The following information is part of the text from the report "Status of killer whales in Canada" by R.W. Baird
Potential sources of natural mortality fall into several categories: predation, parasitism, disease, biotoxins, accidental beaching, entrapment, and starvation. No predators of killer whales have been recorded, but young or sick whales are potentially at risk from attacks by large sharks in some areas, and attacks by other killer whales may also pose a risk (see above). The relatively high incidence of scarring on animals also suggests that intraspecific aggression occurs (see Visser 1998).
A variety of endoparasites have been recorded from killer whales, including trematodes, cestodes, and nematodes (see review in Heyning and Dahlheim 1988). Transmission of such parasites is primarily through ingestion of infected food items, but the role and extent of such parasites in causing natural mortality is unknown. External parasites have not been documented in B.C. killer whales, but killer whales elsewhere have been seen with barnacles on the rostrum and trailing edge of flukes, and with a species of cyamid ectoparasite. The current understanding of the diseases and disease processes (e.g., Ridgway 1979) affecting killer whales is relatively advanced, as a result of the study of animals in aquaria (J. McBain, Sea World San Diego, personal communication). Relatively little of this research has been published however. Mortality due to biotoxins has not been reported for killer whales, though a number of large-scale mortality events in other cetaceans have been linked to this source (e.g., Geraci et al. 1989). Large-scale mortality events due to viral infections have been recorded in several populations of marine mammals in recent years (Osterhaus and Veder 1988; Duignan 1995), and while the occurrence of such die-offs is unpredictable, given their magnitude and apparently increasing frequency of occurrence, they should be taken into account in conservation planning and population viability analysis (Young 1994; Simmonds and Mayer 1997).
Accidental beaching and entrapments of killer whales are an occasional source of natural mortality. Several cases of beaching of live animals have been reported in British Columbia and off eastern Canada, both with large groups (Carl 1946; Dearden 1958; Emery 1960) and lone individuals (Hoyt 1990). There is one recent unpublished record of two adult individuals which live stranded and died during a storm on 28 January 1998, near Terranceville, Fortune Bay, Newfoundland (R. Hudson, personal communication). Mass strandings have also been reported from Alaskan waters (Hanson and Spraker 1996). The cause(s) of large group strandings are usually unclear (though Dearden 1958 reports animals being forced ashore by ice), but it seems more likely to occur for "offshore" whales traveling on a rare occasion in inshore waters, than it does for inshore groups. Hoyt (1990) noted one transient individual apparently accidentally stranded while chasing porpoise in shallow water. Ice entrapments have been reported in the Canadian Arctic (Reeves and Mitchell 1988a), off Newfoundland (Lien et al. 1988) and in the Antarctic (Taylor 1957). Several cases of animals becoming entrapped in tidal lakes or inlets with narrow, shallow openings have also been noted (Emery 1960; Mitchell and Reeves 1988; Bain 1995). In many cases such entrapment has led to mortality of all or part of a group. Considering the small size of inshore populations of killer whales, such periodic events could seriously affect populations. Temporary "entrapment" in narrow inlets has been documented for southern resident killer whales twice in recent years (Shore 1995, 1998). In the most recent case, occurring in southern Puget Sound in 1997, the whales' reluctance to move under a bridge across the mouth of the inlet was suggested as a possible factor preventing their leaving the enclosed area (Shore 1998). Two of the 19 whales which were in the inlet died at some point in the six months after they left the inlet, though it is unknown whether the "entrapment" was a contributing factor to this mortality (Anonymous 1998).
Potentially negative interactions with humans fall under two broad categories. Some impacts may have acute (immediate) effects on individuals or a population, such as directed takes (whaling, culling), live-capture fisheries, entanglement in fishing gear, collisions with vessels, or exposure to acute pollutants (e.g., oil spills). Immunotoxic affects due to accumulation of persistent toxic chemicals may also have an acute impact by increasing susceptibility to diseases, thus causing an increase in mortality. Besides these acute impacts, there are a number of less tangible, longer-term potentially negative human influences, including a reduction in reproductive rates due to accumulation of persistent toxic chemicals, reduced prey availability due to human activities, and disturbance or displacement by vessel traffic or other sources of underwater sounds (Table 3). While each of these is treated independently below, it should also be taken into account that cumulative impacts of all of these factors could be important (or in the case of longer-term stressors, synergistic interactions between impacts could occur; Whitehead et al. 1999).
Killer whales have been hunted for oil and meat (for human or animal consumption, fertilizer or bait) in many areas (e.g., Reeves and Mitchell 1988b; Oien 1988; Berzin and Vladimirov 1983; Miyazaki 1983; Anonymous 1992; Kishiro and Kasuya 1993; Price 1985; Bloch and Lockyer 1988; Barnes 1991; Yu 1995, though the largest fisheries were discontinued in the early 1980s (Norway and Russia) or early 1990s (Japan). Small numbers are probably still taken elsewhere however. Information on catches is currently reported by many countries that are members of the International Whaling Commission through their Annual Progress Reports, though not all countries submit Annual Progress Reports, and some countries may not include killer whales in their lists of catches, as they are considered "small cetaceans" and are thus not covered under the auspices of the IWC. Small numbers of animals may be taken by non-member countries, and such catches would probably be largely unreported. In Canadian Arctic waters, killer whales are only taken very occasionally by native people; Reeves and Mitchell (1988a) noted that there was no tradition of hunting of killer whales in this area. Fourteen killer whales were killed by native hunters in the Canadian Arctic in 1977, but these were individuals that had been trapped in a tidal lake (Mitchell 1979). Small numbers were taken commercially off of Newfoundland and Nova Scotia in the 1940s through 1960s (Sergeant and Fisher 1957; Mitchell and Reeves 1988), and it is possible that more animals were taken but not reported in an early fishery for pilot whales (Sergeant 1962; Mitchell and Reeves 1988). Catches in the 1960s and 1970s off Norway were both age- and sex-biased, and impacts on the current population may still be apparent (Vongraven and Bisther 1995).
Culling (intentional shooting) of animals, because of their perceived (or documented) threat to fisheries, has also occurred in British Columbia (Carl 1946; Olesiuk et al. 1990), off eastern Canada (Lien et al. 1988), and elsewhere (e.g., Heide-Jorgensen 1988). In British Columbia this included the Canadian Air Force using killer whales as practice targets (Carl 1946), as well as opportunistic shooting by fishermen and the federal fisheries department. That such culling may have had an impact on populations earlier in this century is apparent in the population growth curves shown by Olesiuk et al. (1990; see also Figure 5), since both the northern and southern resident populations were growing (presumably recovering) prior to the initiation of the live-capture fishery. As such, it is possible that the populations today are still recovering. Elsewhere, as in Prince William Sound, Alaska, direct killing by fishermen in recent years in response to losses of fish may still be having significant effects on the local population (Dahlheim and Matkin 1994). Lien et al. (1988) note that the shooting of killer whales which congregated around whaling ships to feed on captured baleen whales may have significantly decreased the population in that area (though whaling ceased there in 1972). Kills in Greenland (Heide-Jorgensen 1988) may be from populations which share their range with Canada (Heide-Jorgensen 1993), and whether the ongoing occurrence of such kills is currently having an impact on populations off eastern and Arctic Canada should be investigated. Killer whales in British Columbia are not reported to regularly take fish off fishing gear (G. Ellis, personal communication), as has been reported elsewhere (e.g., Yano and Dahlheim 1995), thus it seems unlikely that illegal shooting because of perceived threats to fisheries is currently occurring to any great degree. One fatal shooting of an adult female northern resident was documented in the 1983 (which also appeared to result in the death of her calf), and at least one other northern resident has a bullet hole in the dorsal fin (Ford et al. 1994). Because of the extremely low potential growth rate of killer whale populations, even occasional shooting could limit population growth, and some monitoring of such activities is warranted. How such monitoring would be undertaken is difficult to envision.
Incidental mortality in fisheries through accidental entanglement in fishing gear appears to be rare for this species. A few gear entanglements have been reported in British Columbia, though not all have resulted in death of the entangled animals (Pike and MacAskie 1969; Jamieson and Heritage 1988; Ford et al. 1994b; Guenther et al. 1995; Baird et al. in press). Entanglements have also been reported from other areas where individuals from the B.C. population range (e.g., Alaska - Barlow et al. 1994; California - Heyning et al. 1994). Off the eastern coast of North America, no reports of incidental mortality in Canadian waters appear to have been published (Read 1994), though there is one record of a killer whale entangling in a groundfish gillnet (though it did not die) in the U.S. waters of the Gulf of Maine (Waring et al. 1997), and one record of a killer whale entangling (but released alive) in a swordfish longline in international waters off of Newfoundland (A. Williams, NMFS, personal communication). As with direct killing, some efforts to estimate the numbers of animals which are killed through incidental mortality are warranted. While questionnaire surveys of fishermen are known to be extremely biased (Lien et al. 1994), reporting of such accidental events might be more likely than reporting of deliberate activities like shooting.
Live-capture fisheries for public display in oceanaria have been focused in two areas, British Columbia/Washington and off Iceland (Asper and Cornell 1977; Bigg and Wolman 1975; Hoyt 1992). The last permit for captures in B.C. was issued in 1982, although no animals were taken; the last animal taken from British Columbia was in 1977, and it is unlikely any further captures would be allowed, due to widespread public opposition (Hoyt 1990). Of 63 residents estimated to be removed from B.C./WA, 48 were thought to originate from the southern resident community (Olesiuk et al. 1990), which currently numbers only 89 animals (van Ginneken and Ellifrit 1998). These captures substantially reduced the southern resident population and it took approximately 20 years to return to levels similar to prior to the fishery (Figure 5). Besides a reduction in numbers, the live-captures also resulted in a skewed age- and sex-composition of the population (Olesiuk et al. 1990), due to selective cropping. Olesiuk et al. (1990) discuss a number of factors which may have resulted in the slow recovery of the southern resident population betwen 1970 and 1985, including the possibility that the selective cropping of males (23 of 35 known-sex individuals were males) may have reduced the number of mature males to below a critical number for optimal productivity (Olesiuk et al. 1990).
In recent years, whale watching focusing on killer whales has become particularly prominent in Washington state and British Columbia, and vessel activity of all types (e.g., sports fishing, whale watching, ferry and freighter traffic) has been increasing (e.g., Osborne 1991). Whale watching in particular has raised a variety of concerns among researchers and members of the public about the potential for disturbance (Kruse 1991; Osborne 1991; Duffus and Dearden 1992, 1993; Phillips and Baird 1993; Duffus and Baird 1995; Burgin and Otis 1995; Baird et al. 1998b; Williams et al. 1998). Numerous behavioural changes have been reported in response to close approaches by boats, although some of the studies undertaken have serious methodological problems, causing researchers to question their validity (Duffus and Dearden 1993). Studies have focused both on northern residents in Johnstone Strait and southern residents in Haro Strait. A number of differences between these sites, the populations of whales which use them, the number and types of boats found in the two areas, and the research methodologies being used in each site, preclude any simple comparison of results from the two areas. Changes in behaviour in response to approach by boats have been demonstrated for northern residents (Trites et al. 1996; R. Williams, personal communication). Unfortunately the implications of such changes in behaviour on reproduction or mortality are unclear. While similar behavioural changes have not yet been demonstrated for southern residents (Osborne 1991; Burgin and Otis 1995; Baird et al. 1998b), there does appear to have been a substantial decrease in the proportion of time southern residents engage in resting behaviour during daylight hours, coincident with the large increase in whale watching activity (Osborne 1986; K.C. Balcomb, R.W. Osborne, personal communications). For transient killer whales, Barrett-Lennard et al. (1996) suggested that vessel noise might impair their ability to detect prey. The impact of a single boat would appear negligible, as Baird and Dill (1996) found that under such circumstances observed food intake rates of transients were more than sufficient to account for the whale's energetic needs. However, at least in some areas of the province and at some times of the year, such impacts could be serious. In the last few years (since 1993), it is not uncommon for small groups of transient killer whales to be accompanied by 5-10 boats when travelling off the Victoria area during summer months (Baird, personal observations), and such large numbers of boats seem more likely to impact foraging success in the way suggested by Barrett-Lennard et al. (1996). In one area in Washington state, the number of vessels found around groups of southern resident killer whales has been increasing (Figure 6), and in 1997 groups were accompanied by an average of 25 vessels (only one quarter of which are commercial whale watching vessels) during daylight hours in the summer months (Baird et al. 1998b; Figure 6). The commercial whale watching fleet in the area (including the ports of Victoria, Sidney and Sooke in British Columbia, and Bellingham and Friday Harbor in Washington) has been increasing rapidly, and numbered over 80 boats in 1997 (Baird et al. 1998b). As noted above (see Protection, National), levels of awareness of, and adherence to, whale watching guidelines are largely unknown (except in a few specific localities during summer months), and virtually no official monitoring or enforcement of whale watching guidelines takes place.
A more direct impact of boats on whales involves injuries or deaths from collisions. Considering the large number of vessels interacting with killer whales during the summer months in British Columbia, vessel collisions are extremely rare. One well-documented case in British Columbia has been reported (Anonymous 1974), with an animal apparently fatally wounded after a collision with a large vessel (a ferry). Ford et al. (1994a) note the animal struck may have been part of the northern resident population. Several other live animals have been seen with scars that might be attributable to vessel interactions, although the evidence for this is inconclusive. One vessel collision with a southern resident killer whale in Haro Strait, Washington, was witnessed in 1998 (V. Shore, personal communication), but the vessel was moving slowly and the animal did not appear to be injured as a result of the collision. A northern resident was struck by a speed boat in 1995 and received a wound to the dorsal fin, which appeared to heal quickly (P. Spong, H. Symonds, personal communications).
The generation of loud underwater sounds through such sources as acoustic deterrent devices ("seal scarers" or ADDs) at aquaculture operations also has the potential to cause disruption of movement patterns or even abandonment of an area (Morton and Symonds 1998). Morton and Symonds (1998) noted a drastic reduction of use of the Broughton Archipelago, off northeastern Vancouver Island, by both resident and transient killer whales, coincident with the installation of several high amplitude ADDs in the area. Residents have shown a decline in use of the area (measured as number of days per year observed) of over 75%, while transient use of the area has declined by over 50%. The lesser decline by transients may be due to their use of specific channels in the area away from the ADDs (Morton and Symonds 1998). Morton and Symonds (1998) compared use of the Broughton Archipelago with the nearby Johnstone Strait, and area where no ADDs were in use, and where resident use of the area has been more-or-less stable over the same periods. Their study provides evidence of killer whale avoidance of areas where ADDs were in operation (Nichol and Sowden 1995 present information on avoidance of another species), thus potential effects by their use by other aquaculture facilities on the B.C. coast should be studied, and increased use of such devices should be strictly regulated.
More critical conservation problems concern two general areas, the effect of pollutants and the reduction of the prey base due to anthropogenic activities. Two general groups of pollutants warrant discussion: 1) persistent toxic chemicals which bioaccumulate; and 2) petroleum products. Killer whales from British Columbia and neighboring areas have been shown to accumulate high levels of persistent toxic contaminants (Calambokidis et al. 1990; Jarman et al. 1996; Matkin et al. 1998; Ross et al. 1998). Populations of resident killer whales in British Columbia spend a large proportion of their time in near-shore waters in close proximity to various sources of pollutants. A recent study using samples collected from free-ranging southern residents demonstrated that levels of PCBs and PCDD/Fs in these animals were three times higher than levels known to be immunotoxic for harbour seals (Ross et al. 1998). Levels in individual southern residents were three to five times higher than in individuals of equivalent age/sex classes of northern residents (P. Ross, personal communication), which live in an area with far fewer sources of pollutants (see Evaluation). Transients appear to spend less time in highly polluted areas, but feed almost exclusively on marine mammals, so may accumulate higher levels of many toxins. Matkin et al. (1998) note that levels of PCBs and DDTs in transients from Prince William Sound were 14 and 22 times higher, respectively, than for residents from the same area. They also note that the group of transients with high levels have shown no recruitment since 1984, suggesting that there may be a linkage between the low rate of reproduction and the high contaminant levels. Although sample sizes are smaller and based on stranded animals, levels of mercury appear to be higher in the tissues of residents than transients (Langelier et al. 1990). One possible candidate for these high levels of toxins in residents is consumption of heavily contaminated prey, but consumption of such prey has not become apparent in the studies of foraging undertaken to date. The high levels found in southern residents could affect reproduction, immune function and endocrine function (Ross et al. 1996a, 1996b, 1998). Reproductive or endocrine function impacts fall into the long-term category of effect. Immune function affects can result in acute (immediate) impacts on individuals or on the population. For example, it is thought that the 1988 morbilivirus-associated mass mortality of harbour seals in northern Europe, which resulted in a population reduction of over 50%, was exacerbated by such immuotoxic effects of contaminants (Ross et al. 1996a, 1996b; de Swart et al. 1996).
Large-scale dumping of oil has the potential for detrimental effects on killer whale populations. Concurrent with the Exxon Valdez spill in Prince William Sound, Alaska, was the unprecedented loss of 14 killer whales from one pod which was seen in the area immediately following the spill (Matkin et al. 1994). Dahlheim and Matkin (1994) reviewed the evidence for a cause-and-effect relationship between the spill and the deaths of these whales, and conclude that while there was a strong spatial and temporal correlation between these events, insufficient evidence is available to determine whether the spill caused the deaths, or other factors, particularly fisheries interactions, were responsible. Given the large amount of tanker traffic on the B.C. and Washington coasts, there is a potential for the loss of a large proportion of a population. In Juan de Fuca Strait, tanker traffic has been increasing, and tankers are aging (existing tankers are not expected to be phased out and replaced with double-hulled tankers until 2015; F. Felleman, personal communication). Thus a population such as the southern residents (considering their tendency to congregate in one area during the summer months) may be at risk from a major spill.
It is beyond the scope of this review to undertake an assessment of trends in the abundance of all the potential prey species of killer whales, and in fact it is likely that such an assessment is impossible (or nearly so) given the data that are available. Regardless, in terms of a reduction in the prey base available for killer whales, it is clear that at least some of the populations of prey species of killer whales are substantially smaller today than historically. In terms of salmon, anthropogenic influences on populations have included destruction, degredation and/or prevention of access to breeding habitat through urbanization, slides associated with road or railroad building, dam building, forestry and agriculture, as well as a reduction in numbers through fishing (Groot and Margolis 1991; Nehlsen et al. 1991; Slaney et al. 1996). Recent reviews of stocks from southeast Alaska through to California document large-scale reductions in many stocks, and extinction of others (Nehlsen et al. 1991; Baker et al. 1996; Slaney et al. 1996; see also e.g., Holtby and Finnegan 1997; Wood et al. 1997; Bradford 1998; Rutherford et al. 1998). These reviews focus primarily on evaluating which stocks are at risk of extinction. Killer whales will be affected by a simple reduction in numbers, rather than only an extinction of stocks. Within British Columbia, the salmon populations most drastically impacted are those in the southern part of the province, particularly the Strait of Georgia (Slaney et al. 1996), coinciding with the population of killer whales (southern residents) which seems most at risk (see Population Size and Trends, and Evaluation). Some evidence is also available for declines of other potential prey species (e.g., Fargo 1997; Leaman and McFarlane 1997; Stanley and Haist 1997; Ware 1997; Yamanaka and Kronlund 1997). Reduced prey availability could result in an increase in the amount of time whales would need to spend foraging, potentially leading to reduced reproductive rates and/or increased mortality rates. Insufficient information is available to assess whether such impacts are currently manifest. Given the inherent difficulty of determining such impacts even if they exist, and the potentially large role they might have on increasing mortality or decreasing reproductive rates, a precautionary approach is warranted (Richards and Maguire 1998).
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