He and three supporters camped on the site until Monday afternoon, and now Te Uri Taniwha has imposed a rāhui against any development in the area, including construction of the road and carpark, as well as dredging.
The rāhui is designed to maintain the site's cultural and spiritual integrity, and has no effect on public access.
Mr Mitchell, who also wanted Windsor Landing to be known by its original name, Rangitoto, said he was "rapt" with Friday evening's show of support, especially from young people and local residents, who he had invited by phone, email and leaflets.
Among them was Hori Parata, a Ngātiwai elder from Whangārei, who said he was concerned about the number of Māori archaeological sites that were being destroyed.
Local resident Jim Johnston, one of several Pākehā who spoke during the pōwhiri, said he netted for mullet in the area, and enjoyed its peaceful atmosphere.
"My first thought when I heard about the ramp was that this is marvellous, I'll be able to launch my boat at any time. But we have so much to lose. I love it and feel at peace here," he said.
Others worried about the little blue penguins that nested in the area or increased traffic on Inlet Rd, while Diana Sandifer spoke of the area's "special spirit," and pledged to "come down and support you every now and then" if an occupation took place.
The development has been approved by Heritage New Zealand's Māori Committee, and was appealed, unsuccessfully, in the Environment Court by Mr Mitchell, although the judge did tighten up some of the conditions. The court found that the middens and fish traps had already been damaged in recent decades, and no evidence that filling in part of an inlet would affect the functionality of the fish trap.
The Far North District Council has been contacted for comment.