The Ministry for Primary Industries is warning fishermen they will reel in and fine anyone caught selling seafood they've caught recreationally.
The cautionary message follows a high volume of calls and emails reporting Facebook posts by people selling seafood since the start of the year.
The 160 calls and emails logged by the ministry related to posts by people selling seafood such as crayfish, kina and pāua. This figure didn't include multiple complaints about the same post.
Just 96 complaints were received last year.
Compliance manager Greg Keys said it was likely most offenders knew their actions were illegal.
"This is simply another vehicle that people use to illegally sell recreational catch," he said.
"Both buying and selling recreationally caught seafood, as well as swapping it, is against the law. These are offences against the Fisheries Act and can result in fines of up to $250,000."
Keys said it was crucial MPI cracks down on every case to ensure the sustainability of New Zealand's fisheries as the warmer weather sets in.
He said it was also crucial to ensure seafood met food safety standards.
Earlier this month Ten cases of paratyphoid were confirmed in Hawke's Bay, linked to contaminated mussels.
Keys was encouraging people to report illegal sales to MPI through email or the department's Facebook page.