It's basically dependent on who is actually in attendance at the meeting. Some jurisdictions aren't always able to attend. Some members can't attend, for whatever reason, and there's no proxy voting. You can only vote if you have received a ministerial appointment to COSEWIC.
At the last meeting, there were 28 votes cast. I think the previous meeting had 27. At a minimum, two-thirds of the votes cast must be in favour of a particular status.