Members of the public are being asked to look out for poachers over Christmas.
Autumn rains force stocks of salmon and trout into the rivers to spawn, and they become easy targets for criminals with nets.
Hoteliers and restaurateurs are being urged not to accept any fish offered for sale, and to report any encounters with poachers to the police.
Manx River Improvement Association spokesman Brian Craig (pictured) says poaching is aganist the law, and is seriously damaging rivers stocks:
Carers: 'They are often the quiet heroes of our Island'
It's believed there are around 1,000 young carers on the Island
Hooper: 'Time to bite the bullet and build new hospital'
MHK says government should be planning replacement for RDCH
'No final decisions' made yet about relocating dementia patients says Manx Care
Meeting due to be held with residents, families and staff
'We want to provide a facility for almost anybody'
Two women have one year keep Ballafesson Hall from being sold on open market
Relatives seeking clarity over potential plans to relocate dementia patients
Rumours there are plans to relocate Martin Ward onto specialist EMI unit