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


5 Threats

Blue, fin, and sei whales share both historic and current threats. These species are currently threatened by a variety of anthropogenic sources, including ship strikes, acute and chronic noise, possible pollution effects, and fishing gear interactions. The influence of some or all of these threats may result in reduced use of available habitat and/or reduced reproduction. Habitat may also be altered by medium and long-term shifts in ocean climate.

5.1 Whaling

Commercial whaling devastated the populations of blue, fin, and sei whales in every ocean of the world in less than 80 years. Whaling continues in a variety of forms including subsistence hunts and scientific research (Clapham et al. 1999). Recent genetic analysis of midden contents in the Pacific Northwest indicate that aboriginal whaling in Pacific Canadian waters did not target balaenopterid species (A. D. McMillan, personal communication. Department of Anthropology, Douglas College, P.O. Box 2503, New Westminster, BC, V3L 5B2). Scientific whaling (i.e., by Japan) is likely to remain directed at more abundant species (i.e., minke, Bryde’s and sperm whales (Physeter macrocephalus)). Therefore whaling is not presently considered a threat to blue, fin or sei whales in the eastern North Pacific.

Blue whales were the first target of modern commercial whaling and were severely depleted in all oceans of the world. The species was protected worldwide in 1966 by the IWC. An estimated 325,000-360,000 blue whales were killed in the Antarctic during the first half of the 20th century, nearly extirpating the Southern Hemisphere population. In the North Pacific, blue whales were hunted by both coastal, shore-based whalers and pelagic whaling fleets, taking an estimated 9500 animals. Almost half of these were killed off the west coast of North America (Sears and Calambokidis 2002).

There is clear evidence that whaling depleted the populations of blue whales off British Columbia. Shore-based stations operating in British Columbia from the early 1900’s through 1967 killed at least 650 blue whales, though the annual catch declined rapidly as the population was depleted (Figure 2). From 1948 to 1965, mean lengths of blue whales killed from British Columbia shore stations declined significantly along with pregnancy rates (Gregr et al. 2000).

Fin whale populations off the coast of British Columbia were reduced by whaling in parallel with blue whales, following the introduction of modern whaling. Local populations suffered further loss when the coastal fleet was upgraded in the 1950s (Figure 2). At least 7605 fin whales were taken by British Columbia coastal stations between 1908 and 1967 (Gregr et al. 2000). Fin whales were most heavily exploited through the 1950s and 1960s, when the annual catch from the North Pacific ranged from 1000 to 1500 animals. Until 1955, most whaling off the west coast of North America was off British Columbia, after which catches began to increase off California. Fin whales in the North Pacific were protected by the IWC in 1976 (Mizroch et al. 1984).

Although not a primary target for whalers until blue and fin whale populations were severely depleted, sei whales were heavily exploited during the last decades of commercial whaling. Following the depletion of blue and fin whales, over 110,000 sei whales were killed in the Antarctic between 1960 and 1970. In the North Pacific, catches peaked at over 25,000 animals per year in the late 1960s. The last year of sanctioned whaling for sei whales in the North Pacific was 1975. On the Pacific coast, at least 4002 sei whales were taken by coastal stations in British Columbia between 1908 and 1967, with the majority taken after 1955 (Gregr et al. 2000). The total sei whale catch from the North Pacific was almost twice the fin whale catch, and close to 20 times the blue whale catch between 1925 and 1985 (IWC Database, J. Breiwick, pers. comm.).

5.2 Current threats

Ship strikes, chronic noise from shipping, and acute noise from low frequency active sonar and seismic exploration are potentially the greatest current threats to balaenopterid whales. Commercial shipping, oil and gas extraction, and seismic surveys, have the potential to reduce potential habitat for these species by making areas uninhabitable due to increased background noise levels, at least for short periods of time. Entanglement in fishing gear and marine debris may also pose threats to individuals. As populations increase, fin whales in particular may become more at risk to interactions with human activities because of their more coastal distribution. Pollution is an increasing concern in the oceans, though there is currently little evidence to suggest a significant impact on balaenopterids. However, synergistic effects of seemingly unrelated stressors have recently been identified in other mammal species and cannot be ruled out for cetaceans (Sih et al.2004 cited in Payne 2004).

While threats are difficult to prioritize given the lack of information, ship strikes should currently be considered the most important threat to individual balaenopterids in Pacific Canadian waters, particularly fin whales because of their more coastal distribution. The possibility that habitat degradation (or loss of use), through increased background noise levels, may limit the recovery of these species near shipping lanes and other areas of high noise production should also be considered a leading threat.

5.2.1 Ship strikes

Blue and fin whales often occupy shelf-break locations that frequently coincide with shipping lanes, which concentrate large vessel traffic. In a review of 292 records of ship strikes, Jensen and Silber (2004) reported that fin whales were the most commonly struck species, while blue and sei whales were two of the least likely to be struck. However, ship strikes offshore are more likely to go undetected. The mortality rate associated with ship strikes is 70-80% (Jensen and Silber 2004). In the St. Lawrence, 16% of observed blue whales have marks associated with large propellers or hulls (Sears and Calambokidis 2002). Between 1980 and 1993, at least four blue whales were struck and killed off California. An additional four injuries and two mortalities of large whales were attributed to ship strikes during 1997-2001 in North Pacific waters (Carretta et al. 2003). At least six fin whales were reported struck and killed in or near Pacific Canadian waters between 1999 and 2004 (COSEWIC 2004), and a single dead sei whale came into the Strait of Juan de Fuca on the bow of a ship in 2003. It appears that large vessels travelling more than 14 knots (26 km/h), particularly high-speed container ships, present the greatest risk of ship strike mortality to whales (Laist et al. 2001). Container and cruise ship traffic through British Columbia ports has increased by 200% since the 1980s (Transport Canada 2005), and growth can be expected to continue.

More data on the distribution of blue, fin, and sei whales and the identification of how their critical habitat overlaps with shipping lanes will help determine the degree to which ship strikes threaten balaenopterid whales.

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 do 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 5m. 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), possible mitigation strategies have been identified (DFO 2005). These strategies typically include ‘soft starts’ (the ramping up of noise levels at the start of surveys), discontinued use if marine mammals are observed, and scheduling to avoid seasons when the majority of animals are believed to be present. 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.

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. These chronic effects remain uninvestigated.

5.2.3 Pollution

Large whales may be exposed to pollution in a number of ways, including the ingestion of marine debris or contaminated prey items, or through contact with oil spills. O'Shea and Brownell (1994) concluded that there was no evidence of toxic effects from metal or organochlorine contamination in baleen species (see also Sanpera et al. 1996), largely because they feed at relatively low trophic levels. No effects of oil contamination were detected for humback whales after the Exxon Valdez oil spill in Prince William Sound (von Ziegesar et al. 1994). However other, primarily piscivorous, marine mammals are thought to be at risk from immunotoxic chemicals (Ross 2002). Pollution effects that have been observed in marine mammals include depression of the immune system, reproductive impairment, lesions and cancers (Aguilar et al. 2002).

Concentrations of organochlorines sufficient to warrant concern were found in fin whale samples taken in the Gulf of St. Lawrence in 1991-92 (Gauthier et al. 1997). However, a retrospective analysis comparing these samples to earlier ones collected in 1971-72 off Newfoundland and Nova Scotia found that the St. Lawrence concentrations were significantly lower (Hobbs et al. 2001). Fin whales feed at a similar trophic level to sei whales, thus, the risk from chemical bioaccumulation in sei whales is likely to be similar, and possibly even lower for blue whales. Decreasing trends have been found for other marine mammals (principally pinnipeds) in eastern Canada (Hobbs et al.2001). However, Muir et al. (1999) found that organochlorine contaminants in cetaceans show both increasing and decreasing trends, depending on species and geographic location.

Marine debris is a recognized threat to smaller marine mammals but poses less risk to larger species. It is possible for balaenopterids to ingest marine debris during feeding. However, the frequency and consequences have not been quantified and no associated mortality has been reported.

5.2.4 Habitat displacement

Balaenopterid habitat can be displaced by changes in ocean climate, or by changes in trophic structure. The Pacific Ocean climate responds to interannual (e.g., El Niño) and decadal scale (e.g., Pacific Decadal Oscillation) variability. These natural cycles can combine to cause regime shifts – significant changes in the physical and biological structure of the ocean. Ocean climate may also be affected over the long-term due to anthropogenic causes (e.g., global warming), however the effect of human-induced changes will be difficult to distinguish from natural variability.

Regime shifts cause major changes in ecological relationships in marine systems over broad oceanographic areas (Francis and Hare 1994), and are manifested earlier at lower trophic levels (Benson and Trites 2002). Significant declines in zooplankton abundance have taken place off California since the 1970s and have been linked to increases in sea surface temperature (Roemmich and McGowan 1995).

The displacement of balaenopterid foraging habitat by regime shifts may occur because the timing and spatial distribution of zooplankton abundance can be directly related to physical conditions. How balaenopterids locate suitable foraging habitats is unknown. However, matrilineal fidelity to feeding grounds has been observed in other baleen species (humpback, right, and grey whales). Such fidelity implies a limited ability to locate new feeding grounds when changing oceanographic conditions lead to a significant shift in prey distribution.

Trophic structure can also be affected by overfishing. For example, the massive reduction in whale biomass due to large-scale commercial whaling in the Antarctic is thought to have released as much as 150 million tonnes of krill annually, resulting in an increase in smaller predators such as seals, small cetaceans, and seabirds. The loss of krill consumers in the Bering Sea due to commercial whaling may also have influenced the dominant fish species observed in the Bering Sea during the 1970s and 1980s (Trites et al. 1999), although this change has also been related to regime shifts.

The krill fishery in Pacific Canada is restricted to a few mainland inlets and the Strait of Georgia, and because there is an existing moratorium on the expansion of this fishery, blue whales are currently not at risk from direct competition with this fishery. Commercial harvesting of herring, sardines, or other forage fish is more wide-spread, and thus has the potential to alter the coastal distribution of fin whales, and, to a lesser degree reduce the frequency with which sei whales venture into coastal waters to feed. However, given the complexity of trophic interactions, it is also possible that feeding habitat of balaenopterid whales could be enhanced through the removal of competing fish stocks.

Blue whales feed exclusively on zooplankton, primarily euphausiids. In Pacific Canada, fin whales eat euphausiids and schooling fish, whereas sei whales have a more diverse diet that includes copepods and forage fish (which prey on zooplankton). All three species require high density prey aggregations for successful feeding. Such concentrations depend on physical oceanographic factors such as current flows, temperature, and phytoplankton growth. Given the narrower range of prey types, the blue whale may be relatively more sensitive to declines in zooplankton production than either the fin or sei whale. However, the true impacts of changes to ocean climate on the abundance and distribution of zooplankton are unknown. A local increase in zooplankton off the British Columbia coast as a result of changing ocean conditions resulting from climate change cannot be ruled out.

5.2.5 Other threats

While gear entanglements do result in some mortality of large whales on the east coast, there has been little evidence of gear-related injury or mortality for balaenopterid whales in the eastern North Pacific. The NMFS Pacific Take Reduction Plan, implemented in 1997 to reduce by-catch from fisheries, has not documented any blue or sei whale kills from 1997-2001 (Barlow and Cameron 2003). A review of stranding reports from 1990 to 1996 for Canada’s Pacific coast reported several incidents of entangled, unidentified large whales, and a fin whale was observed entangled in what appeared to be a crab-pot line during a 2004 survey (COSEWIC 2004). As the species begin to recover, the potential for gear interactions may increase, particularly for fin whales using more nearshore waters where such interactions are more likely to take place.

Whale watching tours targeting blue whales in the North Pacific are based primarily off California and in the Sea of Cortez, Mexico. Whale watching industries in British Columbia primarily target killer whales, grey, and humpback whales. However given their size, blue and fin whale watching would very likely increase should such trips become economically feasible for commercial operators. Potential impacts on blue and fin whales from whale watching would include injury from propellers and vessel strikes, and increased acoustic disturbance (see above). Sei whales are unlikely targets for any whale watching operation in Pacific Canadian waters because of their primarily offshore distribution.