Ministry for Primary Industries staff have found six incidents involving Northlanders offering crayfish for sale on various Facebook buy/sell/swap pages in the past two weeks, prompting a warning from acting district compliance manager Stephen Rudsdale.
It was illegal for people to buy, sell or swap recreational catch, he said, andthe ministry would be speaking to all involved.
The ministry treated breaches "of this nature" seriously, he added, and offenders faced prosecution, penalties potentially including fines of up to $250,000 and the forfeiture of any gear used in the offence.
Mr Rudsdale's warning followed a ministry swoop in South Auckland in March, where five properties were searched after being identified as selling black market seafood from a Facebook page.
Mr Rudsdale said the public reaction to the sites had been positive, most people realising that selling seafood was illegal and posting messages indicating that to the sellers.
" It is illegal to offer to sell, sell, trade and purchase seafood that has been recreationally taken," he added.
"People who buy black market seafood also expose themselves to potential health risks, as there is no assurance that the product has been processed or stored hygienically.
"If you see anything of this nature on social media sites, take a screen shot and contact the MPI hotline, 0800 4 POACHER (0800 476-2243). All calls are confidential."
