Article

Killer whale attacks on minke whales: Prey capture and antipredator tactics

Authors:
  • Fisheries and Oceans Canada, Pacific Biological Station
  • Cook Islands Whale Research Center
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Abstract

We describe nine incidents of predation or attempted predation of minke whales (Balaenoptera acutorostrata) by mammal-hunting “transient” killer whales (Orcinus orca) in coastal waters of British Columbia, Washington, and southeastern Alaska. Pursuits of minke whales were characterized by prolonged chases on a straight heading at velocities of 15–30 km/h. In four of the nine cases the adultsized minke whale gradually outdistanced the killer whales, which abandoned the high-speed pursuit after 0.5–1 h. In one case the minke beached itself and died. Four attacks were successful. In one instance a subadult minke was killed in open water following a chase. In two cases the fleeing minke entered a confined bay and was killed by the killer whales. One adult minke was taken after apparently attempting to seek cover beside a large sailboat. Minke whales made no attempt to physically defend themselves and were killed by repeated ramming or by asphyxiation. Although killer whales are capable of sprinting speeds greater than those of minke whales, it appears that adult minkes can maintain higher sustained speeds and evade capture if sufficient space for an extended escape trajectory is available. Successful predation of minke whales in coastal waters is rare compared to pinnipeds and small cetaceans, the main prey of transient killer whales.

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... These responses may be broadly categorised as fight, flight, or stealth strategies (Ford and Reeves, 2008). They can be expressed at the individual (individual escape manoeuvres: Ford et al., 2005;Whitford et al., 2017) or the collective scale, in same-species groups (group silencing in beaked whales: Soto et al., 2018) or mixed-species assemblages (Hurd, 1996;Dutour et al., 2017). According to their timing within a predator attack, we distinguish primary and secondary responses: ...
... However, if the killer whales catch up to them, they exhibit little or no defence: they may roll belly up so as to get their appendages out of the attackers' reach (Jefferson et al., 1991;Ford et al., 2005;Ford and Reeves, 2008). Many species incorporate stealth in their responses to killer whale attacks: silencing (Jefferson et al., 1991;Laidre et al., 2006;Soto et al., 2018) or hiding in the shallows or in kelp beds, and behind ice clocks and boats (Jefferson et al., 1991). ...
... Resident killer whales produce clicks and calls in almost all behavioural contexts (Morton, 1990), while transient killer whales are only vocal during attacks, after a kill, 49 and when socialising at the surface (Deecke et al., 2005;Ford et al., 2005;Riesch and Deecke, 2011). In particular, resident killer whales rely on echolocation clicks to find their prey (Simon et al., 2007), while transient killer whale remain silent until the attack when hunting (Barrett-Lennard et al., 1996;Deecke et al., 2005). ...
Thesis
It is crucial for animals to use environmental stimuli to locate and evaluate the quality of resources and threats present in their surroundings. In the ocean, acoustic stimuli are privileged. Cetaceans are susceptible to detect acoustic stimuli produced by a multitude of sources, including other cetacean species and anthropogenic sources. I studied the behavioural responses of two cetacean species, the humpback whale and the long-finned pilot whale, to natural and anthropogenic acoustic stimuli (respectively killer whale sounds and naval sonars). I found that humpback whales were able to discriminate between the sounds of different killer whale ecotypes. I developed an unsupervised classification algorithm which takes into account the graded nature of animal vocalisations, and used this algorithm to describe the vocal responses of long-finned pilot whales to killer whale sounds and naval sonars.
... The redistribution kernel accounted for the sequential dependence between telemetry fixes, using a kernel intensity surface to represent the approximate probability of displacements of different lengths away from the animal's simulated position at the time step t − 1. A kernel intensity surface for each time step was estimated based on Equation 4.49 of Hooten et al. (2017), with parameters of (1) maximum sustained travel speeds (defined a priori at 15 km h −1 for both species based on the speed measurements of Ford et al. 2005 andNoad &Cato 2007); (2) the durations of the time step between t and t − 1; and (3) the distances from the animals' positions at time step t − 1 to each other point in the spatial grid. These individual kernel intensity surfaces, which in shape approximately resemble a bivariate normal distribution (Johnson et al. 2013), were summed across each time step in each individual's track to derive an overall redistribution kernel surface for each simulated track (n = 10). ...
... Humpback whale decision making is largely focused on foraging, whereas AMWs must balance foraging with the risks associated with predation (e.g. Brown et al. 1999, Laundré et al. 2010. Predation by killer whales is thought to occur primarily in open water (Fearnbach et al. 2019), where AMWs are chased to the point of exhaustion (Ford et al. 2005). Nearshore bays act to consolidate sea ice and brash ice produced from calving glaciers, creating more suitable habitat for AMWs to avoid predation. ...
Article
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Understanding how closely related, sympatric species distribute themselves relative to their environment is critical to understanding ecosystem structure and function and predicting effects of environmental variation. The Antarctic Peninsula supports high densities of krill and krill consumers; however, the region is warming rapidly, with unknown consequences. Humpback whales Megaptera novaeangliae and Antarctic minke whales Balaenoptera bonaerensis are the largest krill consumers here, yet key data gaps remain about their distribution, behavior, and interactions and how these will be impacted by changing conditions. Using satellite telemetry and novel spatial point-process modeling techniques, we quantified habitat use of each species relative to dynamic environmental variables and determined overlap in core habitat areas during summer months when sea ice is at a minimum. We found that humpback whales ranged broadly over continental shelf waters, utilizing nearshore bays, while minke whales restricted their movements to sheltered bays and areas where ice is present. This presents a scenario where minke whale core habitat overlaps substantially with the broader home ranges of humpback whales. While there is no indication that prey is limiting in this ecosystem, increased overlap between these species may arise as climate-driven changes that affect the extent, timing, and duration of seasonal sea ice decrease the amount of preferred foraging habitat for minke whales while concurrently increasing it for humpback whales. Our results provide the first quantitative assessment of behaviorally based habitat use and sympatry between these 2 krill consumers and offers insight into the potential effects of a rapidly changing environment on the structure and function of a polar ecosystem.
... Cetaceans may respond to human disturbance as they do against natural predators (e.g., killer whales) (Christiansen and Lusseau, 2012). Some species of baleen whales maintain high and sustained speeds to avoid killer whale attacks (Ford et al., 2005;Ford and Reeves, 2008). When chased by orcas, minke whales can keep high velocities for several hours (ca. ...
... 8.5 h) over large distances (ca. 18 km) (Ford et al., 2005). Humpback whales may physical defense themselves when confronting predators. ...
Article
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Interactions between whale-watching boats and cetaceans can lead to changes in their behavior. From a management perspective, it is important to understand how this type of disturbance can be translated into physiological effects, such as changes in their energetic metabolism. Humpback whales (Megaptera novaeangliae) typically do not feed while in breeding grounds, thus they depend on finite energy reserves. The effect of whale-watching boats on the energetic metabolism of humpback whales, in the breeding ground of northern Peru (4 • 10 35 S, 81 • 08 03 W) was evaluated. Groups of humpback whales were tracked from land, under the following scenarios: with, without, and before-during-after the presence of whale-watching boats. Mass-specific cost of transport (COT) was used as a proxy of energetic efficiency and calculated from swimming speed and breath frequency estimations. No differences were detected in breath frequency, swimming speed, and COT when comparing whales with and without boats. However, in the presence of boats, swim speed increased, and COT decreased as the number of boats increased. Exponential increment in breathing frequency at higher swimming speed was not detected. The absence of swimming speeds beyond the assumed optimal range suggested no shifts into metabolic inefficiency. Our results suggest optimal swimming speed between 2 and 4.05 m/s, representing COT values between 0.020 and 0.041 J × (kg × m) −1. In light of our results, we encourage the implementation of regulations of the activity, particularly limiting the number of boats interacting with the same group of humpback whales.
... From the point of view of other cetacean species, the killer whale can be, thus, considered as both a potential predator and/or a competitor for resources (e.g., habitat and prey). A wide variety of observed interactions have been reported between killer whales and other cetaceans (Jefferson et al. 1991) ranging from avoidance behavior (e.g., in beluga whales, Fish and Vania 1971), physical attacks (e.g., in gray whales, Ford et al. 2005), and feeding associations with approach responses (in humpback whales: Pitman et al. 2015;. To date, at least ten different forms of killer whales, also called "ecotypes", have been recognized. ...
... Moreover, herring-feeding killer whales stun herring using their flukes, which produces an audible signal (Simon et al. 2005(Simon et al. , 2007. By contrast, mammal-eating killer whales are usually quiet at the early stage of a hunt, i.e., before attacking, probably to remain undetectable by their prey, and increase their vocalization rate (mainly calls and whistles) once the attack has been engaged, likely to coordinate group members and maintain group cohesion (Ford et al. 2005;Deecke et al. 2011). The fundamental frequency of calls of mammal-eating killer whales is slightly lower than those of fish-eating killer whales (Filatova et al. 2015). ...
Article
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Killer whales (KW) may be predators or competitors of other cetaceans. Since their foraging behavior and acoustics differ among populations (‘ecotypes’), we hypothesized that other cetaceans can eavesdrop on KW sounds and adjust their behavior according to the KW ecotype. We performed playback experiments on long-finned pilot whales (Globicephala melas) in Norway using familiar fish-eating KW sounds (fKW) simulating a sympatric population that might compete for foraging areas, unfamiliar mammal-eating KW sounds (mKW) simulating a potential predator threat, and two control sounds. We assessed behavioral responses using animal-borne multi-sensor tags and surface visual observations. Pilot whales barely changed behavior to a broadband noise (CTRL−), whereas they were attracted and exhibited spyhops to fKW, mKW, and to a repeated-tonal upsweep signal (CTRL+). Whales never stopped nor started feeding in response to fKW, whereas they reduced or stopped foraging to mKW and CTRL+. Moreover, pilot whales joined other subgroups in response to fKW and CTRL+, whereas they tightened individual spacing within group and reduced time at surface in response to mKW. Typical active intimidation behavior displayed to fKW might be an antipredator strategy to a known low-risk ecotype or alternatively a way of securing the habitat exploited by a heterospecific sympatric population. Cessation of feeding and more cohesive approach to mKW playbacks might reflect an antipredator behavior towards an unknown KW ecotype of potentially higher risk. We conclude that pilot whales are able to acoustically discriminate between familiar and unfamiliar KW ecotypes, enabling them to adjust their behavior according to the perceived disturbance type.
... However, there are many occasions when high-speed swimming is demanded by free-ranging marine mammals. Locating and chasing prey (Williams et al., 2004;Guinet et al., 2007;Aguilar de Soto et al., 2008), as well as flight responses to avoid predators (Ford et al., 2005) or anthropogenic disturbance Goldbogen et al., 2013), can result in significant short-and long-term increases in swimming speed. In particular, many odontocete cetaceans will engage in short, extraordinary bouts of high-speed performance. ...
... Escape from aversive stimuli, most notably predators such as killer whales (Ford et al., 2005) and oceanic sound, can also instigate unusual swimming patterns and prolonged levels of increased physical exertion by cetaceans. High-speed swimming, elevated stroke frequencies and rapid ascent from depth are commonly reported for wild, tagged cetaceans following exposure to noise (Todd et al., 1996;DeRuiter et al., 2013), and have been suggested as causative factors for marine mammal strandings (Frantzis, 1998;Jepson et al., 2003). ...
Article
Exponential increases in hydrodynamic drag and physical exertion occur when swimmers move quickly through water, and underlie the preference for relatively slow routine speeds by marine mammals regardless of body size. Because of this and the need to balance limited oxygen stores when submerged, flight (escape) responses may be especially challenging for this group. To examine this, we used open-flow respirometry to measure the energetic cost of producing a swimming stroke during different levels of exercise in bottlenose dolphins ( Tursiops truncatus ). These data were then used to model the energetic cost of high-speed escape responses by other odontocetes ranging in mass from 42 to 2738 kg. The total cost per stroke during routine swimming by dolphins, 3.31±0.20 J kg−1 stroke−1, was doubled during maximal aerobic performance. A comparative analysis of locomotor costs (LC; in J kg−1 stroke−1), representing the cost of moving the flukes, revealed that LC during routine swimming increased with body mass ( M ) for odontocetes according to LC=1.46±0.0005 M ; a separate relationship described LC during high-speed stroking. Using these relationships, we found that continuous stroking coupled with reduced glide time in response to oceanic noise resulted in a 30.5% increase in metabolic rate in the beaked whale, a deep-diving odontocete considered especially sensitive to disturbance. By integrating energetics with swimming behavior and dive characteristics, this study demonstrates the physiological consequences of oceanic noise on diving mammals, and provides a powerful tool for predicting the biological significance of escape responses by cetaceans facing anthropogenic disturbances.
... Killer whales have long been known to prey on marine mammals; Scammon (1874) recorded them feeding on gray whales Eschrichtius robustus in the mid-1800s. While attacks on large whales have been documented (Baldridge 1972, Whitehead & Glass 1985, Flórez-González et al. 1994, Goley & Straley 1994, George & Suydam 1998, Pitman et al. 2001, Ford et al. 2005, such observations are infrequent. Jefferson et al. (1991) summarized accounts of killer whales attacking or harassing 20 species of cetaceans, including humpback whales. ...
... humpback or sperm whales, Weller 2002), would probably be more likely to survive attacks (with rake marks on their flukes) than those with more submissive physical reactions, that are less able to fight back in response to attacks (e.g. minke whales, Ford et al. 2005). The 2 large cetacean species considered to be most frequently killed by killer whales, i.e. gray and bowhead whales (Reeves et al. 2007), however, are species on which rake marks on survivors are also commonly seen (George et al. 1994, Weller 2002. ...
Article
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We examined the incidence of rake mark scars from killer whales Orcinus orca on the flukes of humpback whales Megaptera novaeangliae throughout the North Pacific to assess geo- graphic variation in predation pressure. We used 3650 identification photographs from 16 wintering or feeding areas collected during 1990 to 1993 to determine conservative estimates in the percentage of whales with rake mark scarring. Dramatic differences were seen in the incidence of rake marks among regions, with highest rates on wintering grounds off Mexico (26 vs. 14 % at others) and feeding areas off California (20 vs. 6% at others), 2 areas between which humpback whales migrate. Although attacks are rarely witnessed, the prevalence of scars demonstrates that a substantial portion of animals are attacked, particularly those that migrate between California and Mexico. Our data also suggest that most attacks occur at or near the wintering grounds in the eastern North Pacific. The prevalence of attacks indicates that killer whale predation has the potential to be a major cause of mortality and a driving force in migratory behavior; however, the location of the attacks is inconsistent with the hypothesis that animals migrate to tropical waters to avoid predation. Our conclusion is that, at least in recent decades, attacks are made primarily on calves at the wintering grounds; this contradicts the hypothesis that killer whales historically preyed heavily on large whales in high-latitude feeding areas in the North Pacific.
... Here, we tested if the two patterns matched for odontocete whales. We predicted that odontocete whales with more fusiform body shapes that enabled greater speed could minimize killer whale predation (Domenici, 2001;Ford et al., 2005) and, thus, evolve less investment in offspring and a slower reproduction as indicated by delayed sexual maturation and longer gestation length, interbirth interval, and lifespan. In addition, we predicted that species that evolved enhanced foraging features at the expense of morphology favoring speed would invest more energy in progeny, as shown by larger neonate body size but reduced concurrent adaptations for the same temporal life-history traits. ...
Preprint
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A widespread pattern in vertebrate life-history evolution is for species to evolve towards either fast or slow life histories; however, the possible causes of this pattern are multiple. Toothed whales (Odontoceti) are a particularly speciose group that includes a substantial range of body sizes and life histories and thus represent a model group to test the possible cause of this dichotomy. Using ancestral reconstruction, we find that some groups of odontocetes evolved sleek, presumably fast, body shapes around the same time that killer whales ( Orcinus orca ) evolved to be a predator of other whales approximately 1 Mya during the Pleistocene. A sleek body shape may have evolved as an adaptation to escape killer whale predation and resulted in a longer life-history events. A cluster analysis of odontocete whales confirmed the dual pattern of life-history traits with one group called ‘reproducers’ characterized by early age of maturity, short gestation, short interbirth interval, and short life, and the other group called ‘bet-hedgers’ with the opposite pattern. However, we found life history grouping relatively unrelated to whale shape (sleek or chunky). Results of mixed effects models incorporating principle components, indicated support for body shape as being positively related to neonate length (investment in progeny) but not significantly related to the temporal life-history traits. Thus, whale body shape is not an adequate explanation for the evolution of fast-slow life histories in odontocete whales.
... Na verdade, a origem do nome vem do fato de muitos marinheiros terem visto alguns hábitos alimentares da espécie que configuravam, na perspectiva humana, comportamentos de "tortura" com as presas. (FORD et al., 2005). ...
Article
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O cinema pode criar perspectivas acerca dos temas que retrata, o que inclui abordagens fílmicas voltadas para diferentes espécies de organismos, como ocorre no caso de diferentes animais marinhos. Nesse sentido, este trabalho analisou a construção das representações cinematográficas sobre as orcas (Orcinus orca) e seus possíveis desdobramentos no imaginário popular, além de discutir o seu impacto sobre a manutenção e manejo desses animais em cativeiro e apresentar uma proposta didática na perspectiva da Educação Ambiental que utilize esses filmes. Para isto, foram selecionadas cenas de três filmes nos quais as orcas são protagonistas e as narrativas e cinematografia foram analisadas na perspectiva da construção de personagem e das informações biológicas veiculadas. Nesse sentido, houve uma mudança na forma que as orcas eram representadas, outrora apresentadas como assassinas vingadoras e mais recentemente como animais afetivos, o que as torna mais suscetíveis para a sua utilização em espetáculos aquáticos e, com isso, maior probabilidade de um manejo inadequado. A partir dessa análise, foi possível propor uma ação didática com a utilização desses longas-metragens voltada para o conhecimento sobre esses cetáceos e para a reflexão sobre sua conservação e não-manutenção em cativeiro. Palavras-chave: Orca, a baleia assassina; Free Willy; Blackfish; espécies-bandeira.
... The pack-hunting behaviors of killer whales that attacked the blue whales off Bremer Bay were similar to those recorded during attacks on large rorquals elsewhere. When Balaenoptera whales attempt to escape from their attackers, killer whales often charge along on both sides of the fleeing whale (e.g., Alava et al., 2013;Ford et al., 2005;Silber et al., 1990;Tarpy, 1979; Event 2, Figure 7; Event 3). For killer whales attempting to bite a fastswimming, large whale, the most accessible areas tend to be the lips, dorsal ridge, and appendages, including the dorsal fin, flukes, and flippers (e.g., Alava et al., 2013;Ferguson et al., 2012;Gemmell et al., 2015;Jefferson et al., 1991;Melnikov & Zagrebin, 2005;Silber et al., 1990;Tarpy, 1979). ...
Article
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Killer whale preying effort and predation success on large adult whales has long been in debate. For the past 10 years killer whales off the Western Australian (WA) coast have been observed successfully preying on humpback whale calves, minke whales and beaked whales. More recently, in 2019 and 2021 killer whales off the south coast of WA were observed preying on blue whales. Here we describe three successful attacks, the first a healthy 20m adult.
... Some other vertebrates also have intelligent capabilities. For example, killer whales use strategies to hunt minke whales (Ford et al., 2005). Birds and other more advanced vertebrates all possess the ability of intelligence. ...
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What will be the relationship between human beings and artificial intelligence (AI) in the future? Does an AI have moral status? What is that status? Through the analysis of consciousness, we can explain and answer such questions. The moral status of AIs can depend on the development level of AI consciousness. Drawing on the evolution of consciousness in nature, this paper examines several consciousness abilities of AIs, on the basis of which several relationships between AIs and human beings are proposed. The advantages and disadvantages of those relationships can be analysed by referring to classical ethics theories, such as contract theory, utilitarianism, deontology and virtue ethics. This explanation helps to construct a common hypothesis about the relationship between humans and AIs. Thus, this research has important practical and normative significance for distinguishing the different relationships between humans and AIs.
... With increased areas of open water, killer whales (Orcinus orca) have expanded their range and are now annually present in Foxe Basin [62]. Because killer whales feed selectively on parts of prey [63,64], a large portion of a bowhead whale kill may be left to drift onshore where it becomes accessible to bears [65]. Laidre et al. [66] estimated that the consumable biomass of an adult bowhead was equal to approximately 1300 adult ringed seals, and bears can potentially feed on a carcass for two or more years. ...
Article
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Ecological flexibility of a species reflects its ability to cope with environmental change. Although polar bears (Ursus maritimus) are experiencing changes in foraging opportunities due to sea ice loss, regional prey availability and environmental conditions will influence the rate and severity of these effects. We examined changes in polar bear diet and the influence of sea ice characteristics in Foxe Basin over an 18-year period. We combined previous fatty acid data from bears harvested from 1999 to 2003 (n = 82) with additional data from 2010 to 2018 (n = 397). Polar bear diets were diverse; however, ringed seal (Pusa hispida) was the primary prey throughout the sample period. Prey contribution varied temporally and spatially, and by intrinsic factors, while the frequency of prey in diets varied over time suggesting that diet estimates reflect the variability in available prey. Bowhead whale (Balaena mysticetus), although still a minor dietary component, has more than doubled in frequency of occurrence in diets in recent years in association with increased scavenging opportunities. Higher dietary levels of beluga whale (Delphinapterus leucas) and harbour seal (Phoca vitulina) were linked to later breakup date suggesting heavier ice conditions may promote access to both prey species. The flexible foraging strategies of bears in Foxe Basin may help mitigate their vulnerability to changes in prey distribution and habitat conditions. Our results provide insights into the importance of alternative and supplemental food sources for polar bears during phenological changes in ice conditions that will likely have consequences to Arctic community structure as warming continues.
... Although consumption of gray whale (Eschrichtius robustus) calves and yearlings and minke whales (Balaenoptera acutorostrata) is seasonally important off Alaska [45,53], the vast majority of successful kills (89 to 100%) over 20 years of study off British Columbia, Washington, and Alaska involved pinnipeds and porpoises [4,5,54]. Moreover, killer whales are known to consume relatively small proportions (e.g., the tongue and ventral skin) of baleen whale kills [55,56]. ...
Article
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Ecotypes are groups within a species with different ecological adaptations than their conspecifics. Eastern North Pacific (ENP) killer whale ( Orcinus orca ) ecotypes differ in their diet, behavior, and morphology, but the same is not known for this species in the eastern Canadian Arctic (ECA) and Northwest Atlantic (NWA). Using compound-specific stable isotope analysis (CSIA) of amino acids (AAs), we compared δ ¹⁵ N patterns of the primary trophic and source AA pair, glutamic acid/glutamine (Glx) and phenylalanine (Phe), in dentine collagen of (1) sympatric ENP killer whale ecotypes with well-characterized diet differences and (2) ECA/NWA killer whales with unknown diets. δ ¹⁵ N Glx-Phe was significantly higher in the ENP fish-eating (FE) than mammal-eating (ME) ecotype (19.2 ± 0.4‰ vs. 13.5 ± 0.7‰, respectively). Similar bimodal variation in δ ¹⁵ N Glx-Phe indicated analogous dietary divisions among ECA/NWA killer whales, with two killer whales having higher δ ¹⁵ N Glx-Phe (16.5 ± 0.0‰) than the others (13.5 ± 0.6‰). Inferences of dietary divisions between these killer whales were supported by parallel differences in threonine δ ¹⁵ N (–33.5 ± 1.6‰ and –40.4 ± 1.1‰, respectively), given the negative correlation between δ ¹⁵ N Thr and TP across a range of marine consumers. CSIA-AA results for ECA/NWA whales, coupled with differences in tooth wear (a correlate for diet), are consistent with ecotype characteristics reported in ENP and other killer whale populations, thus adding to documented ecological divergence in this species worldwide.
... Short-finned pilot whales Globicephala macrorhynchus forage on fast moving prey and regularly launch themselves forward with a speed of 9 m/s during foraging events (Aguilar Soto et al., 2008). Similarly, high speed, uninterrupted stroking is sometimes required to escape from predators (Ford et al., 2006), or from anthropogenic disturbance (e.g., DeRuiter et al., 2017;Williams et al., 2017a,b;van Beest et al., 2018). ...
Article
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Deep diving air-breathing species by necessity must balance submergence time and level of exercise during breath-holding: a low activity level preserves oxygen stores and allows longer duration submergence whereas high activity levels consume oxygen quickly and shorten submergence time. In this study, we combined high-resolution multi sensor animal-borne tag data to investigate diving behavior and locomotion styles of the narwhal (Monodon monoceros) ( n = 13, mean record length 91 h)–a deep diving Arctic species. Narwhals in this study dove down to >800 m but despite the deep diving abilities, one-third of the dives (33%) were shallow (>100 m) and short in duration (<5 min). Narwhals utilized energy saving measures such as prolonged gliding during descent with increasing target depth but stroked actively throughout the ascent indicating excess oxygen storages. Foraging behavior, as detected by the presence of buzzes, was a key factor influencing dive depth and spinning behavior—the rolling movement of the animal along its longitudinal axes. Narwhals in East Greenland utilized two foraging strategies, while transiting and while stationary, with different target depths and buzzing rates. The first targeted deep-dwelling, possibly solitary prey items and the latter, more schooling prey closer to the surface. The buzzing rate during stationary foraging was on average twice as high as during transiting foraging. Spinning was an integrated part of narwhal swimming behavior but the amount of spinning was correlated with foraging behavior. The odds for spinning during all dive phases were 2–3 times higher during foraging than non-foraging. Due to the spinning behavior, stroking rate might be better suited for estimating energy consumption in narwhals than ODBA (overall dynamic body acceleration). The narwhal is considered as one of the most sensitive species to climate change–the results from this study can act as a baseline essential for evaluating changes in the behavior and energy usage of narwhals caused by stressors evolving in the Arctic.
... The contrasting results for the beaked whales studied here might be explained by differences in behaviour and trophic niche. Fish-eating orcas and bottlenose dolphins forage most often in shallow waters [54,55] and sometimes coordinate their hunting [56], while Blainville's and Cuvier's beaked whales dive to mean depths of 800 m [22] and hunt individually. The cacophony of clicks and their surface echoes from echolocating conspecifics in large groups of royalsocietypublishing.org/journal/rspb Proc. ...
Article
Echolocating animals that forage in social groups can potentially benefit from eavesdropping on other group members, cooperative foraging or social defence, but may also face problems of acoustic interference and intra-group competition for prey. Here, we investigate these potential trade-offs of sociality for extreme deep-diving Blainville′s and Cuvier's beaked whales. These species perform highly synchronous group dives as a presumed predator-avoidance behaviour, but the benefits and costs of this on foraging have not been investigated. We show that group members could hear their companions for a median of at least 91% of the vocal foraging phase of their dives. This enables whales to coordinate their mean travel direction despite differing individual headings as they pursue prey on a minute-by-minute basis. While beaked whales coordinate their echolocation-based foraging periods tightly, individual click and buzz rates are both independent of the number of whales in the group. Thus, their foraging performance is not affected by intra-group competition or interference from group members, and they do not seem to capitalize directly on eavesdropping on the echoes produced by the echolocation clicks of their companions. We conclude that the close diving and vocal synchronization of beaked whale groups that quantitatively reduces predation risk has little impact on foraging performance.
... Short-finned pilot whales Globicephala macrorhynchus forage on fast moving prey and regularly launch themselves forward with a speed of 9 m/s during foraging events (Aguilar Soto et al., 2008). Similarly, high speed, uninterrupted stroking is sometimes required to escape from predators (Ford et al., 2006), or from anthropogenic disturbance (e.g., DeRuiter et al., 2017;Williams et al., 2017a,b;van Beest et al., 2018). ...
... Predators that demonstrate broad diet as a species are often more specialized at the scale of local populations or ecotypes. For example, the killer whale Orcinus orca is known to feed on many different types of prey from small fish (herring, e.g., Nøttestad, Fernö, & Axelsen, 2002) to large whales (Ford et al., 2005), but whales in a particular population usually focus on a specific type of prey. Prey preferences and handling techniques are culturally transmitted within matrilineal social units (reviewed in Riesch, Barrett-Lennard, Ellis, Ford, & Deecke, 2012). ...
Article
Killer whales are top predators in marine trophic chains, and therefore their feeding preferences can substantially affect the abundance of species on the lower trophic levels. Killer whales are known to feed on many different types of prey from small fish to large whales, but a given killer whale population usually focuses on a specific type of prey. Stable isotope analysis is widely used to study whale diets, because direct observations are often impossible. Killer whale feeding habits in the western North Pacific are poorly studied, and the large‐scale stable isotope analysis provides a unique opportunity to gain insights into the trophic links of this top predator. In this study, we compare the δ¹³C and δ¹⁵N stable isotope values from killer whale skin samples obtained in different areas of the western North Pacific from fish‐eating (R‐type) and mammal‐eating (T‐type) killer whale ecotypes. The effect of ecotype was highly significant: both carbon and nitrogen stable isotope values were lower in R‐type whales than in T‐type whales. The geographical variation also affected killer whale stable isotope values due to both the differences in killer whale diet and the variation in baseline stable isotope values across the study areas.
... The avoidance of predation is a possible explanation because Antarctic minke whales are common preys of the killer whale Orcinus orca (Jefferson et al. 1991;Pitman and Ensor 2003), and killer whale occurrence is strongly correlated with that of minke whales (Kasamatsu et al. 2000). Common minke whales can evade capture after being chased if sufficient space is available (Ford et al. 2005). However, these arguments require further data on the spatial relationships between killer whales and their possible prey during the austral summers. ...
Article
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Antarctic minke whales Balaenoptera bonaerensis are rorquals that migrate to Antarctic waters to forage during the austral summer. Because the species frequents the edges of ice packs in summer, the potential impact of long-term physical environmental changes poses serious conservation concerns. Condition along the ice edge vary regionally, sometimes forming small ice free areas (ice gaps), and little is known about whale movement patterns associated with these small-scale variations in the physical environment. In this study, six minke whales were tracked for an average of 31 days (range 4–77 days) from January to March of 2016 and 2017 between 60° E and 140° E above and off the continental shelf. The tracking data of five animals were fitted to a Bayesian hierarchical switching state-space model assembled from ARGOS data filters to estimate behavioral states. Results show that Antarctic minke whales are likely to search for ice gaps areas and remain there for extended periods until the surrounding ice melts, rather than stay at krill rich shelf breaks or areas with high chlorophyll-a concentration. When no ice gaps were nearby, the whales were likely to move eastward along highly concentrated ice packs to find a gap. Our study found a strong association between minke whale movements and ice dynamics during the summer foraging season in this region.
... Bogstad et al. (2015) suggests that competition occurs between minke whales and other predators with similar diets, like cod, harp seal (Pagophilus groenlandicus) and possibly sea birds, in the Barents Sea. Occasionally, minke whales are subject to predation by killer whales (Orcinus orca) (Ford et al., 2005;Samarra et al., 2018). ...
Technical Report
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Report from the Norwegian Scientific Committee for Food and Environment (VKM) 2019. Opinion of the Panel on Alien Organisms and Trade in Endangered Species (CITES) of the Norwegian Scientific Committee for Food and Environment
... These actions range from selection of vulnerable prey (Cresswell & Quinn, 2004), adaptations of herd size in the vicinity of wolves (Creel & Winnie, 2005), to the use of perfect synchrony and communication observed when killer whales attack seals (Nøttestad, Ferno, & Axelsen, 2002). These and a score of other examples from the animal kingdom (for some intriguing examples see also , Ford, et al., 2005;Harland & Jackson, 2006) illustrate the tactical ingenuity of animals. The previous observations suggest that tactical decisions in sports might be much more driven by environmental constraints, and not defined by cognitive interventions, as some coaches might like to believe. ...
Article
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In sports, strategy and tactics play a decisive role. This is certainly so in sport games like volleyball in which the players need to promptly adapt their actions to the continuously changing game situations. In this paper, we will take a closer look at how strategic and tactical decisions come about. Our goal is twofold. First, we want to tackle this discussion from the angle of the ecological-dynamical approach, in which concepts as perception-action coupling, affordances, and self-organization are put forward as vital elements to explain the control of actions/sport skills. In referring to animal behavior, we will push the idea that cognitive interventions are not a prerequisite for strategic and tactical interventions. Second, we want to translate these theoretical concepts into some general guidelines for coaches and practitioners. In doing so, we hope to increase the understanding that for practice the environmental constraints should be embraced in order to improve the strategic and tactical capacities of the players.
... False killer whales (Pseudorca crassidens) are social animals whose cooperative hunting techniques may fail to sustain a high enough foraging success following a social disruption such as an additive mortality event (75,76). Cooperative hunting techniques are also found in killer whales, which often forage in groups using various techniques including coordinated attacks (9,11,16,49,(77)(78)(79). Group foraging is common among the Crozet killer whales, whose diet includes large prey such as southern elephant seals (Mirounga leonina) and baleen whales (42,43). ...
Article
In highly social top predators, group living is an ecological strategy that enhances individual fitness, primarily through increased foraging success. Additive mortality events across multiple social groups in populations may affect the social structure, and therefore the fitness, of surviving individuals. This hypothesis was examined in a killer whale ( Orcinus orca ) population that experienced a 7-y period of severe additive mortality due to lethal interactions with illegal fishing vessels. Using both social and demographic analyses conducted on a unique long-term dataset encompassing periods before, during, and after this event, results indicated a decrease in both the number and the mean strength of associations of surviving individuals during the additive mortality period. A positive significant correlation between association strength and apparent survival suggested that the fitness of surviving individuals was impacted by the additive mortality event. After this event, individuals responded to the loss of relatives in their social groups by associating with a greater number of other social groups, likely to maintain a functional group size that maximized their foraging success. However, these associations were loose; individuals did not reassociate in highly stable social groups, and their survival remained low years after the mortality event. These findings demonstrate how the disruption of social structure in killer whales may lead to prolonged negative effects of demographic stress beyond an additive mortality event. More importantly, this study shows that sociality has a key role in the resilience of populations to human-induced mortality; this has major implications for the conservation of highly social and long-lived species.
... Surplus killing by killer whales, whereby prey is killed but not consumed, has been previously observed in various regions (see [2]) but the reasons for this behaviour are unknown [2]. The observation in Skjálfandi Bay described in this study resembles those of coordinated attacks by transient killer whales on minke whales in the Pacific, involving prolonged chases and ending in ramming and/or asphyxiation [72]. Further reports [22] and tooth rake marks observed on the skin of minke whales [73] suggest attacks on minke whales are likely to be common in Icelandic waters. ...
Article
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Killer whales have a cosmopolitan distribution and as a species are generalists, feeding on a variety of prey. However, local populations tend to specialise on specific prey types. In Ice-landic waters, killer whales are generally associated with herring and, thus, have been presumed to be herring specialists. However, recent studies suggest a more complex foraging ecology, possibly including a mosaic of strategies. With increased observational effort in recent years due to research and whale-watching activities, there have been several reports of interactions with different prey, including confirmed predation events. In this study we aimed to summarise the range of potential prey of killer whales observed in Icelandic waters. We report on 12 previously unpublished accounts and review 15 accounts published in the scientific literature or local newspapers, making a total of 27 events where killer whales were observed interacting with actual or potential prey. Thirteen different species, including birds (n = 1), cephalopods (n = 1), fish (n = 5) and marine mammals (n = 6), are reported, although herring is by far the species that killer whales are most often observed interacting with. This study provides the first summary of actual and suspected killer whale prey in Ice-landic waters, and contributes towards our understanding of this population's prey preferences. However, describing the diet of individuals/groups was not possible and this study points to a need for continued monitoring to understand the intricacies of killer whale foraging behaviour in this area.
... However, even in areas where killer whale density is low, this species is known to inhibit the vocal activity of their prey (Rankin et al. 2012). We therefore suggest that minke whales may remain relatively quiet in Cormorant Channel due to predation risk, especially considering killer whales have been observed chasing minke whales in Cormorant Channel and attacking and killing them in other nearby waterways (Ford et al. 2005). ...
Article
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The minke whale (Balaenoptera acutorostrata) is a small species of baleen whale with a cosmopolitan distribution. Despite extensive study on the vocalizations of other balaenopterids, the acoustic repertoire of minke whales is not well known. Individuals of the North Pacific subspecies (B. acutorostrata scammoni) produce unique vocalizations (‘boings’) during their putative breeding season from fall to spring. However, no vocalizations have been previously reported for this subspecies in any eastern North Pacific feeding ground. We present two call types recorded in the presence of six minke whales, two of which were confirmed as female, in Cormorant Channel, British Columbia, Canada, during the summer of 2012. The calls consist of downsweeps and pulse chains. These call types share some characteristics with calls described elsewhere, although they are not identical to similar call types observed for other populations. Calling rates for minke whales in this study region are very low compared to those reported for this subspecies on its putative breeding grounds, as well as for other subspecies on their feeding grounds. We propose predation risk, sexual segregation and acoustic masking as potential causes of the low calling rates observed for minke whales in Cormorant Channel.
... However, even in areas where killer whale density is low, this species is known to inhibit the vocal activity of their prey (Rankin et al. 2012). We therefore suggest that minke whales may remain relatively quiet in Cormorant Channel due to predation risk, especially considering killer whales have been observed chasing minke whales in Cormorant Channel and attacking and killing them in other nearby waterways (Ford et al. 2005). ...
Conference Paper
The minke whale (Balaenoptera acutorostrata) is the smallest species of baleen whale and has a cosmopolitan distribution. Despite extensive study on the vocalizations of other balaenopterids, the acoustic repertoire of minke whales is not well known. Individuals of the North Pacific subspecies of common minke whale (B. a. scammoni) are known to produce unique vocalizations ("boings") during their putative breeding season from fall to spring. However, no vocalizations have been previously reported for this subspecies in summer feeding grounds. We present four novel call types recorded in the presence of minke whales in Cormorant Channel, in coastal British Columbia, Canada, during the summer of 2012. These calls consist of broadband pulses, tonal wavers, downsweeps, and pulse trains. Calling rates for minke whales in this study region were very low compared to those reported for North Atlantic minke whales on their feeding grounds. We compare our candidate call types with vocalizations described for other minke whale populations and propose predation risk as a cause of the low calling rates observed for minke whales in Cormorant Channel.
... At the same time, we reject the possibility of sexual selection as a driver of tylosaurine rostrum evolution, given its presence exceptionally early in their postnatal ontogeny. It is a possibility that the bony rostrum was selected for a sex-independent function in tylosaurines, such as for ramming, which killer whales today employ when hunting cetaceans of various sizes (Ford et al., 1998(Ford et al., , 2005Visser et al., 2010). ...
Article
We here report on the smallest-known, neonate-sized Tylosaurus specimen, FHSM VP-14845, recovered from the lower Santonian portion of the Niobrara Chalk exposed in Kansas, U.S.A. Lacking any associated adult-sized material, FHSM VP-14845 comprises fragmentary and associated cranial bones, here considered to represent a single neonatal individual with an estimated skull length of 30 cm. Despite its small size, a suite of cranial characters diagnoses FHSM VP-14845 as a species of Tylosaurus, including the elongate basisphenoid morphology. At the same time, FHSM VP-14845 unexpectedly lacks a conical predental rostrum on the premaxilla, generally regarded as diagnostic of this genus. Further, the first and the second premaxillary teeth are closely spaced, with the second set positioned posterolateral to the first, contributing to the overall shortness of the dentigerous premaxilla. Because a conical predental rostrum is already present in ontogenetically young specimens of T. nepaeolicus and T. proriger with respective skull lengths of approximately 40 and 60 cm, formation of such a rostrum must have taken place very early in postnatal ontogeny. Our recognition of a neonate-sized Tylosaurus specimen without an elongate predental rostrum of the premaxilla suggests hypermorphosis as a likely heterochronic process behind the evolution of this iconic tylosaurine feature. Citation for this article: Konishi, T., P. Jiménez-Huidobro, and M. W. Caldwell. 2018. The smallest-known neonate individual of Tylosaurus (Mosasauridae, Tylosaurinae) sheds new light on the tylosaurine rostrum and heterochrony. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1510835.
... The ecological role of killer whales as predators of baleen whales has been debated for a long time, as predatory attacks have rarely been observed (Whitehead & Glass 1985, Baird 2000, Clap ham 2001, Connor & Corkeron 2001, Springer et al. 2003, Reeves et al. 2006. It seems that even those killer whales specialized in eating marine mammals do not regularly prey on baleen whales, as observed, for example, for transient killer whales from the northeast Pacific that prey mainly on pinnipeds and small cetaceans and only occasionally on baleen whales (Ford et al. 2005, Matkin et al. 2007. Another explanation for the scarcity of records of killer whale attacks on baleen whales could be a shift of killer whale prey preferences due to the de pletion of larger whale stocks caused by commercial whaling (e.g. ...
Article
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The role and impact of killer whales Orcinus orca as predators of baleen whales has been emphasized by studies of humpback whales Megaptera novaeangliae. In this study, rake marks on the fluke were used as a proxy for predatory attacks in a sample of 2909 adult humpback whales and 133 calves from 5 breeding and 2 feeding locations in the eastern South Pacific and the Antarctic Peninsula. The goal of this study was to evaluate how often, at what age, where, and when humpback whales were more susceptible to attacks. Overall, 11.5% of adults and 19.5% of calves had rake marks on their flukes. Significant differences were found in the prevalence of scars in calves when comparing breeding (9%) vs. feeding areas (34%) (Χ² = 10.23, p < 0.01). Multi-year sighting analysis of scar acquisition in 120 adults (82% site fidelity) and 37 calves in the Magellan Strait showed no new marks after the initial sighting for the subsequent 15 yr. This finding indicates that rake marks were most probably acquired when whales were calves, which supports the belief that scar acquisition is a once in a lifetime event. The odds of having rake marks increased with time but with a significantly higher rate in calves (Χ² = 5.04, p < 0.05), which suggests an increase in predation pressure over time. Our results support the earlier hypothesis that killer whale attacks occur mostly on calves, near breeding sites, and during the first migration to feeding areas.
... This could be further subdivided into situations where groups can (1) forage more efficiently, for example by cooperatively capturing large or difficult prey, or (2) obtain information about food sources. Social hunting occurs in a broad array of taxa, from insects and spiders to birds and terrestrial and aquatic mammals (Baird & Dill, 1996;Busse, 1978;Ford et al., 2005;Guinet, Barrett-Lennard, & Loyer, 2000;G€ otmark, Winkler, & Andersson, 1986;Hector, 1986;Packer, 1986;Ward & Enders, 1985). Despite the advantages gained by individuals in this context, it remains unclear whether sociality in these cases evolved because of the advantages gained through cooperative foraging/hunting. ...
... By cooperatively blocking their escape to open water, the killer whales, created panic among Dall's porpoise and killed 2-4 individuals and caused at least 8 others to strand and die. Similar techniques have been used by killer whales attacking minke whales, another cetacean that avoids predation through flight (Ford et al., 2005). The forage fish biomass we observed during strip transect surveys was dominated by walleye pollock and Pacific herring (Arimitsu et al., 2017) and most of this biomass was in the same novel locations where we found Dall's porpoise. ...
Article
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Dall's porpoise, Phocoenoides dalli, are a conspicuous predator in the Prince William Sound ecosystem, yet there has been little effort directed towards monitoring this species since the 1980s, prior to the Exxon Valdez oil spill. We used vessel-based surveys to examine the seasonal distribution of Dall's porpoise in the waters of Prince William Sound during eight years from 2007 to 2015. Over the course of 168 days and 15,653. km of survey effort, 921 Dall's porpoise were encountered in 210 groups. We estimate an encounter rate of 0.061 porpoise/km traveled or 1 porpoise encountered for every 16.5. km traveled. Dall's porpoise were found throughout the year in Prince William Sound, and used a wide range of habitats, including those not considered typical of the species, such as bays, shallow water, and nearshore waters. Dall's porpoise seasonally shifted their center of distribution from the western passages in fall to the bays of the eastern Sound in winter and spring. Dall's porpoises were widely dispersed throughout the Sound in summer. We identified potential Dall's porpoise habitat (depth, slope, and distance from shore) within Prince William Sound using generalized additive models (GAM). Dall's porpoise were found in deeper water during summer and in shallowest water during spring. We propose that their use of novel habitats is a function of reduced predation risk associated with the decline of their main predator, killer whales (Orcinus orca), following the Exxon Valdez oil spill, and the presence of overwintering and spawning Pacific herring (Clupea pallasii). While the size of the Dall's porpoise population within Prince William Sound remains unknown, our encounter rates were lower than those reported in the 1970s. Their high metabolic rate and ubiquitous presence makes them one of the more important, yet understudied, forage fish predators in the region.
... Although changes in Arctic predator regimes are important and widely relevant findings of our analysis, at least as important is the interpretation of marine animal telemetry data worldwide. Killer whales are globally distributed predators of marine mammals (77)(78)(79), and large predatory sharks are also present across large areas of the world's oceans (80). In our study, information about the predator's location was key to understanding how movements of narwhal, as observed via satellite telemetry, were affected by predator threat. ...
Article
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Significance Predators are widely understood to impact the structure and stability of ecosystems. In the Arctic, summer sea ice is rapidly declining, degrading habitat for Arctic species, such as polar bears and ringed seals, but also providing more access to important predators, such as killer whales. Using data from concurrently tracked predator (killer whales) and prey (narwhal), we show that the presence of killer whales significantly changes the behavior and distribution of narwhal. Because killer whales are effective predators of many marine mammals, similar predator-induced changes would be expected in the behavior of tracked animals in marine ecosystems worldwide. However, these effects are rarely considered and may frequently go unrecognized.
... Killer whales tend to target smaller (i.e., younger) individuals (Ford and Reeves 2008; Ferguson et al. 2012b), which subsequently increases the vulnerability of calves and juveniles to killer whale predation in northern Foxe Basin in a reduced sea ice habitat (Higdon et al. 2012). The preference of killer whales to feed on the head and mouthparts of a baleen whale (Jefferson et al. 1991; Ford et al. 2005) generates a large carcass that can drift on shore, potentially creating an important supplementary food source for polar bears. Although dedicated research has yet to be carried out, the increasing bowhead whale population, expansion of killer whales' range, and declining sea ice suggest the possibility of an ongoing ecological regime shift in Foxe Basin. ...
Article
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Polar bear (Ursus maritimus) subpopulations in several areas with seasonal sea ice regimes have shown declines in body condition, reproductive rates, or abundance as a result of declining sea ice habitat. In the Foxe Basin region of Nunavut, Canada, the size of the polar bear subpopulation has remained largely stable over the past 20 years, despite concurrent declines in sea ice habitat. We used fatty acid analysis to examine polar bear feeding habits in Foxe Basin and thus potentially identify ecological factors contributing to population stability. Adipose tissue samples were collected from 103 polar bears harvested during 2010–2012. Polar bear diet composition varied spatially within the region with ringed seal (Pusa hispida) comprising the primary prey in northern and southern Foxe Basin, whereas polar bears in Hudson Strait consumed equal proportions of ringed seal and harp seal (Pagophilus groenlandicus). Walrus (Odobenus rosmarus) consumption was highest in northern Foxe Basin, a trend driven by the ability of adult male bears to capture large-bodied prey. Importantly, bowhead whale (Balaena mysticetus) contributed to polar bear diets in all areas and all age and sex classes. Bowhead carcasses resulting from killer whale (Orcinus orca) predation and subsistence harvest potentially provide an important supplementary food source for polar bears during the ice-free period. Our results suggest that the increasing abundance of killer whales and bowhead whales in the region could be indirectly contributing to improved polar bear foraging success despite declining sea ice habitat. However, this indirect interaction between top predators may be temporary if continued sea ice declines eventually severely limit on-ice feeding opportunities for polar bears.
... Aggressive and coercive behaviors were classified as ''sandwiching,'' ''ramming'' and ''tossing,'' similarly as described in several other studies (Ross and Wilson 1996;Wedekin et al. 2004;Ford et al. 2005, Barrett-Lennard et al. 2011); see Table 1 for details. Group association data (courtesy of ongoing photo-identification research; L. Karczmarski and Y. Wu, study in progress) were used to assess the association pattern among the involved individuals. ...
Article
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Infanticide has been observed in several mammalian taxa and studied in considerable detail in carnivores and primates. Although reported previously in cetaceans, known cases are few and their socio-behavioral context remains poorly understood. We report here on three cases of social coercion directed at mother-neonate pairs of Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary, southeast China. Two of these cases resulted in confirmed infanticide. To aid the interpretation of our field observations, we refer to the results of necropsies of calf carcasses stranded and recovered in our research area between 2003 and 2012, which indicate that in several cases the main cause of death of stranded calves was asphyxia resulting from blunt-force trauma. This is consistent with the aggressive behaviors seen during our field observations. We conclude that male infanticide is the most plausible interpretation of the observed behaviors, never previously reported for the genus Sousa, while the calf-directed aggression is likely a result of socio-sexual harassment by males as part of their reproductive strategy.
... Steller sea lions (Eumetopias jubatus), California sea lions (Zalophus californianus), Dall's porpoises (Phocoenoides dalli), harbor porpoises (Phocoena phocoena), and Pacific white-sided dolphins (Lagenoryhncus obliquidens) are other regular parts of the diet (Ford et al. 1998, Ternullo and Black 2002, Dahlheim and White 2010). Large whales (e.g., gray whale [Eschrichtius robustus] calves, minke whales [Balaenoptera acutorostrata]) are occasionally killed (Ford and Ellis 1999; Ford et al. 2005). A recent report of substantial numbers of squid remains in the stomachs of two west coast transients suggests that squid may be a larger component of the diet than previously recognized (Hanson and Walker 2014). ...
Technical Report
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Killer whales have been listed as a state endangered species in Washington since 2004. Three main populations known as the southern residents, west coast transients, and offshores occur in the state. While closely similar in appearance, these ecotypes differ in their biology, rarely interact with one another, and do not interbreed despite having largely sympatric year-round distributions ranging from California to Alaska. Southern residents totaled just 81 whales as of July 2015 and are the population of greatest concern. Numbers have been relatively stable since 2001, but remain 17% below their recent peak size recorded in 1995. In addition, the population’s growth rate remains well below the downlisting and delisting goals established in the 2008 federal recovery plan. The southern resident population faces significant potential threats from the reduced availability of chinook salmon, interactions with whale-watching vessels and human-generated marine sound, and factors associated with its small population size, including the recent skewing of births towards males, which will constrain productivity over the next few decades. In contrast, the west coast transient population has shown considerable growth since the 1970s in response to the recovery of its marine mammal prey base, and is now estimated to number more than 500 whales and be near its carrying capacity. Offshore killer whales are estimated at 300 individuals and have a stable population trend. All three populations carry heavy loads of environmental contaminants, face a continuing risk of major oil spills in their ranges, are susceptible to a disease outbreak, and will likely experience the impacts of climate change in the future. For these reasons, it is recommended that killer whales remain listed as a state endangered species in Washington.
... Steller sea lions (Eumetopias jubatus), California sea lions (Zalophus californianus), Dall's porpoises (Phocoenoides dalli), harbor porpoises (Phocoena phocoena), and Pacific white-sided dolphins (Lagenoryhncus obliquidens) are other regular parts of the diet (Ford et al. 1998, Ternullo and Black 2002, Dahlheim and White 2010). Large whales (e.g., gray whale [Eschrichtius robustus] calves, minke whales [Balaenoptera acutorostrata]) are occasionally killed (Ford and Ellis 1999; Ford et al. 2005). A recent report of substantial numbers of squid remains in the stomachs of two west coast transients suggests that squid may be a larger component of the diet than previously recognized (Hanson and Walker 2014). ...
Technical Report
Killer whales have been listed as a state endangered species in Washington since 2004. Three main populations known as the southern residents, west coast transients, and offshores occur in the state. While closely similar in appearance, these ecotypes differ in their biology, rarely interact with one another, and do not interbreed despite having largely sympatric year-round distributions ranging from California to Alaska. Southern residents totaled just 81 whales as of July 2015 and are the population of greatest concern. Numbers have been relatively stable since 2001, but remain 17% below their recent peak size recorded in 1995. In addition, the population’s growth rate remains well below the downlisting and delisting goals established in the 2008 federal recovery plan. The southern resident population faces significant potential threats from the reduced availability of chinook salmon, interactions with whale-whaling vessels and marine sound, and factors associated with its small population size, including the recent skewing of births towards males, which will constrain productivity over the next few decades. In contrast, the west coast transient population has shown considerable growth since the 1970s in response to the recovery of its marine mammal prey base, and is now estimated to number more than 500 whales and be near its carrying capacity. Offshore killer whales are estimated at 300 individuals and have a stable population trend. All three populations carry heavy loads of environmental contaminants, face a continuing risk of major oil spills in their ranges, are susceptible to a disease outbreak, and will likely experience the impacts of climate change in the future. For these reasons, it is recommended that killer whales remain listed as a state endangered species in Washington.
... Prey sharing by killer whale ecotypes other than residents is primarily limited to populations that prey on large species that must be cooperatively acquired (e.g. Baird & Dill, 1996;Ford et al., 2005;Guinet, Barrett-Lennard, & Loyer, 2000;Pitman & Durban, 2012;Pitman & Stinchcomb, 2002). Sharing of smaller, individually caught prey has been described in only a few populations of killer whales whose foraging behaviour is so specialized or dangerous that juveniles may be unable to provision themselves. ...
... Prey sharing by killer whale ecotypes other than residents is primarily limited to populations that prey on large species that must be cooperatively acquired (e.g. Baird & Dill, 1996;Ford et al., 2005;Guinet, Barrett-Lennard, & Loyer, 2000;Pitman & Durban, 2012;Pitman & Stinchcomb, 2002). Sharing of smaller, individually caught prey has been described in only a few populations of killer whales whose foraging behaviour is so specialized or dangerous that juveniles may be unable to provision themselves. ...
Article
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The vast majority of social animals exhibit sex-biased dispersal as a strategy to reduce kin competition and avoid inbreeding. Piscivorous ‘resident’ killer whales, Orcinus orca, of the eastern North Pacific, however, are unusual in that both sexes remain philopatric throughout life, forming highly stable, multigeneration matrilines that are closed to immigration. We conducted a 12-year study documenting extensive cooperative prey sharing within these matrilines, and hypothesized that extreme natal philopatry in resident killer whales arose due to inclusive fitness benefits gained by provisioning maternal kin. We found that prey sharing was nonreciprocal, and even though whales routinely foraged in mixed associations containing multiple matrilines, prey sharing among individuals belonging to different matrilines was very infrequent. Furthermore, maternal relatedness was a significant predictor of the frequency of prey sharing between individuals, with close maternal kin sharing more often than distant relatives or nonkin. Adult females were much more likely to share prey than adult males or subadults, probably because they mainly provisioned their offspring. However, food sharing was not limited solely to maternal care; all age–sex classes engaged in this behaviour by sharing with close maternal relatives, such as siblings and mothers. We also investigated the frequency of prey sharing between mothers and their offspring as a function of offspring sex and age, and found that maternal food sharing with daughters declined after daughters reached reproductive maturity, which could help to explain matriline fission events. The evolution of kin-directed food sharing requires the ability to reliably discriminate kin, which resident killer whales likely achieve through social familiarity and vocal dialect recognition. We propose that lifetime philopatry of both sexes has been selectively favoured in this population due to the inclusive fitness benefits of kin-directed food sharing, a cooperative behaviour that may also inhibit dispersal by reducing resource competition among kin.
... As aerobic dive capacity tracks Mb levels [4], these low Mb levels likely contribute to the reduced dive times reported in younger mysticetes [46,50]. Ecologically, the consequences of reduced dive capacity are far-reaching: Predation risks increase [37,59] and increases in surfacing frequency and persistence raise the energetic costs of travel [60][61][62]. Additionally, foraging success for maternal females with dependent calves is impacted, due to the competing needs of offspring vigilance vs. diving [42]. ...
Article
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For marine mammals, the ability to tolerate apnea and make extended dives is a defining adaptive trait, facilitating the exploitation of marine food resources. Elevated levels of myoglobin within the muscles are a consistent hallmark of this trait, allowing oxygen collected at the surface to be stored in the muscles and subsequently used to support extended dives. In mysticetes, the largest of marine predators, details on muscular myoglobin levels are limited. The developmental trajectory of muscular myoglobin stores has yet to be documented and any physiological links between early behavior and the development of muscular myoglobin stores remain unknown. In this study, we used muscle tissue samples from stranded mysticetes to investigate these issues. Samples from three different age cohorts and three species of mysticetes were included (total sample size = 18). Results indicate that in mysticete calves, muscle myoglobin stores comprise only a small percentage (17-23%) of conspecific adult myoglobin complements. Development of elevated myoglobin levels is protracted over the course of extended maturation in mysticetes. Additionally, comparisons of myoglobin levels between and within muscles, along with details of interspecific differences in rates of accumulation of myoglobin in very young mysticetes, suggest that levels of exercise may influence the rate of development of myoglobin stores in young mysticetes. This new information infers a close interplay between the physiology, ontogeny and early life history of young mysticetes and provides new insight into the pressures that may shape adaptive strategies in migratory mysticetes. Furthermore, the study highlights the vulnerability of specific age cohorts to impending changes in the availability of foraging habitat and marine resources.
... Peregrine falcons (Falco peregrinus) and cheetahs (Acinonyx jubatus) pursue prey for hundreds of meters, but rarely for more than 30 s (Cresswell, 1996;Schaller, 1968). Even pursuits of larger game by cooperative hunters typically last b5 min (e.g., Boesch, 1994;Creel and Creel, 1995;Mech, 1981; but see Ford et al., 2005). Animals commonly escape brief encounters with predators (reviewed by Vermeij, 1982), and thus live long enough to experience the presumed resulting GC response. ...
Article
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Researchers typically study "acute" activation of the hypothalamic-pituitary-adrenal (HPA) axis by measuring levels of circulating glucocorticoids in animals that have been exposed to a predator, a cue from a predator (e.g., odor), or have experienced a standardized capture-and-restraint protocol, all of which are many minutes in duration. However, exposure to predators in the "wild" either as the subject of an attack or as a witness to an attack, is generally much shorter as most depredation attempts upon free-living animals last <5s. Yet, whether a stimulus lasting only seconds can activate the HPA axis is unknown. To determine if a stimulus of a few seconds triggers a glucocorticoid response, we measured levels of corticosterone (CORT; the primary avian glucocorticoid) in wild-caught European starlings (Sturnus vulgaris) after they witnessed a brief (< 2-8s) raptor attack upon a conspecific, a human "attack" (i.e., a researcher handling a conspecific), and an undisturbed control. Witnesses of a raptor attack responded with CORT levels comparable to that induced by a standardized capture-and-restraint protocol. Glucocorticoid levels of individuals following the control treatment were similar to baseline levels, and those that witnessed a human "attack" had intermediate levels. Our results demonstrate that witnessing a predator attack of very brief duration triggers a profound adrenocortical stress response. Given the considerable evidence of a role for glucocorticoids in learning and memory, such a response may affect how individuals learn to recognize and appropriately react to predators.
... Mammal-eating killer whales are frequently found in the Salish Sea, the inland waters of Washington state and British Columbia, and are classified as part of the west coast stock of 'transient' killer whales (Bigg et al. 1990, Ford et al. 1998, Allen and Angliss 2011. These killer whales are known to prey upon seals, sea lions, porpoises and occasionally other cetaceans throughout their range (Baird et al. 1992, Baird and Dill 1995, Ford et al. 2006, Dahlheim and White 2010. Several of the most common prey species consumed by mammal-eating killer whales in the Salish Sea have undergone dramatic changes in the last 30 years. ...
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The primary prey species of mammal-eating killer whales in the Salish Sea, the inland waters of southern British Columbia and Washington state, have experienced dramatic increases in population abundances in the last 25 years. It is possible that changes in prey abundance over time have resulted in changes in predator spatial use, occurrence and group size. Focused studies of mammal-eating killer whale behavior in the area were undertaken from 1987-1993, and an extensive record of sightings with confirmed identifications was available from 2004-2010. Changes in occurrence across years, months, and subareas of the Salish Sea were examined as well as changes in group size and in the identity of specific matrilines using the area. Occurrence of mammal-eating whales increased significantly from 2004-2010 with different seasonal peaks compared to 1987-1993. Different matrilines occurred in different seasons, time periods, and subareas. Group size was larger in 2004-2010 than in 1987-1993. The whales may be increasing use of the area due to increasing prey abundance or an overall increase in the whale population size. Changes in seasonal patterns of occurrence and the increase in group size between the two periods could be due to increased prey diversity.
... Some species respond to predators by trying to outswim them (e.g. minke whales; Balaenoptera acutorostrata; Ford et al., 2005) and may use this response template also in response to approaching sonar sources . Our simulations showed that if the source is faster than the animal, moving perpendicular to the line of approach is an effective solution for the whale to increase distance and/or reduce sound exposure. ...
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The feeding ecology of predators can have a profound effect on their life history and behaviour. The killer whale—the apex marine predator—has a cosmopolitan distribution throughout the world’s oceans. Globally, it is a generalist predator with a diverse diet, but regionally, different socially and genetically isolated killer whale populations can have highly specialized foraging strategies involving only a few types of prey. In the eastern North Pacific, the three sympatric killer whale lineages have distinct dietary specializations: one feeds primarily on marine mammals, another on salmon, and the third appears to specialize on sharks. These ecological specializations are associated with distinct patterns of seasonal distribution, group size, social organization, foraging behavior, and acoustic activity. Divergent foraging strategies may have played a major role in the social isolation and genetic divergence of killer whale populations.
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Predators face decisions about which prey to include in their diet in order to maximize fitness. The foraging tactics used to capture prey and the resulting profitability of prey influence these decisions. We present the first evidence of prey-dependent foraging tactics and prey profitability in a free-ranging pinniped. We studied 39 adult male harbour seals Phoca vitulina at Sable Island, Nova Scotia using an animal-borne video system. Each male wore the camera system for 3 d during which 10 min video samples were recorded every 45 min from 06:00 h, resulting in approximately 3 h of videotape per male and a total of 1094 capture attempts of identified prey. Males foraged mainly on sand lance Ammodytes dubius and flounders (Pleuronectids), but salmonid and gadoid fishes were occasionally pursued. Foraging tactics differed among and within prey types based on differences in prey behaviour. Sand lance was both a cryptic prey, when in the bottom substrate, and a conspicuous schooling prey. Seal swimming speed, handling time and capture success differed between cryptic and conspicuous sand lance. The highest capture success and handling time was recorded for flounders. Estimated profitability, i.e. net energy intake per unit time, also differed with prey type and prey size. Our results suggest that diet selection may have important implications on the foraging energetics of pinnipeds.
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Most analyses of the relationship between group size and food intake of social carnivores have shown a discrepancy between the group size that maximizes energy intake and that which is most frequently observed. Around southern Vancouver Island, British Columbia, killer whales of the so-called transient form forage in small groups, and appear to prey exclusively on marine mammals. Between 1986 and 1993, in approximately 434 h of observations on transient killer whales, we observed 138 attacks on five species of marine mammals. Harbor seals were most frequently attacked (130 occasions), and the observed average energy intake rate was more than sufficient for the whale's energetic needs. Energy intake varied with group size, with groups of three having the highest energy intake rate per individual. While groups of three were most frequently encountered, the group size experienced by an average individual in the population (i.e., typical group size) is larger than three. However, comparisons between observed and expected group sizes should utilize only groups engaged in the behavior of interest. The typical size of groups consisting only of adult and subadult whales that were engaged primarily in foraging activities confirms that these individuals are found in groups that are consistent with the maximization of energy intake hypothesis. Larger groups may form for (1) the occasional hunting of prey other than harbor seals, for which the optimal foraging group size is probably larger than three; and (2) the protection of calves and other social functions.
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The prey preferences of African lions (Panthera leo) in Serengeti National Park, Tanzania, were examined in three ways. First, lion encounter rates with prey types were measured and compared with a random sample of the prey population. Lions encountered more wart hogs (Phacochoerus aethiopicus), Grant's gazelles (Gazella granti), wildebeests (ConnochaeUs taurinus), and zebras (Equus burchelli) than expected. Second, preferred prey types of lions were identified using conditional logit analysis. Lions preferred to hunt small prey groups, groups that were closer than 200 m, and groups that contained wart hogs, wildebeests, or zebras. Third, a risk-minimization optimal foraging model and a rate-maximization model were used to predict lion preferences. The foraging theory models predict that preferences should change with season and with lion group size. Qualitative support was found for most of these predictions.
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We studied the occurrence and behaviour of so-called transient killer whales (Orcinus orca) around southern Vancouver Island from 1986 to 1993. Occurrence and behaviour varied seasonally and among pods; some pods foraged almost entirely in open water and were recorded in the study area throughout the year, while others spent much of their time foraging around pinniped haulouts and other nearshore sites, and used the study area primarily during the harbour seal (Phoca vitulina) weaning-postweaning period. Overall use of the area was greatest during that period, and energy intake at that time was significantly greater than at other times of the year, probably because of the high encounter rates and ease of capture of harbour seal pups. Multipod groups of transients were frequently observed, as has been reported for "residents," but associations were biased towards those between pods that exhibited similar foraging tactics. Despite the occurrence of transients and residents within several kilometres of each other on nine occasions, mixed groups were never observed and transients appeared to avoid residents. Combined with previous studies on behavioural, ecological, and morphological differences, such avoidance behaviour supports the supposition that these populations are reproductively
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Optimisation of energy by aquatic mammals requires adaptations that reduce drag, and improve thrust production and efficiency. Drag is minimised by streamlining the body and appendages. Highly derived aquatic mammals have body shapes close to the optimal hydrodynamic design for drag reduction. There is no conclusive evidence for specialised drag reduction mechanisms, although decreasing hair density is associated with reduced drag. Improvement in thrust production and efficiency is accomplished by changes in propulsive mode and appendage design. Semiaquatic mammals employ drag-based propulsion using paddles, whereas fully aquatic mammals use lift-based propulsion with hydrofoils. Because paddling generates thrust through half the stroke cycle, propulsive efficiency is low and energetic cost is high compared with that for mammals using hydrofoils. Lift-based swimming is a rapid and high-powered propulsive mode. Oscillations of the hydrofoil generate thrust throughout the stroke cycle. For cetaceans and pinnipeds, propulsive efficiency is approximately 80%, and transport cost is below that of semiaquatic mammals. Behavioural adaptations help minimise energy expenditure by swimming mammals. Submerged swimming avoids increased drag from energy lost in formation of surface waves. Porpoising and wave riding, characteristic of dolphins, can reduce the transport costs, allowing for longer-duration swimming at high speeds.
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Two forms of killer whale (Orcinus orca), resident and transient, occur sympatrically in coastal waters of British Columbia, Washington State, and southeastern Alaska. The two forms do not mix, and differ in seasonal distribution, social structure, and behaviour. These distinctions have been attributed to apparent differences in diet, although no comprehensive comparative analysis of the diets of the two forms had been undertaken. Here we present such an analysis, based on field observations of predation and on the stomach contents of stranded killer whales collected over a 20-year period. In total, 22 species of fish and 1 species of squid were documented in the diet of resident-type killer whales; 12 of these are previously unrecorded as prey of O. orca. Despite the diversity of fish species taken, resident whales have a clear preference for salmon prey. In field observations of feeding, 96% of fish taken were salmonids. Six species of salmonids were identified from prey fragments, with chinook salmon (Oncorhynchus tshawytscha ) being the most common. The stomach contents of stranded residents also indicated a preference for chinook salmon. On rare occasions, resident whales were seen to harass marine mammals, but no kills were confirmed and no mammalian remains were found in the stomachs of stranded residents. Transient killer whales were observed to prey only on pinnipeds, cetaceans, and seabirds. Six mammal species were taken, with over half of observed attacks involving harbour seals (Phoca vitulina). Seabirds do not appear to represent a significant prey resource. This study thus reveals the existence of strikingly divergent prey preferences of resident and transient killer whales, which are reflected in distinctive foraging strategies and related sociobiological traits of these sympatric populations. 1471
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In October 1997 we observed a herd of approximately 35 killer whales (Orcinus orca) attack a pod of nine sperm whales (Physeter macrocephalus) 130 km off the coast of central California. During the four hours we watched, adult female killer whales, including some with calves, attacked in waves of four to five animals in what was apparently a “wound and withdraw” strategy. Adult male killer whales stood by until the very end when one charged in and quickly killed a seriously wounded sperm whale that had been separated from the group. The sperm whales appeared largely helpless: their main defensive behavior was the formation of a rosette (“marguerite”-heads together, tails out). When the killer whales were successful in pulling an individual out of the rosette, one or two sperm whales exposed themselves to increased attack by leaving the rosette, flanking the isolated individual, and leading it back into the formation. Despite these efforts, one sperm whale was killed and eaten and the rest were seriously, perhaps mortally, wounded. We also present details of two other encounters between sperm whales and killer whales that we observed. Although sperm whales, because of various behavioral and morphological adaptations, were previously thought to be immune to predation, our observations clearly establish their vulnerability to killer whales. We suggest that killer whale predation has potentially been an important, and underrated, selective factor in the evolution of sperm whale ecology, influencing perhaps the development of their complex social behavior and at-sea distribution patterns.
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Killer Whales are well-known as predators of other marine mammals, including the large Sperm and baleen whales. Members of all marine mammal families, except the river dolphins and manatees, have been recorded as prey of Killer Whales; attacks have been observed on 20 species of cetaceans, 14 species of pinnipeds, the Sea Otter, and the Dugong. Ecological interactions have not been systematically studied and further work may indicate that the Killer Whale is a more important predator for some populations than previously believed. Not all behavioural interactions between Killer Whales and other marine mammal species result in predation, however. Some involve ‘harassment’ by the Killer Whales, feeding by both species in the same area, porpoises playing around Killer Whales, both species apparently ‘ignoring’ each other, and even apparently unprovoked attacks on Killer Whales by sea lions. These non-predatory interactions are relatively common. We conclude that interactions between Killer Whales and marine mammals are complex, involving many different factors that we are just beginning to understand.
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Measurements of an immature fin whale (Balaenoptera physalus), which died as a result of entrapment in fishing gear near Frenchmans Cove, Newfoundland (47 degrees 9' N, 55 degrees 25' W), were made to obtain estimates of volume and surface area of the animal. Detailed measurements of the flukes, both planform and sections, were also obtained. A strip theory was developed to calculate the hydrodynamic performance of the whale's flukes as an oscillating propeller. This method is based on linear, two-dimensional, small-amplitude, unsteady hydrofoil theory with correction factors used to account for the effects of finite span and finite amplitude motion. These correction factors were developed from theoretical results of large-amplitude heaving motion and unsteady lifting-surface theory. A model that makes an estimate of the effects of viscous flow on propeller performance was superimposed on the potential-flow results. This model estimates the drag of the hydrofoil sections by assuming that the drag is similar to that of a hydrofoil section in steady flow. The performance characteristics of the flukes of the fin whale were estimated by using this method. The effects of the different correction factors, and of the frictional drag of the fluke sections, are emphasized. Frictional effects in particular were found to reduce the hydrodynamic efficiency of the flukes significantly. The results are discussed and compared with the known characteristics of fin-whale swimming.
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Populations of seals, sea lions, and sea otters have sequentially collapsed over large areas of the northern North Pacific Ocean and southern Bering Sea during the last several decades. A bottom-up nutritional limitation mechanism induced by physical oceanographic change or competition with fisheries was long thought to be largely responsible for these declines. The current weight of evidence is more consistent with top-down forcing. Increased predation by killer whales probably drove the sea otter collapse and may have been responsible for the earlier pinniped declines as well. We propose that decimation of the great whales by post-World War II industrial whaling caused the great whales' foremost natural predators, killer whales, to begin feeding more intensively on the smaller marine mammals, thus "fishing-down" this element of the marine food web. The timing of these events, information on the abundance, diet, and foraging behavior of both predators and prey, and feasibility analyses based on demographic and energetic modeling are all consistent with this hypothesis.
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Describes the behaviour of a group of fin whales in the presence of 3 killer whales in the Gulf of California, Mexico. -from Authors
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In June 1994, we observed a herd of killer whales (Orcinus orca) attack a school of pantropical spotted dolphins (Stenella attenuata) in the Gulf of Mexico. The killer whales cut out up to three dolphins from the school, then proceeded to take turns chasing a single dolphin and keeping it within a confined area for 1.5 h. They could have killed the dolphin at any time, but apparently chose to prolong the encounter instead. An adult female killer whale appeared to use the opportunity as a training session for her calf. The single adult male present did not participate until the end of the encounter. He made several loud percussions by slapping his flippers, dorsal fin, and flukes against the water surface, then he swam to the dolphin and quickly killed it. Neither the role of the adult male killer whale in cooperative feeding situations nor the significance of the marked sexual dimorphism in this species has ever been adequately explained. We suggest that size differences between the sexes may have evolved as an 'ecological sex trait', allowing groups of related individuals to take a wider diversity of prey sizes.
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Aerial observations of humpback whales in the region of Point Cloates, Western Australia, during 1952 are recorded. The first southward-moving humpback whale was sighted on July 21, while decreasing numbers were seen moving northwards until early October. In 1952 the change from a predominantly northward migration of humpback whales to a southward migration occurred close to August 24. The speed of migration of a number of these whales is recorded, the mean value being 4.3 kt. A few humpback whale calves were sighted early in July and a peak in their occurrence in August suggests maximum frequency of parturition early in August. A very great increase in the occurrence of calves in the area late in the season suggests that female humpback whales rearing calves move southwards later than other individuals. Some evidence is presented that Exmouth Gulf is a nursery area. The presence of some killer, fin, blue, and minke whales in the area is noted.
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The severely depleted bowhead whale Balaena mysticetus has failed to recover from overexploitation during the 18th and 19th centuries in the Eastern Arctic. Although commercial whaling for bowheads ended in this region about 1915, bowhead whaling by native people has continued until recently in parts of the Eastern Arctic. Low-level but persistent hunting by Inuit (Eskimos) may have inhibited bowhead population increase. Two natural mortality factors can be documented—ice entrapment and predation by killer whales Orcinus orca. There is little direct evidence of ice-related mortality but a strong circumstantial argument that ice conditions affect survival. Killer whales are known to prey on most species of large whales, and we believe bowhead whales and right whales Eubalaena glacialis are especially vulnerable. The bowhead's apparent failure to recover in the Eastern Arctic may be due to a combination of continued low-level hunting, habitat instability, and predation. Complete protection from all forms of hunting is necessary to ensure the bowhead's survival. Environmental disturbances due to industrial development in the Arctic may have direct and indirect impact on bowhead habitat and behaviour, creating an urgent need for further study.
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Despite well-documented experimental evidence of echolocation in toothed whales, virtually nothing is known about the use and functional significance of cetacean sonar in the wild. Here, the patterns of echolocation sounds produced by killer whales,Orcinus orca, off British Columbia and Alaska are described. Two sympatric populations with divergent food habits differed markedly in sonar sound production. Individuals belonging to the fish-eating ‘resident’ population produced trains of characteristic sonar clicks, on average, 4% of the time, 27 times more often than marine mammal-eating ‘transient’ killer whales. The click trains of residents averaged 7s, more than twice as long as the trains of transients. Click repetition rates within resident's trains were constant or changed gradually; within transient's trains they often fluctuated abruptly. Transients produced isolated single or paired clicks at an average rate of 12/h, four times as often as residents. In general, the isolated clicks and infrequent, short and irregular trains of transients were less conspicuous against background noise than the sonar of residents. This difference in acoustic crypticity may reflect a flexible response to the probability of alerting prey, because marine mammals have more acute hearing than fish in the frequency range of sonar clicks. In both populations, echolocation use per individual decreased with increasing group size, suggesting the sharing of information between group members. No relationships were found between echolocation activity and water clarity for whales of either population. Transient whales often travelled or foraged without discernibly echolocating, suggesting that passive listening provides cues for prey detection and orientation.
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An observer may wonder whether a school of `running' dolphins, consisting of numerous, wildly splashing individuals, is using the most efficient mode of locomotion, because splashing wastes energy. Dolphins exhibit at least three modes of swimming. In leisurely, unhurried motion, they break the surface briefly and gently, often showing little more than the blowhole. At a faster, `cruising' speed, frequently at 3-3.5 ms-1 (6-7 knots), the animals are seen swimming primarily just beneath the surface, and there is still little splashing. (Behaviour and speeds of dolphin schools were observed from a helicopter and will be described elsewhere by D. A. and W. Ferryman.) Swimming speeds in this mode have been measured up to 4.6 ms-1 (9.3 knots). But in the fastest `running' mode, the animals clear the water in sequential, parabolic leaps, accompanied by considerable splashing on exit and re-entry (Fig. 1). Leaps are interspersed with relatively brief, subsurface swimming. This swimming is common when dolphins are alarmed by vessels approaching within 500 m. We have examined dolphin swimming in terms of energy required per unit distance travelled and report here that beyond a certain `crossover' speed, leaping must be more efficient than swimming.
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Bowheads were observed from shore on virtually every day of adequate visibility in late summer, early fall of 1984-88, but in 1983 only 2 whales appeared. Peak numbers occurred in September, when as many as 68 whales were counted on one day. The whales congregated in specific areas corresponding to significant underwater topographic features. Most feeding took place in one of 2 deep (>200m) troughs and most social activity occurred on a shallow bank (<30m). Earliest arrivals were large subadults that engaged in social-sexual activities on the bank; adults arrived later and fed in deep troughs. Migrants from the N arrived in October. -from Author
Article
In the first half of the twentieth century, harbor seal (Phoca vitulina richards i) numbers were severel y reduced in Washington state by a state-financed population control program. Seal numbers began to recover afte r the cessation of bounties in 196 0 and passage of the Marine Mammal Protection Act (MMPA) in 197 2 . From 197 8 to 199 9 , aerial surveys were flown at midday low tides during pupping season to determine the distribution an d abundance of harbor seals in Washington. We used exponential and generalized logistic models to examine po p - ulation trends and size relative to maximum net productivity level (MNPL) and carrying capacity (K). Observe d harbor seal abundance has increased 3 - fold since 197 8 , and estimated abundance has increased 7 to 1 0 -fold sinc e 197 0 . Under National Marine Fisheries Service (NMFS) management, Washington harbor seals are divided into 2 stocks: coastal and inland waters. The observed population size for 199 9 is very close to the predicted Kfor bot h stocks. The current management philosophy for marine mammals that assumes a density-dependent response i n population growth with MNPL >K / 2 is supported by growth of harbor seal stocks in Washington waters .
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In an effort to stimulate debate, Corkeron and Connor (1999) provide a valuable summary and critique of existing hypotheses regarding the long-standing mystery of why some baleen whales undertake extensive seasonal migrations into biologically unproductive waters. More or less convincingly, they dismiss existing arguments and propose instead that migration evolved as a predator-avoidance strategy. They suggest that, by migrating to tropical or subtropical waters during the winter calving season, whales remove themselves and their vulnerable offspring from the high-latitude range of most killer whales (Orcinus orca). Here, I examine this idea further and suggest that predation is unlikely to be the primary force influencing mysticete migratory behavior.
Article
The annual migrations of baleen whales are a conspicuous but unexplained feature of their behavioral repertoire. Some hypotheses offered to explain whale migration focus on direct benefits to the calf (thermoregulation, calm water) and some do not (resource tracking, and the “evolutionary holdover” hypothesis). Here, we suggest that a major selective advantage to migrating pregnant female baleen whales is a reduced risk of killer whale (Orcinus orca) predation on their newborn calves in low-latitude waters. Killer whale abundance in high latitudes is substantially greater than that in lower latitudes, and most killer whales do not appear to migrate with baleen whales. We suggest that the distribution of killer whales is determined more by their primary marine mammal pr