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Recovery Strategy for the Northern and Southern Resident Killer Whale

2.  Threats

2.1 Historic Threats

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.

2.1.1 Harvest and Live Captures

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. 

2.1.2  Intentional Shootings

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.

2.1.3  Acoustic Harassment Devices

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).

2.2 Current Threats

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. 

2.2.1 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 I.

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).