Police suspect a run of rustling on East Coast farms is the work of experienced farm workers.
Farms in the Whatatutu and Te Karaka areas have been hit hard by the thefts, with one station losing 145 sheep over several months, and others losing more than 50 hoggets and 20 ewes.
In all cases, the sheep were slaughtered in their paddocks and the heads and guts left behind.
Police believe those responsible have farm experience, know how to slaughter stock properly, have access to equipment and dogs and have vehicles large enough to carry the carcasses away.
Te Karaka police constable Paul Cleaver said the thefts were having a devastating effect on local farmers and frustration was very high in the local community.
He said as well as the stock thefts, there had been burglaries, damage and thefts of equipment from farms.