The Federation of Commercial Fishermen says a plan to increase the protection zone for Maui's dolphins is pointless because they may not even be in that area.
Conservation Minister Nick Smith on Friday announced plans for a 350 square kilometre extension to a set net ban out to seven nautical miles off the Taranaki coast.
The proposed ban is to protect the last remaining 55 Maui's dolphins.
Federation president Doug Saunders-Loder says during the past year the Government has put a huge effort into finding Maui's dolphins in the area, but none have been found.
Mr Saunders-Loder says it is relying on historical sightings, none of which were by professional observers, and no photos or videos have been provided.
He says it's more likely the sightings are of the closely related and more common Hector's dolphin, which are known to swim into those waters.
Commercial fishermen in Taranaki say their livelihood will be further squeezed if the ban on set nets is extended.
Rob Ainsley, who runs Ocean Pearl Fisheries in New Plymouth, said he has gone from 18 employees down to two in the past 12 months, because of the initial ban out to two nautical miles.
He said that has all but destroyed his business.
Ian McDougall, another fishermen, said three commercial fleets depend on set-net fishing within the proposed ban area. He said there is no proof any Maui's dolphins remain in the area.
The plan is open to consultation until 10 October.