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We applied multi–temporal 1D magnetotelluric (MT) surveys to identify space–time anomalies of apparent resistivity ( ρ a ) in the upper lithosphere in the Antarctic Peninsula (the border between the Antarctic and the Shetland plates). We used time series over several weeks of the natural Earth's electric and magnetic fields registered at one MT station of the Universidad Nacional de Colombia (RSUNAL) located at Seymour–Marambio Island, Antarctica. We associated resistivity anomalies with contrasting earthquake activity. Anomalies of ρ a were detected almost simultaneously with the beginning of a seismic crisis in the Bransfield Strait, south of King George Island (approximately 85.000 events were reported close to the Orca submarine volcano, with focal depths < 20 km and MWW < 6.9). We explained the origin of these anomalies in response to fluid migration near the place of the fractures linked with the seismic swarm, which could promote disturbances of the pore pressure field that reached some hundreds of km away. [ABSTRACT FROM AUTHOR]

This is the first comprehensive review of marine mammal records from the Haswell archipelago (Davis Sea, East Antarctica), collected in 1912-2016. The goal of the review is to provide baseline ecological and faunal information on the marine mammals during the historical period (species diversity and status). Eight marine mammal species were recorded within the survey area. Ross seals (Ommatophoca rossii) and sei whales (Balaenoptera borealis) were seen very rarely. Killer whales (Orcinus orca), southern elephant seals (Mirounga leonina) and leopard seals (Hydrurga leptonyx) appeared rarely and few in numbers. Crabeater seals (Lobodon carcinophaga) were rare in general but common during the rare seasons of early fast ice breaking. Weddell seals (Leptonychotes weddellii) were common year-round. Antarctic minke whales (Balaenoptera bonaerensis) were seasonally common. Weddell seals and Antarctic minke whales were recorded annually. Only Weddell seals were found year-round. Leopard seals were seasonal residents, the remaining species were seasonal visitors in the area. The archipelago is an annual breeding site for Weddell seals (up to 10 pups per breeding season). Rare breeding of crabeater seals is possible. The information presented in this paper was obtained mostly through random observations and few historical records. During the long-term monitoring, a single agreed-upon data collection protocol was not used. As a result, the status of each marine mammal species in this paper should be regarded as preliminary. The review represents a basis for the development of further research programs. A unified protocol for the year-round registration of marine mammals under the conditions of the Mirny Station for the program for monitoring the biota of the Haswell archipelago is proposed. [ABSTRACT FROM AUTHOR]

The Antarctic Peninsula (AP) is rapidly warming and empirical data on abundance trends of marine organisms are required to understand the impact of these physical changes, and interacting anthropogenic impacts, on the ecosystem. Recent estimates inferred increasing abundance of Type A killer whales at the top of this food chain, and here we provide new data on the abundance of Type B1 and B2 killer whales using photographic mark‐recaptures collected during austral summers from 2008/2009 to 2017/2018. Both ecotypes were regularly photographed around the AP coastline, particularly off the west side, and individuals of both showed site fidelity across years. B1s had a higher re‐identification rate (58% photographed in multiple years, range: 1–7 years) compared to B2s (31%, 1–4 years). We fit mark‐recapture models that allowed temporary emigration beyond the study area, to effectively monitor the size of wide‐ranging populations and documented contrasting trends for B1s and B2s. A smaller population size (~102) of B1s was estimated to use the area, with a declining trend in abundance (−4.7% per year) and reduced apparent survival in recent years. In contrast, a much larger population size (~740) of B2s was estimated to be generally stable in abundance and apparent survival over the past decade. [ABSTRACT FROM AUTHOR]

The Orca Seamount is a submarine volcanic structure, located in a tectonic area of the Bransfield Strait, characterized by cortical extension and roll back-type subduction. Recent investigations have described the presence of hydrothermal activity and thermophilic microorganisms in this submarine volcano, raising questions regarding the role these microorganisms might play in the environment. The presence of hydrothermal activity interacting with cold Antarctic marine waters has probably exerted a great impact on the chemistry of the Orca Seamount area, providing different types of substrates capable to support complex microbial communities. In this work, we further study the Orca Seamount area with respect to the mineralogy present in this environment and the role microorganisms might play in the biogeochemical cycles. Here we show that the assemblage of minerals detected in the Orca Seamount area is like those commonly found in other hydrothermal environments, consistent with previous investigations reporting hydrothermal activity in this zone. Sulfur- and iron-bearing minerals in addition to inorganic soluble compounds are able to support chemosynthetic microbial communities inhabiting the Orca Seamount. The role of these microorganisms on the sulfur, iron, and carbon cycle is discussed and analyzed in the context of the mineralogy and conditions of the environment. [ABSTRACT FROM AUTHOR]

The fish‐eating, type‐C ecotype, killer whale is a top predator in the Ross Sea, Antarctica. Increasing knowledge of this animal's foraging habitats, diet and movement patterns is listed amongst the research priorities adopted under the framework of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).To contribute to this goal, satellite transmitters were deployed on 10 type‐C killer whales and skin biopsies were obtained from seven individuals in Terra Nova Bay (Ross Sea) during austral summer (January–February) 2015. Hierarchical switching state–space models (hSSSM) were applied to Argos satellite tracking data to describe the movements of tagged whales, which were then paired with available diving data. Stable isotopes analyses were performed on the biopsy samples to describe the diet.A total of 8,803 Argos locations were available to fit the hSSSM. All whales engaged in potential foraging activity in localized areas along the Ross Sea coastline, followed by uninterrupted travel (i.e. migration) outside Antarctic waters, with no evidence of foraging activity. The pattern of deeper dives matched the occurrence of encamped behaviour indicated by the hSSSM results. The stable isotopes analysis indicated that Antarctic toothfish comprised the largest component (35%) of the prey biomass, raising concerns since this species is targeted by commercial fishery in the Ross Sea Region.These results provide new insights into the ecology of type‐C killer whales in the Ross Sea Region, underlining a potential threat from commercial fishing in the area. Considering the recent establishment of the Ross Sea Region Marine Protected Area, these findings will contribute to the required Research and Monitoring Programme of the Marine Protected Area and provide new empirical evidence to inform conservation measures in the existing Terra Nova Bay Antarctic Special Protected Area. [ABSTRACT FROM AUTHOR]

Long‐distance migration in whales has historically been described as an annual, round‐trip movement between high‐latitude, summer feeding grounds, and low‐latitude, winter breeding areas, but there is no consensus about why whales travel to the tropics to breed. Between January 2009 and February 2016, we satellite‐tagged 62 antarctic killer whales (Orcinus orca) of four different ecotypes, of which at least three made short‐term (6–8 weeks), long‐distance (maximum 11,000 km, round trip), essentially nonstop, migrations to warm waters (SST 20°C–24°C), and back. We previously suggested that antarctic killer whales could conserve body heat in subfreezing (to −1.9°C) waters by reducing blood flow to their skin, but that this might preclude normal (i.e., continuous) epidermal molt, and necessitate periodic trips to warm waters for routine skin maintenance ("skin molt migration," SMM). In contrast to the century‐old "feeding/breeding" migration paradigm, but consistent with a "feeding/molting" hypothesis, the current study provides additional evidence that deferred skin molt could be the main driver of long‐distance migration for antarctic killer whales. Furthermore, we argue that for all whales that forage in polar latitudes and migrate to tropical waters, SMM might also allow them to exploit rich prey resources in a physiologically challenging environment and maintain healthy skin. [ABSTRACT FROM AUTHOR]

Killer whales, Orcinus orca, are top predators occupying key ecological roles in a variety of ecosystems and are one of the most widely distributed mammals on the planet. In consequence, there has been significant interest in understanding their basic biology and ecology. Long-term studies of Northern Hemisphere killer whales, particularly in the eastern North Pacific (ENP), have identified three ecologically distinct communities or ecotypes in that region. The success of these prominent ENP studies has led to similar efforts at clarifying the role of killer whale ecology in other regions, including Antarctica. In the Southern Hemisphere, killer whales present a range of behavioural, social and morphological characteristics to biologists, who often interpret this as evidence to categorize individuals or groups, and draw general ecological conclusions about these super-predators. Morphologically distinct forms (Type A, B, C, and D) occur in the Southern Ocean and studies of these different forms are often presented in conjunction with evidence for specialised ecology and behaviours. Here we review current knowledge of killer whale ecology and ecotyping globally and present a synthesis of existing knowledge. In particular, we highlight the complexity of killer whale ecology in the Southern Hemisphere and examine this in the context of comparatively well-studied Northern Hemisphere populations. We suggest that assigning erroneous or prefatory ecotypic status in the Southern Hemisphere could be detrimental to subsequent killer whale studies, because unsubstantiated characteristics may be assumed as a result of such classification. On this basis, we also recommend that ecotypic status classification for Southern Ocean killer whale morphotypes be reserved until more evidence-based ecological and taxonomic data are obtained. [ABSTRACT FROM AUTHOR]

Foraging events and related trends in numbers of Type-B and -C killer whales (Orcinus orca) are reported for the vicinity of Ross Island, Ross Sea, Antarctica between 2002 and 2010. Updating an earlier report, the frequency of sightings and the number of individuals per sighting of Ross Sea killer whales (Type-C; RSKWs), a fishing-eating ecotype, has continued to decrease in a pattern coincident with a decrease in the number and size of an important prey: Antarctic toothfish (Dissostichus mawsoni). Increasingly rare, large fish are much more energetically dense and may also be socially important to the whales, a rela-tionship with potential parallels to that known between well-studied fish-eating killer whales and large Chinook salmon (Oncorhynchus tshaw-ytscha) in the northeast Pacific. In contrast, the prevalence of the larger, mammal-eating Type-B killer whales has not changed in the southern Ross Sea study area. Predation events by Type-B killer whales involving Weddell seals (Leptonychotes weddellii), interest in large penguins, such as emperors (Aptenodytes forsteri), and lack of inter-est in small penguins, such as Adélies (Pygoscelis adeliae), are presented. In the case of both killer whale forms, the progressive seasonal breakup of fast ice in large bays bordering the Ross Sea likely provides reliable, enhanced foraging oppor-tunities as prey are exposed one area at a time during summer. Given the apparent relationship between RSKW prevalence and the availability of large toothfish, we speculate that the current management strategy of Antarctic toothfish in the Ross Sea region threatens current population levels of RSKWs. [ABSTRACT FROM AUTHOR]

The article presents a study which observes killer whales (Orcinus orca) during a survey off East Antarctica. It says that 24 killer whale groups were sighted south and classified to Types A, B, or C according to their external morphology while nine groups were categorized as two groups of Type A, one mixed group of Type A and Type B, three groups of Type C, and three groups with eyepatch pigmentation intermediate. Results show variations in pigmentation and group associations. It adds that one of the intermediate groups feed in a multi-species aggregation with other cetaceans in deep water.

Recent research has clearly shown that the fear of predation, i.e. aversion to taking risks, among mesopredators or grazers, and not merely flight from an apex predator to avoid predation, is an important aspect of ecosystem structuring. In only a few, though well-documented cases, however, has this been considered in the marine environment. Herein, we review studies that have quantified behavioral responses of Adélie penguins Pygoscelis adeliae and emperor penguins Aptenodytes forsteri to the direct presence of predators, and question why the penguins avoid entering or exiting the water at night. We also show, through literature review and new analyses of Adélie penguin diving data, that Antarctic penguins are capable of successful prey capture in the dark (defined here as <3.4 lux). Finally, we summarize extensive data on seasonal migration relative to darkness and prey availability. On the basis of our findings, we propose that penguins' avoidance of foraging at night is due to fear of predation, and not to an inability to operate effectively in darkness. We further propose that, at polar latitudes where darkness is more a seasonal than a year-round, daily feature, this 'risk aversion' affects migratory movements in both species, consistent with the 'trade-off' hypothesis seen in other marine vertebrates weighing foraging success against predation risk in their choice of foraging habitat. Such non-consumptive, behavioral aspects of species interactions have yet to be considered as important in Southern Ocean food webs, but may help to explain enigmatic movement patterns and choice of foraging grounds in these penguin species. [ABSTRACT FROM AUTHOR]

Currently, there are three recognized ecotypes (or species) of killer whales ( Orcinus orca) in Antarctic waters, including type B, a putative prey specialist on seals, which we refer to as 'pack ice killer whale' (PI killer whale). During January 2009, we spent a total of 75.4 h observing three different groups of PI killer whales hunting off the western Antarctic Peninsula. Observed prey taken included 16 seals and 1 Antarctic minke whale ( Balaenoptera bonaerensis). Weddell seals ( Leptonychotes weddellii) were taken almost exclusively (14/15 identified seal kills), despite the fact that they represented only 15% of 365 seals identified on ice floes; the whales entirely avoided taking crabeater seals ( Lobodon carcinophaga; 82% relative abundance) and leopard seals ( Hydrurga leptonyx; 3%). Of the seals killed, the whales took 12/14 (86%) off ice floes using a cooperative wave-washing behavior; they produced 120 waves during 22 separate attacks and successfully took 12/16 (75%) of the Weddell seals attacked. The mean number of waves produced per successful attack was 4.1 (range 1-10) and the mean attack duration was 30.4 min (range 15-62). Seal remains that we examined from one of the kills provided evidence of meticulous postmortem prey processing perhaps best termed 'butchering.' [ABSTRACT FROM AUTHOR]

Forty-nine species of cetaceans have been recorded in the literature with cookie cutter shark (Isistius sp.) bites. The first record of a cookie cutter shark bite mark on orca (Orcinus orca) was from New Zealand waters in 1955. We present 37 unpublished records of cookie cutter shark bite marks on orca in tropical to cold waters; a further six published records were collated, and additionally 35 individuals with bite marks were noted in photo-identification catalogues. A total of 120 individuals and 198 bite marks were recorded, with the northernmost at 70° 44′ N and the southernmost at 77° 14′ S. We provide the first healing rate of a cookie cutter shark bite mark on an orca in New Zealand waters, with a maximum of 150 d between open wound and healed scar. Longevity of scars is considered, with one particular bite mark still visible as a dark grey oval/elliptic mark 1,158 d post photographing the open wound. Open cookie cutter shark bite marks were not observed on orca photographed in Antarctic waters, despite the majority of bite marks being recorded on Antarctic orca. This suggests a high level of movement outside the Antarctic cold water regions as the known distribution of cookie cutter sharks is in warm temperate to tropical waters. Supporting evidence for these movements is given by records of Antarctic orca in New Zealand waters with open cookie cutter shark bite marks. [ABSTRACT FROM AUTHOR]

The diet of killer whales Orcinus orca was investigated from 48 predation events observed during 823 sightings at sub-Antarctic Marion Island between 2006 and 2009. From these events, there were 10 cases where prey could be identified. Killer whales fed on fur seals Arctocephalus tropicalis, elephant seals Mirounga leonina and penguins. Constant effort (dedicated) observations (259 hours, 2008-2009) showed that the peak in killer whale abundance was between September and December with a secondary peak between April and May, which coincided with peaks in the abundance of seals and penguins. [ABSTRACT FROM AUTHOR]

During January and February 2004, data on presence and distribution of killer whales (Orcinus orca) and other cetaceans were collected by helicopter surveys along the coastline of Terra Nova Bay and adjacent localities (western Ross Sea, Antarctica). A total of 37 sightings of killer whale, of both B and C types, were recorded as well as 17 sightings of Antarctic minke whales (Balaenoptera bonaerensis), nine of Balaenoptera spp., two of Arnoux’s beaked whale (Berardius arnuxii) and four of undetermined species. The type C killer whale was the most abundant, with 23 sightings, whereas we recorded type B only twice. Group size ranged between 1 and 30 animals, with an average of eight individuals. Seventeen killer whales were photo-identified and 13 resightings occurred during the study period. Killer whales showed a differential pattern in partitioning the study area. Their encounter rate was significantly higher (t-test = 2.6045, P < 0.05) in the northern area extending from Edmonson Point to the Campbell Glacier Tongue (encounter rate, ER = 0.031), compared to the southern area from Mario Zucchelli Station to the Drygalski Ice Tongue (ER = 0.003). [ABSTRACT FROM PUBLISHER]

Studies have shown that killer whale ( Orcinus orca) communities in high latitudes regularly comprise assemblages of sympatric 'ecotypes'-forms that differ in morphology, behavior, and prey preferences. Although they can appear superficially similar, recent genetic evidence suggests that breeding is assortative among ecotypes within individual communities, and species-level divergences are inferred in some cases. Here, we provide information on a recently recognized 'type D' killer whale based on photographs of a 1955 mass stranding in New Zealand and our own six at-sea sightings since 2004. It is the most distinctive-looking form of killer whale that we know of, immediately recognizable by its extremely small white eye patch. Its geographic range appears to be circumglobal in subantarctic waters between latitudes 40°S and 60°S. School sizes are relatively large (mean 17.6; range 9-35; n = 7), and although nothing is known about the type D diet, it is suspected to include fish because groups have been photographed around longline vessels where they reportedly depredate Patagonian toothfish ( Dissostichus eleginoides). [ABSTRACT FROM AUTHOR]

We report here the first published observations of killer whales ( Orcinus orca) feeding on penguins in Antarctica. The sightings took place in the Gerlache Strait off the western Antarctic Peninsula during February 2010. Two species of pygoscelid penguins were taken-gentoo ( Pygoscelis papua, at least four individuals) and chinstrap ( P. antarctica, 2). From remains left at the surface, it was clear that the killer whales fed mainly on the breast muscles, although some penguins may have been swallowed whole. The killer whales were ecotype B, which are purported seal specialists, but we also saw ecotype A, prey specialists on Antarctic minke whales Balaenoptera bonaerensis, chase, but not catch penguins. Because of their small relative size, if penguins are regularly targeted by killer whales in Antarctica, the impact on their populations could be significant. [ABSTRACT FROM AUTHOR]

Killer whales (Orcinus orca), both ecotype-B and -C, are important to the Ross Sea, Antarctic ecosystem. The ecotype-C is referred to as "Ross Sea [RS] killer whale." Herein, we review data on occurrence patterns and diet of RS killer whales and present new information on numbers observed in the southwestern Ross Sea, 2002-2003 to 2008- 2009 austral summers. These "resident" whales appear to feed principally on fish, including the large Antarctic toothfish (Dissostichus mawsoni). On the basis of sea watches from Cape Crozier, Ross Island, sighting frequency and average group size appears to have decreased; prevalence as indicated by casual observations from helicopter pilots flying over the area on a daily basis has also decreased in nearby McMurdo Sound. Consistent with a decrease in the catch-per-unit-effort of scientific fishing for toothfish in McMurdo Sound, we suggest and review evidence that the change in RS killer whale numbers in the southern Ross Sea is related to an industrial fishery-driven, densitydependent northward contraction of the toothfish stock and not to changes in the physical (and, in turn, biological) environment. We surmise that in this closely coupled foodweb, composed of very abundant penguin, seal, and whale components, loss of the toothfish option for RS killer whales would force more direct competition with other predators for capture of the smaller-fish prey. Therefore, we propose, the RS killer whales have opted to move elsewhere, in a scenario consistent with that of the Pacific coast of Canada, where numbers of resident killer whales have decreased following the loss of large fish as a prey choice. [ABSTRACT FROM AUTHOR]

During January/February 2006, we satellite-tracked two different ecotypes of killer whales ( Orcinus orca) in McMurdo Sound, Ross Sea, Antarctica, using surface-mounted tags attached with sub-dermal darts. A single Type B whale (pinniped prey specialist), tracked for 27 days, traveled an average net distance of 56.8 ± 32.8 km day−1, a maximum of 114 km day−1, and covered an estimated area of 49,351 km2. It spent several days near two large emperor penguin ( Aptenodytes forsteri) colonies, a potential prey item for this form. By contrast, four Type C killer whales (fish prey specialists) tracked for 7–65 days, traveled an average net distance of 20 ± 8.3 km day−1, a maximum of 56 net km day−1, and covered an estimated area of only 5,223 km2. These movement patterns are consistent with those of killer whale ecotypes in the eastern North Pacific where mammal-eating ‘transients’ travel widely and are less predictable in their movements, and fish-eating ‘residents’ have a more localized distribution and more predictable occurrence, at least during the summer months. [ABSTRACT FROM AUTHOR]

Measuring chemical tracers in tissues of marine predators provides insight into the prey consumed and the predator's contaminant exposure. In this study, samples from Type C killer whales ( Orcinus orca) biopsied in Antarctica were analyzed for chemical tracers ( i.e., stable isotopes of carbon and nitrogen, fatty acids, and persistent organic pollutants [POPs]). Profiles of these individual tracers were very different from those of killer whale populations that have been studied in the eastern North and eastern Tropical Pacific. For example, δ13C and δ15N stable isotope values and most POP concentrations were significantly lower in the Antarctic population. In addition, multivariate statistical analyses of both fatty acid and POP profiles found distinctly different patterns for Antarctic Type C whales compared to those from whales in the other populations. Similar assays were conducted on four species of Antarctic marine fish considered potential prey for Type C killer whales. Results were consistent with a diet of fish for Type C whales, but other species ( e.g., low trophic-level marine mammals or penguins) could not be eliminated as supplemental prey. [ABSTRACT FROM AUTHOR]

The article presents a study about events involving attacks by Antarctic peninsula killer whales on preys, including five seals and a penguin, that were hauled out on ice floes. The total size of the ice floes in these events were estimated by comparing them to the average size of the seal. The study also determined the sex and age class of the individual killer whales based on their relative size. The attack on a penguin using wave-washing method by a single juvenile killer whale is also discussed.

We conducted 239.5 h and 3,494 km of cetacean surveys in the Amundsen and Bellingshausen seas, from 15 February to 31 March 1994; most of the area, the large portion of which was ice covered, had never before nor has it since been surveyed for cetaceans, even to the date when this paper was prepared (2006). Logistic regression and an information-theoretic approach related the occurrence of Antarctic minke whales Balaenoptera bonaerensis (the most abundant species) to whether we were in open- or pack-ice-covered pelagic or neritic waters, in or out of the marginal ice zone (MIZ), and north or south of the Antarctic Circumpolar Current southern boundary. Other variables included date and distance to the MIZ and shelfbreak front. Statistical analysis showed that the probability of sighting a minke, as well as killer whale—but not the case for an index to whale density—was related to the proximity of coastal polynyas in early autumn, switching offshore to the MIZ once waters within the pack began to freeze persistently later in the season. Probability of detection was higher with distance into the MIZ. Supporting these findings, the density index was strongly related to ice concentration in an inverse relationship. The strong relationship to polynyas and the MIZ indicate that sea-ice divergence altered by decadal or longer-term climate change, as described in the recent literature, could well affect any apparent, long-term trends evident in this species' abundance if surveyed only in open or near-to-ice waters. We speculate on how the minke whale's pagophilic nature (1) could have been encouraged by large-scale industrial whaling and by competition with species more characteristic of open waters and the outer MIZ, and (2) may have protected the population somewhat during industrial whaling resulting in the much greater abundance of this species now compared to other targeted species. [ABSTRACT FROM AUTHOR]

In the early 1980s, 2 groups of Soviet scientists independently described 1, possibly 2 new dwarf species of killer whales (Orcinus) from Antarctica. We used aerial photogrammetry to determine total length (TL) of 221 individual Type C killer whales--a fish-eating ecotype that inhabits dense pack ice--in the southern Ross Sea in January 2005. We confirmed it as one of the smallest killer whales known: TL of adult females (with calves) averaged 5.2 m ± 0.23 SD (n = 33); adult males averaged 5.6 ± 0.32 m (n = 65), with the largest measuring 6.1 m. Female Type A killer whales--offshore mammal-eaters--from Soviet whaling data in the Southern Ocean were approximately 1-2 m longer, and males were 2-3 m (up to 50%) longer (maximum length 9.2 m). Killer whale communities from the North Atlantic and in waters around Japan also appear to support both a smaller, inshore, fish-eating form and a larger, offshore, mammal-eating form. We suggest that, at least in Antarctica, this degree of size dimorphism could result in reproductive isolation between sympatric ecotypes, which is consistent with hypotheses of multiple species of killer whales in the Southern Ocean. [ABSTRACT FROM AUTHOR]

An apparent trophic cascade that appears during summer in the western Ross Sea. Antarctica, explains why the Antarctic silverfish (Pleuragramma antarcticum) there becomes cannibalistic; its principal prey, crystal krill (Euphausia crystallorophias) becomes scarce: and the diatom community is minimally grazed compared to adjacent areas. The krill is the major grazer of diatoms. On the basis of fieldwork at Ross Island, we suggest that the cascade results from foraging by unusually numerous Adélie Penguins (Pygoscelis adeliae), minke whales (Balaenoptera bonaerensis), and fish-eating killer whales (Orcinus orca). These species and other top predators apparently deplete the krill and silverfish. In drawing our conclusions, we were aided by two ‘natural experiments.’ In one ‘experiment,’ large, grounded icebergs altered the seasonal pattern of change in regional sea-ice cover, but not the seasonal change in penguin diet and foraging behavior that was also detected during the pre-iceberg era. In the other ‘experiment,’ a short-term polynya (opening in the ice) brought penguins and whales together in a confined area, this time altering both penguin diet and foraging behavior. We conclude that the foraging of penguins and whales, and not a formerly hypothesized seasonal decrease in sea-ice cover, explains (1) the annual switch in the penguins' prey from krill to silverfish, (2) the subsequent lengthening of penguin foraging trips, and (3) a marked decline of cetaceans in the area later in the season. Reduction in the middle-trophic-level prey is expressed in the relaxed grazing pressure on phytoplankton. [ABSTRACT FROM AUTHOR]

The Brasfield rift and South Shetland trench are part of the active margin of the Antarctic continent. From the records of a seismic station at the King George Island installed by the Observatorio Geofísico del Uruguay, 3186 seismic events during August 26 and September 11, 2020 were retrieved with an average of 187 earthquakes per day and a maximum of 359 on August 30. 217 events with a local magnitude of ≥4 were well recognized and located by a single-station method. The events show that an earthquake swarm close to the South Shetland Islands and at a short hypocentral distance (~25 km) to the station occurred in August of 2020. The earthquakes in the swarm are near Orca seamount and the listric normal faults, with a ENE-WSW trend of the Bransfield Basin, suggesting their volcano and volcanotectonic origin. In addition to the swarm, several earthquakes in the same time period related to the Artigas Fault with NW-SE trend are also located, which indicates the reactivation of this structure. From all the earthquakes, a relatively high b -value (1.22) is estimated, which might suggest variable resistance for stress accumulation in the Bransfield rift. • 3186 events from an earthquake swarm in the South Shetland Islands (Antarctica) were parameterized. • Two groups of epicenters were found, the first one near Orca seamount and the second ones related to the Artigas Fault. • The tectonic framework suggests two genetic origins: magmatic and tectonic. [ABSTRACT FROM AUTHOR]

This article discusses observations of the foraging behavior of predators like killer whales, minke whales Adelie penguins and emperor penguins in the Ross Sea of Antarctica. According to the authors, the whales appeared to be feeding on fish probably toothfishes or silverfish. Both whales and penguins were generating bubbles or vortices and feeding from the center. The prey of the Adelie penguins seemed to be primarily silverfish and the emperor penguins were seen feeding most likely silverfish to their nearly-fledged chicks.

The article discusses killer whale harassment of Adélie penguins at Ross Islands. On innumerable occasions, Adélie and emperor penguins have been observed in close proximity to killer whales, with no whale-penguin interactions reported. On the other hand, killer whales reportedly harass and eat seabirds on occasion. Killer whales are known to prey on young king penguins as they are fledging and occasionally take emperor penguins. It is believed that killer whales generally do not eat Adélie penguins based on the lack of published observations and extensed observations, with thousands of penguins in jeopardy among up to three dozen whales. Probably Adélies are not worth the effort, being extremely agile swimmers and only about 4 kg of bone, feather, and penguin meat, especially compared with larger emperor penguins, Weddell and leopard seals and Antarctic toothfish. However, if killer whales wanted to eat Adélie penguins, they do have ample opportunities at Cape Crozier and other colonies in the Ross Sea.

The article focuses on the potential new species of orcas or killer whales discovered by the U.S. Coast Guard in the channel into McMurdo Sound in Antarctica. Biologist Robert Pitman contended that the killer whales could be a new species. The killer whales that inhabit the cracked ice around McMurdo Sound have different coloring and are shorter than the typical killer whales. Pitman's strongest evidence has been the lack of interbreeding of the killer sharks and that different Antarctic killer whales may have different feeding habits.