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Killer whales (Orcinus orca) are the apex predator in global oceans, and as such they are afforded access to prey species at all trophic levels and sizes. Due to their enhanced cognitive abilities, they are frequent predators of other ocean giants, including large sharks. Observations of these predator-prey interactions are rare globally; however, records appear to be increasing in recent years, possibly due to increased access to surveillance. Here we present reports of killer whales hunting and preying on the world's largest fish species, the whale shark (Rhincodon typus), by collating and analyzing photo and video footage collected from four unique predation events spanning six years (2018 – 2024) in the southern Gulf of California. Across all events, orcas displayed a seemingly approach to collaboratively hunting and killing whale sharks, characterized by focusing on attacking the pelvic area (claspers and pelvic fins) which exsanguinates the prey and allows access to the lipid-rich liver. Photo identification of the killer whales revealed that an individual adult male "Moctezuma" was engaged in three of the four events, and the females involved in event four had previously been sighted with him. We suggest the potential existence of a specialized pod of elasmobranch-hunting killer whales occurring in the Gulf of California. [ABSTRACT FROM AUTHOR]

Knowledge of killer whale (Orcinus orca) feeding ecology in tropical waters is scarce. In the southwest Indian Ocean, opportunistic sightings provide a valuable source of information to better understand their behaviour, diet and distribution. Here, we compile existing records of killer whale predation on elasmobranchs in the southwest Indian Ocean, including sightings of three undescribed prey species regionally: a giant manta ray (Mobula birostris), a sicklefin devil ray (Mobula tarapacana) and a tiger shark (Galeocerdo cuvier). Documenting such observations is important to increase knowledge on killer whale ecology in the tropics and the cascading impact they might have on prey populations. [ABSTRACT FROM AUTHOR]

Orcas (Orcinus orca) have a worldwide distribution and as apex predators feed on a wide variety of prey, including marine mammals, seabirds, sea turtles, cephalopods, teleost fish and elasmobranchs. Historically, there have been few observations of orca predation on large elasmobranch species nor are they commonly identified in the stomach contents of deceased orcas. In recent years there has been an increase in observational records of orca predation, such as on white sharks (Carcharodon carcharias) in South Africa, which could indicate that elasmobranchs serve a greater importance in their diet than previously considered. These events are often documented by members of the public due to the development and affordability of innovative cameras, including the use of the drones (unoccupied aerial vehicles). Here we describe new predator-prey interactions between orcas and large shark species in Cabo Pulmo National Park (CPNP), a small no-take marine protected area located in the Gulf of California. In this paper, we were able to successfully identify individuals from the described orca pods in the region; specifically, the same individuals hunting sharks over a period of nearly two years. We discuss the potential implications of these new ecological interactions, given the importance of tourism to sustain the management of CPNP, as cascading impacts have been documented elsewhere in light of orca predations on sharks. [ABSTRACT FROM AUTHOR]

Photography and video footage, captured by researchers and tourists on board two vessels, provided insights into the predation techniques employed by an adult male killer whale Orcinus orca in Mossel Bay, South Africa. The incapacitation of its prey, a juvenile white shark Carcharodon carcharias (∼2.5 m TL), followed by consumption of the liver, occurred within less than 2 minutes, highlighting the predator proficiency of the killer whale. Notably, another adult male killer whale, and constant traveling companion with the first, was observed approximately 100 m away and was not involved during the predation. The following day a second carcass of a different eviscerated white shark (3.55 m TL) washed ashore in the vicinity, indicating that at least two white sharks may have been killed during the interaction. [ABSTRACT FROM AUTHOR]

This paper provides a novel, unique, and improved optimization algorithm called the modified Orca Predation Algorithm (mOPA). The mOPA is based on the original Orca Predation Algorithm (OPA), which combines two enhancing strategies: Lévy flight and opposition-based learning. The mOPA method is proposed to enhance search efficiency and avoid the limitations of the original OPA. This mOPA method sets up to solve the global optimization issues. Additionally, its effectiveness is compared with various well-known metaheuristic methods, and the CEC'20 test suite challenges are used to illustrate how well the mOPA performs. Case analysis demonstrates that the proposed mOPA method outperforms the benchmark regarding computational speed and yields substantially higher performance than other methods. The mOPA is applied to ensure that all load demand is met with high reliability and the lowest energy cost of an isolated hybrid system. The optimal size of this hybrid system is determined through simulation and analysis in order to service a tiny distant location in Egypt while reducing costs. Photovoltaic panels, biomass gasifier, and fuel cell units compose the majority of this hybrid system's configuration. To confirm the mOPA technique's superiority, its outcomes have been compared with the original OPA and other well-known metaheuristic algorithms. [ABSTRACT FROM AUTHOR]

Quantifying the diet composition of apex marine predators such as killer whales (Orcinus orca) is critical to assessing their food web impacts. Yet, with few exceptions, the feeding ecology of these apex predators remains poorly understood.Here, we use our newly validated quantitative fatty acid signature analysis (QFASA) approach on nearly 200 killer whales and over 900 potential prey to model their diets across the 5000 km span of the North Atlantic.Diet estimates show that killer whales mainly consume other whales in the western North Atlantic (Canadian Arctic, Eastern Canada), seals in the mid‐North Atlantic (Greenland), and fish in the eastern North Atlantic (Iceland, Faroe Islands, Norway). Nonetheless, diet estimates also varied widely among individuals within most regions. This level of inter‐individual feeding variation should be considered for future ecological studies focusing on killer whales in the North Atlantic and other oceans.These estimates reveal remarkable population‐ and individual‐level variation in the trophic ecology of these killer whales, which can help to assess how their predation impacts community and ecosystem dynamics in changing North Atlantic marine ecosystems.This new approach provides researchers with an invaluable tool to study the feeding ecology of oceanic top predators. [ABSTRACT FROM AUTHOR]

The approximate degree reduction of ball non-uniform rational B-splines (NURBS) curves is a pivotal and knotty technique in computer-aided design/computer-aided manufacture. As we all know, the multi-degree reduction of NURBS ones is a mathematical optimization problem that a swarm intelligence algorithm can deal with. This paper uses an improved orca predation algorithm (IOPA) to accomplish the optimal multi-degree reduction of NURBS curves. Firstly, by incorporating a dimension learning strategy and opposition-based learning strategy into the orca predation algorithm (OPA), an IOPA is developed to increase the population diversity and enhance its capability of jumping out of the local minima. Secondly, the superiority of the proposed IOPA is comprehensively verified by comparing it with the original OPA and numerous celebrated and newly developed algorithms on the IEEE Congress on Evolutionary Computation (CEC) 2014 test suite and IEEE CEC2017 benchmark functions, respectively. Meanwhile, the practicability of IOPA is also highlighted by solving three real-world engineering design problems. Furthermore, statistical testing of IOPA has been conducted to validate its significance. Finally, the optimization model of multi-degree reduction for NURBS curves is established by minimizing the distance between the original curve and the approximate curve. The IOPA is utilized to solve the optimization model, and the optimal approximate NURBS curves are obtained. Some representative numerical examples illustrate the ability of the proposed IOPA to effectively solve the multi-degree reduction problem of NURBS curves in terms of precision, robustness, and convergence characteristics. [ABSTRACT FROM AUTHOR]

Historically, there has been only one documented fatal killer whale (Orcinus orca) attack on a fin whale (Balaenoptera physalus)--from Baja California, Mexico (BC), in 2005. We compiled records of seven more recent fatal attacks, including four more from BC. Two male killer whales that we identified were involved, separately or together, in at least four of the five fin whale kills off BC as they traveled with their groups the length of the Baja Peninsula on both sides. They were also involved in two Bryde's whale (Balaenoptera edeni) kills, and we suggest that they might specialize on large whale prey. We discuss offensive and defensive strategies during these attacks and the role (or lack thereof) of adult male killer whales. One of the fin whales taken appeared to be a healthy adult, which raises questions about large whales as prey for killer whales. We also discuss the burgeoning role of citizen science in this type of research, noting that most of our data came from social media postings. [ABSTRACT FROM AUTHOR]

Information on factors contributing to the morbidity and mortality of the Bering–Chukchi–Beaufort seas stock of bowhead whales (Balaena mysticetus) is fundamental to its successful management and recovery. The Alaska Arctic coastline is remote and expansive, making monitoring for and gross examination of carcasses difficult. However, sighting data and imagery collected during aerial surveys in the eastern Chukchi (EC) and western Beaufort (WB) seas from 2009 through 2019 provide information on bowhead whale mortality. We present bowhead whale carcass data from the 2019 aerial surveys that add to the long series of consistent information on floating and beach-cast bowhead whale carcasses. The 2019 carcass data suggest an increased occurrence of probable killer whale (Orcinus orca) predation on bowhead whales in the WB. Eleven bowhead whale carcasses were photo-documented from July to October 2019 in the EC and WB study areas. Of the 11 carcasses documented, 7 had injuries consistent with probable killer whale predation—2 in the EC and 5 in the WB. Probable cause of death could not be assigned to four carcasses. No carcasses were associated with aboriginal subsistence hunting. Despite similar annual survey effort from 2009 to 2019, several compelling deviations in carcass numbers and locations were observed in 2019. Compared to 2009–2018, 2019 had the highest yearly number of documented carcasses and the most categorized as probable killer whale predation. Carcass locations exhibited a striking shift from the EC to the WB. Lastly, more carcasses were categorized as probable killer whale predation in the WB during 2019 than in 2009–2018 combined. [ABSTRACT FROM AUTHOR]

The rapid emergence of new marine developments (e.g., marine renewables, port infrastructure) alongside the substantial growth of existing industries has ultimately resulted in an unprecedented increase in anthropogenic structures within the marine environment over the previous century. Knowledge of whether marine species interact with, avoid, or accommodate and adapt to such structures is essential to ensure that further development of marine environments do not compromise conservation objectives of marine species. This article documents one such interaction. Herein, we describe the observation of a harbour seal (Phoca vitulina) seeking refuge from a group of foraging killer whales (Orcinus orca) within a blue (aka common) mussel (Mytilus edulis) farm. Aerial video footage (38 min 27 s) was collected using an unmanned aerial system during an encounter at an aquaculture site in Dury Voe, Shetland, UK. Analysis of the footage showed the killer whale group spent 73.7% of the total encounter time exhibiting predatory associated behaviours and that they were observed interacting with the mussel farm infrastructure only during "predation activity" for a total of 26 min 52 s (72.8%). The harbour seal interacted with the mussel farm infrastructure during re- and proactive anti-predator behaviour and when exhibiting fatigue for 27 min 59 s, 94.4% of the total time the seal was observed. It is clear that both marine and terrestrial predator-prey interactions are increasingly occurring in settings that are in some way defined by the Anthropocene. The implications of this are discussed, including potential entanglement risk and human-altered "landscapes of fear." As comprehension of the potential effects of human-altered risk grows, such knowledge should be taken into consideration prior to further modification of marine habitats. [ABSTRACT FROM AUTHOR]

Examining Eastern North Pacific gray whale (Eschrichtius robustus) carcasses and tracking mortality and morbidity are essential for assessing the health of this stock. In the eastern Chukchi Sea, the expansive coastline relative to few coastal communities makes monitoring for and physical examination of gray whale carcasses difficult. The Aerial Surveys of Arctic Marine Mammals (ASAMM) project offers an unparalleled dataset of gray whale carcasses, documented and photographed from July to October 2009–2019, providing a unique opportunity to investigate imaged gray whale carcasses for possible cause of death. Surveys covered expanses of gray whale and killer whale (Orcinus orca) summer and autumn habitat. ASAMM documented a total of 59 gray whale carcasses, distributed across the eastern Chukchi Sea (67.5° N–72.0° N, 155.5° W–169.0° W). Carcass sighting rates ([CPUE] carcasses per 1000-km of effort) varied by month and year. The highest numbers of carcasses were observed in 2012 (13) and 2019 (8). August had the highest number of gray whale carcass sightings (22) and the highest carcass sighting rate (0.231 CPUE). Images were obtained for 56 gray whale carcasses. The majority (41) of imaged gray whale carcasses had injuries consistent with probable killer whale predation, and were photo-documented every year except 2010 (when no carcasses were seen) and 2011. Eight carcasses were suspect killer whale predation, and cause of death could not be determined for seven carcasses. These results will be valuable for evaluating mortality, concurrent with rapid oceanographic changes, and increases in anthropogenic activities. [ABSTRACT FROM AUTHOR]

This study investigates survival and abundance of killer whales (Orcinus orca) in Norway in 1988–2019 using capture–recapture models of photo‐identification data. We merged two datasets collected in a restricted fjord system in 1988–2008 (Period 1) with a third, collected after their preferred herring prey shifted its wintering grounds to more exposed coastal waters in 2012–2019 (Period 2), and investigated any differences between these two periods. The resulting dataset, spanning 32 years, comprised 3284 captures of 1236 whales, including 148 individuals seen in both periods. The best‐supported models of survival included the effects of sex and time period, and the presence of transients (whales seen only once). Period 2 had a much larger percentage of transients compared to Period 1 (mean = 30% vs. 5%) and the identification of two groups of whales with different residency patterns revealed heterogeneity in recapture probabilities. This caused estimates of survival rates to be biased downward (females: 0.955 ± 0.027 SE, males: 0.864 ± 0.038 SE) compared to Period 1 (females: 0.998 ± 0.002 SE, males: 0.985 ± 0.009 SE). Accounting for this heterogeneity resulted in estimates of apparent survival close to unity for regularly seen whales in Period 2. A robust design model for Period 2 further supported random temporary emigration at an estimated annual probability of 0.148 (± 0.095 SE). This same model estimated a peak in annual abundance in 2015 at 1061 individuals (95% CI 999–1127), compared to a maximum of 731 (95% CI 505–1059) previously estimated in Period 1, and dropped to 513 (95% CI 488–540) in 2018. Our results indicate variations in the proportion of killer whales present of an undefined population (or populations) in a larger geographical region. Killer whales have adjusted their distribution to shifts in key prey resources, indicating potential to adapt to rapidly changing marine ecosystems. [ABSTRACT FROM AUTHOR]

Killer whale (Orcinus orca) populations specialize in both prey and prey acquisition tactics around the world and may be a primary evolutionary driver of the habits of small cetaceans. Entanglement in fishing gear is the most significant anthropogenic threat to the survival of cetaceans worldwide. Distinguishing between natural and human-caused sources of mortality and injury is a key task in marine mammal conservation and management. In British Columbia (BC), Canada, mammal-eating killer whales co-occur with Pacific white-sided dolphins (Lagenorhynchus obliquidens). Bycatch mortality rates are unknown here due to lack of systematic fisheries observer coverage. Drawing from more than three decades of first-hand observations of killer whale attacks on Pacific white-sided dolphins, we identify common themes with respect to predatory behavior of killer whales and anti-predatory responses of dolphins. With input from veterinary pathologists, we outline clues to distinguish killer whale rake marks from scars and wounds likely to be caused by fishery interactions. We examined photographs of 415 well-marked Pacific white-side dolphins for evidence of injuries and scars consistent with either killer whale attacks or fishery interactions. In this case study, healed scars from interactions with killer whale predators were ∼8× more common than scars from fishery interactions (3.9 vs. 0.5%), suggesting that predation is a much bigger threat to Pacific white-sided dolphins in the study area than anthropogenic impacts, or that dolphins are much less likely to survive a fishery interaction than a predation attempt. To advance our knowledge on poorly studied species, multiple lines of evidence will be needed.

Understanding diet is critical for conservation of endangered predators. Southern Resident killer whales (SRKW) (Orcinus orca) are an endangered population occurring primarily along the outer coast and inland waters of Washington and British Columbia. Insufficient prey has been identified as a factor limiting their recovery, so a clear understanding of their seasonal diet is a high conservation priority. Previous studies have shown that their summer diet in inland waters consists primarily of Chinook salmon (Oncorhynchus tshawytscha), despite that species' rarity compared to some other salmonids. During other times of the year, when occurrence patterns include other portions of their range, their diet remains largely unknown. To address this data gap, we collected feces and prey remains from October to May 2004–2017 in both the Salish Sea and outer coast waters. Using visual and genetic species identification for prey remains and genetic approaches for fecal samples, we characterized the diet of the SRKWs in fall, winter, and spring. Chinook salmon were identified as an important prey item year-round, averaging ~50% of their diet in the fall, increasing to 70–80% in the mid-winter/early spring, and increasing to nearly 100% in the spring. Other salmon species and non-salmonid fishes, also made substantial dietary contributions. The relatively high species diversity in winter suggested a possible lack of Chinook salmon, probably due to seasonally lower densities, based on SRKW's proclivity to selectively consume this species in other seasons. A wide diversity of Chinook salmon stocks were consumed, many of which are also at risk. Although outer coast Chinook samples included 14 stocks, four rivers systems accounted for over 90% of samples, predominantly the Columbia River. Increasing the abundance of Chinook salmon stocks that inhabit the whales' winter range may be an effective conservation strategy for this population. [ABSTRACT FROM AUTHOR]

Imagery and sighting data on bowhead whale (Balaena mysticetus) carcasses documented from 2009 to 2018 during aerial surveys in the eastern Chukchi and western Beaufort seas have provided evidence for killer whale (Orcinus orca) predation on bowhead whales of the Bering–Chukchi–Beaufort Seas stock. The Aerial Surveys of Arctic Marine Mammals (ASAMM) project provides information on distribution, behavior, and relative density of marine mammals. ASAMM surveys large areas of bowhead whale and killer whale summer and autumn habitat and offers consistent information on bowhead whale carcasses. Thirty-three bowhead whale carcasses were documented in July–October, from 2009 to 2018. Carcasses were distributed across the eastern Chukchi and western Beaufort seas from 141.6° W to 168.1° W and 68.9° N to 72.0° N. Carcass sighting rates (carcasses/1000 km) varied by month, year, and region. Statistical results suggest an alternating series of high and low annual carcass sighting rates. Eighteen bowhead whale carcasses having injuries consistent with probable killer whale predation were photo-documented: four each in 2016 and 2018, three each in 2013 and 2015, two in 2012, and one each in 2010 and 2017. Four carcasses, two in 2015 and one each in 2013 and 2018, were likely whales struck and lost during aboriginal subsistence hunting. Cause of death could not be determined for 11 carcasses. This study is the first systematic inquiry into non-harvest related mortality of bowhead whales in the U.S. Pacific Arctic and provides multi-year evidence for killer whale predation on bowhead whales in this portion of their range. [ABSTRACT FROM AUTHOR]

Range expansions and increases in the frequency of killer whale (Orcinus orca) sightings have been documented in the eastern Canadian Arctic, presumably the result of climate change‐related sea‐ice declines. However, the effects of increased predator occurrence on this marine ecosystem remain largely unknown. We explore the consequences of climate change‐related range expansions by a top predator by estimating killer whale abundance and their possible consumptive effects on narwhal (Monodon monoceros) in the Canadian Arctic. Individual killer whales can be identified using characteristics such as acquired scars and variation in the shape and size of their dorsal fins. Capture–mark–recapture analysis of 63 individually identifiable killer whales photographed between 2009 and 2018 suggests a population size of 163 ± 27. This number of killer whales could consume >1,000 narwhal during their seasonal residency in Arctic waters. The effects of such mortality at the ecosystem level are uncertain, but trophic cascades caused by top predators, including killer whales, have been documented elsewhere. These findings illustrate the magnitude of ecosystem‐level modifications that can occur with climate change‐related shifts in predator distributions. [ABSTRACT FROM AUTHOR]

• The proposed strategy improves skin cancer diagnosis and patient outcomes. • Gated Recurrent Unit Network optimized by Orca predation Algorithm is used as a tool. • The tool is modified by an improved version of Orca predation Algorithm. • The tool shows an admirable result compared with some other techniques. • The method improves skin cancer diagnostics, enabling more accurate and efficient methods. Skin cancer is a risky ailment that can be effectively managed if detected promptly. However, timely recognition of skin cancer remains a challenge. In this study, a robotic computer-assisted tactic is proposed for the early detection of skin cancer. The motivation behind this research is to improve the accuracy and efficiency of skin cancer recognition. The proposed methodology involves a series of steps. Initially, the input images undergo preprocessing to enhance their quality and extract relevant features. These preprocessed images are then fed into a Gated Recurrent Unit (GRU) Network, a type of deep learning model known for its ability to capture sequential information. To optimize the performance of the GRU Network, we employ an enhanced variant of the Orca Predation Algorithm (OPA). This algorithm helps fine-tune the network parameters, improving its diagnostic capabilities. To validate and evaluate the effectiveness of our skin cancer diagnosis algorithm, we conducted experiments using the HAM10000 dataset, which contains a large collection of skin lesion images. We compared the results obtained from our proposed method, named GRU/IOPA, with eight existing techniques commonly used for skin cancer diagnosis. Five execution indices, namely sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy, were used to assess the performance of these methods. Our findings demonstrate that the GRU/IOPA system outperforms other existing methods in terms of sensitivity (0.95), specificity (0.97), PPV (0.95), NPV (0.96), and accuracy. These results indicate the effectiveness of our proposed method in diagnosing skin cancer compared to traditional approaches. The superior performance of GRU/IOPA highlights its potential impact on improving skin cancer diagnosis and reinforces its promise as an advanced tool in the field. In conclusion, our study presents a novel approach for timely skin cancer recognition through a robotic computer-assisted tactic. By utilizing the GRU/IOPA system, we achieve superior accuracy and efficiency in diagnosing skin cancer compared to existing techniques. This research offers significant contributions to the field of skin cancer diagnosis and opens up new avenues for future advancements in this area. [ABSTRACT FROM AUTHOR]

• Sightings of white sharks have declined at historical aggregation sites in South Africa since 2013. • Despite local declines, Bowlby et al. (2023) concluded the population as a whole is stable and likely redistributed. • We argue that data, analyses and interpretations by Bowlby et al. (2023) cannot support population stability or redistribution. • We suggest a precautionary approach to the conservation management of white sharks to be undertaken in South Africa. Bowlby et al. (2023) assessed spatio-temporal trends in South Africa's white shark (Carcharodon carcharias) population using a range of different proxies of white shark occurrence. The authors concluded that, despite significant declines in white shark sightings in several historical aggregation sites, the population as a whole has remained relatively stable throughout South Africa since its protection in 1991. The study also suggests a population redistribution eastward, likely driven by natural predator–prey dynamics (i.e., predation and related risk from orcas, Orcinus orca). Here, we highlight several issues with the methods and the inferences made in that study and argue that the data, as currently analysed and interpreted, cannot support population stability, or redistribution, of South Africa's white sharks. We also point out that the onset of the decline of white sharks at historical aggregation sites began before the documented appearance of specialist shark-eating orcas (the main alleged cause of the decline put forward in Bowlby et al. 2023). Our concern is that unsupported claims of population stability could jeopardize conservation actions urgently needed for white sharks, if the declines documented at their historical aggregations are representative of the population trend. Below we summarize our arguments. [ABSTRACT FROM AUTHOR]

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 Icelandic 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 Icelandic 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. [ABSTRACT FROM AUTHOR]

The inland waters of Washington State and southern British Columbia, collectively known as the Salish Sea, comprise key habitat for two regional populations of killer whales (Orcinus orca): the mammal-eating West Coast Transients and the endangered fish-eating Southern Residents. These two populations are genetically distinct and may avoid each other. Transient killer whale usage of the Salish Sea has been previously assessed over two seven-year time periods, showing an increase from 1987 to 2010. We documented a continued significant increase in mammal-eating killer whale presence in the Salish Sea from 2011 to 2017, with intra- and inter-annual variability and with record sightings in 2017. This continued increase, likely in response to abundant marine mammal prey, is related to both a growing population and an increase in the number of West Coast Transients visiting the area. Additionally, a negative binomial regression shows that absence of Southern Residents is correlated to transient presence. Finally, both populations of killer whales have been linked to regional harbor seal populations; harbor seals are salmonid-eating competitors of the Southern Residents and are prey for the mammal-eating transients. With Southern Residents listed as endangered, culling harbor seals has been proposed as a measure to help in their recovery. With this in mind, we developed an energetic model to assess the minimum number of harbor seals consumed by transient killer whales. Using the actual number of whales present in each age-sex class for each day of the year, we estimate that, at a minimum, transients in the Salish Sea consumed 1090 seals in 2017. This is more than 2% of the 2014 estimated harbor seal population the Salish Sea. The population controlling effects of transient killer whale predation on harbor seals should be considered when evaluating any pinniped management actions in the Salish Sea. [ABSTRACT FROM AUTHOR]

The article presents the results of a study which analyzed bite marks and scars on western gray whales (Eschrichtius robustus) by killer whales (Orcinus orca). Topics of discussion include photoidentification of gray whales off Sakhalin Island, Russia, in the North Pacific Ocean, new scars by non-calf whales, and sex ratio among gray whales.

The salmon-eating Southern Resident killer whales (Orcinus orca) of the north-eastern Pacific Ocean are listed as endangered both in the United States and Canada. Their critical habitat has been defined as the region of the inland waters of Washington State and British Columbia known as the Salish Sea, where they have traditionally spent much of their time from spring through fall. Using reports from experienced observers to sightings networks, we tracked the daily presence of the Southern Residents in these waters from 1 April to 30 June from 1994 through 2016. We found that the escapement estimates of spring Chinook salmon (Oncorhynchus tshawytscha) on the Fraser River in British Columbia were a significant predictor of the cumulative presence/absence of the whales throughout the spring season. There was also a difference in both whale presence and salmon abundance before and after 2005, suggesting that the crash in Chinook salmon numbers has fallen below threshold where it is worthwhile for the whales to spend as much time in the Salish Sea. The use of the Salish Sea by the Southern Residents has declined in the spring months as they are either foraging for Chinook salmon elsewhere or are shifting to another prey species. In order to continue providing necessary protections to this endangered species, critical habitat designations must be re-evaluated as this population of killer whales shifts its range in response to prey availability. [ABSTRACT FROM AUTHOR]

Historically, Fin Whales (Balaenoptera physnlus) were relatively common off the west coast of North America but very few records of their occurrence in waters between Vancouver Island and continental North America exist. To confirm their presence in these waters we collected photographs documenting at least 13 unique individuals during 43 encounters from 1999 to 2017. These records are the first of live Fin Whales in Queen Charlotte, Johnstone, Georgia and Juan De Fuca Straits and are also the only confirmed sightings between Vancouver Island and continental North America since 1930. Additionally, 12 dead Fin Whales all with evidence of ship strikes are reported in these waters between 1986 and 2017. Most (88%) sightings of live Fin Whales occurred between July and October and no individuals were documented dead or alive between January and April. We suggest that Fin Whales in coastal waterways may be at greater risk to ship strikes and predation by mammal-eating Killer Whales (.Orcimis oral) than in less confined waters further offshore. [ABSTRACT FROM AUTHOR]

The Southern Resident killer whale population (Orcinus orca) was listed as endangered in 2005 and shows little sign of recovery. These fish eating whales feed primarily on endangered Chinook salmon. Population growth is constrained by low offspring production for the number of reproductive females in the population. Lack of prey, increased toxins and vessel disturbance have been listed as potential causes of the whale’s decline, but partitioning these pressures has been difficult. We validated and applied temporal measures of progesterone and testosterone metabolites to assess occurrence, stage and health of pregnancy from genotyped killer whale feces collected using detection dogs. Thyroid and glucocorticoid hormone metabolites were measured from these same samples to assess physiological stress. These methods enabled us to assess pregnancy occurrence and failure as well as how pregnancy success was temporally impacted by nutritional and other stressors, between 2008 and 2014. Up to 69% of all detectable pregnancies were unsuccessful; of these, up to 33% failed relatively late in gestation or immediately post-partum, when the cost is especially high. Low availability of Chinook salmon appears to be an important stressor among these fish-eating whales as well as a significant cause of late pregnancy failure, including unobserved perinatal loss. However, release of lipophilic toxicants during fat metabolism in the nutritionally deprived animals may also provide a contributor to these cumulative effects. Results point to the importance of promoting Chinook salmon recovery to enhance population growth of Southern Resident killer whales. The physiological measures used in this study can also be used to monitor the success of actions aimed at promoting adaptive management of this important apex predator to the Pacific Northwest. [ABSTRACT FROM AUTHOR]

Although predators influence behavior of prey, analyses of electronic tracking data in marine environments rarely consider how predators affect the behavior of tracked animals. We collected an unprecedented dataset by synchronously tracking predator (killer whales, N = 1; representing a family group) and prey (narwhal, N = 7) via satellite telemetry in Admiralty Inlet, a large fjord in the Eastern Canadian Arctic. Analyzing the movement data with a switching-state space model and a series of mixed effects models, we show that the presence of killer whales strongly alters the behavior and distribution of narwhal. When killer whales were present (within about 100 km), narwhal moved closer to shore, where they were presumably less vulnerable. Under predation threat, narwhal movement patterns were more likely to be transiting, whereas in the absence of threat, more likely resident. Effects extended beyond discrete predatory events and persisted steadily for 10 d, the duration that killer whales remained in Admiralty Inlet. Our findings have two key consequences. First, given current reductions in sea ice and increases in Arctic killer whale sightings, killer whales have the potential to reshape Arctic marine mammal distributions and behavior. Second and of more general importance, predators have the potential to strongly affect movement behavior of tracked marine animals. Understanding predator effects may be as or more important than relating movement behavior to resource distribution or bottom-up drivers traditionally included in analyses of marine animal tracking data. [ABSTRACT FROM AUTHOR]

The killer whale (Orcinus orca) has a worldwide distribution and its feeding habits varies greatly among populations. In the southern Atlantic Ocean, knowledge about the distribution and diet of the species is still scarce. Herein we report the first evidence of a killer whale's attack on a southern right whale (Eubalaena australis) in Brazilian waters and provide new records of killer whale sightings in coastal waters of the southernmost Brazilian region. [ABSTRACT FROM AUTHOR]

Humpback whales ( Megaptera novaeangliae) are known to interfere with attacking killer whales ( Orcinus orca). To investigate why, we reviewed accounts of 115 interactions between them. Humpbacks initiated the majority of interactions (57% vs. 43%; n = 72), although the killer whales were almost exclusively mammal-eating forms ( MEKWs, 95%) vs. fish-eaters (5%; n = 108). When MEKWs approached humpbacks ( n = 27), they attacked 85% of the time and targeted only calves. When humpbacks approached killer whales ( n = 41), 93% were MEKWs, and ≥87% of them were attacking or feeding on prey at the time. When humpbacks interacted with attacking MEKWs, 11% of the prey were humpbacks and 89% comprised 10 other species, including three cetaceans, six pinnipeds, and one teleost fish. Approaching humpbacks often harassed attacking MEKWs (≥55% of 56 interactions), regardless of the prey species, which we argue was mobbing behavior. Humpback mobbing sometimes allowed MEKW prey, including nonhumpbacks, to escape. We suggest that humpbacks initially responded to vocalizations of attacking MEKWs without knowing the prey species targeted. Although reciprocity or kin selection might explain communal defense of conspecific calves, there was no apparent benefit to humpbacks continuing to interfere when other species were being attacked. Interspecific altruism, even if unintentional, could not be ruled out. [ABSTRACT FROM AUTHOR]

The article discusses the spatial variation in shark-inflicted injuries to Indo-Pacific bottlenose dolphins of the southwestern Indian Ocean. Topics include predation risk critical in shaping the behavior and population dynamics of prey taxa, populations of small delphinids at risk from predators, and predation risk from Killer whales primarily in temperate waters.

Observations of killer whales (Orcinus orca) feeding on the remains of beaked whales have been previously documented; however, to date, there has been no published account of killer whales actively preying upon beaked whales. This article describes the first field observations of killer whales interacting with, hunting and preying upon beaked whales (Mesoplodon spp.) on four separate occasions during 2014, 2015 and 2016 in the Bremer Sub-Basin, off the south coast of Western Australia. [ABSTRACT FROM AUTHOR]

Killer Whales (Orcinus orca) were observed on 4 August 2012 attacking Belugas (Delphinapterus leucas) at high tide near the mouth of the Seal River (59°9T9"N, 94°45'28"W) in southwest Hudson Bay, near the location where six Belugas had been fitted with satellite transmitters three weeks earlier. The distribution of Belugas was analyzed before, during, and after the attack. In the presence of Killer Whales, the six Belugas altered their behaviour by reducing their combined range size from 285 km2 four days before the attack to 172 km2 on the day of the attack. Their range more than tripled, to 655 km2, in the days immediately following the attack before returning to the pre-attack size. Following the attack, the tagged Belugas expanded their range northward, going from a mean pre-attack distance of 9.4 km from the attack site to a maximum of 23.5 km. Visual observations of Belugas clumping together and moving toward shore corroborated satellite data. This evasive behaviour by Belugas was different from that reported for Narwhals (Monodon monoceros) suggesting that the two monodontid species may have evolved different survival strategies related to the risk of Killer Whale predation. With predicted changes to Arctic sea ice, the summering habitat of Belugas will be available to their main predator for longer periods. A better understanding of Beluga behaviour and risk of predation is required for Beluga conservation and stock management. [ABSTRACT FROM AUTHOR]

Killer whales (Orcinus orca) in the Mediterranean Sea are currently restricted to the Strait of Gibraltar and surrounding waters. Thirty-nine individuals were present in 2011, with a well-differentiated social structure, organized into five pods. Killer whale occurrence in the Strait is apparently related to the migration of their main prey, Atlantic bluefin tuna (Thunnus thynnus). In spring, whale distribution was restricted to shallow waters off the western coast of the Strait where all pods were observed actively hunting tuna. In summer, the whales were observed in the shallow central waters of the Strait. A relatively new feeding strategy has been observed among two of the five pods. These two pods interact with an artisanal drop-line fishery. Pods depredating the fishery had access to larger tuna in comparison with pods that were actively hunting. The Strait of Gibraltar killer whales are socially and ecologically different from individuals in the Canary Islands. Molecular genetic research has indicated that there is little or no female-mediated gene migration between these areas. Conservation threats include small population size, prey depletion, vessel traffic, and contaminants. We propose the declaration of the Strait of Gibraltar killer whales as an endangered subpopulation. A conservation plan to protect the Strait of Gibraltar killer whales is urgently needed, and we recommend implementation of a seasonal management area where activities producing underwater noise are restricted, and the promotion of bluefin tuna conservation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Estimating diet composition is important for understanding interactions between predators and prey and thus illuminating ecosystem function. The diet of many species, however, is difficult to observe directly. Genetic analysis of fecal material collected in the field is therefore a useful tool for gaining insight into wild animal diets. In this study, we used high-throughput DNA sequencing to quantitatively estimate the diet composition of an endangered population of wild killer whales (Orcinus orca) in their summer range in the Salish Sea. We combined 175 fecal samples collected between May and September from five years between 2006 and 2011 into 13 sample groups. Two known DNA composition control groups were also created. Each group was sequenced at a ~330bp segment of the 16s gene in the mitochondrial genome using an Illumina MiSeq sequencing system. After several quality controls steps, 4,987,107 individual sequences were aligned to a custom sequence database containing 19 potential fish prey species and the most likely species of each fecal-derived sequence was determined. Based on these alignments, salmonids made up >98.6% of the total sequences and thus of the inferred diet. Of the six salmonid species, Chinook salmon made up 79.5% of the sequences, followed by coho salmon (15%). Over all years, a clear pattern emerged with Chinook salmon dominating the estimated diet early in the summer, and coho salmon contributing an average of >40% of the diet in late summer. Sockeye salmon appeared to be occasionally important, at >18% in some sample groups. Non-salmonids were rarely observed. Our results are consistent with earlier results based on surface prey remains, and confirm the importance of Chinook salmon in this population’s summer diet. [ABSTRACT FROM AUTHOR]

Predators are critical components of ecosystems. Globally, conservation efforts have targeted depleted populations of top predators for legal protection, and in many cases, this protection has helped their recoveries. Where the recovery of individual species is the goal, these efforts can be seen as largely successful. From an ecosystem perspective, however, predator recovery can introduce significant new conservation and legal challenges. We highlight three types of conflicts created by a single-species focus: (1) recovering predator populations that increase competition with humans for the same prey, (2) new tradeoffs that emerge when protected predators consume protected prey, and (3) multiple predator populations that compete for the same limited prey. We use two food webs with parallel conservation challenges, the Northeast Pacific Ocean and the Greater Yellowstone Ecosystem, to demonstrate legal/policy conflicts and the policy levers that exist to ameliorate conflicts. In some cases, scientific uncertainty about the ecological interaction hinders progress towards resolving conflicts. In others, available policy options are insufficient. In all cases, management decisions must be made in the face of an unknown future. We suggest a framework that incorporates multispecies science, policy tools, and tradeoff analyses into management. [ABSTRACT FROM AUTHOR]

Acoustic parameters of killer whale (Orcinus orca) whistles were described for the western South Atlantic Ocean and highlight the occurrence of high frequency whistles. Killer whale signals were recorded on December of 2012, when a pod of four individuals was observed harassing a group of sperm whales. The high frequency whistles were highly stereotyped and were modulated mostly at ultrasonic frequencies. Compared to other contour types, the high frequency whistles are characterized by higher bandwidths, shorter durations, fewer harmonics, and higher sweep rates. The results add to the knowledge of vocal behavior of this species. [ABSTRACT FROM AUTHOR]

Behavioural plasticity of top marine predators to adapt to seasonal changes in the behaviour of their prey is little understood. Here, we used data from 16 multi-sensor archival tags attached to killer whales in 2005, 2006 and 2009 to evaluate whether and how their feeding behaviour varied according to seasonal life-stages (overwintering, feeding and spawning) of their herring prey. Feeding periods with tail slaps were consistently characterized by non-directional movement with the production of calls and echolocation clicks, but angular deviation in heading during feeding periods was lower during overwintering than spawning prey life-stages. Tail slaps were produced more often at depths >10 m in the feeding and spawning prey life-stages, while during overwintering, they often occurred at <10 m depth, indicating the depth of feeding changed with predicted positions of prey in the water column. Echolocation clicks were produced less often during feeding upon overwintering herring, suggesting that visual cues may be used more in winter during daytime due to better underwater visibility. Thus, while maintaining an encircling strategy to exploit the year-round anti-predator schooling behaviour of their herring prey, observed variations in details of killer whale feeding behaviour across prey life-stages are likely driven by the size and depth of herring schools, and the cost-benefit balance of bringing herring schools to the surface in different environmental contexts. However, observed variations do not appear strong enough to indicate reciprocal phenotypic plasticity by the herring prey which seem to rely primarily upon general anti-predator strategies. [ABSTRACT FROM AUTHOR]

Reports of killer whales ( Orcinus orca) preying on large whales have been relatively rare, and the ecological significance of these attacks is controversial. Here we report on numerous observations of killer whales preying on neonate humpback whales ( Megaptera novaeangliae) off Western Australia ( WA) based on reports we compiled and our own observations. Attacking killer whales included at least 19 individuals from three stable social groupings in a highly connected local population; 22 separate attacks with known outcomes resulted in at least 14 (64%) kills of humpback calves. We satellite-tagged an adult female killer whale and followed her group on the water for 20.3 h over six separate days. During that time, they attacked eight humpback calves, and from the seven known outcomes, at least three calves (43%) were killed. Overall, our observations suggest that humpback calves are a predictable, plentiful, and readily taken prey source for killer whales and scavenging sharks off WA for at least 5 mo/yr. Humpback 'escorts' vigorously assisted mothers in protecting their calves from attacking killer whales (and a white shark, Carcharodon carcharias). This expands the purported role of escorts in humpback whale social interactions, although it is not clear how this behavior is adaptive for the escorts. [ABSTRACT FROM AUTHOR]

Interspecific interactions can be based on positive or negative outcome. Within antagonist interactions, predation refers to a predator attacking and feeding on a prey while competition is an interaction where individuals compete for a common resource. Worldwide distributions of long-finned pilot whales and killer whales rarely overlap, and they are not known to feed on the same preys. However, in this study, we described the interactions between long-finned pilot whales and killer whales in the Strait of Gibraltar. The former was seen pursuing away the latter in all observations. The main hypotheses for the cause of these interactions are predation or competition. To test both hypotheses, movement patterns and isotopic niches of both species were investigated in the Strait of Gibraltar through satellite tagging and stable isotopes, respectively. Satellite tracks showed no overlap between one tagged pilot whale and one tagged killer whaler's distributions during 21 days. Similarly, Euclidian distances between centroids of Bayesian standard ellipse areas of carbon and nitrogen stable isotopes were significantly different from zero, showing different isotopic niches for each species. This shows that no competition for the resources should exist between both species in the Strait of Gibraltar and that they do not feed on each other, suggesting that the interactions would not be related to predation. A possible historical presence of marine mammal-eating killer whales in the area, today disappeared, could explain the antipredator defense mobbing-like behavior of pilot whales observed in the Strait. [ABSTRACT FROM AUTHOR]

1. Killer whales Orcinus orca are found in all oceans of the world, but most of our knowledge on the species comes from studies conducted at higher latitudes. Studies on killer whales in the Caribbean have been scarce. 2. We compiled 176 records of killer whales from the Caribbean, including 95 previously unreported records and 81 records recovered from the literature, consisting of 27 capture or kill records, 4 stranding records and 145 sighting records. 3. Our results indicate that killer whales are widespread in the Caribbean Sea and can be found year-round in the region. Mean group size was 3.7 animals. A diversity of prey items was recorded, including sea turtles and marine mammals and possibly fish. We cannot exclude ecotype or morphotype-specific dietary specialization in the Caribbean population. A preliminary morphological analysis of 10 characters in 52 individuals from 21 different groups suggests that Caribbean killer whales do not represent any of the four Antarctic and subantarctic types, type 1 from the northwest Atlantic, or 'resident' and 'transient' killer whales from the northwest Pacific. Some Caribbean killer whales share a combination of characters typical of type 2 in the North Atlantic, whereas others share those typical of 'offshore' killer whales in the northwest Pacific. The significance of this is unclear. Comparison of Caribbean killer whales to previously described morphotypes and ecotypes is hampered by the lack of detailed, quantitative data on variation within other types, as well as by the lack of comparisons of genetic diversity. 4. Our study adds to the growing knowledge of the diversity of killer whales worldwide but underscores that additional research is warranted in the tropics. [ABSTRACT FROM AUTHOR]

Killer whales occur in Chilean waters, but their seasonality, diets, and overall distribution are poorly known. Here, we present data on group composition, site fidelity, and prey species of individual killer whales recorded in 63 sightings between 2004 and 2012 in the Chilean Patagonian fjords. Group sizes were small (mean = 5, SD = 2.5 for calf groups; mean = 3, SD = 1.5 for non-calf groups), and occurrence was significantly lower in summer months. Photographs enabled identification of 55 individuals from natural markings, and all resembled Southern Ocean type A killer whales. The species was transient in the area; the average presence was 1.7 days with 60 % of individuals seen only once. Occupancy was 3-44 days, and low levels of site fidelity were recorded (64 % of individuals were seen in only 1 year). Group composition at short time scales (3 months) remained stable, but we detected changes at longer time scales. Prey included fish, otariids, and seabirds. Twelve individual killer whales showed a broad dietary spectrum: 3 ate otariids and fish, 2 ate birds and otariids, and 7 ate otariids, birds, and possibly fish. Further research is needed to increase basic biological knowledge of these killer whales and to determine the relationship with type A killer whales from the Southern Ocean. [ABSTRACT FROM AUTHOR]

Abstract: Cetaceans are widely diversified in their sonometric characteristics but no comparative research has determined the general patterns that condition their bio-acoustic evolution across a large number of species. Echolocation calls of 69 cetaceans species has been obtained from different data sources. Through analysis by a Hierarchical Partitioning test, a non-parametric substitute of variance analysis, the absence of statistical differences between bioacoustic data sources has been demonstrated. Sounds were normalized and the fundamental frequency of each species was determined by autocorrelation. Also, the average swimming speed of each species was obtained from published papers. Finally, the intensity of the Doppler effect was calculated for each species using the mathematical equation of underwater sound physics. Doppler shifts lower than 160Hz were found for the majority of species. This can be explained as a behavioral strategy to avoid depredation by Killer Whales. Only certain species of Ziphidae (genus Mesoplodon, Indopacetus pacificus and Ziphius cavirostris) and six species of Delphinidae (from Lagenorhynchus and Cephalorhynchus genus) present higher Doppler shifts. These species had found other strategies to avoid depredation such as the use of echolocation only in deep waters, very high average swimming speeds, large flocks or the use of very high frequencies. From these results it is possible to conclude that depredation conditions all the evolution of echolocation signals of cetaceans except in a reduced number of species that had developed different behavioral strategies to escape from Killer Whales. [Copyright &y& Elsevier]

Highlights: [•] Global trade involves ships that can make important whale habitats noisy. [•] Northern resident killer whales showed subtle behavioral responses to large ships. [•] Endangered southern resident killer whales may experience ship transits hourly. [•] Half the whales demonstrated subtle behavioral changes at received levels of ∼130dB re: 1μPa. [•] Future work will address effects on foraging efficiency and population dynamics. [ABSTRACT FROM AUTHOR]

Increasing evidence links exposure to Navy sonar with certain mass stranding events of deep diving beaked whales. Although the cause of these strandings is unknown, one theory suggests that the animals confuse the sonar signals with vocalizations of killer whales, a known predator. Here we analyze the movement patterns of a tagged female Blainville's beaked whale in reaction to playback of killer whale predation calls. During a deep foraging dive, the whale was exposed to a playback of killer whale vocalizations with the source level slowly increased until the whale prematurely ceased foraging. The heading data from the tag were analyzed using a rotation test with a likelihood ratio calculated for a nonparametric kernel density estimate. We found a significant difference ( P < 0.005) in the distribution of Δheading (the change in heading averaged over 200 s) after the cessation of the killer whale playback. A test of the angular standard deviation (SD) of the Δheading showed that after the playback, the SD was significantly reduced ( P = 0.0064), which indicates that the animal maintained a straighter than normal course for an extended period of time. The prolonged directed avoidance response observed here suggests a behavioral reaction that could pose a risk factor for stranding. [ABSTRACT FROM AUTHOR]

Killer whales ( Orcinus orca) are increasing in occurrence and residence time in the eastern Canadian Arctic (ECA) in part due to a decrease in sea ice associated with global climate change. Killer whales prey on bowhead whales ( Balaena mysticetus) of the Eastern Canada-West Greenland (EC-WG) population, but their patterns of predation pressure and effect on the EC-WG population's ability to recover from historical whaling remain unknown. We analyzed photographs of individual bowhead whale flukes from five regions within the EC-WG population's geographic range (Cumberland Sound, Foxe Basin, Isabella Bay, Repulse Bay and Disko Bay), taken during 1986 and from 2007 to 2012, to estimate the occurrence of rake marks (parallel scars caused by killer whale teeth). Of 598 identified whales, 10.2 % bore rake marks from killer whales. A higher occurrence of rake marks was found in Repulse and Disko Bays, where primarily adult bowhead whales occur seasonally, than in Foxe Basin, where juveniles and females with calves occur. Older bowheads, which have had greater exposure time to killer whales due to their age, had higher occurrences of rake marks than juveniles and calves, which may indicate that younger whales do not survive killer whale attacks. A high proportion of adult females also had rake marks, perhaps due to protecting their calves from killer whale predation. In order to quantify the effect of killer whales on EC-WG population recovery, further research is needed on the relationship between the occurrence of rake marks and bowhead adult, calf, and juvenile mortality in the ECA, as well as more information about Arctic killer whale ecology. [ABSTRACT FROM AUTHOR]

Group hunting by killer whales for walruses was observed in August 18, 2008, in the littoral area (3 km from the haulout of walruses, Retkyn Spit, Chukotka). The group of killer whales consisted of seven adults (one adult male did not participate in attacks) and two calves. Based on prey type, these killer whales were mammal-eating. The total duration of their hunt activity was not less than 95 min. The hunt consisted of three phases. The first phase was an attack on the group of walruses and choice of individual prey; the second phase was attacks on the chosen walrus; and the third (final) phase was a decrease in activity of killer whales and leaving group with walrus from sea shore. The main behavioral patterns of killer whales during the hunt were discerned. Two killer whales tried to kill walruses by chasing them and jumping out of the water on the shore. The video analysis of the 'attack phase' showed that killer whales made 55 attacks on the walrus during 17.3 min. On average, each killer whale attacked the walrus seven times. The attack tactics of killer whales, the number of movements, and the location of killer whales (adults and calves) relative to each other and to the walrus were described. Well coordination of their movements and group actions was observed. [ABSTRACT FROM AUTHOR]