People are being asked to help protect salmon and seat trout from illegal fishing.
The Department of Environment, Food and Agriculture is urging the public to report suspected illegal activity either to the Fisheries Directorate or to the police.
Typical signs to look out for are tyre marks going onto the beach, vehicles on the beach during the hours of darkness and small boats near the shore.
Suspicious activities during the hours of darkness include lights on rivers, as it is illegal to locate or disturb any fish in inland waters with a light.
Fishing for salmon and sea trout in Manx rivers is now closed until April to allow fish to spawn undisturbed and there is a complete prohibition on fishing for these fish at any time at sea, in a harbour or from the foreshore.
The Sea-Fisheries (Protection of Migratory Fish Species) Bye-Laws 2005 mean that unless licensed by the Department it is an offence to use or even be in possession of gill and other specified nets within 750m of the high water mark between The Stack at the northern point of Peel Bay, clockwise round to the northern side of Ramsey Harbour.
The Department has brought a number of successful prosecutions over the years.
Penalties for poaching usually take the form of a fine, confiscation of fishing equipment (potentially including the boat or vehicle) and the catch itself.
Confiscated items may be destroyed on the advice of the courts.
Minister Geoffrey Boot says: "I would urge people to report any suspicious activities immediately.
"Fisheries officers conduct regular night-time patrols during high-risk periods, liaising closely with the Isle of Man Constabulary, which takes wildlife crime very seriously.
"However neither my officers nor the police can be everywhere at once.
"Information on suspicious activity helps resources to be deployed efficiently and effectively."
Police Wildlife Crime Officer PC John Hills says: "The Isle of Man Constabulary has two wildlife crime officers who liaise with our partners at the Department on wildlife crime-related matters.
"The unit is committed to the sustainable use of the countryside and we will support our partners at the Department in the apprehension and prosecution of anyone fishing unlawfully.
"If you have suspicions about illegal fishing taking place then please report it to your local police station, to Police Headquarters on 631212 or call the anonymous Crimestopper’s Line on 0800 555 111."