Killer whales depend on echolocation and acoustic communication to forage, socialize, and find mates. The sophisticated echolocation system of killer whales is likely their primary sensory mode, and allows them to navigate and find prey in turbid, dark waters².  Communication is also key to foraging success for resident killer whales.  Southern and northern resident killer whales are highly social animals that live out their entire lives in family groups.  Resident (fish-eating) killer whales travel together in matrilines, maintaining contact through a series of distinct underwater dialects that are unique to the group³.  While foraging, members of a group can spread out over several kilometres, maintaining contact and coordinating movements through the frequent exchange of loud vocalizations².  When an individual captures a prey item, it is often shared among members of its matriline⁴.  Bigg’s (transient) killer whales, in contrast, often forage in silence².  They depend on passive listening to hunt other marine mammal prey, since vocalizing could increase the chance of their prey detecting them.

Vessel noise can interrupt critical life processes for killer whales. In areas of high vessel traffic, killer whale echolocation and communication can be almost completely masked by boat noise⁵, and can interrupt important behaviours such as foraging, group cohesion, resting, and mating⁶.  Studies have shown that southern resident killer whales increase the duration of their calls when boats are present, likely as an adaptation to the masking effects caused by increased noise levels⁵.  Vessel noise can also increase a whale’s stress level and cause them to avoid certain areas^5,6.  Avoidance of key foraging areas due to acoustic disturbance places additional stress on the endangered southern resident killer whale population, whose survival is already threatened by a reduction in prey availability and environmental contamination⁶.

Vessel speed reduction may help decrease underwater noise. In order to determine how vessel noise impacts killer whale foraging behaviour, the Port of Vancouver’s ECHO (Enhancing Cetacean Habitat and Observation) Program conducted a research trial to slow down vessels through Haro Strait. Haro Strait is known to be a key foraging area for southern resident killer whales during the summer months⁷.  It is also geographically constrained area with a busy shipping lane, which creates the potential for loss of foraging as a result of vessel noise. The trial requested piloted commercial vessels to voluntarily slow down to 11 knots while transiting Haro Strait from August 7^th to October 16^th, 2017.  Previous studies have indicated that slower ships are quieter; a one knot reduction in vessel speed may result in one decibel reduction in vessel noise⁸.  The trial aims to better understand the relationship between vessel speed and sound, the effects of reduced speed on the total underwater ambient noise in critical killer whale habitat, and the potential benefit that reduced speed might have on killer whale foraging behaviour. To analyze the potential noise benefits achieved by slower speeds for different vessel classes, two hydrophones were deployed in the shipping lanes in Haro Strait to directly measure the acoustic signature of passing vessels and compare noise levels before, during and after the trial. Monitoring of total ambient underwater noise was conducted at the Lime Kiln hydrophone off San Juan Island, which serves as an indicator of potential received noise levels by killer whales in this important foraging area. Comparison between trial and non-trial months will identify important factors affecting ambient noise levels. Visual observations and acoustic detection will be used in conjunction with a computer model, developed by JASCO Applied Sciences, in order to analyze the relative change in southern resident killer whale behavioural response. Preliminary results of the trial suggest that speed reduction is an effective method for reducing vessel noise. Approximately 60% of piloted vessels participated in the slow down trial.  On average, vessels reduced their mean speed by 2.2 to 5.8 knots, resulting in a 4.9dB to 9.3dB reduction in vessel noise.  Slowing speed by 40% reduced noise emissions by approximately 10dB.  During the trial, there was a 44% reduction in ambient noise levels when a vessel was within acoustic detection range (6km) of the Lime Kiln hydrophone. These initial findings support speed reduction as a promising mitigation measure to help reduce underwater noise in the Salish Sea. The next steps will include a fine scale analysis of changes in ambient noise levels and behavioural modelling of killer whale response. Read more about the Port of Vancouver’s ECHO program here!

Low frequency ambient noise from human activity can mask the calls of baleen whales. Hearing is as important to cetaceans as vision is to humans. In response to the limited visibility of most ocean environments, cetaceans have adapted to take advantage of the physics of sound underwater. Sound travels approximately 4.5 times faster and 100 times further in salt water than in air².  Low frequency sound experiences little attenuation, making it particularly effective for underwater communication over great distances¹;   Baleen whales rely on these low frequency calls primarily for social communication, and their vocalizations can be heard by other individuals for hundreds of kilometres⁹.  Increasing levels of low frequency ambient noise from shipping, seismic exploration, and military sonar have been identified as a major threat to the recovery of blue, fin, and humpback whales in B.C. waters, as it may mask their vocalizations and displace them from their critical habitat^9,10.