It will also capture seabed exploration permits held by Trans-Tasman Resources and Ironsands Offshore Mining, within the 12-mile nautical limit.
Seismic ban disproportionate
The Petroleum Exploration and Production Association of NZ welcomed the exemption for existing permit holders, but said the proposed seismic ban was a disproportionate response to a non-existent problem.
"It's hard to see why there needs to be a blanket ban on new surveys given they are already strictly regulated and there is no evidence of any permanent harm to dolphins," chief executive John Carnegie said.
"The government's own discussion paper acknowledges there is no evidence of harm to dolphins from seismic surveys, and no man-made causes of death apart from toxoplasmosis and fishing."
Mining lobby group Straterra said marine mammal protection is important, but said earlier consultation on the department's plan showed no evidence that seismic surveys and mining were a threat to them.
While there are a small number of permits in the areas to be protected, the area where mining could actually take place would be "infinitesimal" by comparison, chief executive Chris Baker said.
"There is significant economic potential in the vanadium-rich ironsands resource on the seabed of the western seaboard of the North Island, and potential for a variety of high-tech mineral deposits to be found in other coastal and marine areas.
"Such minerals could play a major role in the move to a low-carbon economy.
"A case by case approach would be able to address the economic and environmental trade-offs. But today's decisions means these green minerals will be further out of reach."
Endangered species
Hector's dolphins are considered nationally vulnerable, while the Maui dolphin is classed as critically endangered.
In the lead-up to the 2017 election, Sage's Green Party had campaigned to declare most of the South Taranaki Bight – about 30,000 square-kilometres - a blue whale sanctuary in order to prevent seabed mining and phase out oil and gas activities.
Among the new protections announced today are a nationwide ban on drift netting and an extension of trawling restrictions along the Northland-Taranaki coast and set-net bans down the length of the North Island.
DoC is also going to advance a toxoplasmosis action plan to better understand how the parasite is entering the marine environment and investigate ways of reducing or eliminating it.
"Fishing activities and the disease toxoplasmosis pose the biggest threats to Hector's and Maui dolphins," Fisheries Minister Stuart Nash said. "The changes will significantly increase fishing restrictions in dolphin habitats, focusing on methods with the highest potential to affect dolphins.
"However, I want to be clear – fishing vessels will be able to keep fishing if they move to different methods. There is new support from government to help them make that transition."
The government is receiving submissions on the proposed changes to the marine mammal protection areas until July 21.