A vehicle has been seized because its owner had gathered more than 600 cockles - 12 times the legal limit for the Auckland and Coromandel areas.
The Ministry for Primary Industries' compliance manager for North Harbour, Mike Simmons, said the person was caught at Eastern Beach, where cockle gathering is banned.
"Anyone who is caught with three times their daily limit, we seize all fishing equipment including vehicles, boats, dive gear, etcetera."
He said such property seizures were a monthly occurrence.
In the Auckland and Coromandel regions, the per-person limit for cockles is 50. Elsewhere in New Zealand it is 150.
Mr Simmons said the lower limit was introduced because cockle populations were shrinking as increasing numbers of people gathered them.
But compliance with shellfish-gathering rules was declining, either because people didn't know the rules or were ignoring them.
"In the Auckland part of the region, we have huge issues with people taking excess shellfish, and compliance rates for some beaches are as low as 35 per cent."
Some of the worst beaches for limit breaches were Okoromai, Umupuia and Kawakawa Bay.
"It's really disappointing that at some beaches two out of every three gatherers are taking excess."
He said the rules were intended to ensure sustainability, and limits were worked out by scientists who did beach surveys every few years.
Penalties range from instant fines of $250 to $500, to court appearances and the possibility of losing fishing equipment, boats and vehicles on the spot.
Mr Simmons said fishers paid more attention to size and catch limits.
"We're currently getting about a 90 per cent compliance rate or slightly under, which is encouraging, though it's still a worry that one in every 10 has under-size fish or excess fish."
Most boaties clear on fishing rules
A trip out on the Hauraki Gulf yesterday with four fishery officers showed most boaties were sticking to the recreational fishing rules.
Of about 10 boats approached by Ministry for Primary Industries staff over four hours, only two under-size fish were found.
Leaving from Okahu Bay in the Kaitiaki II, the officers took the Herald through the Rangitoto Channel, between Motutapu and Rakino Islands, past Waiheke and Motuihe Islands and back to Okahu Bay.
The first person caught by fisheries officer Erin Lawrence was a man with a less than impressive 29cm snapper (the minimum length is 30cm).
Ms Lawrence and district intelligence analyst Crystal Trudel spent 20 minutes talking to the man about the recreational fishing rules.
A call to head office revealed the man had been caught with undersize fish and excess scallops on three occasions. District compliance manager Mike Simmons said he would be contacted if it was decided he would be fined.
The next group of fishermen caught with an undersize fish had mistaken a 56cm kingfish for a trevally.
The legal size for kingfish is 75cm, making their catch more than 19cm under (the size for trevally is 25cm). The first-time offender was given a warning, and the kingfish, like the snapper, was put back in the water.
What you can take
• Daily shellfish limits for Auckland/Coromandel, per person
• Cockles 50
• Kina 50
• Green-lipped mussels 25
• Oysters 100 (must not be opened while they adhere to object on which they grow)
• Paua 10
• Pipi 50
• Scallops 20
• Tuatua 50
• Rock lobster 6 (illegal to collect if it is carrying external eggs or has soft shell)
• Toheroa prohibited
• Other 50 (combined, mixed species bag limit, applies to all shellfish not specifically named above including paddle crabs)