As you said, prevention is a very important part of the program for aquatic invasive species. We know that when a species is established in an area, it's very difficult to remove it. The costs for the ecosystem and for the economy could be very high. The example of zebra mussels you use is a good one.
What you should also know is that each region has been allocated not only personnel but also some budget. Depending on the species and the risks they have to manage, they may decide to put more of the budget on prevention or on control. The Asian carp program is a good example of the type of prevention that we're doing because the Asian carp is not established in the Great Lakes. It stopped with the barrier.
Another example could be with the smallmouth bass. The early detection program monitoring downstream of tributaries in Miramichi Lake is also very efficient and helps us to better manage the species.
Usually, we do it with the province, when they manage that species, or we do it with some groups—NGOs or committee groups—and manage the species to do the prevention when possible.