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Earlier this month, the 32-year-old captained Harbour for the 150th time - a feat which former club rugby writer Alistair McMurran, who covered the competition from 1976 until his retirement at the end of last season, could not recall anyone else achieving.
Whether it is a first or not, it is certainly remarkable.
The affable front-rower is in his 12th season with Harbour and has played 165 games for the club.
He has also played 44 games for Otago and would love to get to 50, although he felt there were too many players ahead of him.
It is unclear how many games Peter Merrielees, Peter Mirrelees or any other variation of the correct spelling has played over the years.
But that tricky surname has cost him.
''You don't get your air points if your name is spelled wrong,'' he joked.
''There have been a few managers who have had to shout me a few pints or a beer along the way for that mistake. But there have not been too many dramas.''
Mirrielees stood down as captain last season to allow Hadleigh May an opportunity but resumed the role later in the year.
No 8 Charles Elton and centre Aleki Morris are sharing the captaincy this season but Mirrielees stood in during the 34-10 win over Dunedin on May 16 to reach the milestone.
He started out with Dunedin in 2003 but with Jason Macdonald also in the side, Mirrielees transferred to Harbour the following season, and he became a permanent fixture.
He owns a gym in Dunedin and has two children - Luna-Marama (23 months) and Enya-Mahuika (12 weeks) - with wife Julie Cheyne.
While his body is ''holding up'', the demands of family life may dictate whether he returns for another season.
He rates this Harbour side as the ''most promising'' in his time with the club.
The team has been in excellent form and is in a three-way tie at the top of the table with Southern and Taieri. Dunedin is 14 points behind in fourth place.
Harbour's home game against Taieri tomorrow will have a big impact on the top of the standings.
The teams had a 31-31 draw in round three and appear very evenly matched, although Mirrielees felt his side would have the edge up front.
Harbour has not lost since its opening-round defeat to Dunedin and recent wins over Southern and University A have given the camp plenty of confidence.