There are three ecotypes of orcas which are all members of the same species but tend to display different behaviours, communicate differently and have different prey preference. The most common ecotype near Vancouver are the Resident Orcas, specifically the Southern Resident Orca population. This population is comprised of the J-pod, K-pod and L-pod. These populations feed mainly on salmon which as scarce in the Salish Sea during the winter. Therefore, resident orcas tend to disperse in search of food during winter months in the as far north as Alaska and as far south as Califorina.
As salmon travel to the ocean from inland rivers for food during the summer, the Southern Resident Orcas return to the Salish Sea to feed. By October, many salmon return to their natal stream to spawn and therefore, the abundance of prey for the Southern Resident Orcas depletes. During this time, orcas will begin to disperse North and Southward in search of more abundant prey but some will linger to feed on the salmon late for spawning.
If you're interested in more information about this population, check out Orcas of the Salish Sea