"When he approached, the man became very aggressive and belligerent, and the threat was repeated twice - with the poacher's body language also very threatening.
"After he'd refused requests to co-operate, the man ran off."
Mr van Dorp said the officer involved was praised for his handling of the incident.
"He withdrew from the encounter at an early stage following staff safety training procedures to the letter, and alerted police who are now investigating."
Fish & Game appealed to anyone who was in the upper Utuhina area on Saturday afternoon who may have seen the poacher, thought to be in his early 20s, to make contact.
Mr van Dorp said a man was recently sentenced in Rotorua District Court to 250 hours' community work for his part in taking 25 trout from a spawning stream, while an associate was given 150 hours' community work.
And another man was caught on Sunday with 13 rainbow trout taken from a Rotorua closed spawning stream.
"He is facing charges and officers are following up on two other people believed to have been involved.
"None of the weekend incidents prompted any calls from the public to Eastern Fish & Game's 0800 POACHING line, which is quite unusual and concerning so we do take this opportunity to remind the public of the number and its purpose, to protect the district's vulnerable spawning streams in particular."
