Disturbance by large and small vessels may disturb and alter activities that are crucial for survival such as foraging, feeding, socializing and breeding. For example, when vessels are nearby, both northern and southern killer whales reduce the time spent foraging in favour of traveling^5,11. The interruption of feeding may impact the energy intake of these animals, which if persistent over time, may have individual and population-level impacts.  Southern resident killer whales also exhibit more energy-intensive surface active behaviours (spy hops, breaches, tail slaps, pectoral fin slaps) when vessels are within 200m⁸. Large whales can also be disturbed.  In Glacier Bay Alaska, humpback whales displayed avoidance behaviours such as diving, swimming away, reducing surface time, and changing respiration rates in the presence of cruiseships⁷.

Motorized vessels contribute to underwater noise that can reduce the ability of whales to detect their prey, navigate, communicate, rest and avoid danger.  In high vessel traffic areas, whale communication and echolocation can be almost completely masked by noise¹.   Vessel noise can also cause stress in cetaceans and may result in the avoidance of noisy areas³.  Learn more about the effect of noise on cetaceans here.

Like cars, vessels using gas or diesel create exhaust, which can be harmful when inhaled. In particular, marine engines burning diesel contribute significant amounts of sulphur dioxide (SO2), particular matter (PM2.5) and nitrogen oxides (NOx) in B.C.⁹ Whales are particularly vulnerable to emissions as, unlike terrestrial mammals, they do not have sinuses to filter air and they have no sense of smell to help them detect, and possibly avoid, engine exhaust. Whales also spend much of their time diving, which increases pressure in their lungs and causes air pollutants to enter their blood more rapidly than for non-diving animals.  While studies have shown that current whale- watching guidelines are usually effective in limiting pollutant exposure, during some summertime weather conditions, a build-up of air pollutants caused by the formation of a stable atmospheric inversion layer over the ocean traps air pollutants at the surface where the whales breathe⁴.

Vessel disturbance is a cumulative issue. Although one boat may have a small effect, numerous boats and chronic exposure to vessels can lead to significant disturbance of cetaceans. Increased marine traffic around whales has been particularly dramatic in the trans-boundary region of Haro Strait (near Victoria), where a plethora of recreational boaters, both Canadian and American whale-watching boats, and heavy shipping traffic all converge in critical habitat for endangered southern resident killer whales. Data collected by Straitwatch, an on-the-water monitoring group, indicate that southern resident killer whales experience approximately 100 incidents of non-compliance with the guidelines per day from May to September¹⁰.  While longer-term studies are required to understand the effect of vessel disturbance on cetaceans in B.C., in Shark Bay, Australia, short-term responses to disturbance has resulted in a decline in abundance of bottlenose dolphins⁶.  It is also important to note that kayak and other self-propelled vessels can also disturb animals, especially in heavily-used recreational areas¹².