Dolphin Conservation Society chairman Taison Chang Ka-tai also expressed doubts over the Sustainable Lantau Blueprint, which cites four separate marine parks as effective protection measures for the mammals.

“None of it is new. They are just using flowery language to make development easier and easier to pass,” he said.

Chang said that two of the parks – in Southwest Lantau and the Soko Islands – had been demanded a decade ago and would not be in place until 2018 and 2019. The other two were “compensation” measures that were conditions of environmental permits to make up for the habitat loss before work was allowed on the runway and a waste incinerator.

All of them were small, fragmented and lacked protected “corridors” for dolphins to travel between, he said, meaning they would not be effective in providing protection. No dolphins at all were sighted at Brothers Marine Park last year.

The society suggested three measures that would have an immediate impact. First, divert a high-speed ferry traffic route in southern Lantau further south, off the southern coast of the Soko Islands.

“We believe this is the fastest, most feasible measure and will have immediate impact,” Chang said.

Second, connect the southwest and Soko Islands parks, which are separated by the ferry route.

Third, establish one large protected area connecting all the parks around Lantau Island and Chek Lap Kok. This new zone would measure more than 10,000 hectares, double the current area, Chang said.

The department said marine parks provided better habitats for marine life and safeguarded and enhanced fisheries resources and biodiversity.

Designating a marine park involved consideration of scientific, conservation and education value as well as consultations with stakeholders.

From 87 Chinese white dolphins in 2010/11, numbers fell to 65 in 2015/16 and 47 in 2016/17. The estimate in 2003 was 188 dolphins.