There could be deaths of native fur seals at a breeding colony north of Kaikoura as part of the State Highway 1 rebuild, says the Department of Conservation (DoC).
But DoC and the New Zealand Transport agency say they are doing everything to protect the breeding colony of about 2000 seals between Paparoa Pt and Half Moon Bay, with many pups living directly below the big slips at Oahu Point.
DoC's northern South Island operations director Roy Grose said there may "some mortality" due to impending roadworks at Ohau Point, but a trial involving electric fences to keep them back from the works area has been encouraging.
After some small adjustments, the fencing is working well to keep the seals out of harm's way
The first phase of the strategy involves a two-week trial, now underway at a 20,000cu m slip site, north of Ohau.
The trial is using 'seal-proof fencing' and on site seal herding to keep adults and pups away from the immediate base of the slip site, clear of falling rocks and debris while helicopter sluicing and slip clearance work is carried out.
"After some small adjustments, the fencing is working well to keep the seals out of harm's way. Inspections have shown no seals on the landward side near the slip base, which is a successful result," he said.
Grose said at the end of the trial, the results will be reviewed by DoC, NZTA and iwi to develop methods to protect seals for the full period of construction.
NZTA earthquake recovery manager Steve Mutton said the state highway rebuild was a massive construction job involving millions of tonnes of rock and it would be foolish to say there was no chance of marine mammals being hurt.
"The slips brought down by the November earthquake at Ohau Point are massive, and the task of clearing them is huge. It is an ecologically and culturally significant site.
"We are doing everything we can to protect the seals where we have got to bring machinery in or reconstruction activity is occurring," he said.