Most cetacean species are highly mobile, following their prey over long distances or migrating regularly between breeding or feeding ranges. In the ASCOBANS Area they encounter a variety of man-made threats, of which bycatch, the accidental entanglement in fishing gear, is considered the most serious. Every year, several thousand cetaceans drown because they become ensnared in fishing nets, preventing them from coming up to the surface to breathe.

Marine pollution is another serious threat that calls for an international, coordinated approach. Toxic substances like heavy metals and persistent organic compounds, most notably the PCBs, enter the food chain and accumulate in the body tissues of marine mammals, adversely affecting their health.

Commercial shipping, industrial activity (e.g. pile-driving and seismic explorations), explosions and navy sonar cause underwater noise. Such acoustic disturbance can lead to behavioural changes, physical injury and even death. Moreover, the expanding shipping fleets result in increasing numbers of ship strikes, collisions between the vessels and the cetaceans, which is of growing concern.

The extent and the effects of the threats faced by small cetaceans vary among areas and species. The combined effects of all human activities are unknown, but it is clear that cetaceans are under additional pressure from prey depletion, habitat degradation and climate change, which have a detrimental effect on whales, dolphins and porpoises.