Cetaceans can be struck and fatally injured by ships
Studies have demonstrated that the probability of striking cetaceans increases with ship speed. Ships traveling below 10 knots have a low risk of striking and fatally injuring a cetacean, whereas travelling at greater than 17.5 knots greatly increases that risk. Reducing speed in areas commonly used by cetaceans allows more time for the animal to avoid the oncoming vessel and/or the vessel to adjust its course. For example, speed restrictions in the eastern U.S. that require vessels greater than 65 meters in length to travel at speeds of 10 knots or less in areas frequented by endangered North Atlantic right whales have decreased strike-related mortality of this species by 80-90%.
Cetacean populations are also vulnerable to general disturbance by vessels. The presence of vessels may disturb and alter activities essential to cetacean survival, such as foraging, diving, resting, avoiding predators, communicating, socializing, mating and nursing calves. Interrupting these activities negatively affects individuals. In small populations (e.g. southern resident killer whales), these impacts on individuals can have population-level effects. To reduce disturbance, vessels should keep a distance of at least 200 meters; greater distances are even more beneficial.
Vessel noise can increase a whale’s stress level, cause it to move away from or avoid entering an area, and mask crucial echolocation and vocalizations. Vessel noise can generally be decreased by operating below cavitation inception speed and avoiding rapid acceleration, as well as rerouting when in the immediate vicinity of cetaceans and known sensitive marine areas.
The importance of reducing vessel-associated impacts is highlighted in the SARA Recovery Strategies and Management Plans for all 12 of listed cetacean species. Increasing mariners’ awareness of whale presence will allow them to mitigate the impact of their vessels by slowing down or rerouting in the vicinity of these vulnerable animals.
Ways to Reduce your Impact
When safety considerations allow, mariners can reduce their chance of striking or disturbing whales in the following ways:
1. Keep your distance. Stay at least 200 metres away when possible; greater distances are more beneficial. Learn more about the Be Whale Wise Guidelines here.
2. Reduce your speed. Slowing below your vessel’s cavitation inception reduces underwater noise that may affect whale foraging and communication. The chance of a ship striking and killing or seriously injuring a whale is greatly reduced when a ship travels at 10 knots or less.
3. Avoid rapid acceleration. Limit changes in RPM while transiting past whales.
4. Reroute. Consider the whale’s direction of travel and avoid entering their path.