By Sally Murphy of RNZ
Kaipara Mayor Jason Smith, who is also a sheep and beef farmer, has had $40,000 worth of stock stolen.
Smith had 307 new season lambs disappear from his Ruawai farm between 17 November and 1 December.
Smith said the farm manager noticed they were missing last week when they were being mustered to be sold.
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"This is not just a small number of like 10 sheep or three steer missing, this is 307 lambs - it's a sizeable mob for someone to walk or drive away.
"It's beyond me, so we've got the police involved because it's a sizeable theft, those lambs were worth at least $40,000."
Smith said there was no insurance on stock thefts so the farm would simply have to cop the loss.
He said there were no obvious signs of where or how the stock were removed from the property - but he was now going to install security systems.
Northland Federated Farmers president Colin Hannah said stock thefts had increasingly become a problem in the region over the past 12 months.
He said police were aware of the issue.