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ABSTRACT: Ultrasonic whistles were previously found in North Atlantic killer whales and were suggested to occur in eastern North Pacific killer whales based on the data from autonomous recorders. In this study ultrasonic whistles were found in the recordings from two encounters with the eastern North Pacific offshore ecotype killer whales and one encounter with the western North Pacific killer whales of unknown ecotype. All ultrasonic whistles were highly stereotyped and all but two had downsweep contours. These results demonstrate that specific sound categories can be shared by killer whales from different ocean basins.
The Journal of the Acoustical Society of America 12/2012; 132(6):3618-21. · 1.55 Impact Factor
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ABSTRACT: The development of an area-based polychlorinated biphenyl (PCB) food-web bioaccumulation model enabled a critical evaluation of the efficacy of sediment quality criteria and prey tissue residue guidelines in protecting fish-eating resident killer whales of British Columbia and adjacent waters. Model-predicted and observed PCB concentrations in resident killer whales and Chinook salmon were in good agreement, supporting the model's application for risk assessment and criteria development. Model application shows that PCB concentrations in the sediments from the resident killer whale's Critical Habitats and entire foraging range leads to PCB concentrations in most killer whales that exceed PCB toxicity threshold concentrations reported for marine mammals. Results further indicate that current PCB sediment quality and prey tissue residue criteria for fish-eating wildlife are not protective of killer whales and are not appropriate for assessing risks of PCB-contaminated sediments to high trophic level biota. We present a novel methodology for deriving sediment quality criteria and tissue residue guidelines that protect biota of high trophic levels under various PCB management scenarios. PCB concentrations in sediments and in prey that are deemed protective of resident killer whale health are much lower than current criteria values, underscoring the extreme vulnerability of high trophic level marine mammals to persistent and bioaccumulative contaminants.
Environmental Science & Technology 10/2012; · 4.80 Impact Factor
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ABSTRACT: Human evolution has clearly been shaped by gene–culture interactions, and there is growing evidence that similar processes also act on populations of non-human animals. Recent theoretical studies have shown that culture can be an important evolutionary mechanism because of the ability of cultural traits to spread rapidly both vertically, obliquely, and horizontally, resulting in decreased within-group variance and increased between-group variance. Here, we collate the extensive literature on population divergence in killer whales (Orcinus orca), and argue that they are undergoing ecological speciation as a result of dietary specializations. Although we cannot exclude the possibility that cultural divergence pre-dates ecological divergence, we propose that cultural differences in the form of learned behaviours between ecologically divergent killer whale populations have resulted in sufficient repro-ductive isolation even in sympatry to lead to incipient speciation.
Biological Journal of the Linnean Society 05/2012; 106(1):1-17. · 2.19 Impact Factor
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ABSTRACT: Killer whales in the NE Pacific Ocean are among the world's most PCB-contaminated marine mammals, raising concerns about implications for their health. Sixteen health-related killer whale mRNA transcripts were analyzed in blubber biopsies collected from 35 free-ranging killer whales in British Columbia using real-time quantitative polymerase chain reaction. We observed PCB-related increases in the expression of five gene targets, including the aryl hydrocarbon receptor (AhR; r(2) = 0.83; p < 0.001), thyroid hormone α receptor (TRα; r(2) = 0.64; p < 0.001), estrogen α receptor (ERα; r(2) = 0.70; p < 0.001), interleukin 10 (IL-10; r(2) = 0.74 and 0.68, males and females, respectively; p < 0.001), and metallothionein 1 (MT1; r(2) = 0.58; p < 0.001). Best-fit models indicated that population (dietary preference), age, and sex were not confounding factors, except for IL-10, where males differed from females. While the population-level consequences are unclear, the PCB-associated alterations in mRNA abundance of such pivotal end points provide compelling evidence of adverse physiological effects of persistent environmental contaminants in these endangered killer whales.
Environmental Science & Technology 12/2011; 45(23):10194-202. · 4.80 Impact Factor
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Marine Mammal Science 11/2011; 27:793-818. · 1.61 Impact Factor
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ABSTRACT: Northern resident killer whale pods (Orcinus orca) have distinctive stereotyped pulsed call repertoires that can be used to distinguish groups acoustically. Repertoires are generally stable, with the same call types comprising the repertoire of a given pod over a period of years to decades. Previous studies have shown that some discrete pulsed calls can be subdivided into variants or subtypes. This study suggests that new stereotyped calls may result from the gradual modification of existing call types through subtypes. Vocalizations of individuals and small groups of killer whales were collected using a bottom-mounted hydrophone array in Johnstone Strait, British Columbia in 2006 and 2007. Discriminant analysis of slope variations of a predominant call type, N4, revealed the presence of four distinct call subtypes. Similar to previous studies, there was a divergence of the N4 call between members of different matrilines of the same pod. However, this study reveals that individual killer whales produced multiple subtypes of the N4 call, indicating that divergence in the N4 call is not the result of individual differences, but rather may indicate the gradual evolution of a new stereotyped call.
The Journal of the Acoustical Society of America 02/2011; 129(2):1067-72. · 1.55 Impact Factor
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ABSTRACT: ABSTRACT We estimated carrying capacity for sea otters (Enhydra lutris) in the coastal waters of British Columbia, Canada, by characterizing habitat according to the complexity of nearshore intertidal and sub-tidal contours. We modeled the total area of complex habitat on the west coast of Vancouver Island by first calculating the complexity of the Checleset Bay-Kyuquot Sound (CB-KS) region, where sea otters have been at equilibrium since the mid-1990s. We then identified similarly complex areas on the west coast of Vancouver Island (WCVI model), and adapted the model to identify areas of similar complexity along the entire British Columbia coast (BC model). Using survey data from the CB-KS region, we calculated otter densities for the habitat predicted by the 2 models. The density estimates for CB-KS were 3.93 otters/km2 and 2.53 otters/km2 for the WCVI and BC models, respectively, and the resulting 2 estimates of west coast of Vancouver Island complex habitat carrying capacity were not significantly different (WCVI model: 5,123, 95% CI = 3,337–7,104; BC model: 4,883, 95% CI = 3,223–6,832). The BC model identified the region presently occupied by otters on the central British Columbia coast, but the amount of coast-wide habitat it predicted (5,862 km2) was relatively small, and the associated carrying capacity estimate (14,831, 95% CI = 9,790–20,751) was low compared to historical accounts. We suggest that our model captured a type of high-quality or optimum habitat prevalent on the west coast of Vancouver Island, typified by the CB-KS region, and that suitable sea otter habitat elsewhere on the coast must include other habitat characteristics. We therefore calculated a linear, coast-wide carrying capacity of 52,459 sea otters (95% CI = 34,264–73,489)—a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.
Journal of Wildlife Management 12/2010; 72(2):382 - 388. · 1.52 Impact Factor
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Marine Mammal Science 09/2010; 27(4):793-818. · 1.61 Impact Factor
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ABSTRACT: A few species of mammals produce group-specific vocalisations that are passed on by learning, but the function of learned vocal variation remains poorly understood. Resident killer whales live in stable matrilineal groups with repertoires of seven to 17 stereotyped call types. Some types are shared among matrilines, but their structure typically shows matriline-specific differences. Our objective was to analyse calls of nine killer whale matrilines in British Columbia to test whether call similarity primarily reflects social or genetic relationships. Recordings were made in 1985-1995 in the presence of focal matrilines that were either alone or with groups with non-overlapping repertoires. We used neural network discrimination performance to measure the similarity of call types produced by different matrilines and determined matriline association rates from 757 encounters with one or more focal matrilines. Relatedness was measured by comparing variation at 11 microsatellite loci for the oldest female in each group. Call similarity was positively correlated with association rates for two of the three call types analysed. Similarity of the N4 call type was also correlated with matriarch relatedness. No relationship between relatedness and association frequency was detected. These results show that call structure reflects relatedness and social affiliation, but not because related groups spend more time together. Instead, call structure appears to play a role in kin recognition and shapes the association behaviour of killer whale groups. Our results therefore support the hypothesis that increasing social complexity plays a role in the evolution of learned vocalisations in some mammalian species.
Naturwissenschaften 03/2010; 97(5):513-8. · 2.28 Impact Factor
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ABSTRACT: Resident killer whales in the coastal waters of British Columbia and Washington are heavily
contaminated with persistent organic pollutants (POPs), including polychlorinated biphenyls
(PCBs). The northern and southern populations of resident killer whales are listed, respectively,
as threatened and endangered under the Canadian Species at Risk Act (SARA), which protects
species at risk from being killed or harmed (section 32) and protects any part of their Critical
Habitat from destruction (section 58). The Resident Killer Whale Recovery Strategy identified
contaminants, reduced prey and disturbance (noise and physical) as threats to population
recovery.
Sediment dredged from the lower Fraser River and other locations is periodically disposed of at
marine sites in coastal British Columbia, both within and outside killer whale Critical Habitat.
Ocean disposal is regulated by Environment Canada under the Canadian Environmental
Protection Act (CEPA). Sediments contain complex mixtures of contaminants, and material
intended to be disposed of at sea is screened for a select list contaminants. Because killer
whales are long-lived and occupy a very high trophic level, they are at particular risk to
accumulating high concentrations of PCBs and related compounds.
This report provides a response to the following questions identified by Fisheries and Oceans
Canada SARA and Habitat Managers: Are current Ocean Disposal Rejection/Screening Limits
for environmental contaminants (including PCBs, mercury and PAHs) under CEPA 1999
adequate to prevent northern and southern resident killer whale Critical Habitat from
destruction, as required by SARA Section 58?; and, Do PCBs in materials deposited in any area
of killer whale habitat increase the risk of harm or mortality of northern and southern resident
killer whales, as required by SARA Section 32?
In order to answer these questions given the complexity of killer whale ecology and that of their
primary prey (Chinook salmon), we developed a novel food web modeling tool. This effort
includes the following components: i) the designation of seven geographic areas that relate to
management-related priorities (e.g. Critical Habitat) and/or international boundaries in the NE
Pacific Ocean; ii) an assignment of time spent in each of these areas by southern and northern
resident killer whales and their prey (Chinook salmon and non-salmonid species) based on best
available information; iii) the adaptation of sediment-biota PCB bioaccumulation models to killer
whales and their prey; iv) a compartmentalized approach to modeling sediment-food web
uptake of PCBs within each of the seven areas identified so as to be able to evaluate sitespecific
impacts of disposal operations; and v) a comparison of model outcomes to three
established health effects thresholds for PCBs in marine mammals. The modeling approach is
based on the distribution of PCBs among sediments, the water column, and biota, and
estimates concentrations that will accumulate in animals throughout a lifetime of exposure. This
model does not evaluate the existing PCB distribution and pathways in the BC abiotic
environment, but rather predicts the incremental consequences to killer whales of altering
bottom sediments to reflect PCB concentrations following a series of disposal scenarios.
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Our model indicates that disposal of material with PCB concentrations lower than those in the
ambient sediments in the disposal sites would not increase PCB delivery to killer whales.
However, the disposal of sediments into Critical Habitat sites from some of the more
contaminated sites for which data are available could increase the PCB concentrations in killer
whales by as much as 8%. These predictions assume that the sediments and water were in
equilibrium, and that the Strait of Georgia was a closed system. Some processes may decrease
uptake of PCBs by the food web relative to the model result (e.g. burial by sedimentation and
exchange with the open ocean), while others may increase the uptake (e.g. direct uptake of
PCBs by food web during disposal operations).
Under current practices, the scrutiny and approval of disposal applications in the Pacific Region
is constrained by shortcomings in analytical measurement standards and by the definition of the
CEPA Action Level based on only effects at low trophic levels. High Resolution instrumental
analysis would reduce Detection Limits by up to 350 times, and improve risk management
assessment of disposal applications. The current CEPA Action Level is too high to protect killer
whales because PCBs biomagnify. Disposal of sediment containing PCBs at a concentration
matching the current CEPA Action Level could hypothetically lead to a 32-fold increase in PCB
levels in male southern resident killer whales.
We derived a sediment PCB concentration range that would protect 95% of resident killer
whales of 0.012 to 0.200 μg·kg-1, dry weight. Results reveal the profound vulnerability of killer
whales to accumulation of persistent contaminants, since only 4/61 (6.6%) sediment sites for
which we have PCB measurements in BC and Washington State fall below the least protective
of these sediment values. This suggests that there continues to be widespread contamination of
resident killer whale habitat by the legacy PCBs.
This newly developed food web model can be employed as a risk management tool in support
of SARA protections for killer whales. We suggest that the ambient sediment PCB concentration
becomes an important benchmark for a management-based evaluation of risks to killer whales
and to killer whale Critical Habitat. Disposal of materials with PCB concentrations lower than
ambient in Critical Habitat in areas of high sedimentation will not increase sediment PCB
concentrations, might help to bury contaminated sediments, and should not lead to increased
PCB concentrations in killer whales. The decision about whether or not to dispose of materials
with PCB concentrations that exceed ambient levels in the marine environment, particularly in
Critical Habitat, will have consequences for killer whales.
Can. Sci. Advis. Sec. Res. Doc. 01/2010;
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ABSTRACT: Blue whales were widely distributed in the North Pacific prior to the primary period of modern commercial whaling in the early 1900s. Despite concentrations of blue whale catches off British Columbia and in the Gulf of Alaska, there had been few documented sightings in these areas since whaling for blue whales ended in 1965. In contrast, large concentrations of blue whales have been documented off California and Baja California and in the eastern tropical Pacific since the 1970s, but it was not known if these animals were part of the same population that previously ranged into Alaskan waters. We document 15 blue whale sightings off British Columbia and in the Gulf of Alaska made since 1997, and use identification photographs to show that whales in these areas are currently part of the California feeding population. We speculate that this may represent a return to a migration pattern that has existed for earlier periods for eastern North Pacific blue whale population. One possible explanation for a shift in blue whale use is changes in prey driven by changes in oceanographic conditions, including the Pacific Decadal Oscillation (PDO), which coincides with some of the observed shifts in blue whale occurrence.
Marine Mammal Science 09/2009; 25(4):816 - 832. · 1.61 Impact Factor
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ABSTRACT: A dataset of killer whale female (mother), juvenile, and calf vocalizations was collected with a hydrophone array in Johnstone Strait in the summers of 2006 and 2007. The vocalizations were spatially and temporally localized together with behavioral observations. The analysis is focused on pulsed call production variation when a mother is with her juvenile(s) andor calf and when she is separated from one or more of them. Analysis is centered on the frequency-time structure of the vocalizations. This circumstance provides a unique opportunity to gain insight into the communication between individuals within a common social subset of a matriline or pod. This subset is characteristically tighter in association than many other intramatrilineal groups and can offer a glimpse into early vocal exchange and development.
The Journal of the Acoustical Society of America 11/2008; 124(4):2507. · 1.55 Impact Factor
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ABSTRACT: Combining different stereotyped vocal signals into specific sequences increases the range of information that can be transferred between individuals. The temporal emission pattern and the behavioral context of vocal sequences have been described in detail for a variety of birds and mammals. Yet, in cetaceans, the study of vocal sequences is just in its infancy. Here, we provide a detailed analysis of sequences of stereotyped whistles in killer whales off Vancouver Island, British Columbia. A total of 1140 whistle transitions in 192 whistle sequences recorded from resident killer whales were analyzed using common spectrographic analysis techniques. In addition to the stereotyped whistles described by Riesch et al., [(2006). "Stability and group specificity of stereotyped whistles in resident killer whales, Orcinus orca, off British Columbia," Anim. Behav. 71, 79-91.] We found a new and rare stereotyped whistle (W7) as well as two whistle elements, which are closely linked to whistle sequences: (1) stammers and (2) bridge elements. Furthermore, the frequency of occurrence of 12 different stereotyped whistle types within the sequences was not randomly distributed and the transition patterns between whistles were also nonrandom. Finally, whistle sequences were closely tied to close-range behavioral interactions (in particular among males). Hence, we conclude that whistle sequences in wild killer whales are complex signal series and propose that they are most likely emitted by single individuals.
The Journal of the Acoustical Society of America 10/2008; 124(3):1822-9. · 1.55 Impact Factor
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Margaret M Krahn,
M Bradley Hanson,
Robin W Baird,
Richard H Boyer,
Douglas G Burrows,
Candice K Emmons, John K B Ford,
Linda L Jones,
Dawn P Noren,
Peter S Ross,
Gregory S Schorr,
Tracy K Collier
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ABSTRACT: "Southern Resident" killer whales include three "pods" (J, K and L) that reside primarily in Puget Sound/Georgia Basin during the spring, summer and fall. This population was listed as "endangered" in the US and Canada following a 20% decline between 1996 and 2001. The current study, using blubber/epidermis biopsy samples, contributes contemporary information about potential factors (i.e., levels of pollutants or changes in diet) that could adversely affect Southern Residents. Carbon and nitrogen stable isotopes indicated J- and L-pod consumed prey from similar trophic levels in 2004/2006 and also showed no evidence for a large shift in the trophic level of prey consumed by L-pod between 1996 and 2004/2006. Sigma PCBs decreased for Southern Residents biopsied in 2004/2006 compared to 1993-1995. Surprisingly, however, a three-year-old male whale (J39) had the highest concentrations of Sigma PBDEs, Sigma HCHs and HCB. POP ratio differences between J- and L-pod suggested that they occupy different ranges in winter.
Marine Pollution Bulletin 01/2008; 54(12):1903-11. · 2.50 Impact Factor
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ABSTRACT: Polychlorinated biphenyl (PCB) concentrations declined rapidly in environmental compartments and most biota following implementation of regulations in the 1970s. However, the metabolic recalcitrance of PCBs may delay responses to such declines in large, long-lived species, such as the endangered and highly PCB-contaminated resident killer whales (Orcinus orca) of the Northeastern Pacific Ocean. To investigate the influence of life history on PCB-related health risks, we developed models to estimate PCB concentrations in killer whales during the period from 1930 forward to 2030, both within a lifetime (approximately 50 years) and across generations, and then evaluated these in the context of health effects thresholds established for marine mammals. Modeled PCB concentrations in killer whales responded slowly to changes in loadings to the environment as evidenced by slower accumulation and lower magnitude increases in PCB concentrations relative to prey, and a delayed decline that was particularly evident in adult males. Since PCBs attained peak levels well above the effects threshold (17 mg/kg lipid) in approximately 1969, estimated concentrations in both the northern and the more contaminated southern resident populations have declined gradually. Projections suggest that the northern resident population could largely fall below the threshold concentration by 2030 while the endangered southern residents may not do so until at least 2063. Long-lived aquatic mammals are therefore not protected from PCBs by current dietary residue guidelines.
Environmental Science and Technology 10/2007; 41(18):6613-9. · 5.23 Impact Factor
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Paul R. Wade,
Vladimir N. Burkanov,
Marilyn E. Dahlheim,
Nancy A. Friday,
Lowell W. Fritz,
Thomas R. Loughlin,
Sally A. Mizroch,
Marcia M. Muto,
Dale W. Rice,
Lance G. Barrett-Lennard, [......], John K. B. Ford,
Jeff K. Jacobsen,
Craig O. Matkin,
Dena R. Matkin,
Amee V. Mehta,
Robert J. Small,
Janice M. Straley,
Shannon M. McCluskey,
Glenn R. VanBlaricom,
Phillip J. Clapham
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ABSTRACT: Springer et al. (2003) contend that sequential declines occurred in North Pacific populations of harbor and fur seals, Steller sea lions, and sea otters. They hypothesize that these were due to increased predation by killer whales, when industrial whaling's removal of large whales as a supposed primary food source precipitated a prey switch. Using a regional approach, we reexamined whale catch data, killer whale predation observations, and the current biomass and trends of potential prey, and found little support for the prey-switching hypothesis. Large whale biomass in the Bering Sea did not decline as much as suggested by Springer et al., and much of the reduction occurred 50–100 yr ago, well before the declines of pinnipeds and sea otters began; thus, the need to switch prey starting in the 1970s is doubtful. With the sole exception that the sea otter decline followed the decline of pinnipeds, the reported declines were not in fact sequential. Given this, it is unlikely that a sequential megafaunal collapse from whales to sea otters occurred. The spatial and temporal patterns of pinniped and sea otter population trends are more complex than Springer et al. suggest, and are often inconsistent with their hypothesis. Populations remained stable or increased in many areas, despite extensive historical whaling and high killer whale abundance. Furthermore, observed killer whale predation has largely involved pinnipeds and small cetaceans; there is little evidence that large whales were ever a major prey item in high latitudes. Small cetaceans (ignored by Springer et al.) were likely abundant throughout the period. Overall, we suggest that the Springer et al. hypothesis represents a misleading and simplistic view of events and trophic relationships within this complex marine ecosystem.
Marine Mammal Science 09/2007; 23(4):766 - 802. · 1.61 Impact Factor
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ABSTRACT: We describe an experiment conducted to assess the impact of the sound generated by an acoustic harassment device (AHD) on the relative abundance and distribution of harbor porpoises (Phocoena phocoena) in Retreat Passage, British Columbia. During control periods when the AHD was inactive, the mean number of porpoises observed in the study area was 0.39 for broad area scans conducted with the naked eye and 0.48 for narrow sector scans conducted with binoculars. Abundance declined precipitously when the AHD was activated, to 0.007 porpoises per broad area scan and 0.018 per narrow sector scan. The mean number of porpoise resightings while tracking their movements also declined from 12.2 to 13.6 per sighting during control periods to 1.1–1.9 per sighting when the AHD was activated, which suggested that the few porpoises that ventured into the study area spent less time within it when the AHD was activated. The effect of the AHD diminished with distance. No porpoises were observed within 200 m of the AHD when it was activated. The number of sightings and resightings observed when it was activated was less than 0.2% of the number expected had there been no AHD effect at a range of 200–399 m, 1.4% the number expected at a range of 400–599 m, varied between 2.5% and 3.3% of the number expected at a range of 600–2,499 m, and was 8.1% the number expected at a range of 2,500–3,500 m, which suggested that the impact of the AHD extended beyond our maximum sighting range of 3.5 km.
Marine Mammal Science 08/2006; 18(4):843 - 862. · 1.61 Impact Factor
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ABSTRACT: The hypothesis that commercial whaling caused a sequential megafaunal collapse in the North Pacific Ocean by forcing killer whales to eat progressively smaller species of marine mammals is not supported by what is known about the biology of large whales, the ecology of killer whales, and the patterns of ecosystem change that took place in Alaska, British Columbia, and elsewhere in the world following whaling. A comparative analysis shows that populations of seals, sea lions, and sea otters increased in British Columbia following commercial whaling, unlike the declines noted in the Gulf of Alaska and Aleutian Islands. The declines of seals and sea lions that began in western Alaska around 1977 were mirrored by increases in numbers of these species in British Columbia. A more likely explanation is that the seal and sea lion declines and other ecosystem changes in Alaska stem from a major oceanic regime shift that occurred in 1977. Killer whales are unquestionably a significant predator of seals, sea lions, and sea otters—but not because of commercial whaling.
Marine Mammal Science 07/2006; 23(4):751 - 765. · 1.61 Impact Factor
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ABSTRACT: Resident killer whales off British Columbia form four acoustically distinct clans, each with a unique dialect of discrete pulsed calls. Three clans belong to the northern and one to the southern community. Resident killer whales also produce tonal whistles, which play an important role in close-range communication within the northern community. However, there has been no comparative analysis of repertoires of whistles across clans. We investigated the structural characteristics, stability and group specificity of whistles in resident killer whales off British Columbia. Acoustic recordings and behavioural observations were made between 1978 and 2003. Whistles were classified spectrographically and additional observers were used to confirm our classification. Whistles were compared across clans using discriminant function analysis. We found 11 types of stereotyped whistles in the northern and four in the southern community with some of the whistle types being stable over at least 13 years. In northern residents, 10 of the 11 whistle types were structurally identical in two of the three acoustic clans, whereas the whistle types of southern residents differed clearly from those of the northern residents. Our study shows that killer whales that have no overlap in their call repertoire use essentially the same set of stereotyped whistles. Shared stereotyped whistles might provide a community-level means of recognition that facilitates association and affiliation of members of different clans, which otherwise use distinct signals. We further suggest that vocal learning between groups plays an important role in the transmission of whistle types.
Animal Behaviour 01/2005; 71(1):79-91. · 3.49 Impact Factor
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ABSTRACT: Fish-eating "resident"-type killer whales (Orcinus orca) that frequent the coastal waters off northeastern Vancouver Island, Canada have a strong preference for chinook salmon (Oncorhynchus tshawytscha). The whales in this region often forage along steep cliffs that extend into the water, echolocating their prey. Echolocation signals of resident killer whales were measured with a four-hydrophone symmetrical star array and the signals were simultaneously digitized at a sample rate of 500 kHz using a lunch-box PC. A portable VCR recorded the images from an underwater camera located adjacent to the array center. Only signals emanating from close to the beam axis (1185 total) were chosen for a detailed analysis. Killer whales project very broadband echolocation signals (Q equal 0.9 to 1.4) that tend to have bimodal frequency structure. Ninety-seven percent of the signals had center frequencies between 45 and 80 kHz with bandwidths between 35 and 50 kHz. The peak-to-peak source level of the echolocation signals decreased as a function of the one-way transmission loss to the array. Source levels varied between 195 and 224 dB re: 1 microPa. Using a model of target strength for chinook salmon, the echo levels from the echolocation signals are estimated for different horizontal ranges between a whale and a salmon. At a horizontal range of 100 m, the echo level should exceed an Orcinus hearing threshold at 50 kHz by over 29 dB and should be greater than sea state 4 noise by at least 9 dB. In moderately heavy rain conditions, the detection range will be reduced substantially and the echo level at a horizontal range of 40 m would be close to the level of the rain noise.
The Journal of the Acoustical Society of America 03/2004; 115(2):901-9. · 1.55 Impact Factor
