Two men have been fined after being caught illegally taking more than 40 rare shellfish from 90 Mile Beach.
The pair have been fined $500 each after being caught with 43 toheroa from the beach - a number the Ministry for Primary Industries described as "very large".
The toheroa fishery was closed across New Zealand 35 years ago after toheroa numbers began to plummet.
Ministry for Primary Industries spokesman Steve Rudsdale said the incident was extremely disappointing especially when toheroa on 90 mile Beach were just beginning to re-establish themselves.
"It's heartbreaking, really. If this sort of illegal take continues, it won't bode well for a fishery that is already very fragile. Even disturbing toheroa can have an extremely detrimental effect on them.
"We have observed a resurgence of toheroa on 90 Mile Beach, but their numbers are still very low. They're off-limits for a very good reason."
Toheroa looked very similar to tuatua but tuatua were much more prolific than toheroa so were not subject to the same gathering ban, he said.
Toheroa shells were more brittle and slightly rounder than tuatua and had a slight lump at the base, while tuatua shells were slightly glossy compared to toheroa and had a square, flat base.
A simple test was to sit the shellfish on its base on the sand with the sharp end standing up. A tuatua should stay standing, balanced on the flat base while the toheroa should fall over.
The two species could be the same size and colour depending on their age but toheroa would eventually grow twice as big as tuatua and have a darker shell.
"We'll be taking a zero-tolerance approach to any taking of toheroa in this area," Mr Rudsdale said.
"Fisheries officers will be out and about patrolling regularly as always and I understand locals will be stepping up their efforts to patrol the beach as well."
The penalty for being caught with up to 50 toheroa or even disturbing them is a fine of up to $500. If you are caught with more than 50 toheroa, you face prosecution and a maximum fine of $20,000.