NSWDPI Fisheries Officers seized 5379 illegally harvested fish and shellfish during a year long state-wide operation named "Small Fry" which focused on prohibited size fish offences.

NSWDPI Director of Fisheries Compliance, Patrick Tully said there were 20 locations where NSWDPI fisheries officers found most offences occurring during the year long operation.

Eden rated as number five and Merimbula number 10.

Regional areas in the top 10 offending locations also included Port Kembla, Woolgoolga and Shellharbour.

Officers detected 1350 offences during the operation with a whopping $102,500 worth of on-the-spot fines handed out to those caught possessing or selling prohibited size fish.

Twenty six others will, or already have faced the courts for serious offences involving prohibited size fish.

Men were the most prolific offenders by far with 30-34 year olds being the most over-represented age group.

Mr Tully said whiting, snapper, bream, tarwhine and kingfish were the finfish species most commonly involved.

"Turban snails, abalone, crabs and lobsters were the most common invertebrates seized by fisheries officers," he said.

"DPI appreciates the wider community's help bringing these offenders to account with 652 reports about prohibited size fish coming through the Fishers Watch service.

"Reports to Fishers Watch have grown year on year, doubling since 2013, with people now able to report to DPI through a smartphone and the free FishSmart NSW app," Mr Tully said.

"We've learnt a lot through Operation Small Fry and continuing to reduce the prevalence of prohibited size fish offences in NSW will remain an enduring priority for us.

"We'll be refocusing our efforts on these problem areas later in the year through another state-wide operation tentatively named Operation Bigger Fish."