected with major dredging and recovery could take up to year for short-lived species, but longer-lived species could take several years to recover, Dr James said.
"Communities are expected to recover once major capital dredging is completed, but his could take several months to a few years." Dr James was one of four scientists to provide evidence at the fourth day of Port Otago's resource consent hearing yesterday on the effects that Project Next Generation might have on marine mammals, birds and the fishery.
He said the most significant effects were likely through direct removal of organisms and the increase of suspended sediment and sediment deposition.
There would be "little if any impact" during incremental dredging with a New Era-type dredge (owned by Port Otago) but with major dredging there could be significant impacts on soft-sediment communities in the lower harbour although they would be localised, short-term to medium-term and confined to the main channel and some side channels.
"These impacts will be site-specific, but with major capital dredging most animals and plants from Port Chalmers to the entrance where it is to be dredged will be removed, destroyed or heavily disturbed, resulting in loss or modifications of communities or habitats.
"Communities in most intertidal areas would be expected to survive and patches that were lost would be expected to recolonise in the short to medium term." It was unlikely that new habitats would be created by the dredging operation or that existing habitats would be lost, he said.
"I would not expect any community types to be lost from the harbour because there is a mosaic of communities with no type restricted to only one habitat."
Most of the impacts would be localised and significant long-term effects were not expected, he said.
"In order to minimise impacts, if they did unexpectedly occur, and to allow recovery, a comprehensive monitoring and adaptive management plan has been developed."
No rare, unique or endangered species were found in the sampling programmes undertaken.
National Institute of Water and Atmospheric Research (Niwa) scientist Paul Sargar, in an affidavit presented to the hearing panel, said within Otago Harbour bird life was dominated by gulls, waders and shags, while outside the harbour shearwaters, terns, penguins, gulls and albatross dominated.
Of these, the grey-headed mollymawk, black-billed gull and black-fronted tern were considered to be nationally significant, while a further 12 were of conservation concern.
"In my opinion, incremental capital dredging ... is unlikely to have any discernible adverse effects against a background of natural variation of any of the birds."
Major dredging might adversely affect seabirds if the sediment plume reduces their ability to see their prey and reduce their prey, he said. However, most seabirds found in the area off Otago fed well offshore or were predominantly bottom-feeders.
Some species such as blue penguins, shags and gulls might have to forage more widely during and immediately after. This was of concern for blue penguins as any reduction in their foraging ability could result in them providing insufficient food to their chicks, he said.
He recommended managing the dredging operation where possible to avoid the critical part of the recruitment and breeding period for birds over spring and summer at Aramoana and off Taiaroa Head.
"It is also proposed that when godwits are foraging on the intertidal flats at Aramoana in February and March that capital dredging is only undertaken when tidal height is above half-tide."
The hearing panel will make a site visit today and the hearing will resume on Monday, with evidence from submitters to be heard.
Panel
- John Lumsden (chairman), Hugh Leersnyder, Mike Johnston
Proposal
- Upgrade channel berth and swinging areas disposing 7.2 million cu m at sea
- Extend multipurpose wharf by 135m
- Construct fishing wharf at end of Boiler Point walkway Where: Otago Regional Council offices, Dunedin.
Day 4
- Final day of Port Otago's evidence
Giving evidence yesterday: Aquatic ecologist Mark James, affidavit presented by Niwa zoologist Paul Sagar, marine mammal and fisheries consultant Martin Cawthorn, fisheries consultant Richard Boyd, environmental consultant Philip Mitchell.
Quote of day
"This will not impact on the availability of cockles for recreational or customary cockle gatherers" - consultant fisheries scientist Richard Boyd
