Mr Ker began consultation with staff in June after an unexpected decline in student numbers in the applied business and automotive studies departments.
A proposal by business staff for 4.9 positions to go via voluntary redundancies was accepted yesterday, he said.
They would leave at various times from "quite soon" to the end of the year.
However, no-one in the automotive studies department had offered to take voluntary redundancy and Mr Ker had told them three positions would go.
Staff had a "week or so" to decide whether they were prepared to take voluntary redundancy, after which a final decision would be made.
All staff had redundancy payout clauses in their employment agreements, he said.
Enrolments in the applied business department were below target this year by about 60 full-time equivalent students.
Asked what would happen if enrolments climbed next year, Mr Ker said the polytechnic would cope.
"I feel we have the capacity to cope. [Enrolment] numbers are expected to remain relatively stable next year, but we could accommodate an increase of 10% [with the staff we will have]."
Numbers had dropped by about 25 to 30 in automotive studies this year.
Asked whether business department staff had been happy about taking voluntary redundancy, Mr Ker said they had not.
"Staff were upset and angry, as you would expect them to be. No-one likes to be put in a situation where they have to make life decisions like that."
