The distinctive Subantarctic (Type D) killer whale (DKW) (Orcinus orca) is a highly divergent and apparently inbred form previously known only from three mass strandings and several dozen at-sea sightings, primarily from Patagonian toothfish (Dissostichus eleginoides) longline vessels in the southern Indian Ocean and from tourism vessels in the Scotia Sea. Its range appears to be circumpolar throughout the Subantarctic, but very little is known about total numbers and overall movements. We summarize photo-identification data from 352 of 406 sightings collected between 44 degrees S and 62 degrees S from 2003 to 2024. Among 207 photo-identified individuals there were two distinct clusters of 78 and 29 toothfish depredators, one in the southern Indian Ocean and the other off southern Chile, respectively. An additional 100 DKW were photo-identified throughout the wider Subantarctic. Discovery curves indicate that DKW may be more abundant than some less divergent or inbred killer whale populations. Depredating DKW showed seasonal and interannual site fidelity, but 10 depredating individuals identified in the southern Indian Ocean were also resighted in the southern South Atlantic, 4428 km away. Probable re-sightings of two other DKW occurred in the Scotia Sea over distances of 1070 and 41 km, respectively. These latitudinally narrow, long-distance inter-ocean movements are unique among killer whales. During the study period, the entirely pelagic distribution of encounters appears to have shifted significantly southward.

Relatively little is known about the ranging patterns, diving behavior, or prey preferences of killer whales (Orcinus orca) in tropical latitudes. However, they are suspected to be prey-generalists rather than the prey-specialists that are typically found in high latitudes. In February 2025, we satellite-tagged three killer whales from a pod of seven in Bah & iacute;a de Banderas, Mexico. The tags transmitted for 8-41 days. The tagged whales traveled a total of 4002 km along a narrow, 1000 km stretch of coastline. While tagged, they remained within 50 km of shore 92.5% of the time and in water < 500 m deep 69% of the time, but ranged up to 87 km offshore, to water deeper than 1000 m. Dives were slightly deeper during the day (mean dive depth 44 m) than at night (34.5 m), and they dived deeper (max 528 m) in deeper water. The group was observed attacking/consuming marine mammals, including a humpback whale (Megaptera novaeangliae) calf, a dwarf sperm whale (Kogia sima), common bottlenose (Tursiops truncatus) and spinner (Stenella longirostris) dolphins, and attacking/harassing two species of sea turtles. These data provide the first high-resolution records of movements and dive behavior of killer whales in the Eastern Tropical Pacific and support the existence of a unique ecotype in the region.

A Mottled Petrel (Pterodroma inexpectata) seen and photographed at a distance off San Felipe in the Gulf of California on 15 May 2024 represents a first of its species to be noted in Mexico. On its passage north the Mottled Petrel, a transequatorial migrant, crosses the central Pacific mainly in March and April, suggesting that the bird seen off San Felipe in May could have been trapped and delayed in the Gulf of California while heading north, albeit far to the east of its normal route.

In 2024, an expedition was conducted off northwestern Baja California, M & eacute;xico, to find and identify the beaked whale species that produced the BW43 echolocation pulse previously recorded in this area and elsewhere in the North Pacific. There were five Mesoplodon sightings and 21 BW43 acoustic detections on both a towed array and drifting pole buoy recorders over the course of the survey. Three of the sightings had concurrent acoustic detections, and a biopsy sample and environmental DNA were also collected from one of the sightings. The genetic identification confirms that the Mesoplodon sighted and acoustically recorded was the ginkgo-toothed beaked whale (Mesoplodon ginkgodens), and the co-occurrence of these sightings with the BW43 acoustic detections definitively links the species and its echolocation pulse. This is the first time that genetically confirmed ginkgo-toothed beaked whales have been observed at sea and definitively linked to the BW43 pulse. This paper details the encounters, acoustic behavior, genetics, coloration, and external morphology of this species, including a comprehensive review of its distribution using historical sightings, strandings, and acoustic detection data from the North Pacific Ocean.

Although Hubbs' beaked whale (Mesoplodon carlhubbsi) was previously known from over 60 strandings on both sides of the North Pacific, it had been identified alive in the wild only once, off Oregon in 1994. In September 2021, we conducted a search effort for beaked whales off the coast of Oregon using a towed hydrophone array and a visual search team. Approximately 350 km off the Columbia River mouth, we detected the vocalizations of an unidentified mesoplodont whale; we stopped our vessel and waited in the area until two unidentified juvenile Mesoplodon surfaced and stayed near our vessel for almost 2 hr. During that time, we took numerous photographs and videos, made behavioral observations, and recorded their vocalizations. The DNA sequence from a biopsy sample identified them as M. carlhubbsi. In this paper, we discuss our biological observations, including color patterning and acquired markings, behavioral observations, and describe for the first time the acoustic characteristics of this species. We confirm that M. carlhubbsi is the source of a previously unidentified acoustic signal known as BW37V, and we update what is known about the at-sea distribution of this species based on previous recordings and observational records.

Deraniyagala's beaked whale, Mesoplodon hotaula, was previously known from eight published strandings and no confirmed live sightings, making it one of the least-known cetaceans. We conducted six cetacean survey cruises in the South China Sea between 2019 and 2023, and during 120 sea-days we recorded 12 sightings of unidentified Mesoplodon. From biopsy samples and acoustic recordings, five sightings were subsequently confirmed as M. hotaula. Using photographs, we provide the first field descriptions and observations of this species. The calf/juvenile has a distinctive facial coloration and dorsal striping pattern that appear to be diagnostic among Indo-Pacific Mesoplodon; among adult males, the dark rostrum of M. hotaula and the distinctively white-tipped beak of ginkgo-toothed beaked whale, M. ginkgodens, distinguish these similar-looking, partially sympatric species. Mean group size was small (3.0, n = 5), with a preference for deep (2,156 m, n = 5), warm (30.3 degrees C, n = 3) water. We update the known distribution of this species, present evidence of fishery interactions, and document the first reported mixed-species Mesoplodon group: a juvenile Blainville's beaked whale M. densirostris associated with four M. hotaula. These sightings identify the South China Sea as a potentially important area for this almost completely unknown species.

Size-class distributions and sex ratio data provide critical information to assess the demography and reproductive potential of animal populations, such as sea turtles. Sea turtle sex is determined by incubation temperature, whereby warmer temperatures during a certain period of embryonic development produce more female hatchlings. Whereas hatchling sex ratios have been well-studied, sex ratios of sea turtle foraging aggregations are less known for most populations. Here we report on sex ratios of immature and mature olive ridley sea turtles Lepidochelys olivacea in the Eastern Tropical Pacific (ETP) and Central North Pacific (CNP) based on blood plasma hormone analysis, refined with Bayesian modeling, or gonad examination. Our findings established that (1) the commercial enzyme-linked immunosorbent assay used in the present study was appropriate to analyze testosterone concentration in olive ridley blood plasma to determine foraging ground sex ratios (via a Bayesian model); (2) size-at-maturity is generally larger in males than females in the ETP; (3) the overall sex ratio among all turtles was 1.2F:1.0M; and (4) the sex ratio of smaller-sized immature turtles from both study regions was female-biased (ETP, 1.6F:1.0M and CNP, 2.1F:1.0M). These are the first sex ratio estimates for olive ridleys foraging in the high seas of the North Pacific Ocean. The data can inform population models for species conservation, particularly those that contribute to the development of conservation plans that consider climate change projections.

We investigated surface feeding behaviors of Eden's whales (Balaenoptera edeni edeni) in northern Beibu Gulf, southern China, between April 3, 2018, and April 26, 2021. During 122 days at sea, 1,065 individual feeding events were recorded, and eight feeding behaviors were identified: two nonlunging (tread-water and/or trap-feeding, 7.7%, and a novel behavior we call "pirouette feeding," 15.3%) and six lunging (right lateral lunging, RLL, 10.9%; left lateral lunging, 0.2%; upright lunging, 6.3%, vertical lunging, 18.5%; inverted lunging, 0.3%; cooperative lateral lunging, COL, 40.9%). During COL, 2-8 whales swam clockwise around a fish school and simultaneously performed RLL on surfacing-the first cooperative feeding behavior recorded for a Balaenoptera whale. Five lateralized feeding behaviors (entailing either a left or right rotation on the long-body axis) accounted for 65.8% of individual feeding events, with a strong right-side bias (99.7%). Lateralized behavior is prevalent in many vertebrates, including several species of rorquals, and we suggest that the right-biased foraging lateralization among rorquals specifically allows them to keep their right eye on their prey (i.e., a sensory versus motor lateralization), and that this shared asymmetry among conspecifics may have preadapted Eden's whale for cooperative foraging.

Information regarding beaked whales is so sparse that even the most basic aspects of their biology, such as their distribution, remain poorly defined for some species. We have reviewed the known distribution of each beaked whale species and where possible, used this information to infer its global distribution. While for some species, such as the relatively commonly recorded Cuvier’s beaked whale, the inferred distribution is likely to be an accurate reflection of the species’ actual distribution, for other lesser known species, such as the spade-toothed whale, the inferred distribution is more tentative. However, even such limited distribution information is essential when assessing and mitigating potential anthropogenic impacts on beaked whales and serves to highlight gaps in our knowledge that need to be filled if assessment and mitigation are to be successfully conducted.

The giant anteater (Myrmecophaga tridactyla) ranges widely in northern South America and southern Central America, where its main predators are jaguars (Panthera onca) and pumas (Puma concolor). The species’ bold color pattern has been attributed to predator avoidance through both aposematism and disruptive camouflage. Its powerful front claws can be used not only for ripping open ant and termite nests but also as a lethal defense against attacking jaguars (and humans!); this has led to the suggestion that the conspicuous black “bracelets” on its forelimbs could be an aposematic warning signal to potential predators (Philos T R Soc B 2009; doi.org/10.1098/rstb.2008.0221). After photographing this unaccompanied pair of giant anteaters in the Brazilian Pantanal in September 2022, we suggest another function for their distinctive coloration – mimicry. The forelimb “bracelets” create a panda-like pattern with a black nose, eyepatch, and ear. The paleness of the anteater's near forelimb extends up and back toward its rump, creating the visual impression of an upper body of another animal. The pale inner side of the anteater's far forelimb makes it appear to be a near forelimb, adding to the illusion of a separate, smaller animal. The resulting pattern strongly suggests a bear (Ursidae) and could be an example of Batesian mimicry, but we propose a more novel form of mimicry. As a knuckle-walker, M tridactyla moves relatively slowly; this, when coupled with its small head, long snout, and absence of teeth, makes the giant anteater especially vulnerable to a large predator. Procyonids (eg raccoons [Procyon spp] and coatis [Nasua spp]) are smaller than the giant anteater and common throughout its current range; notably, some procyonid species have dark noses, eyepatches, and ears, and larger felids regularly prey upon them. By projecting the likeness of a smaller prey species, an anteater might lure an attacker to a less vulnerable part of its body, which could then allow it to respond with its formidable claws. Or are we just seeing things?

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.

This paper provides field descriptions and biological observations of three different forms of killer whale (Orcinus orca) that occur in Antarctica based on field observations and a review of available photographs. Identifications were based on the relative size and orientation of the white eyepatch and the presence or absence of a dorsal cape. Type A (presumably the nominate form) has a medium-sized eyepatch oriented parallel to the body axis, no dorsal cape, it occurs mainly off-shore in ice-free water, has a circumpolar distribution and apparently preys mainly upon Antarctic minke whales (Balaenoptera bonaerensis). Type B also has an eyepatch oriented parallel to the body axis, but the eyepatch is at least twice as large as in Type A, it has a dorsal cape, mainly inhabits inshore waters, regularly occurs in pack-ice, is distributed around the continent and is regularly sighted in the Antarctic Peninsula area. Although it may also prey upon Antarctic minke whales and possibly humpback whales (Megaptera novaeangliae), seals seem to be the most important prey item. Type C has a small, forward-slanted eyepatch, a dorsal cape, inhabits inshore waters and lives mainly in the pack-ice; it occurs mostly off East Antarctica, and to date it has been recorded feeding only on Antarctic toothfish (Dissostichus mawsoni). Type C appears to be referable to Orcinus glacialis as described by Berzin and Vladimirov (1983). Although similar ecological specialisations have been reported for sympatric killer whale populations in the Northeast Pacific (i.e. an inshore mammal-eater, an inshore fish-eater and an offshore form), the extent of morphological divergence, habitat segregation and, perhaps, reproductive isolation, appears to be more pronounced among Antarctic populations. Although under a Biological Species Concept these forms appear to warrant separate species status, it will be important to show that this interpretation is consistent with results of molecular genetic analyses and additional morphological studies.

AbstractBeaked whales (Ziphiidae), with 24 currently recognized species, are arguably the least known large animals on the planet, despite being widespread and at times abundant.Mesoplodon, with 16 currently recognized species, is by far the most speciose cetacean genus. Recent technological and taxonomic advances, long-term photographic-identification studies, and historical whaling data have allowed new insights into their social and mating strategies and how these may have driven diversification within the family. In most beaked whales, only adult males have exposed teeth—a single “tusk” erupts from each lower jaw and is used in contests to determine access to breeding females. How forcefully males of different species engage conspecifics varies widely based mainly on differences in tooth size/placement and jaw structure. We compiled data on key dimorphic traits including beak modification, tooth size and location, and prevalence of scarring in adults, for all beaked whales. More detailed information is given for the four best-studied species—northern bottlenose whale and Baird’s, Cuvier’s, and Blainville’s beaked whales. We then compared these traits with what is known about their social organization and reproductive anatomy to make inferences about mating strategies. More aggressive species tend to occur in small groups with only one dominant adult male present and have small testes relative to body size, suggesting that male reproductive success is largely determined by precopulatory contest competition and female defense polygyny. Less aggressive species tend to occur (at least at times) in larger, mixed-sex groups with multiple adult males present, and females may mate with multiple males, which favors postcopulatory sperm competition and polygynandry. We further discuss how conflicting pressures arising from males using their beaks for both feeding and fighting could have sparked an adaptive radiation in tooth development and beak morphology among beaked whales, especially withinMesoplodon, which would have had implications for male-male competition, social structure, sexual strategies, and, perhaps ultimately, evolutionary divergence and speciation within this group.

Killer whale (Orcinus orca) populations in high latitude, nearshore areas appear to regularly exhibit prey specialisation among two or more sympatric ecotypes, but nearly nothing is known about populations that inhabit open ocean areas or tropical latitudes. On 26 September 2003, during a cetacean survey in the eastern tropical Pacific Ocean, a group of an estimated 19 killer whales was encountered feeding on a calf of a blue whale (Balaenoptera musculus); the location was 10°58’N, 88°40’W, 230km west of Nicaragua. The whales were studied for 2.5 hours and during this time skin biopsy samples were collected, acoustic recordings made, aerial and lateral photographs taken and behavioural observations recorded. The 19 individuals identified included 4 males (3 adults, 1 subadult), 5 cow-calf pairs and 5 other females/subadult males. Using aerial photogrammetry, body lengths of 17 different animals were measured: the largest male (who carried the carcass most of the time) was 8.0m long; and the largest female (with a calf) was 6.1m. From 10 biopsy samples, two distinct haplotypes were identified that differed from resident (i.e. fish-eating ecotype) killer whales in the northeastern Pacific by one and two base pairs, respectively. The single discrete call recorded was a typical killer whale call but it had a two-part pitch contour that was structurally distinct from calls recorded to date in the North Pacific. These observations reaffirm that calves of even the largest whale species are vulnerable to predation, although by migrating to calving areas in the tropics, where killer whale densities are lower, baleen whales should be able to increase their overall reproductive fitness, as suggested by Corkeron and Connor (1999).

In April 1998, as part of a project to collect biopsy samples of putative pygmy blue whales (Balaenoptera musculus brevicauda) in the waters around the Republic of the Maldives, Indian Ocean, incidental sightings of cetaceans encountered were recorded. Using modified line-transect methods and handheld binoculars, a total of 267 sightings of 16 species of whales and dolphins were recorded during 20 at-sea days in the northeastern part of the atoll. Significant results include the following: (1) cetaceans were abundant and species diversity was high, including nearly every pantropical species of pelagic cetacean; (2) the spinner dolphin (Stenella longirostris) was by far the most common species encountered (56 sightings) and also had the largest mean school size ( = 50.3 individuals); (3) blue whales were rare; only four individuals were sighted; (4) a large concentration of Bryde’s whales (28 sightings in two days) was apparently feeding in nearshore waters; (5) this paper reports the first records for the Maldives of Cuvier’s beaked whale (Ziphius cavirostris), Blainville’s beaked whale (Mesoplodon densirostris) and the dwarf sperm whale (Kogia sima): the latter was particularly common (17 sightings); (6) the spotted dolphin (Stenella attenuata) was rare and almost always associated with yellowfin tuna (Thunnus albacares), spinner dolphin, or seabirds, as has been reported in the eastern Pacific and western Indian oceans.

Genome sequences can reveal the extent of inbreeding in small populations. Here, we present the first genomic characterization of type D killer whales, a distinctive eco/morphotype with a circumpolar, subantarctic distribution. Effective population size is the lowest estimated from any killer whale genome and indicates a severe population bottleneck. Consequently, type D genomes show among the highest level of inbreeding reported for any mammalian species (FROH ≥ 0.65). Detected recombination cross-over events of different haplotypes are up to an order of magnitude rarer than in other killer whale genomes studied to date. Comparison of genomic data from a museum specimen of a type D killer whale that stranded in New Zealand in 1955, with 3 modern genomes from the Cape Horn area, reveals high covariance and identity-by-state of alleles, suggesting these genomic characteristics and demographic history are shared among geographically dispersed social groups within this morphotype. Limitations to the insights gained in this study stem from the nonindependence of the 3 closely related modern genomes, the recent coalescence time of most variation within the genomes, and the nonequilibrium population history which violates the assumptions of many model-based methods. Long-range linkage disequilibrium and extensive runs of homozygosity found in type D genomes provide the potential basis for both the distinctive morphology, and the coupling of genetic barriers to gene flow with other killer whale populations.

Most knowledge on the biology and ecology of the spectacled porpoise (Phocoena dioptrica) has been obtained from stranded specimens, with less than fifteen confirmed sightings in the sea. Published photographs of live animals in their natural environment are also very rare. In this study, 28 live sightings are summarised, from Antarctic and sub Antarctic waters (mainly from the 1978-2004 IWC-IDCR/SOWER cruises). These sightings supported the suggested circumpolar and offshore distribution of this species; however, this was extended further south than previously thought, into Antarctic waters. The sea surface temperature recorded at the time of each sighting ranged from 0.9- 10.3°C, with most of the sightings (52.0%) in waters 4.9-6.2°C. Group size was small, averaging 2.0 (SD=0.92) animals per group. A total of six cow-calf pairs were observed and all such pairs were accompanied by one or two additional adults, always including a mature male. Based on observations at sea and new photographs of live animals, a pale ‘saddle’ around the dorsal fin was noticed and is described for the first time. The porpoises generally showed fast swimming behaviour when the vessel approached, resembling the swimming behaviour of harbour porpoises.