As a result, the school was not in a position to employ new staff, and staff members who were resigning and retiring were not being replaced, he said.
"It is staff management through attrition.
"We are exploring new ways of managing the impact of falling rolls."
He expected next year's roll to be "in the early 500s", including a significant number of international pupils.
The school this year posted its lowest March roll return in a decade, at 595.
Bayfield High School principal Judith Forbes said year 9 enrolments were similar to last year, but a large cohort of senior pupils leaving the school at the end of this year meant the school's overall roll would drop by about 20 in 2013.
The school posted a March roll return this year of 624. .
Both Mrs Forbes and Mr Geerlofs said staff numbers would have to be cut, but it was too early to say how many would go at this stage.
Mrs Forbes said she too was hoping to resolve the excess in teaching staff through attrition.
"It won't be a large number. We've got some staff retiring at the end of the year and we're hoping that will cover it."
Earlier this year, Statistics New Zealand senior demographer Kim Dunstan said the roll decline, particularly in Dunedin, was caused by a drop in the birth rate which began in the early 1990s.
He said there were 1700 births a year on average in Dunedin around 1992, but the number had fallen to, and plateaued at, about 1300 a year since 2000.
