Snapper is often a by-product of the fishing method and fetches a lower price.
Scoles cut the net free and steamed the vessel away from the area and into port, leaving the net to drift about 3km with a "fish slick" in its wake, according to the summary of facts. A passing tug captain noticed the floating net and reported it.
The Navy and Air Force were called in to recover the floating fish and passed the net on to the Ministry of Fisheries.
The net was labelled "Gavin Scoles Seine Net", pointing to the company Scoles Fishing Limited as its owner.
The net underwent forensic tests, which showed it had been cut with a knife.
In his defence, Scoles said he lost the net after it had got caught on something and snapped off.
He said he had never seen the net or any fish inside it, according to the summary of facts.
Under the Fisheries Act, fishermen found with snapper over the quota amount are required to pay per tonne for the fish.
Anyone found abandoning legal-sized fish can face a fine of up to $250,000 and/or a community-based sentence.
The vessel used on the day, Diana, was forfeited by Scoles Fishing and is now the property of MAF.
MAF northern regional manager Greg Keys said the sentence was a great outcome and served as a warning to other fishermen thinking of dumping fish.
He said there had been other reports of fish-dumping throughout the North Island, including on the west coast near Raglan, in the Hauraki Gulf, and off the Coromandel.