Resident marine mammal species often reside in the one area, but many species show a variety of movement behaviours at a location. For example, around Tenerife, in the Canary Islands, some short-finned pilot whales are resident, some undergo small-scale migrations, and some are thought to be transient [3]. Therefore, the monitoring frequency should reflect the goal of the monitoring. If the purpose of the monitoring is to generate an absolute or relative census, then once per year or every two years may be sufficient. However, where monitoring relates to, for example, habitat use over time, or developing an understanding of subpopulations, multiple surveys may be required each year.