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Cr Vandervis was among 13 mayoral contenders taking part in a mayoral forum at the University of Otago on Thursday, when all candidates were asked how they would encourage young people to vote.
Cr Vandervis rejected the notion, saying he wanted "educated" voters - not more young voters.
"They don't know enough about candidates. They don't care enough about candidates," he said, as the crowd reacted with cries of "sit down".
In a subsequent email, Cr Vandervis claimed he had intended to say his preference was for more informed voters rather than just more people voting, but had "completely stuffed up my comment" before being "drowned out".
"What I did say was entirely inappropriate, given that those few of Otago's 20,000 students attending the electoral forum were exactly those who did take an interest and were making an effort to be informed.
"To these informed and interested young voters, I unreservedly apologise, and hope that perhaps as a result of my gaffe, there may be more of them engaged and interested enough to lift the traditionally small number of student engaged voters as the election campaign progresses."
OUSA did not respond to a request for comment yesterday, but fellow mayoral candidate Aaron Hawkins - judged the winner of Thursday's debate in an informal exit poll - said Cr Vandervis' intentions had been "quite clear".
"Misspeaking or not, it's always disappointing to hear people in our community being told that they shouldn't take up their right to vote, especially by an elected representative and candidate."