Blackmarket seafood sales on social media are a growing trend in Northland and around the country, but the "closed" status of some of the sites means fisheries staff need public help to catch the illegal sellers.
Figures from the Ministry for Primary Industries (MPI) show that, when illegal selling on social media first came to light in 2012, four cases of blackmarket fish trading were identified online.
But this quickly grew to 39 cases in 2013, including four in Northland, 173 in 2014 (16 in Northland), and 117 cases to the end of August, including seven in Northland.
In June alone, Northland staff found six incidents of people offering crayfish for sale on various Facebook "buy/sell/swap" pages in just over two weeks.
It is illegal to buy, sell or swap recreational catches. Depending on the scale of offending, people risk facing prosecution and fines of up to $250,000, as well as forfeiture of any gear used in the offence, including computers and cellphones.