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Recovery Strategy for the Northern and Southern Resident Killer Whale

Underwater Noise

At the time the COSEWIC status report on killer whales was written (Baird 2001), relatively little was known about the effects of underwater noise on marine mammals. Previous research had focused primarily on powerful noise sources with the potential to cause immediate injury or death, rather than chronic lower level noise sources (Richardson et al. 1995).  Since then, there has been a rapidly growing awareness that noise is a significant threat that degrades habitat and adversely affects marine life (IUCN 2004, IWC 2004).  It is estimated that ambient (background) underwater noise levels have increased an average of 15 dB in the past 50 years throughout the world’s oceans (NRC 2003). 

Killer whales have evolved in the underwater darkness using sound much the way terrestrial animals use vision: to detect prey, to communicate and to acquire information about their environment. Anthropogenic noise can interfere with all these activities in critically important ways, such as disrupting communication, reducing the distance over which social groups can detect each other, masking echolocation and hence reducing the distance over which the animals can detect their prey, potentially displacing them from preferred feeding habitats, displacing prey, impairing hearing, either temporarily or permanently, and in extreme cases causing death (Bain and Dahlheim 1994, Barrett-Lennard et al. 1996; Erbe 2002, Bain 2002, NRC 2003,  Au et al. 2004). 

The challenges of using and interpreting behavioural responses of marine mammals to noise as a measure of disturbance are discussed above.  Opportunities to measure physiological responses to anthropogenic noise are much rarer, but provide insight into the mechanisms by which noise could impact animals at the individual, and potentially population level.  Physiological responses to anthropogenic noise that have been measured in marine mammals include both temporary and permanent hearing threshold shifts, the production of stress hormones, and tissue damage, likely due to air bubble formation or as a result of resonance phenomena (Ketten et al. 1993, Crum and Mao 1996, Evans and England 2001, Finneran 2003, Jepson et al. 2003, Fernandez et al. 2004).  Marine mammals, including killer whales, may be particularly vulnerable to resonance because of the air-filled cavities in their sinuses and middle ear, their lungs, and small gas bubbles in their bowels.  While the mechanism by which high-intensity sound can cause lethal and sub-lethal effects on cetaceans is not completely understood (Piantadosi and Thalmann 2004, Fernandez et al. 2004), loud anthropogenic sources of noise, particularly low and mid-frequency military sonars, have been implicated in mass stranding and mortality events around the world, and the subject urgently merits further study.  Animals already affected by anthropogenic stressors such as environmental contaminants may be particularly vulnerable to additional stresses such as noise (Sih et al. 2004).

Sounds travel as waves much more quickly through water than air (1530 vs. 340 m/s). The perceptual features of sound, “pitch” and “loudness,” have physical analogs.  How high or low pitched a sound is can be described in terms of its frequency, and is measured in hertz (Hz).  Human hearing ranges from approximately 20 to 20,000 Hz (20 kHz), and is best between 600 and 2000 Hz.  The peak hearing sensitivity of killer whales is at approximately 20 kHz, although they show behavioural responses to sound from 75 Hz to over 100 kHz (Hall and Johnson 1972, Syzmanski et al. 1999).  Killer whale calls contain energy throughout this frequency range, and many echolocation clicks are centered at 20 kHz.

The ‘loudness’ of a sound is described in terms of its pressure.  For the purposes of consistency, the units of measure used here are dB RMS re 1 mPa.  By convention, noise sources are compared in terms of their “source levels” by estimating the level that would be measured at 1 m from the underwater sound source.  In general, the further away from a sound source, the quieter the received sound level, although physical and oceanographic features of the marine environment can affect how quickly a sound attenuates (gets quieter). High frequency sounds attenuate much more rapidly than low frequency sounds under uniform conditions in the open ocean , but a number of factors influence sound propagation and high frequencies may propagate further than low frequencies in shallow water or places with complex bottom terrain.  Temperature, salinity, depth, bottom topography and other physical factors must all be taken into account to accurately predict the intensity of sound reaching a whale.

The characteristics of some underwater noise sources are briefly described in Table 2.  It is important to consider the length of time that animals are exposed to sounds, their loudness and their frequency.  As well, some sounds are continuous, whereas others are pulses of sound that are generated intermittently.  The frequency composition also varies, ranging from broadband sounds such as seismic surveys, to narrowband sounds such as military sonar that are only broadcast across a limited range of frequencies. 

Sounds at received levels of 120 dB typically disrupt the behaviour of 50% of exposed cetaceans (Richardson et al. 1995).  Williams et al. (2002) found behavioural changes in northern residents at received levels estimated at about 105-110 dB.  However, with increasing use of loud, low frequency noise in activities such as ocean acoustic tomography and low frequency active sonar, which are detectable at ranges of thousands of kilometres, there has been pressure to raise the threshold for regulatory intervention. In the United States, NMFS is currently developing comprehensive guidance on what levels of sound exposure are likely to cause behavioral responses or injury, in the context of the Marine Mammal Protection Act (MMPA).  Until formal guidance is available, NMFS is using an interim sound exposure level for impulsive sources of 180 dBRMS re 1µPa, as a threshold for temporary or permanent hearing loss of cetaceans, and 160 dBRMS re 1µPa for behavioural disruption  (NMFS 2005b).

Table 2: Signal structure, frequency range and source levels of anthropogenic noise. Modified from Table 2-1b in NRC (2003) and Table 6.8 in Richardson et al. (1995).

Source Signal Structure Frequency Range

Source Level

(dB re 1 m Pa at 1 m)

Seismic surveysimpulsive


>0 Hz to >100kHz


Military Sonar



   weapon/ counter


pulsed tones

pulsed tones

pulsed tones and

 wideband pulses


>1kHz to < 10kHZ

>10kHz to 100kHz


200 to 235+

190 to 220

Construction   broadband and tones<10kHz to 10+kHzNA
Dredging broadband and tones<10Hz to <10kHzNA
Commercial shippingcontinuous10Hz to >1kHz160 to 200
Commercial sonarspulsed tones28kHz to >200kHz160 to 210

Military Sonar

Military active sonar is used in military operations for target detection, localization and classification (NRC 2003).  Unlike passive sonar systems, which listen for sounds, active sonar units transmit pulses of tones at frequencies from <1 to >100 kHz and source levels of 200-235 (or more) dB re 1 µPa at 1 m depending on the application (Evans and England 2001).  There is now a growing weight of evidence that these sources of underwater noise may pose a significant threat to cetaceans.  Active military sonar has been associated with increased strandings of beaked whales and humpback whales (numerous incidents summarized in IWC 2004).  In October 2004, the European Parliament called on its member nations to suspend the use of all high-intensity military sonar until further research can determine what effects it may have on marine life (European Parliament Resolution P6 TA, 2004).

For security reasons, information on the specifications of military active sonar is difficult to obtain, and much of what is available is based on US Navy equipment.  Given that the US Navy engages in joint operations with the Canadian military in both the Strait of Georgia and off the west coast of Vancouver Island, and that both northern and southern resident whales travel in US waters, the threat that active sonar may pose must be considered and precautionary measures should be considered by both navies.  Southern resident killer whales may be especially vulnerable because they spend significant time in the waters of Washington State, where a large naval exercise area runs parallel to the coast.

Military active sonars may be categorized as: surveillance (low frequency, < 1 kHz), tactical (mid frequency, 1 to 10 kHz), and weapon/counter weapon (high frequency, >10 - 100 kHz) (see Table 2).  Tactical sonars can have detection ranges of 10s of kms, and surveillance low frequency active sonars can be detected at ranges of 100s of km (NRC 2003; Tomaszeski 2004).  The use of SURTASS (Surveillance Towed Active Sensor System) LFA (Low Frequency Active) sonar has been controversial because of concerns about its potential effects on marine life (EIS 2007).  The US Navy is now forbidden from deploying these units except in an area in the western Pacific Ocean and during periods of war (Malakoff 2003), but this ruling is currently being appealed by the US government. 

The Canadian Department of National Defence’s Research Agency (DRDC) conducted research to investigate low frequency active tactical sonar through the Towed Integrated Active Passive Sonar (TIAPS) off the Atlantic Coast (Bottomely and Theriault, 2003).  The maximum source level of the TIAPS system was 223 dB re 1mPa @ 1m (J. Theriault, Defence Research and Development Canada, personal communication 2007).  Mitigation measures were applied (see Bottomely and Theriault, 2003, for details) and no incidents involving marine mammals were reported.  There are no plans to acquire this particular sonar for Canadian military use, and present defence policy requires that any future acquisition and testing of sonar systems will include environmental considerations (D. Freeman, Department of National Defence, personal communication, 2007).

Mid-frequency tactical sonar systems operating at 1-10 kHz are used to detect mines and submarines.  They have been associated with mass stranding events in the Bahamas, Canary Islands, Greece and the Gulf of California (IWC 2004).  Mid-frequency sonar exercises conducted by the USS Shoup on May 5, 2003 in Haro Strait were reported to correspond with changes in behaviour in members of J pod that were foraging 47 km away at the time, and resulted in behaviour more extreme than observed in response to any other disturbance.  The pod was observed trying to leave the area while the ship was 22 km away and ultimately pod members separated and left the area in different directions when the USS Shoup passed by at a range of 3 km (D. Bain, personal observation and personal communication; K.C. Balcomb, in Wiles 2004).  Up to 100 Dall’s porpoises and a minke whale were also seen leaving the area at high speed.Extensive examination of the 11 concurrent harbour porpoise strandings found no definitive signs of acoustic trauma, but the cause of death could not be determined for six animals, and the possibility of acoustic trauma as a contributory factor in the deaths of the remaining five porpoises could not be ruled out (lesions consistent with both acoustic trauma and alternative explanations were observed; NMFS 2004).  Further, all members of J pod were still alive more than two years after the incident.

The Canadian Navy has five principal types of military sonar emitters.  The SQS 510 sonar is the primary mid-frequency sonar used for anti-submarine search and is the most powerful.  It is currently fitted to 6 ships on the west coast.  In comparison, the US Navy’s SQS 53C sonar, such as that used on the USS Shoup, emits 10 times more energy than the Canadian 510 sonar.  The Canadian Navy also uses helicopter dipping sonars and active sonobuoys, though these emit far less energy than the 510 (D. Freeman, Department of National Defence, personal communication, 2007).

The Canadian Navy uses active sonar during training exercises and equipment testing in designated training areas.  However, sonar operations may also take place in other waters along the Pacific coast.  To mitigate the potential impacts of sonar use, Department of National Defence (DND) ship personnel receive training in marine mammal identification and detection.  The current Maritime Command Order 46-13 for marine mammal mitigation is to avoid transmission of sonar any time a marine mammal is observed within the defined mitigation avoidance zone specific to each type of sonar.  However, an evaluation of the effectiveness of the Maritime Command Order, particularly the ability of observers to detect marine mammals in the zone of influence, has not been completed to date.  These zones are determined using the interim NMFS thresholds for potential behavioural disturbance (160 dB) and physical injury (180 dB)  (D. Freeman, DND, personnel communication 2007).   Concerns remain that some impacts may occur beyond the visible horizon, and these will be difficult or impossible to observe or mitigate.  

Canadian test ranges are also used by other navies to test equipment and train personnel.  They follow Canadian procedures for use of these ranges, which includes marine mammal impact assessment and mitigation (D. Freeman, DND, personal communication 2005).  When conducting joint exercises in Canadian waters, other navies are provided direction including sonar mitigation protocols, prior to and during exercises.  As little is known about the offshore distribution of resident killer whales, especially during the winter months, they may be vulnerable to the use of sonar in the offshore ranges.  There are no military active sonar exercise ranges within the proposed critical habitat areas that have been identified to date.

Seismic Surveys

Airguns are used in geophysical surveys and to detect and monitor earthquake faults and other structures such as oil and gas deposits beneath the sea floor. The following information on the characteristics of seismic surveys comes from NRC (2003) unless mentioned otherwise.  Like military sonar, seismic surveys generate high intensity sounds. Most of their energy is concentrated at frequencies between 5-300 Hz and maximum pressure levels of 260 dB re 1m Pa at 1 m. However, unlike military sonars, airgun arrays used for seismic surveys generate broadband noise that extends to over 100 kHz (Calambokidis et al. 1998).

Current survey methods use one or more airguns that are towed behind a ship.  Airgun arrays range in size from 2000-8000 cu in, depending on the application.  The pulses of noise fired from these guns penetrate the seafloor surface for distances of up to 10 km deep. The arrays are towed at approximately 2.6 m/s (5 knots) and the airguns are fired every 10-12 seconds. The question of whether killer whales could sustain swimming the long distance necessary to avoid these sound sources needs to be addressed.   Seismic surveys using powerful airgun arrays have been detected at distances of over 3,000 km from their source (Niekurk et al. 2004). 

DFO receives occasional applications for permits for geophysical surveys from industry, government agencies such as Natural Resources Canada, and from universities. 

At the time the COSEWIC status report on killer whales was written (Baird 2001) both the federal and provincial moratorium on oil and gas exploration was in place. Since 2001, the BC provincial government has lifted the moratorium on oil and gas exploration and has requested that the federal government do the same.  As awareness is growing on the potential threats of high intensity sound on marine life (IUCN 2004, IWC 2004), the potential impacts of broadband high energy noise on killer whales must be considered.  DFO is currently developing standards for seismic surveys, and a draft policy for the mitigation of seismic surveys (DFO, 2005a) is currently being revised following public consultation.  In the Pacific Region, each proposed seismic survey is reviewed and case by case mitigation measures are developed based on the species of concern in the area of the survey.

Systematic observations of cetaceans during seismic surveys have been carried out in UK waters, and have shown that killer whales and other cetaceans were generally seen further away during periods when airgun arrays were firing (Stone 2003).  Behavioural studies in other areas have shown mixed responses to seismic surveys.  Gray and bowhead whales appeared to avoid seismic surveys (Malme and Miles 1987, Ljungblad et al. 1988, Myrberg 1990).  Male sperm whales and feeding humpback whales did not avoid seismic surveys (Malme et al. 1985, Madsen et al. 2002).  A seismic survey in Puget Sound showed mixed results between species, with some, such as gray whales, exhibiting ambiguous responses to the survey while others, such as harbour porpoises, tolerating only relatively low exposure levels before leaving the area (Calambokidis et al. 1998).

For obvious ethical reasons, there are no experimental studies of the physical effects of seismic surveys on cetaceans.  However the internal structure of the cetacean ear resembles that of both fish and terrestrial mammals (Fay and Popper 2000).  A small (20 cu in) airgun has been shown to cause permanent hearing loss in caged fish (McCauley et al. 2003), so it is possible that airguns may be capable of damaging cetacean ears if the whales cannot avoid the sound source.  Since killer whales are known to be exquisitely dependent on sound for orientation, navigation, locating and catching food, communication, and social interactions, the consequences of severe hearing loss could be fatal.

Commercial Sonar

Commercial sonar systems are used in a wide variety of vessels for fishing, navigation (depth sounders), bottom-mapping and detecting obstacles (e.g. side scan sonars).  They are generally standard equipment on any vessel over 5 m.  These sonars typically generate narrowband sounds at higher frequencies and lower power than military sonars.  High frequency sounds are more easily focused into narrow beams and attenuate more quickly than low frequency sounds.   Thus the volume of water they influence is smaller.  There are many models of commercial sonars, but it is only the units that operate below 100 kHz, the upper limit of killer whale hearing, that are of concern.  Whales may be able to avoid these sources of sound when boats are widely dispersed, but when boats are concentrated in high traffic areas killer whales may have no choice but to travel through heavily ensonified areas. 


Commercial shipping has increased dramatically in recent years.  For example, between 1995 and 1999 the worldwide commercial shipping fleet increased 12% (NRC 2003).   There are few studies that have measured changes in the background underwater noise levels over time, but those that do suggest that increased vessel traffic is responsible for the increase in ambient noise over the last 100 years (e.g. Andrew et al. 2002).  In the northern hemisphere, shipping noise is the dominant source of ambient noise between 10 to 200 Hz (NRC 2003).  While shipping energy is concentrated at low frequencies, ships produce significant amounts of high frequency noise as well. The consequences of these chronic sources of noise on killer whales have not been assessed.

Permitted Close Approaches

Certain activities have the potential to disturb and/or injure whales because they require physical contact with whales or close approaches by boats for extended periods of time. As a result, in both Canada and the United States, researchers and filmmakers must obtain federal permits if their projects require close approaches or physical contact with killer whales.  Close approaches can disturb whales both physically and acoustically. Much of the research on killer whales is conducted using boats ranging in size from a few meters to vessels over 30 m, although some is land based (e.g. Orcalab on Hanson Island, the Warden Program on West Cracroft Island, Johnstone Strait). A boat at 10 m from a whale will be approximately 20 dB louder than a boat at 100 m based on spherical spreading (Richardson et al. 1995). Photo-identification studies require that all whales in the group be photographed before the encounter is considered complete, and good quality photographs typically mean that whales must be approached to within 30 m (approximately 10 dB louder than at 100 m).   Prey fragment sampling, which is providing insight into the diet of resident killer whales, involves approaching the area where a whale has surfaced after it has finished actively feeding.  Biopsy darting, a method used in genetic and contaminant studies, also involves close approaches by boats, and recent recommendations arising from the NOAA Cetacean Systematics Workshop in La Jolla California, in April-May 2004 include darting juveniles (Waples and Clapham 2004).  The possible health risks of darting young calves have not been evaluated. Satellite tags and the use of time-depth recorders (TDRs) are applied externally to killer whales. They are used to monitor the movements of whales, but may disturb them during the initial application and /or during the time that they adhere to the skin.  Newer technologies involving satellite tags and TDRs that are implanted in the skin or muscle pose the additional risk of injuring killer whales.

Other Forms of Disturbance

The number of boats on the water has increased dramatically in recent years.  This increase in traffic has the potential to disrupt killer whales simply because more vessels are passing through their habitat and potentially disturbing how whales move through the available space.  This is most evident when whales are interrupted from their normal activities in order to avoid a collision.  While collisions between whales and vessels are relatively rare, when they do occur they can cause significant injury or death (Ford et al. 2000). 

Personal watercraft (PWC) or ‘jet skis’ may be another potential source of disturbance or injury to killer whales.  PWC are capable of much more erratic or unpredictable manoeuvres than traditional high speed vessels.  As a result they pose a collision risk to killer whales and other wildlife.  PWC have been banned in the San Juan Islands and in portions of the Monterey Bay National Marine Sanctuary, but they are not banned in the coastal waters of British Columbia, with the exception of the inner waters of Vancouver Harbour.  The underwater noise levels of PWC have not been reported.

While resident killer whales must travel in high vessel traffic areas such as Johnstone Strait and the Strait of Georgia, they also must negotiate both commercial and recreational sports fishing boats specifically targeting salmon in ‘hot spots’ that are also good feeding areas for killer whales. This includes areas in the vicinity of sports fishing lodges.  Conflict for space may force killer whales to alter their foraging behaviour in order to successfully capture prey or to avoid collision or entanglement (see Section 2.2.5). 

Certain industrial activities such as construction, drilling, pile driving, pipe laying and dredging may also disrupt killer whales.  Construction is also a source of underwater noise.  Physical structures, including net pens for aquaculture and permanent structures (e.g. wharves), may damage foraging habitat such as kelp beds, or physically displace resident killer whales from areas they have historically travelled in.  If the finfish aquaculture industry continues to expand on the north coast, the placement of net pens may become an issue for northern residents. 

2.2.4 Oil Spills

While the probability of either northern or southern resident killer whales being exposed to an oil spill is low, the impact of such an event is potentially catastrophic.  Both populations are at risk of an oil spill because of the large volume of tanker traffic that travels in and out of Puget Sound and the Strait of Georgia (Baird 2001, Grant and Ross 2002) and the proposed expansion of tanker traffic in the north and central coast of BC.  In 2003, 746 tankers and barges transported over 55 billion litres of oil and fuel through the Puget Sound (WDOE 2004). If the moratorium on oil and gas exploration and development is lifted in British Columbia, the extraction and transport of oil may put northern resident killer whales at additional risk.

Killer whales do not appear to avoid oil, as evidenced by the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska.  Less than a week after the spill, resident whales from one pod were observed surfacing directly in the slick (Matkin et al. 1999).  Seven whales from the pod were missing at this time, and within a year, 13 of them were dead.  This rate of mortality was unprecedented, and there was strong spatial and temporal correlation between the spill and the deaths (Dahlheim and Matkin 1994, Matkin et al. 1999).  The whales probably died from the inhalation of petroleum vapours (Matkin et al. 1999).  Exposure to hydrocarbons can be through inhalation or ingestion, and has been reported to cause behavioural changes, inflammation of mucous membranes, lung congestion, pneumonia, liver disorders, and neurological damage (Geraci and St. Aubin 1982). 

2.2.5 Incidental Mortality in Fisheries

Killer whales are rarely entangled in fishing gear, based on anecdotal accounts and an absence of net marks in identification photographs, but the actual numbers of whales caught are unknown (Baird 2001).  Several stranded killer whales have been found with gear from commercial or recreational line fisheries in their stomachs and the possibility of mortality as a result is unknown (Ford et al. 1998).  A few entanglements have been reported from BC, Alaska, and California (Pike and MacAskie 1969, Guenther et al. 1995, Barlow et al. 1994, Heyning et al. 1994), but they usually have not resulted in death.  It is likely that fisheries pose little direct threat to killer whale populations at present. However, killer whales in other areas are known to have learned to take fish from fishing gear and once this behaviour is adopted, it can spread quickly throughout a population.  This problem, referred to as depredation, is severe in many parts of the world (Donogue et al. 2002) and could affect resident killer whales in the future.  Where depredation occurs, deterrent methods, entanglement, or accidental hooking, increases the injury or mortality rates of whales.