The Rise of Killer Whales as a Major Arctic Predator S.H. Ferguson, J.W. Higdon, and E.G. Chmelnitsky Abstract Anecdotal evidence, sighting reports, Inuit traditional knowledge, and photographic identification indicate that killer whale (Orcinus orca) occurrence in Hudson Bay is increasing. Killer whales were not known to be present in the region prior to the mid-1900s but have since shown an exponential increase in sightings. More sightings from Foxe Basin, Nunavut in the north to Churchill, Manitoba in the south appear to be related to a decrease in summer sea ice in Hudson Strait. Killer whale activity during the open water season has been concentrated in the northwest Hudson Bay region that includes the Repulse Bay and northern Foxe Basin areas. Here, prey items are diverse and abundant. Killer whales are reported in western Hudson Bay on an annual basis with sighting reports and anecdotal evidence suggesting they are first observed heading through Hudson Strait in July and returning to the northwest Atlantic in September. However, arrival, occupancy, and departure times are likely related to yearly ice conditions and prey availability. Killer whales have been observed preying on a number of marine mammal species in Hudson Bay. Of particular concern is predation on bowhead whales in Foxe Basin, narwhal in northwest Hudson Bay, and beluga in southwest Hudson Bay. The impact of killer whale predation on marine mammal species is unknown without long-term studies and direct observation of killer whale hunting behaviour. However, by defining population energetic requirement and considering population demography of prey, we can begin to assess the basic requirements of predator–prey dynamics in Hudson Bay marine ecosystem. To estimate predation impact we used a simple mass-balanced marine mammal model that includes age structure, population size, and predation rate inputs. Estimates of killer whale population size were variable, with the majority of information suggesting that at least 25 whales use the area each S.H. Ferguson (*) Fisheries and Oceans Canada, Central and Arctic Region, Winnipeg, MB, Canada and Department of Environment and Geography, University of Manitoba, Winnipeg, MB, Canada and Department of Biological Sciences, University of Manitoba, Winnipeg, MB, Canada e-mail: steve.ferguson@dfo-mpo.gc.ca S.H. Ferguson et al. (eds.), A Little Less Arctic: Top Predators in the World’s Largest Northern Inland Sea, Hudson Bay, DOI 10.1007/978-90-481-9121-5_6, © Springer Science+Business Media B.V. 2010 117 118 S.H. Ferguson et al. summer. Results suggest that the Northern Hudson Bay narwhal population may be negatively impacted by continued killer whale predation. We conclude that conservation of marine mammals in Hudson Bay should consider killer whale effects since they have the potential to regulate population growth of prey populations. Keywords Beluga • Bioacoustics • Bowhead • Inuit observations • Movements • Narwhal • Photo-identification • Rake marks Introduction The killer whale (Orcinus orca) exists in all oceans of the world but occurs at highest densities in productive temperate waters (Baird 1999). With climate change resulting in warming oceans and loss of sea ice, a major redistribution of whale species is underway with a predicted increase in killer whale abundance in Arctic waters (Moore and Huntington 2008). Historically, the presence of killer whales in Arctic waters has been limited by the presence of pack ice in winter (Reeves and Mitchell 1988; Dyke et al. 1996). The eastern and western Canadian Arctic is becoming more accessible to killer whales as the concentration of sea ice in choke points decreases with climate change (Higdon and Ferguson 2009). Here, we summarize research results from sighting reports, Inuit traditional ecological knowledge, acoustics, and photo-identification to better understand the ecology of killer whales in the Hudson Bay region. Killer whales pose a potential dilemma for the Arctic ecosystem as they can exert significant regulatory effects to prey populations which may cause declines (Estes et al. 1998). Information on killer whale behaviour, group size, social structure, geographic movements, morphological characteristics, genetics, vocalizations, acoustic, and foraging behaviour is needed to understand changes occurring in the Arctic. Our summary of the history of use in this region by killer whales, seasonal movement patterns, feeding behaviour, photographic identification, bioacoustics, and predation by killer whales in the Hudson Bay region provides context in understanding potential ecosystem shifts and predation consequences for marine mammals. History of Killer Whale Use of Greater Hudson Bay Region Killer whales have received little directed study in the eastern Canadian Arctic, with the exception of two comprehensive reviews of available information (Reeves and Mitchell 1988; Higdon 2007). Killer whales were historically (1800s) present in Baffin Bay and Davis Strait and were often reported in commercial bowhead (Balaena mysticetus) whaling logbooks (Reeves and Mitchell 1988). However, all lines of evidence suggest that they are a recent addition to the marine mammal community in Hudson Bay (Higdon and Ferguson 2009). Inuit knowledge also The Rise of Killer Whales as a Major Arctic Predator 119 Fig. 1 Four of seven to nine killer whales observed in Western Hudson Bay (offshore of Rankin Inlet, Nunavut) by a “Students on Ice” cruise on August 5, 2007 (Photo by Trevor Lush) suggests killer whales were not present prior to the mid-1900s but are now observed on a regular basis (Gonzalez 2001). Higdon and Ferguson (2009) summarized killer whale sighting records in Hudson Strait, Hudson Bay, James Bay and Foxe Basin from 1900 to 2006 and demonstrated an exponential increase in sightings per decade (Fig. 1). The first killer whale sighting within Hudson Bay occurred in the 1940s. Most sightings in Hudson Bay have occurred since the 1960s, with the majority along the western coast. The majority of sighting reports are coastal, although the lack of offshore sightings is likely due to human effort being concentrated coastally. There is one offshore record provided by a wildlife observer program for oil and gas development (Milani 1986), and increased effort in the offshore region would likely increase the number of sightings. Killer whales appear to be rare in James Bay and the south and east coasts of Hudson Bay (Higdon and Ferguson 2009). There is less effective reporting of killer whales along the Ontario coast, and our research efforts have focussed on Nunavut. However local knowledge does suggest that killer whales are rare along the southern coast. Cree residents report seeing killer whales “very occasionally” and note that they are more common further west (i.e., towards Churchill, Manitoba) (Higdon and Ferguson 2009). Ontario Cree do not have a word for killer whale (Johnston 1961), which suggests that their sporadic observations are a recent phenomenon. Higdon and Ferguson (2009) also found few sightings for the Nunavik region of northern Quebec (eastern Hudson Bay and the south coast of Hudson Strait). Nunavik researchers have heard anecdotal reports of killer whales sightings but there is no systematic data collection. It is possible that killer whales make relatively rapid movements through Hudson Strait on their way to western Hudson Bay and this would reduce the likelihood of observations. In recent years killer whales have been observed attacking beluga in Hudson Strait, and Inuit hunters report that killer whale numbers are increasing (J. Peters, Makivik Corp., personal communication 2008). 120 S.H. Ferguson et al. Chronological reporting by authors illustrates a progression in killer whale use of the Hudson Bay region, from no evidence (Degerbøl and Freuchen 1935; Peterson 1966; Banfield 1974), to sporadic occurrence (Davis et al. 1980), to occasional and possibly annual use (Reeves and Mitchell 1988), to an exponential increase (Higdon and Ferguson 2009), so that now killer whales occur in Hudson Bay on an annual basis. Higdon and Ferguson (2009) examined correlations between sighting frequency and a long-term sea ice dataset (Rayner et al. 2003) and found that the increase in killer whale sightings was significantly correlated to a decline in sea ice in Hudson Strait. Tynan and Demaster (1997) suggested that marine mammal responses to sea ice declines would first be shown with changes in distribution, and the analyses in Higdon and Ferguson (2009) provides a real-world example. There are inherent biases in using sighting reports to infer changes in species abundance and distribution such as the clusters of where observers live. Despite this, there is reasonably good evidence that killer whales were historically absent in Hudson Bay. There is a long history of European exploration in the region, with over 600 voyages undertaken between 1610 and the early 1900s (Cooke and Holland 1978). A large volume of literature exists, but we know of no mention of killer whales previous to the twentieth century. Sailors were familiar with killer whales, and published accounts have included observations made in the North Atlantic while in transit (Chappell 1817), but no observations were recorded in Hudson Bay. In addition, all of the typical marine mammal species found in Hudson Bay were known well prior to the nineteenth century (Pinkerton and Doyle 1805). To our knowledge no Hudson Bay whaling logbooks mentioned killer whales, despite extensive effort there from 1860 to 1915 and several thorough reviews of the logs (Mitchell and Reeves 1982; Reeves et al. 1983; Reeves and Cosens 2003; Reeves and Mitchell 1988; Ross 1974; Stewart 2008). Hudson Bay whalers were also familiar with killer whales, and several logbooks mentioned trying to hunt them in the North Atlantic while travelling to the Hudson Bay whaling grounds (B. Stewart, Arctic Biological Consultants, Winnipeg, MB, personal communication 2009). It seems likely that the logbooks would have contained killer whale sightings had they occurred in the Hudson Bay region. Degerbøl and Freuchen (1935) traveled extensively in the area from 1921 to 1924, conducting surveys and having many discussions with local Inuit. They heard no evidence of killer whales in Hudson Bay, and were told by Inuit that the whales were turned around in Hudson Strait by the presence of walrus (Odobenus rosmarus). Degerbøl and Freuchen (1935) felt that sea ice represented a more likely barrier to movement, and the analyses of Higdon and Ferguson (2009) supports this, suggesting that declining sea ice conditions are the most reasonable explanation for recent killer whale colonization of the Hudson Bay region. A change in ice conditions in central Hudson Strait in the 1930s opened up a former choke point (c.f. Wilson et al. 2004) and allowed a punctuated advancement of killer whales in the region. The Rise of Killer Whales as a Major Arctic Predator 121 Seasonality and General Movement Patterns Killer whales are first seen in Hudson Strait in July, and reports in Hudson Bay peak in August (Higdon and Ferguson 2009). This was based on analyses of 80 records, and we have since updated the database with additional sightings (18) in the Hudson Bay region. Many of these new sightings (105) have come from an extensive effort to collect Inuit traditional knowledge (or Inuit Qaujimajatuqangit) in a number of Nunavut communities. Inuit observations have been collected and compiled from six communities in Hudson Strait (Kimmirut, 5 interviewees), Hudson Bay (Arviat [5], Rankin Inlet [10], and Repulse Bay [17]) and Foxe Basin (Hall Beach [7] and Igloolik [16]) (Westdal 2009). The most recent version of the killer whale sightings database (used in Higdon et al. in review) contains 203 records for the four Hudson Bay ecoregions (as identified by Stewart and Lockhart 2005). Over half of the 207 records (n = 107) provide the month of the sighting, and an additional 31 include the season (two each in “spring” and “fall” and 27 in “summer”) (Fig. 2). The updated database now contains records of sightings in June (n = 6). Most of these reports are from late June; including Inuit observations from Repulse Bay of occasional sightings of killer whales at the floe edge (Westdal 2009). More of the July sightings are in Hudson Strait not Hudson Bay and the peak 70 Number of sighting reports Hudson Strait 60 Hudson Bay Foxe Basin eastern Hudson Bay-James Bay 50 40 30 20 10 ll Fa m er g Su m N Sp rin be r ov em be r D ec em be r r be ct o O t te m y us Se p Au g Ju l Ju n e 0 Month or season Fig. 2 Seasonality of killer whales in the Hudson Bay region, separated into the four ecoregions identified by Stewart and Lockhart WL (2005) (and used by Higdon and Ferguson 2009). Data on sighting records from the DFO database as summarized by Higdon et al. (in review) (n = 107 with month of sighting and 31 with season only). The one record from the eastern Hudson Bay–James Bay ecoregion is of a dead killer whale that washed up on shore (Reeves and Mitchell 1988) 122 S.H. Ferguson et al. in Hudson Bay records still occurs in August. In September there is a significant decline in the number of reports throughout the region, and the single October report occurred in Hudson Strait. There are no reports from November, and the one record from December is of an ice entrapment that occurred in Foxe Basin in the 1950s (Reeves and Mitchell 1988; Irngaut 1990; Kappianaq 2000; Higdon 2009). These reports indicate that killer whales generally travel west through Hudson Strait in July occurring most often in Hudson Bay and Foxe Basin in August, and typically depart in September. Inuit knowledge of movement patterns is summarized in Fig. 3. Killer whales migrate in and out of Hudson Strait and use Frozen Strait to enter Repulse Bay in the summer. Many Inuit respondents in Repulse Bay felt that the same killer whales seen in Repulse Bay go south towards Arviat and north to Hall Beach (Westdal 2009). Some hunters suggest that killer whales head south through Roes Welcome Sound towards Arviat and Rankin Inlet, then return to the Repulse Bay area before travelling back through Frozen Strait and out into Hudson Strait (Higdon 2009; Westdal 2009). Inuit often report killer whale sightings via radio communication between coastal communities providing a chronology of seasonal sightings. For example, when killer whales are seen in Foxe Basin or in Rankin Inlet, they are generally seen near Repulse Bay about 5 days later (Westdal 2009). This suggests that the same groups of whales make north-south movements along the coast. Inuit suggest that killer whales generally arrive in Foxe Basin from southern areas (around Cape Dorset and from Repulse Bay) when most of the ice has left (Higdon 2009). It is thought that they travel through the centre of Foxe Basin, following their prey (especially bowhead whales), and avoiding the coast. Some return south after coming north into Foxe Basin, but they have also been observed travelling through Fury and Hecla Strait in both eastern and western directions, following bowhead whales west, and smaller numbers following narwhal east in the fall (Higdon 2009). Interviewees in Kimmirut noted that killer whales are rarely seen in their area and do not stay for long, and they also did not provide any information on killer whale migration patterns. This supports the suggestion by Higdon and Ferguson (2009) that killer whales make rapid movements through Hudson Strait possibly to access the prey-rich Foxe Basin and western Hudson Bay coast. Inuit observers have also noted several concentration areas in the Hudson Bay region (Fig. 3), specifically Repulse Bay (also see Higdon and Ferguson 2009), Lyon Inlet, and the area north of Igloolik. The first two areas are important summer concentration areas for narwhal, and the area in northern Foxe Basin contains large numbers of bowhead whales. Inuit in Igloolik note a direct link between increasing bowhead numbers and increasing presence of killer whales (Higdon 2009). Interviewees in Hall Beach noted that killer whales migrate quickly past their community, following bowhead to the region north of Igloolik. Many Inuit respondents in Hudson Bay and Foxe Basin indicate that, while numbers are increasing, killer whales are not as abundant as they are in other areas of Nunavut. For example, they identified Admiralty Inlet as an important concentration area (Fig. 3). The Rise of Killer Whales as a Major Arctic Predator 123 Arctic Bay IgIoolik Hall Beach Repulse Bay Cape Dorset 200 0 200 400 Km Fig. 3 Movements of killer whales into the Hudson Bay region and important concentration areas (Admiralty Inlet near Arctic Bay, Foxe Basin near Igloolik, and Repulse Bay near Repulse Bay) as identified by Inuit observations (Higdon 2009) Killer Whale Prey Items and Evidence for Different Ecotypes Killer whales eat a wide variety of prey items. In the North Pacific and Antarctica, there are sympatric ecotypes that consume specific (non-overlapping) prey. In the eastern North Pacific three ecotypes have been identified: (1) transients, which prey exclusively on marine mammals; (2) residents, which are exclusively fish eaters (mostly salmon); and (3) offshores, which have been little studied but appear to 124 S.H. Ferguson et al. prey on a variety of fish species (Ford 2002; Ford et al. 2000; Dahlheim et al. 2008). These ecotypes also differ in vocal behaviour, genetics, morphology and group size and structure. Three different types also occur in Antarctic waters, referred to as Types A, B, and C, which preferentially consume Antarctic minke whales (Balaenoptera bonaerensis), seals and occasionally baleen whales, and a single fish species (Antarctic toothfish, Dissostichus mawsoni), respectively (Pitman and Ensor 2003). Conversely, some killer whale populations worldwide exhibit little prey specialization. In New Zealand, Visser (2000) identified four main prey types (rays, sharks, fin-fish and cetaceans) consumed by three proposed killer whale sub-populations. In the Northeast Atlantic, some killer whale populations and some killer whales within populations display a broad niche width that, for example, includes seals and herring (Clupea harengus) as prey (Foote et al. 2009). Killer whale ecotypes have not been identified in the Northwest Atlantic including the Canadian eastern Arctic. Therefore, the degree of foraging specialization, if any, is not known. Killer whales have been observed feeding on a variety of cetacean and pinniped species, and there are occasional reports of predation on fish in the North Atlantic and West Greenland. Higdon (2007) summarized 132 recorded attempted or successful predation events in the Canadian Arctic, West Greenland, and northern Labrador. Marine mammal predation events dominated, and there were no recorded fish predation events in the Canadian Arctic, although several reports are available from West Greenland and Davis Strait. Stomach contents of whales harvested in West Greenland provide evidence that at least some Arctic killer whales eat fish (Heide-Jørgensen 1988 (species not provided); Laidre et al. 2006 (lumpsucker fish, Cyclopterus lumpus)). Degerbøl and Freuchen (1935) also stated that killer whales in Davis Strait preyed on Greenland halibut (Reinhardtius hippoglossoides), and Vibe (1980a, in Jensen and Christensen 2003) stated that Greenland killer whales prey on cephalopods “a large degree”. Killer whales have also been observed scavenging around longline fishing vessels of northern Newfoundland, coastal Labrador and southern Davis Strait (Sergeant and Fisher 1957; Mitchell and Reeves 1988; Lawson et al. 2007) and eating herring (Clupea harengus) off eastern Newfoundland (Steiner et al. 1979). Bluefin tuna (Thunnus thynnus) have been found in the stomachs of two stranded whales in Newfoundland (Lawson et al. 2007). Thus, it is apparent that at least some killer whales in the Northwest Atlantic and eastern Arctic (West Greenland/Davis Strait) consume fish. Using the available published information, the vast majority of killer whales in the Canadian Arctic and the Hudson Bay region preferentially, if not exclusively, consume marine mammals (versus fish; Higdon 2007; Higdon et al. in review). Killer whales have been observed preying on all the typical Arctic marine mammal species. The most current version of the sightings database (as analysed by Higdon et al. in review) includes 111 reported predation events throughout the Canadian Arctic. Predation on monodontids (narwhal and beluga) was reported significantly more often than other prey groups, followed by predation on bowhead whales and phocid seals. The database includes 24 predation records from Hudson Bay, 20 from Foxe Basin, and 13 from Hudson Strait. Predation on monodontids, bowheads and The Rise of Killer Whales as a Major Arctic Predator 125 30 Number of reported predation events Phocid seals Bowhead 25 Narwhal Beluga 20 15 10 5 0 Hudson Bay (24) Hudson Strait (13) Foxe Basin (20) Ecoregion Fig. 4 Marine mammal prey items of killer whales reported in the Hudson Bay region (Modified from data in Higdon et al. in review). Data are shown by ecoregions; with no predation records reported for eastern Hudson Bay–James Bay. Values in parentheses are number of predation reports; the total is higher than the number of reports because some records included multiple species groups (particularly records from Inuit knowledge interviews) seals was reported in Foxe Basin and Hudson Bay, and on monodontids and bowheads in Hudson Strait. Monodontid predation was most often reported in Hudson Bay and Hudson Strait, and bowhead predation most often in Foxe Basin (Fig. 4). A number of published sources provide accounts of killer whale predation on marine mammals in the eastern Canadian Arctic (reviewed by Higdon 2007). However much of the information on predation summarized by Higdon et al. (in review) has been gathered through semi-directed interviews with Inuit hunters (Westdal 2009). Local Inuit are extremely knowledgeable on their local environment, and the wildlife species occurring there, and interviews have provided significant information on killer whale movements, distribution, and ecology. No interviewees in Arviat, Kimmirut, or Repulse Bay noted fish as a prey item, although one respondent in Rankin Inlet suggested that killer whales possibly ate shrimp and capelin (Mallotus villosus) (Westdal 2009). Foxe Basin interviewees were unsure whether or not killer whales ate fish, although several hunters thought they might. Ultimately, none of the interviewees provided a direct observation of killer whales preying on fish, and the results suggest that marine mammals are the primary, if not only, prey for killer whales in this area. In certain cases Inuit observations can provide important information that scientific research approaches have difficulty addressing. The impact of killer whales on bowhead whales is one example. Several recent studies have used photo-identification 126 S.H. Ferguson et al. Fig. 5 Tooth rake marks on the flukes of an adult bowhead whale caused by killer whales (Photo credit Jeff Higdon: Foxe Basin floe edge, summer 2007) methods (analyses of rake marks; Fig. 5) to conclude that killer whale attacks on large whales are rare (Mehta et al. 2007; Steiger et al. 2008). However photoidentification methods only identify survivors, as successful kills are not available. Observations of large whale attacks are rare, but they have occurred and been documented (reviewed by Reeves et al. 2006; Springer et al. 2008). Inuit hunters spend a considerable amount of time on the ocean hunting and fishing throughout Nunavut and have observed attacks on bowhead whales (NWMB 2000; Westdal 2009). Inuit regard killer whale predation as one of the major threats to bowhead recovery (Moshenko et al. 2003). Foxe Basin is an important nursery area for bowhead cow-calf pairs (Cosens and Blouw 2003; NWMB 2000). Killer whales preferentially select baleen whale calves (Naessig and Lanyon 2004; Mehta et al. 2007; Steiger et al. 2008), and Foxe Basin should thus represent an important area for attempted predation. Inuit interviewees have confirmed this and have regularly seen attacks and found dead bowheads. The majority of Foxe Basin interviewees (91%, 15/16 in Igloolik and 6/7 in Hall Beach) identified bowhead whales as an important prey of killer whales. Many interviewees (eight in Igloolik and one in Hall Beach) noted a direct cause and effect relationship between bowhead population growth and increased killer whale presence (Higdon 2009; also see Piugaattuk 1994). Eleven interviewees recounted either direct observation of killer whale attacks on bowheads (n = 7) or second-hand stories passed on by others, for a total of 13 independent predation events witnessed (Higdon 2009). These observations provided extensive descriptions of the different cooperative hunting techniques that killer whales use on bowheads. Seven interviewees noted that killer whales will go on top of the The Rise of Killer Whales as a Major Arctic Predator 127 bowhead to cover the blowhole and suffocate it. Five hunters noted that killer whales will often kill the bowhead by ramming it from below and tearing chunks out of the belly, and six interviewees reported that killer whales will bite the bowhead’s flippers (see Westdal 2009 for similar information from other communities). Inuit observations agree with scientific research and note that smaller bowheads are usually attacked, although several hunters did note that killer whales are capable of killing larger whales, particularly in other areas (e.g., Admiralty Inlet) where they tend to occur in larger groups. Fifteen interviewees reported observations of dead bowhead whales that had been killed by killer whales determined by the condition of the carcass (e.g., bite marks, chunks removed, broken ribs). A total of 32 observations of dead bowheads were reported, and after correcting for overlapping reports, a minimum of 22 different kills were documented (most observed in 1999). Interviewees were asked to estimate how many bowhead whales are typically killed in Foxe Basin each year, and eight provided an opinion. The minimum estimated kill every summer was three to four whales, with a maximum of ten. Overall the responses indicate that on average about five bowhead whales are killed each year in Foxe Basin but in some years many more are killed (Higdon 2009). For example, in 1999 ice conditions were less extensive than usual, and killer whales were more abundant than usual (also see Cosens and Blouw 2003). In that year at least eight dead bowhead whales were discovered, including one fresh enough for Inuit to utilize. However, many hunters (n = 12) felt that current predation rates were not enough to negatively impact the growing bowhead population, although loss of sea ice could result in increased predation pressure on bowhead whales in this area. Photo-Identification In the 1970s, a technique was developed that uses photographs of the dorsal fin and gray saddle patch at the base of the killer whale fin to uniquely identify individual whales (Bigg 1982). The pigmentation, shape and scar pattern on these areas are unique for each whale. Scars in the saddle patch behind the dorsal fin show as clear permanent white or black marks and some whales also have saddle patches with a unique, easily recognizable shape. Nicks, cuts, and tears on the dorsal fin of killer whales also leave semi-permanent marks on the fin. The photo-identification method identified individuals photographed in some of the Hudson Bay sightings and provided inference on movement patterns. Photo-identification studies indicate that there are at least 21 distinct killer whales within the western portion of Hudson Bay (Young et al. in review). There is no evidence of killer whale movements between Hudson Bay and the Baffin Bay, although there have been resightings of the same individuals within a region. Furthermore, the discovery curve, representing the number of new individuals identified each year, has increased linearly from 2004 to 2009 with no clear asymptote, 128 S.H. Ferguson et al. which suggests that the entire killer whale population visiting the Hudson Bay region has not yet been identified. Continued and expanded photo-identification studies will likely refine estimates of the potential killer whale population numbers and distributions in the Canadian Arctic as well as movements between regions. Bioacoustics of Killer Whales and Their Prey Acoustic monitoring studies are become increasingly important in marine mammal science. Bioacoustics can answer many questions such as species and population distribution, abundance and behaviour (Marques et al. 2009; Burtenshaw et al. 2004). For killer whales, acoustic monitoring can detect presence and predation. Killer whale ecotypes in the North Pacific exhibit different acoustic behaviour while hunting; marine mammal eating killer whales reduce communication during prey searching to avoid detection and celebrate successful kills acoustically (Barrett-Lennard et al. 1996; Deecke et al. 2005). Three areas in the Hudson Bay region were chosen for acoustic monitoring during the ice-free season (July–September) from 2006 to 2009 (Fig. 6). Repulse Bay N Seal River Estuary Nelson River Churchill Estuary 0 200 400 600 800 1000 Fig. 6 Location of deployment of AURAL-M2 autonomous recording devices used to record whale acoustic calls The Rise of Killer Whales as a Major Arctic Predator 129 The areas were chosen based on past killer whale sightings and large aggregations of potential prey, including narwhal, beluga, bowhead, and seals. From 2006 to 2009, an AURAL-M2 (Multi-Électronique Inc., Rimouski, Quebec) was deployed in the Seal River Estuary near Churchill, Manitoba. In 2006, an AURAL-M2 was deployed near Repulse Bay, Nunavut and in 2008 and 2009 one was deployed in the Nelson River Estuary, Manitoba. An AURAL-M2 is an autonomous recording device that detects sounds within a frequency range up to 16 kHz, which includes most calls made by killer whales, belugas, bowhead, narwhal, and seals. In 2009 in addition to the AURAL-M2, a C-POD (Chelonia Limited, Cornwall, United Kingdom) was attached to the mooring at the Seal River and Nelson River Estuaries. C-PODs record echolocation clicks produced by toothed whales (killer whales, narwhal, and beluga) that are used for navigation and prey detection. Automated detection algorithms were used by JASCO Inc. to analyze the 2006 to 2008 recordings. Marine mammal calls were detected every day during all deployments however further analysis revealed that there were many false positive detections. Therefore, a more detailed analysis is planned to locate marine mammal calls. Simple Predator–Prey Model Large-bodied predators, such as killer whales, have high caloric demands that require a proportionally large intake of prey. The effect of predation on prey populations depends on predator and prey abundance and distributional overlap in time and space that influences kill rates (Lima and Dill 1990). If killer whales hunt in a focused area or on a particular prey then predation can have significant impact (Williams et al. 2004; Laidre et al. 2006). Anti-predator behaviour in response to killer whales has been observed in marine mammal species in the eastern Canadian Arctic by local residents and researchers. Narwhal and bowheads were observed grouping and swimming close to shore in the presence of killer whales (Finley 1990; Campbell et al. 1988). Narwhal also ceased vocalizing presumably to decrease probability of detection (Campbell et al. 1988). Richard (2005) found extreme aggregations of beluga whales near Churchill, Manitoba most likely in response to seven killer whales observed during the same aerial survey. Inuit have long-recognized fleeing to shallow nearshore waters as a response to killer whale presence (“aarlirijuk”, or “fear of killer whales”, in the south Baffin dialect of Inuktitut; NWMB 2000). We apply a simple demographic model to predict the impact of killer whales on marine mammal prey populations in the greater Hudson Bay region. We chose this type of analysis because direct experimental analyses are logistically intractable due to low densities, rapid movements, and large seasonal ranges of these carnivorous marine predators. Also, killer whales can hunt underwater making direct assessment of foraging behaviour and predator–prey interactions challenging. The simple predator–prey model provides a scenario for possible trophic consequences of the current killer whale population residing in the Hudson Bay region during the ice-free period (Fig. 7). 130 S.H. Ferguson et al. Killer Whales 29% N = 25 34% Narwhal 8% 29% Population size = 5100 Bowhead Beluga Seals Population size = 1525 Population size = 57300 Population size = 516000 Fig. 7 Simple graphic showing prey selection by a group of killer whales in Hudson Bay used to model the possible effects of predation on marine mammal prey populations We use the following assumptions. First, a group of 25 killer whales resides in Hudson Bay area for 3 months (1 July – 30 Sept.). We assume killer whales eat 3% of their body weight per day (2–4%; Kriete 1995; Hickie et al. 2007). The sex-age composition of the killer whale groups using the eastern Canadian Arctic region according to photo-identification work is 26% large males, 60% females or juvenile males, and 14% small young (Young et al. submitted). For 25 whales, this translates into 6.5 males, 15 females (and juvenile males), and 3.5 young killer whales. We assume large males weigh 5000 kg, females (or juvenile males) 2700 kg, and small young whales 1350 kg (Clark et al. 2000). We assume that the sightings database of predation events (Fig. 4) relates directly to amount of prey eaten. The biomass of prey eaten includes the likelihood that a number of beluga and narwhal are killed during an attack whereas only one seal or bowhead is killed during an attack. For the purposes of this scenario, we believe this assumption compensates for the inverse relationship between human observer ability to detect a predation event and prey size. Thus, we assume 29% of killer whale diet consisted of narwhal, 29% beluga, 34% bowhead whale, and 8% seals. The Hudson Bay regional sighting database estimates of predation events are comparable with results for the entire eastern Canadian Arctic (Higdon et al. in review). Further, we assume that during this summer period killer whales eat the majority (50% used in model) of their annual food intake as observed elsewhere for mammal-eating killer whales (Condy et al. 1978, Lopez and Lopez 1985, Baird and Dill 1995). We used the following average weights of prey: for beluga 313 kg, 325 kg for narwhal (Trites and Pauly 1998; but see Heide-Jørgensen and Teilmann 1994 and Garde et al. 2007), 6,000 kg for a calf or juvenile bowhead (Węskawski et al. 2000) and 17,000 kg for a subadult (George et al. 2007), and 69 kg for ringed seals (Krafft et al. 2006). However, we consider that killer whales only eat 40% of a bowhead, 80% of beluga and narwhal, and 90% of seals due to selection of particular The Rise of Killer Whales as a Major Arctic Predator 131 parts and loss of carcass at depths. For the killed and eaten bowhead, we assume killer whales select preferentially mostly (75%) calves and juveniles and some (25%) subadults. We make this assumption due to the novice behaviour and smaller size characteristic of juveniles resulting in reduced energetic costs, time associated with capture, and risk of injury to killer whales. When a large whale is killed, killer whales typically consume only a small amount, leading Martinez and Klinghammer (1970) to report that they “feed very selectively”. Observations of successful kills on a variety of baleen whale species indicate that usually only the tongue, throat area (possibly torn away for access to the tongue), skin, and occasionally a small portion of the blubber are consumed (Hancock 1965; Baldridge 1972; Silber et al. 1990; Jefferson et al. 1991; Ford et al. 2005). In longer feeding events (over several days) more substantial amounts of blubber and other flesh may be consumed (Ford et al. 2005). In many instances dead whales have open wounds on their abdomen with parts of the viscera extruding, although the organs are often uneaten (Hancock 1965; Silber et al. 1990). Observations of killer whales consuming grey whales (Eschrichtius robustus) in Alaskan waters indicate that substantially more of the whale is consumed if the mortality occurs in relatively shallow waters (C. Matkin personal communication 2009). Foxe Basin is relatively shallow and we assume a greater amount of killed bowhead may be consumed, and therefore we chose 40% consumption as a conservative estimate. Similarly, killer whales have been observed killing more monodontids than they eat and only eating part of the carcass (Laidre et al. 2006). Here, we assumed 80% of narwhal and beluga are actually consumed by killer whales. Similar considerations were used to estimate 90% of seals consumed. The results of our simple predation model estimate that a group of 25 killer whales kill and eat 51 bowhead (45.4 calves and 5.3 subadults), 476 narwhal, 495 beluga, and 550 seals each year. Using summarized population estimates, this mortality represents 1% of the available beluga (57,300; Richard 2005) and less than 1% ringed seals (516,000; Stewart and Lockhart 2005), 9% of the narwhal (5,100; DFO 2009), and 3% of the available bowhead. For bowhead we used the population estimate provided by the International Whaling Commission Scientific Committee, who agreed on a fully corrected strip transect estimate of 1,525 (333–6,990) whales for Hudson Bay–Foxe Basin in 2004 (IWC 2009) using 0.24 correction according to Heide-Jørgensen et al. (2007). An additional consideration is that the bowheads in Foxe Basin and Hudson Bay are part of the larger East Canada-West Greenland bowhead population (COSEWIC 2009) of approximately 6,344 whales. Wade (1998) suggested using 4% as the intrinsic population growth rate for cetaceans which would suggest that killer whale predation in the Hudson Bay region has the potential to limit narwhal population growth. Altering the risk of predation by age classes changes these calculations considerably. If juvenile marine mammal prey is selected, as assumed for bowhead whales, then greater numbers of monodontid whales and seals are needed for killer whale consumption (due to smaller size of prey). To summarize, we consider the formulated predation model to be overly simplistic and based on numerous untested assumptions. The results should not be used as a realistic model of the Hudson Bay killer whale predation system. Instead, we consider these preliminary results necessary 132 S.H. Ferguson et al. to foster interest in gathering the information required to appropriately assess possible impact of killer whale predation on prey populations. Conclusion Our research provides confirmation of the added value of combining Inuit Traditional Knowledge with western science in understanding the activities of a cryptic predator living at low densities and capable of moving rapidly across vast scales. Also, combining methods such as sighting reports, photographic identification, acoustic research, and oral knowledge can significantly improve our understanding of complex processes such as the ecosystem effects of killer whale activity in Hudson Bay. The spatial and temporal occurrence of killer whales is related to predictable and abundant prey resources (Nichol and Shackleton 1996). Killer whale predation has been cited as a potential factor in the decline of several marine mammal populations (Guinet et al. 1992; Keith et al. 2001; Estes et al. 1998; Springer et al. 2003, 2008; but see DeMaster et al. 2006; Wade et al. 2007). We emphasize the need for longterm studies and direct observation of killer whale hunting behaviour to determine the factors that influence prey choice. However, by defining population energetic requirements and considering population demography of prey, we can begin to assess the basic requirements of predator–prey dynamics in Hudson Bay marine ecosystem. 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