If you don't know your toheroa from your tuatua you're risking a $500 fine, Northland fisheries officers are warning.
Juvenile toheroa are making a comeback on Ninety Mile Beach after many years, but the Ministry of Primary Industries says their recovery is fragile.
The toheroa fishery was closed across the country in 1982, after a massive drop in numbers.
MPI officer Steve Rudsdale said the ban on collecting the shellfish was there for a good reason; they do not survive if people do not leave them alone.
"One of the difficulties is that toheroa look very similar to tuatua - which are plentiful and not subject to the same gathering ban."
Mr Rudsdale said toheroa shells were more brittle and slightly rounder than tuatua, and had a slight lump at the base.
"The two species can be the same size and colour depending on their age but toheroa will eventually grow twice as big as tuatua and have a darker shell."
Steve Rudsdale said a simple test for pickers in doubt was to sit the shellfish on its base on the sand with the sharp end standing up.
A tua tua should stay upright - while the toheroa should fall over.
Fisheries officers would be out and about on Ninety Mile Beach teaching gatherers how to tell the difference.
Mr Rudsdale said that while they would exercise some discretion they would not be tolerating repeat offenders.
"If you're caught with up to 50 toheroa or you've disturbed them you face a $500 fine.
"And if you're caught with more, you face prosecution and a fine of up to $20,000."
The only exception to the ban on gathering the shellfish is a customary fishing permit.