Recovery Strategy for the Northern and Southern Resident Killer Whales (Orcinus orca) in Canada
Pliny the Roman scholarfirst described a killer whale as an "enormous mass of flesh armed with savage teeth" during the first century AD. Since then written records have often depicted killer whales as savage, destructive, ferocious, and a danger to humans. However, they were rarely hunted, with the exception of Japanese, Norwegian and Russian whalers. Contemporary fishermen have viewed the killer whale as a competitor for their fish and a threat to their livelihood (Olesiuk et al. 1990; Ford et al. 2000). The live capture of killer whales for aquariums in the 1960s and early 1970s reduced local populations, some drastically.
Killer whales were hunted commercially, but whaling operations generally targeted other species of whales. In Canada, there are only a few harvest records of killer whales, most of which took place on the east coast and in the Arctic (e.g. Mitchell and Reeves 1988, Reeves and Mitchell 1988). However, large numbers of whales were taken in other areas of the world. The Japanese killed 60 killer whales per year between 1948 and 1957 (Nishiwaki and Handa 1958). Norwegian whalers culled 2,345 killer whales between 1938 and 1981(Øien 1988). The former USSR captured approximately 25 killer whales per year in the Antarctic and harvested 906 whales in one season (Berzin and Vladimirov 1983). In 1982, the International Whaling Commission recommended a halt to the harvest of killer whales until the impact on populations was better understood. No killer whales have been reported taken since then, though small numbers may continue to be caught but remain unreported. For example, genetic testing has revealed the presence of killer whale in meat sold in Japanese and Korean markets (Baker et al. 2000).
In the late 1960s and early 1970s, killer whales were sought extensively for display in public aquariums. While they were captured from various areas throughout the world, the majority came from the waters of the northeastern Pacific Ocean. Between 1962 and 1974, 68 killer whales were taken from this area, 47 of which are known or assumed to be southern residents (Olesiuk et al. 1990). This cropping clearly had a major impact on the southern resident community, which numbered only 70 animals in 1974, and likely affected productivity of the community for many years after the live captures ended in 1975.
Historically, negative attitudes towards killer whales in BC led to efforts by both government and individuals to cull local populations through shooting. In 1960, the federal Fisheries Department mounted a land-based machine gun near sports fishing lodges near Campbell River to reduce the number of killer whales (Ford et al. 2000). Fortunately it was never fired. In the 1960s and 1970s, approximately one quarter of whales live captured for aquaria had gunshot wounds (Ford et al. 2000). Societal attitudes towards killer whales have changed since 1974, and fresh bullet wounds are now rarely, if ever, seen on whales in BC and Washington (Ford et al. 2000), although even occasional shootings could limit population growth.
Aquaculture farms in Washington and BC have used acoustic harassment devices (AHDs) that emit loud signals underwater to reduce depredation by harbour seals and sea lions. Some signals may be heard from up to 50 km away (Morton and Symonds 2002). Their use at a farm near northern Vancouver Island was associated with significant declines in the use of nearby waters by both resident and transient killer whales (Morton and Symonds 2002). Harbour porpoise abundance was also found to drop dramatically when AHDs were in active use (Olesiuk et al. 2002). AHDs are no longer used at fish farms in BC or in Washington. They are still used at Ballard Locks in Seattle to deter sea lions, but the configuration of the canal limits the amount of noise escaping to the open ocean (Bain 1996).
A variety of threats may directly impact northern and southern resident killer whale populations in British Columbia, particularly because of their small population size. Threats include environmental contaminants (including oil spills), reduced prey availability, disturbance, and noise pollution, each of which is discussed in more detail below. Other threats such as mortality in fishing gear, have posed a threat to cetacean populations in other areas, and could potentially impact resident killer whales. Climate change is affecting entire ecosystems, and it is likely that in order to survive, killer whales will have to adapt to the consequences of local changes in their prey base. How current threats may act synergistically to impact killer whales is unknown, but in other species multiple stressors have been shown to have strong negative and often lethal effects, particularly when animals carry elevated levels of environmental contaminants (Sih et al. 2004).
The extent to which northern and southern resident killer whales are affected by anthropogenic threats varies, depending on the threat. For example, northern resident killer whales may be more vulnerable to seismic surveys on the north coast, particularly if the moratorium on oil and gas exploration is lifted, whereas southern residents, by virtue of the waters they spend significant time in, may be more vulnerable to environmental contaminants.
There are numerous chemical and biological pollutants that may directly or indirectly impact resident killer whales, ranging from persistent organic pollutants (POPs) to antibiotic resistant bacteria and exotic species. Below we describe the major types of contaminants, their sources and their potential effects on killer whales (where known). (For a list of the acronyms mentioned below, see Appendix A) There have been only a handful of studies that have measured contaminant levels in killer whales, and for obvious reasons no controlled experiments have been done to assess how these contaminants may affect them directly. However, the effects of contaminants on other species such as pinnipeds are better understood, and in many cases can be generalized to killer whales, particularly because the physiological processes of mammals are similar across different species. Such an extrapolative approach encompassed using a 'weight of evidence' is outlined elsewhere for marine mammals (Ross 2000).
Although it is important to assess the direct effects of contaminants, Fleeger et al. (2003) make an important case for considering their 'indirect' effects on community structure, as well as on individual organisms and their behaviour. In a review of 150 studies, contamination resulted in changes in species abundance and community structure. Sixty percent of the communities that were experimentally manipulated showed a reduction in upper trophic level predators, which masked, enhanced or confused the interpretation of any direct effects of contaminants on individual organisms or species.
Persistent Organic Pollutants (POPs)
There are likely thousands of chemicals to be found in the killer whales of BC, but a few key classes are of particular concern today. Recent studies of environmental contaminants in resident and transient killer whales in BC and Washington have revealed that they are among the most contaminated mammals in the world (Ross et al. 2000, 2002). Killer whales are vulnerable to accumulating high concentrations of POPs because they are long-lived animals that feed high in the food web (Ross et al. 2000, 2002, Rayne et al. 2004; Ross 2006). POPs are persistent, they bioaccumulate in fatty tissues, and are toxic, features that have led to increased regulatory scrutiny of these chemicals by authorities around the world. POPs include 'legacy' contaminants such as the polychlorinated biphenyls (PCBs), and the organochlorine pesticide DDT, which are no longer widely used in industrialized countries, but remain persistent in the environment. The so-called 'dirty dozen' POPs are encompassed under the terms of the Stockholm Convention which aims to phase out use of chemicals of global ecotoxicological concern. They also include the polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs or furans), by-products of incomplete combustion, of pesticide manufacture, and of the (now regulated) use of elemental chlorine and pentachlorophenol (PCP) in pulp and paper bleaching and wood treatment processes, respectively. In recent years, regulations have resulted in a reduction in the release of such contaminants into the marine environment (Hagen et al. 1997).
Contaminants of 'current concern' in the industrial world include the new generation of polybrominated trienylethers (PBTs), flame retardants such as polybrominated diphenylethers (PBDEs), as well as currently used pesticides. Table 1 lists the POPs that are a concern for resident killer whales, and the reader is referred to Grant and Ross (2002), for a more thorough synthesis of what is known about the risks that contaminants pose to southern resident killer whales. The acronyms used for many of the contaminants are listed in Appendix A.
Polychlorinated Biphenyls (PCBs)
Surprisingly high concentrations of PCBs are found in both southern and northern resident killer whales relative to marine mammals from other parts of the world (Ross et al. 2000). The PCB levels found in transients and southern residents exceed those found in St. Lawrence beluga whales (Delphinapterus leucas) by a factor of two to four times, and are considerably higher than thresholds for PCB-associated reproductive impairment, skeletal abnormalities, immunotoxicity and endocrine disruption in pinnipeds (reviewed in Ross 2000). Ross et al. (2000) found that PCB concentrations increase with age in male killer whales, but decline in reproductively active females. Consistent with observations in other mammals, including humans, reproductive females pass PCBs to their offspring, particularly the first born, during gestation and lactation (Tanabe and Tatsukawa 1992, Borrell et al. 1995, Ylitalo et al. 2001).
Dioxins and Furans
Levels of dioxins and furans were found to be low in the blubber of resident or transient killer whale populations in BC (Ross et al. 2000). This may be partly explained by low levels of dioxins and furans in their diet, but killer whales may also metabolize and excrete dioxin-like compounds more effectively than PCBs (Ross 2000).
|pesticide used in some countries, banned in North America, persists in terrestrial runoff 30 years post ban, enters atmosphere from areas where still in use||yes||yes||reproductive impairment, immunosuppression, adrenal and thyroid effects|
Polychlorinated Biphenyl s
|electrical transformer and capacitor fluid, limited use in North America but enters environment from runoff, spills and incineration||yes||yes||reproductive impairment, skeletal abnormalities, immunotoxicity and endocrine disruption|
|Dioxins and Furans||by-product of chlorine bleaching, wood product processing and incomplete combustion. Mills less of a source now. Current sources include burning of salt-laden wood, municipal incinerators, and residential wood and wood waste combustion, in runoff from sewage sludge, wood treatment||yes||yes||thymus and liver damage, birth defects, reproductive impairment, endocrine disruption, immunotoxicity and cancer|
Persistent Polycyclic aromatic hydrocarbons
|by-product of fuel combustion, aluminium smelting, wood treatment, oil spills, metallurgical and coking plants, pulp and paper mills||yes||no||carcinogenic|
|flame retardants, esp. PBBs and PBDEs
Polybrominated diphenyl ethers
|flame retardants; in electrical components and backings of televisions and computers, in textiles and vehicle seats, ubiquitous in environment. 2/3 product PBDEs banned in Europe. Same two products withdrawn from North American marketplace in 2005, but one (deca) product still used globally.||yes||yes||endocrine disruption, impairs liver and thyroid|
|stain, water and oil repellent (included in Scotchgard until recently), fire fighting foam, fire retardants, insecticides and refrigerants, ubiquitous in environment||yes||yes but in blood, liver, kidney and muscle||promotes tumour growth|
|antifoulant pesticide used on vessels||yes||Yes||unknown but recently associated with hearing loss|
|flame retardants, plasticizers, paints, sealants and additives in lubricating oils||yes||yes||endocrine disruption|
|ship insulation, electrical wires and capacitors, engine oil additive, municipal waste incineration and chlor-alkali plants, contaminant in PCBs||yes||Yes||endocrine disruption|
|detergents, shampoos, paints, pesticides, plastics, pulp and paper mills, textile industry found in sewage effluent and sediments||moderate||moderate||endocrine disruption|
|fire retardants, plasticizers, lubricants, inks and sealants, enters environment in runoff||yes||yes||endocrine disruption and reproductive impairment|
References: Primarily Grant and Ross 2002, but also Lindstrom et al. 1999, Hooper and MacDonald 2000, Kannan et al. 2001, Hall et al. 2003; Van deVijver et al. 2003, Rayne et al. 2004, Song et al. 2005.
Polybrominated Diphenylethers ( PBDEs)
Preliminary evidence suggests that flame retardants may be a significant and emerging concern for resident killer whales (Ross 2006). Moderate levels of the as-yet largely unregulated PBDEs were observed in 39 biopsy samples collected between 1993-1996 from southern resident and transient killer whales, and relatively low levels were observed in northern residents (Rayne et al. 2004). Unlike an earlier study on PCB levels in resident killer whales (Ross et al. 2000), Rayne et al. (2004) did not find any significant age-related trends in PBDE levels, but that may have been an artefact of their small sample size or the fact that PBDEs were relatively new in the environment in the 1990s. In a sample of 70 long-finned pilot whales in the North Atlantic, Lindstrom et al. (1999) found that juveniles had two to three times higher levels of PBDEs than did adults (Lindstrom et al. 1999), suggesting that reproductive females may pass PBDEs on to their offspring during gestation and lactation.
Although the toxicity of PBDEs is not well understood, they have been associated with endocrine disruption in laboratory animals (Darnerud, 2003). While no conclusive link could be established as a result of the numerous other lipophilic contaminants present, PBDE concentrations were negatively associated with thyroid hormones in grey seals (Halichoerus grypus, Hall et al. 2003). As more than 10 years have passed since some of the killer whale samples were collected, and since PBDE levels persist in the environment and their use has been increasing exponentially (Hooper and McDonald 2000), it is likely that killer whales today in 2007 are carrying significantly higher concentration loads of these contaminants than were found in whales sampled in the mid 1990s. Numerous captive and semi-field studies of pinnipeds provide evidence that POPs are affecting immune function (hence, resistance to disease), hormone levels, and reproductive health (Ross 2000; Reijnders 1986; Nyman et al. 2003; De Swart e al., 1996).
Using this weight of evidence as a foundation, it is not possible to ignore the substantial risks that PCBs and other POPs present to killer whales in the northeast Pacific. Transients from Prince William Sound, Alaska (AT1 population) are highly contaminated, and have had no successful reproduction since 1984, providing perhaps a population-level glimpse into the effects of high POP burdens (Ylitalo 2001). High levels of toxic chemicals may also make killer whales more vulnerable to disease (Ross, 2002). Jepson (1999) found that harbour porpoises that died from infectious diseases had two to three times higher concentrations of PCBs than those that died from trauma.
Biological pollution may also threaten the health of resident killer whales, their habitat and their prey. These pollutants may take the form of 'spill-over' pathogens from human activities (e.g. pets, livestock, migrations, habitat change) virulent, antibiotic- resistant bacterial strains arising as a result of the use of antibiotics or exotic species. Emerging infectious diseases are a growing concern for marine life, as naturally occurring host-pathogen relationships are altered through human activities such as disturbance, over-fishing, habitat destruction, climate change or pollution (Ross 2002). Killer whales whose immune system is compromised through chemical contaminants may be increasingly vulnerable to biological pollutants. Although no disease-related mass mortalities have been observed among BC's marine mammals, Morbillivirus has been detected in marine-dwelling river otters (Mos et al. 2003), highlighting the potential risk of this or related pathogens to killer whales. In other areas, Morbillivirus outbreaks have caused mass mortalities of seals (Grachev et al. 1989, Kennedy et al. 2000) and dolphins (Aguilar and Borrell 1994). Pathogens such as Morbillivirus are capable of spreading extremely quickly (3000 km/yr), likely because in the marine environment there are few barriers to dispersal (McCallum et al. 2003).
The introduction of exotic species has changed habitats in other areas (e.g. zebra mussels in the Great Lakes, Eurasian milfoil into freshwater lakes) and introduced species have the potential to impact local ecosystems here. In British Columbia, Atlantic salmon that have escaped from aquaculture operations have successfully spawned in freshwater (Volpe et al. 2000). The extent to which this is occurring and how Atlantic salmon would compete with Pacific salmon, the preferred prey of residents (Ford et al. 1998), is not well known at this time.
Trace metals occur naturally in the marine environment, but elevated concentrations sufficient to be a concern to marine mammals may be found in localized areas such as urban and industrial centers (Grant and Ross 2002). Some, such as cadmium, mercury, copper and lead may have toxic effects even at relatively low concentrations, and could impact killer whales, although effects on their prey and/ or habitat are more likely.
Little information is available on the levels and effects of trace metals on marine mammals in the Pacific. However, in a small sample of stranded killer whales, residents showed higher levels of mercury than transients (Langelier et al. 1990). In the western Pacific, all odontocete meat sampled from Japanese markets contained amounts of mercury that exceeded the level permitted for human consumption (Endo et al. 2003). However, the historical exposure of high trophic level marine mammals to naturally elevated concentrations of mercury in prey has resulted in their evolved ability to detoxify this toxic metal through the formation of mercury-selenium crystals in the liver (Martoja and Berry, 1980).
Sources of Contaminants
Monitoring the sources and levels of environmental contaminants is particularly challenging given that each year, up to 1000 new chemicals are released into the environment globally (Haggarty et al. 2003). The high contaminant levels found in southern residents may arise from consuming prey that are from industrialized areas near the BC-Washington border, which may be more contaminated than the prey of northern residents (Ross et al. 2000). In Japan, odontocetes that travelled in more industrialized areas carried higher contaminant loads than those found in more remote areas (Endo et al. 2003). In a study of harbour seals in British Columbia and Washington, Ross et al. (2004) found that although PCB levels were a concern in all areas, seals from Puget Sound are seven times more PCB-contaminated than were seals from the Strait of Georgia. This suggests that the food web within Puget Sound has been contaminated with PCBs, such that killer whales consuming prey items from this region may be vulnerable to increased contaminant exposure. Chinook salmon, one of the resident killer whales' preferred prey species (Ford et al. 1998, Ford and Ellis 2005), feed in the upper trophic levels in the food web, and those from Puget Sound are relatively contaminated with PCBs (O'Neill et al. 1998). Studies suggest that most salmonids are 'importing' contaminants from their time at sea, reflecting global environmental contamination (O'Neill et al 1998; Ewald et al 1998).
Although DDT was banned in Canada in 1989 and over 30 years ago in the United States, it continues to enter the ocean from terrestrial runoff (Hartwell 2004) as well as from atmospheric transport from countries where it is still in use. Dioxins (PCDDs) and furans (PCDFs) represent highly toxic by-products of chlorine bleaching and associated wood treatment, and incomplete combustion. Source controls and regulations have greatly reduced their input in to the coastal environments of BC and Washington over the past 15 years.
Contaminants enter the marine environment from local, regional and international sources. These are discussed in detail in Haggarty et al. (2003). Local point sources of contaminants into the marine environment include:
- pulp and paper mills,
- wood treatment facilities,
- municipal effluent outfalls,
- petrochemical facilities, and
Indirect sources (non-point source pollutants) include
- sewer overflows (e.g. organic wastes, household products, pharmaceuticals and personal care products)
- urban runoff and storm-water drainage (e.g. pesticides, metals, hydrocarbons, herbicides, and animal wastes)
- agriculture (e.g. pesticides, herbicides, animal wastes and antibiotics),
- forestry (e.g. pesticides, herbicides, fire-control chemicals, anti-sapstain chemicals, log booms and storage areas), and
- aquaculture (e.g. organic wastes , chemical contaminants [antibiotics, feed additives, pharmaceuticals, pesticides and antifouling on nets]).
Garrett and Ross (in press) describe the Canadian and US federal, provincial and state agencies responsible for the monitoring, mitigation and regulation of environmental contaminants and their sources.
Shipping also represents a risk to the ecological integrity of coastal regions. Both intentional and unintentional discharge of chemicals and biological waste are added sources of pollution in all coastal areas, but particularly in high traffic zones. In addition, the introduction of exotic and invasive species carried on ship hulls and in ballast water have the potential to dramatically alter the habitats they have colonized (e.g. European green crabs, zebra mussels, the alga Caulerpa taxifola). Numerous invasive invertebrates have been found in the ballast water of ships at anchor in Vancouver Harbour (Levings et al. 2004), although the ecological significance of such introductions is unclear.
In addition, some pollutants such as PCBs, DDT and other chemicals, are transported through atmospheric processes and ocean currents, and may travel to the west coast of North America from as far away as Asia in less than 5-8 days (Wilkening et al. 2000). Consequently, the northeastern Pacific may be a sink for globally produced POPs (Ross et al. 2000, 2004, 2006).
Certain 'legacy' POPs such as PCBs and DDT have been phased out of industrialized countries and their concentrations are slowly decreasing in the marine environment (Muir et al. 1999), although these declines have levelled off (Addison and Stobo 2001). However, levels of other 'new' POPs such as the flame retardant PBDEs have increased exponentially over the past 25 years, and represent the PCBs of the future (Hooper and McDonald 2000; Ross 2006). Unlike PCBs, which were generally used in a limited range of applications such as electrical transformers and capacitors, PBDEs are widely used in many industrial and consumer applications and are incorporated into plastics, textiles and foam.
Answering the question as to whether killer whales may be prey limited is complex. While the complete diet of resident killer whales is not known, at certain times of the year salmon, particularly chinook and chum, appear to be important prey (see Section 1.4.1 Diet). Ford et al. (2005) found that trends in the mortality rates of southern and northern resident killer whales were correlated with each other, and that both were strongly related to fluctuations in the abundance of chinook salmon, but not chum salmon. Birth rates were also correlated with chinook salmon abundance, but more weakly than mortalities.
Unfortunately, there is very little known about the prey of resident killer whales and their distribution and abundance during the months of November to April. This is due to the inherent challenges of studying whales during the winter months, and because the whales move from their Summer concentrated areas and range widely along the exposed coast during the winter and early spring. Thus when considering the availability of prey to resident killer whales, it should be noted that we have very little knowledge of what other prey species may be important to them, and the discussion below focuses on species that are known to be important.
Changes in Salmon Abundance and Availability
Assessing the status of salmon stocks and their availability to resident killer whales is challenging to interpret and often fraught with controversy. Until the middle of the 20th century, many wild salmon stocks experienced significant declines due to overfishing, habitat degradation, restrictions in access to spawning grounds due to landslides, and changes in ocean productivity (summarized in Krahn et al. 2002 and Wiles 2004). The situation changed between 1975 and 1993, and the total abundance of North Pacific salmon doubled (Bigler et al. 1996) due to hatchery enhancement, changes in fisheries management practices and a favourable climatic regime (Bigler et al. 1996, Beamish et al. 1997). Since the early 1990s many of these stocks have declined in number and specific causes have not been identified. Some studies have questioned the role of enhancement (Beamish et al. 1997, and reviewed in Gardner et al. 2004) but other potential problems such as marine survival appear to be a factor. At present 26 of 52 different wild Pacific salmon stocks in the lower 48 states of the US are considered at risk under the US Endangered Species Act (NWR 2004). In British Columbia, salmon from one-third of the spawning rivers in southwestern BC had been lost or were seriously depleted by 1990 (Riddell 1993). Recognizing that many salmon stocks are under threat, Fisheries and Oceans Canada announced a new wild salmon policy in December 2004 (DFOb 2005), designed to restore and maintain healthy and diverse wild salmon populations and their habitat. If these actions are successful, salmon may gradually become more available to resident killer whales.
Resident killer whales tend to be found in concentrated areas during the period when salmon are returning to rivers to spawn. This likely reflects the fact that salmon are not as widely dispersed at this time as they are during the rest of their life cycle. There is a great deal of diversity in the timing of the spawning period for salmon. For example, the Upper Columbia River has a spring run and a summer/fall run of chinook. These runs are considered distinct stocks because they do not interbreed. The spring run is endangered under the ESA in the US, yet the summer/ fall run is not at risk (NWR 2004). This illustrates the need to consider the timing of the spawning period of each salmon stock when assessing the availability of salmon for killer whales, in order to ensure an adequate year-round food supply. Chinook salmon are longer lived than other salmon species and spawn at different ages (Healey 1991). It is likely that their year-round availability in nearshore waters is a key factor, along with body size and lipid content, in chinook being the preferred salmonid prey of resident killer whales (Ford and Ellis 2005).
To address the scientific uncertainty regarding the impact of sea lice on salmon, and the relationship of this to killer whales, DFO and others (e.g., Pacific Salmon Forum) are conducting scientific research to assess and protect the health of the wild pink and chum salmon resource in the Broughton Archipelago.
Depressed Chinook Stocks
Chinook salmon, the principal prey of BC's resident killer whales, is one of the least abundant species of salmon in BC (Riddell 2004). However, unlike other salmon, many populations of chinook remain in nearshore waters during the ocean phase of their life cycle. As a result they are available on a more year-round basis to killer whales, but are also more vulnerable to pollution (discussed in 2.2.1 Environmental Contaminants).
Chinook abundance dropped in the 1970s and 1980s, but escapements increased until the early 1990s in some rivers, primarily due to hatchery production (Beamish et al. 1997). In Washington, hatchery fish now account for about 75% of all harvested chinook (Mahnken et al. 1998 in Wiles 2004). In un-enhanced river systems in central and northern British Columbia, chinook numbers remain depressed (Riddell 2004) and 10 of 17 chinook stocks in Washington, Oregon and California are listed under the ESA (NWR 2004). Thus it is plausible that chinook may be limiting for killer whales (Ford et al. 2005). This may explain why southern resident killer whales have appeared in places as distant as off the Columbia River and off northern California to the south and off Langara Island in the north (unpublished data CRP-DFO). Their presence was associated with unusually large returns of chinook salmon, which they may have had to seek out because of less abundant prey within their traditional range. When prey availability is reduced, killer whales may be forced to spend more time and travel greater distances to forage for their food, or switch to less profitable prey, which could lead to lower reproductive rates and higher mortality rates.
In addition to reduced chinook abundance, the quality of individual fish appears also to have declined over recent decades. Average weights of chinook salmon in nine populations from British Columbia to California declined by up to 45% between 1975 and 1993 (Bigler et al. 1996). Thus, the nutritional yield of each chinook salmon is significantly less today than it was in past years, which may have an impact on the overall foraging energetics of resident killer whales.
All cetaceans, including resident killer whales, are being subjected to increasing amounts of disturbance from vessels, aircraft, and anthropogenic noise (IWC 2004). Both private and commercial boat traffic have increased dramatically in recent years, and killer whales must navigate in increasingly busy waters (Osborne 1999, Foote et al. 2004). Industrial activities such as dredging, drilling, construction, seismic testing, and military sonar and other vessel use of low and mid-frequency sonars also impact the acoustic environment (Richardson et al. 1995, NRC 2003). The means by which physical and/ or acoustic disturbance can affect resident killer whales at both the individual and population level are not well understood, but may depend on whether the disturbance is chronic (such as whale watching) or acute (such as seismic surveys). Other factors, including the animal's condition, previous exposure (potentially causing sensitization or habituation), age, sex, and behavioural state also influences how disturbance affects whales. In addition, environmental factors, such as El Niño events that may change the availability of prey, may make animals more vulnerable to disruption than they would be otherwise. The sources of both physical and acoustic disturbance and their potential impact on resident killer whales are discussed in greater detail below.
A current challenge in studying the effects of disturbance is in finding informative ways to describe and measure them, and to date the question of whether a source of disturbance is likely to result in effects at the population level can be difficult to answer. Responses to disturbance may range from slight differences in surfacing and breathing rates to active avoidance of an area. Even if the disturbance causes immediate death, carcasses are rarely recovered. (Regardless of the cause of death, only 6% of killer whale carcasses are recovered, unpublished data CRP-DFO). As well, animals may show no obvious behavioural responses to disturbance, yet still be negatively affected. For example, Todd et al. (1996) found that humpback whales remained in the vicinity of underwater explosions, and showed no obvious behavioural responses to them. However they experienced significantly higher entanglement rates during this time, and necropsies of two whales that drowned in nets revealed acoustic trauma (Ketten et al. 1993). Thus a lack of a measurable behavioural response to a stimulus does not necessarily imply the disturbance does not have negative consequences. A parallel may exist with humans, since people exposed to chronic noise lose their hearing more quickly than those that are not exposed to chronic noise. The consequences of hearing loss for cetaceans are likely fatal.
Measures for changes in behaviour may also not be subtle enough to detect disturbance. Whitehead (2003) re-analyzed data that were reported to show that sperm whales did not show behavioural responses to surveys using high-intensity sound. He segregated the responses according to whale density in the area and found that contrary to earlier conclusions, when whale density was low, sperm whales avoided seismic activity. When densities were high, whales remained in the vicinity. He suggested that whales may have been reluctant to leave a rich feeding area despite the disturbance.
Commercial whale watching has grown dramatically in British Columbia, with just a few boats carrying less than 1,000 passengers per year in the late 1970s and early 1980s to 80 boats carrying half a million passengers per year in 1998 (Osborne 1991, Baird 2002, Osborne et al. 2003). Whale watchers tend to target resident killer whales in their most predictable locations, Haro Strait and Johnstone Strait. In the summer, an average of 19-22 boats have been observed near southern resident killer whales in Haro Strait, commonly from 9 am to 9 pm (Osborne et al. 2003) although some begin as early as 6 am (personal communication David Bain, February 2005). These include privately owned kayaks, sailboats and powerboats as well as commercial whale watch vessels. While the benefits of public education and increased awareness that can be achieved through guided whale watching are well established, concern over the effects of whale watching on killer whales has grown with the industry itself. This concern has prompted the development of industry initiated watching guidelines and has resulted in studies that have attempted to measure responses of the whales to such focused attention (Kruse 1991, Williams et al. 2002a, b), as well as the behaviour of boaters around whales (Jelinski et al. 2002). Whale watching activities have the potential to disturb marine mammals through both the physical presence and activity of boats, as well as the increased underwater noise levels boat engines generate.
Under the Fisheries Act in Canada and the MMPA in the US, disturbance (harassment) of marine mammals, including killer whales, by the public is prohibited. No special provisions or exemptions to this prohibition have been made for commercial whale watch operators and the commercial fleet is subject to the same regulatory restrictions as recreational boaters. It is not known what the biological significance of disturbance is to resident killer whales, but voluntary whale watching guidelines for Canadian vessels have been developed (Be Whale Wise, DFO 2004). From June through to November, an additional set of guidelines has been developed to minimize disturbance to whales when whales are in the Special Management Zone in Johnstone Strait (see www.straitwatch.org for details). The Whale Watch Operators Association Northwest (WWOANW) has developed an even more comprehensive 'Best Practices Guidelines' for commercial operators to follow when observing southern residents (WWOANW 2004). These guidelines have evolved over a 10 year period to reflect new knowledge and minimize the negative effects of vessel traffic. They remain a work in progress and will evolve as further research reveals if and how whale watching may have population level consequences for resident killer whales.
There are several projects that focus on educating the boating public both on and off the water about appropriate conduct in the vicinity of marine mammals. They also monitor vessel activity in the presence of whales. Current projects include the Soundwatch Boater Education Program in the San Juan Islands, and Straitwatch in Johnstone Strait, while past projects include the Marine Mammal Monitoring Project in Victoria, BC,. All these programs are run by non-profit organizations that do not have guaranteed funding. Smith and Bain (2002) found that commercial operators increased their compliance with a voluntary 0.4 km 'no boat' zone in the San Juan Islands from less than 80% to over 90% when Soundwatch was present on the water.
Boat activity has been linked to short-term behavioural changes in resident killer whales (Kruse 1991, Smith and Bain 2002, Williams et al. 2002a, b). They have been known to swim faster, travel in less predictable paths, alter dive lengths, move into open water, and alter normal behaviour patterns at the surface in response to vessel presence (Kruse 1991, Williams et al. 2002a, b). Foote et al. (2004) found that southern resident killer whales significantly increased the duration of their calls when boats were present, and suggested that this was an adaptation to the masking effects caused by increased noise levels.
Although studies have shown short- term responses of killer whales to whale watching vessels, the long- term effects of whale watching on the health of killer whale populations are not known (Trites et al. 2002). Increased whale watching operations between the mid-1980s and 2001 may have resulted in a potential 20% increase in energetic expenditures of killer whales due to increased swimming velocity (Kriete 1995, 2002). Bain (2002) found that although the decline of southern residents followed the increase in commercial whale watching, the relationship was much more complex. He suggested that other variables, such as changes in the availability of prey, were also likely significant. Whether whale watching is a significant threat to killer whales or not, both the northern and southern resident populations continue to return to their traditional summer ranges despite increased whale watching activity. This may reflect their strong cultural behaviours or the distribution of their prey.
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 1 µPa, as a threshold for temporary or permanent hearing loss of cetaceans, and 160 dBRMS re 1µPa for behavioural disruption (NMFS 2005b).
|Source||Signal Structure||Frequency Range||Source Level
(dB re 1 µPa at 1 m)
>0 Hz to >100kHz
- weapon/counter weapon
pulsed tones and
>1kHz to < 10kHZ
>10kHz to 100kHz
200 to 235+
190 to 220
|Construction||broadband and tones||<10kHz to 10+kHz||NA|
|Dredging||broadband and tones||<10Hz to <10kHz||NA|
|Commercial shipping||continuous||10Hz to >1kHz||160 to 200|
|Commercial sonars||pulsed tones||28kHz to >200kHz||160 to 210|
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 1µPa @ 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.
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 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 NOAACetacean 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.
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).
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.
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