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Recovery Strategy for Blue, Fin, and Sei Whales in Pacific Canadian Waters [Proposed]

5. Threats (cont'd)

5.2.2. Noise

Baleen whales rely on sound primarily for social communication. Whales may also use sound for predator detection, orientation, navigation, and possibly prey detection. Underwater noise has the potential to disrupt these behaviours. Potential effects depend on the nature of the noise. Chronic noise may result in population level changes in both short and long-term behaviour, while acute sounds may result in hearing damage leading to drastically reduced fitness or death. Noise is therefore a potential threat to individuals, the population, and the habitat of these species (COSEWIC 2003).

While few data are available to assess physiological responses of marine mammals to anthropogenic noise, observed effects 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, Jepsonet al. 2003).

The ‘loudness’ of a sound is described in terms of pressure. How quickly a sound attenuates depends on the physical and oceanographic features of the local marine environment, and on its frequency – higher frequencies attenuate more quickly than lower frequencies. Some sounds are continuous, whereas others are pulses generated at specific intervals. Frequency ranges are also variable, ranging from broadband seismic surveys, to narrowband military sonar. The impact on marine mammals is thus a function of the length of exposure, loudness, frequency, and nature of the sound.

There has been a rapidly growing awareness that noise may be a significant threat to animals that degrades habitat and adversely affects marine life. It is estimated that background underwater noise levels have increased an average of 15 dB in the past 50 years throughout the world’s oceans (NRC 2003). One result is that in certain parts of Northern Hemisphere oceans, the area over which a fin whale can hear a conspecific has decreased by four orders of magnitude (Payne 2004). Thus any activities, including research, that make use of acoustics have the potential for incidental harm.

Functional models indicate that hearing in larger marine mammals extends to 20 Hz, and may extend to frequencies as low as 10-15 Hz in several species, including blue, fin and bowhead (Balaena mysticetus) whales. The upper range of mysticetes is predicted to extend to 20-30 kHz (Ketten 2004). Thus, anthropogenic noises produced primarily in these frequencies are of concern for balaenopterids. These include air guns and drilling used for oil and gas exploration and extraction, active sonar and explosives used for military operations, and commercial shipping traffic.

Commercial shipping has increased dramatically in recent years, and is largely responsible for the increased noise levels in the marine environment over the last 100 years. In the northern hemisphere, shipping noise is the dominant source of background noise between 10 to 200 Hz(NRC 2003). This chronic noise likely reduces the ability of large whales to maintain contact with conspecifics, potentially reducing mating and foraging opportunities (Payne 2004). The noise from these vessels is at a frequency capable of masking blue whale calls (Richardson et al. 1995). The degree to which such acoustic pollution may, or already has, degraded habitat located near commercial shipping lanes has not been determined. However, background noise levels will continue to increase with vessel traffic, such as with the planned port expansion near Vancouver to accommodate the largest ‘super’ tankers (VPA 2004).

Active military sonars transmit pulses of tones at frequencies within the acoustic range of balanenopterid whales, and at source levels that may be heard underwater for tens to hundreds of km, depending on the frequency (Evans and England 2001). There is growing evidence that these noises may pose a significant threat to cetaceans. Active military sonars have been associated with increased strandings of beaked whales (Ziphiidae spp.) and humpback whales, and with the displacement of western North Pacific grey whales (Eschrichtius robustus) from their feeding grounds (see studies cited in IWC 2004). Active sonar must be considered a threat to northeast Pacific balaenopterids, as the U.S. and Canadian Navies conduct joint operations in Canadian waters. However, information on the use of active military sonar is limited for security reasons.

Low Frequency Active (LFA) sonars send out ‘pings’ to detect submarines, and operate at frequencies between 0.75 and 3 kHz. Their range can extend tens to hundreds of km (Tomaszeski 2004). As an acute source, LFA could disrupt food sources or abruptly displace or injure foraging whales. The U.S. Navy is now forbidden from deploying these units except in one area in the western Pacific Ocean and during periods of war (Malakoff 2003), however this ruling is under appeal. A Canadian LFA sonar was recently tested off the Atlantic coast (Bottomley and Theriault 2003), however there are no plans for procurement at this time (D. Smith, personal communication. Environment Office, CFB Esquimalt, Maritime Forces Pacific, Department of National Defence, Building 199 Dockyard Room 302 PO Box 1700 Station Forces Victoria, BC V9A 7N2).

Mid-frequency (MF) sonars operating between 3-30 kHz are used to detect mines and submarines, and have been associated with mass stranding events in the Bahamas, Canary Islands, and Greece (IWC 2004). MF sonars are suspended into the water by helicopters, and are hull-mounted on some classes of Canadian military vessels (Wainwright et al. 1998). The current policy is to avoid transmission of sonar any time a marine mammal is observed (D. Smith, pers. comm.), although the adequacy of this policy has not been evaluated. In addition, crews are trained to identify marine mammals, and sightings are reported to local sightings programs. The Canadian Navy is also developing maps that will identify sensitive marine areas, allowing bridge personnel to incorporate this information into project planning and general navigation (D. Smith, pers. comm.).

Commercial sonar systems are generally standard equipment on any vessel over 5 m. While units operating below 100 kHz may be of concern to balaenopterid whales, the majority of these units are operated in near-shore, shelf areas less likely to be used by blue or sei whales. Fin whale distributions tend to overlap with areas of increased commercial sonar use. However, the predictable nature of this sound should provide an opportunity for avoidance, potentially mitigating any acute effects.

The potential for oil and gas exploration and extraction may be an acoustic concern for balaenopertid species in some areas such as Queen Charlotte Sound and Hecate Strait. As recommended by the Royal Society panel (RSC 2004), a rigorous regulatory regime should be implemented, and numerous data gaps (including the collection of baseline data and the definition of critical habitat for endangered species) should be addressed prior to the commencement of any exploratory activities.

Seismic surveys generate high intensity sounds with most of their energy concentrated at frequencies (5-300 Hz) relevant to balaenopterids. Current survey methods involve towing airgun arrays at approximately 2.6 m/s (5 knots), and firing the guns every 10-12 seconds. Airgun arrays have been detected over 3000 km from their source (Nieukirk et al. 2004).

Systematic observations in the eastern North Atlantic found that cetaceans were generally seen further away from the survey vessel during periods when airgun arrays were firing (Stone 2003). Grey and bowhead whales appear to avoid seismic surveys (Malme and Miles 1987, Ljungblad et al. 1988, Myrberg 1990), although in some cases male sperm whales and feeding humpback whales did not (Malme et al. 1985, Madsen et al. 2002). Mortality has been associated with the use of seismic surveys in the Gulf of Mexico (IWC 2004). It could be that the degree of tolerance exhibited by cetaceans to noise is related to the behavioural state of the animals.

No experimental studies of the physical effects of seismic surveys on cetaceans have been conducted. However, mammalian ears share certain structural similarities with other vertebrates (Fay and Popper 2000), and a small (20 cu in) airgun has been shown to cause permanent hearing loss in caged fish (McCauley et al. 2003). It is thus reasonable to assume that airguns are capable of damaging cetacean ears if the whales cannot avoid the sound source.

Mitigation strategies exist, to some extent, for the acute effects of military sonar and seismic surveys. In the U.S., military sonar use is to be discontinued if marine mammals are observed. Various mitigation strategies to reduce potential disturbance from seismic surveys have been used on Canada’s east coast and elsewhere. Based on the summary of available information on impacts of seismic sound on marine animals (DFO 2004), DFO has developed a statement of practice outlining possible mitigation strategies (DFO 2005). These strategies typically include ‘soft starts’ (the ramping up of noise levels at the start of surveys), and discontinued use if marine mammals are observed. It also recommends that surveys be scheduled to avoid seasons when the majority of animals are believed to be present, although specific seasonal restrictions are not included. The effectiveness of these mitigation strategies remains equivocal. As the disturbance of marine mammals is prohibited under the Fisheries Act, DFO Pacific Region currently restricts impacts from geophysical surveys by reviewing each application and providing project specific advice on mitigation in addition to those outlined in the draft statement of practice.

Seismic surveys are localized to shelf regions. The potential acute effects associated with these surveys are thus likely of limited concern for sei and blue whales because of their primarily offshore distribution. However, fin whales’ use of shelf habitat may be impacted.

Habitat loss (actual and/or loss of use) due to chronic background noise from a variety of sources may ultimately prove to be a greater concern. As with acute noise, chronic noise would likely be more severe for fin whales, however it is also a concern for blue and sei whales because of the potential for sound propagation in water. However, these chronic effects remain uninvestigated.