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Recent research on mysticete fossils from the Late Eocene and Oligocene has revolutionised our understanding of the diversity and evolutionary scenarios for early baleen whales. For example, aetiocetids are a possible, though controversial, lineage that bridges the gap between the toothed and baleen-bearing mysticetes, and eomysticetids show a further transitional step towards the baleen-bearing status, with the presence of non-functional dentition in adults. However, information about the origin of crown mysticetes, including the most recent common ancestor of all extant lineages and its descendants, is critical to further understanding the evolution of baleen whales. The phylogenetic positions of the Oligocene Toipahautea, Whakakai, Horopeta, and Mauicetus from New Zealand remain unresolved and problematic, but all four genera show a close relationship with crown mysticetes. The original and subsequent cladistic analyses have consistently revealed a sister relationship between the Toipahautea-to-Mauicetus grade and crown mysticetes, and Horopeta has been placed close to the cetotheriids within the crown group. This review aims to stimulate more research on this topic by elucidating the origin of crown mysticetes, which likely experienced a poorly known radiation event during the Oligocene that established the modern lineages. [ABSTRACT FROM AUTHOR]

Individual specialization may occur relative to diet, behaviour or spatial distribution, potentially leading to differential resource and space use within a population. While specializations have been documented across many animal populations, the underlaying causes of individual specialization (e.g. morphology, age or sex) are not always identified. Causes of specialization can be especially challenging to uncover for large, long-lived marine animals. We used a Bayesian multilevel, multinomial logistic regression model to study the relationships between grey whale, Eschrichtius robustus , use of foraging tactics and morphology (body length and condition), while accounting for habitat characteristics and individual variation in tactic use. The model was informed by a 7-year longitudinal data set of concurrent morphology and foraging behaviour collected using drones. We found evidence of an ontogenetic shift in the use of foraging tactics associated with body length (a proxy for age). Individual specialization in behaviour was also associated with water depth and habitat. After accounting for the effects of these covariates, there was some residual individual level variation in the use of different foraging tactics. Our findings demonstrate variation in resource and habitat use within a baleen whale population at the individual level relative to body length and habitat, suggesting that individual spatial distribution and access to prey may vary by age class. Our results can be applied to investigate whether juveniles and adults differ in their foraging success and resilience to stressors. • We used drones to measure behaviour and morphology of eastern grey whales. • Whale foraging behaviours were associated with morphology and habitat type. • Different foraging tactics were associated with different depths and habitat types. • Whales switched foraging tactics as they grew in length. • Morphology affected habitat and prey accessibility and consequently tactic use. [ABSTRACT FROM AUTHOR]

Baleen whales are key consumers in marine ecosystems and can serve as ecosystem sentinels. Body condition, defined as an individual’s energy stores relative to its structural size, can provide a useful proxy for health in baleen whales. As capital breeders, important life history events in baleen whales such as seasonal migrations and reproduction depend on having sufficient energy stores. Spatiotemporal variability of body condition of baleen whales can reflect differences in energy accumulated during the foraging season. Here we assess and compare the body condition and mass of humpback whales (Megaptera novaeangliae) across four different foraging areas from the West Indies distinct population segment in the Northwest Atlantic. Morphometric measurements of humpback whales were obtained using unoccupied aerial systems (UAS, or drones) from the New York Bight, the Gulf of Maine, Iceland, and Greenland. Uncertainty in morphometric estimates was incorporated and propagated using a bootstrapping approach. Measurements were used to estimate body volume and calculate a body condition index (BCI) for each individual whale. Since body mass is a key parameter for understanding animal physiology and bioenergetics, we further compared whale body mass to body size between foraging areas by converting body volume to body mass using estimates of tissue density from tagging studies. BCI showed significant differences between foraging areas with a large effect size (ANCOVA: mean η² = 0.168; all p< 0.001) when incorporating day of year and year as covariates. Humpback whales in the Gulf of Maine showed significantly higher BCI than those in the New York Bight, Iceland, and Greenland. Standardized Major Axis (SMA) regressions comparing log-log relationships of both body volume and body mass, respectively, to total length reinforced these results. Humpback whales in the Gulf of Maine showed significantly higher elevation in the SMAs than those in the other study regions (p<0.001), implying that humpback whales foraging in the Gulf of Maine accumulated greater energy reserves for a given body size. Estimates of body mass indicate that for a given body length, humpback whales in the Gulf of Maine have an 18% greater body mass than those in the New York Bight, Iceland, or Greenland. Regional differences in prey availability or anthropogenic threats could contribute to the observed patterns in body condition. Our findings highlight the importance of regional environmental factors to the nutritional health of baleen whales. [ABSTRACT FROM AUTHOR]

Abstract Background The life cycle of most baleen whales involves annual migrations from low-latitude breeding grounds to high latitude feeding grounds. In most species, these migrations are traditionally considered to be carried out according to information acquired through vertical social learning during the first months of life and made individually. However, some recent studies have suggested a more complex scenario, particularly for the species of the Balaenoptera genus. Methods Here, we studied the variation of δ15N and δ13C values along the growth axis of the baleen plate from 24 fin whales feeding off western Iceland to delve into their pattern of movements and to identify potential associations between individuals. The segment of baleen plate analyzed informed about at least two complete migratory cycles. We performed cluster analyses through two different methodologies and, whenever possible, we genotyped 20 microsatellite loci to determine potential existence of kinship. Results Results of the of δ15N and δ13C values agree with a dispersion strategy in the winter breeding grounds. However, and despite the overall large variability, several pairs or groups of individuals with no kinship showed highly similar isotopic patterns for two consecutive years for both δ15N and δ13C values. Conclusions Our results suggest that, notably, some whales without kinship share the same migratory regime and destinations. We hypothesize that this could reflect either: (i) the sharing of particularly beneficial migratory regimes, and/or (ii) long-term association between individuals.

Anthropogenic stressors threaten large whales globally. Effective management requires an understanding of where, when, and why threats are occurring. Strandings data provide key information on geographic hotspots of risk and the relative importance of various threats. There is currently considerable public interest in the increased frequency of large whale strandings occurring along the US East Coast of the United States since 2016. Interest is accentuated due to a purported link with offshore wind energy development. We reviewed spatiotemporal patterns of strandings, mortalities, and serious injuries of humpback whales (Megaptera novaeangliae), the species most frequently involved, for which the US government has declared an “unusual mortality event” (UME). Our analysis highlights the role of vessel strikes, exacerbated by recent changes in humpback whale distribution and vessel traffic.  Humpback whales have expanded into new foraging grounds in recent years. Mortalities due to vessel strikes have increased significantly in these newly occupied regions, which show high vessel traffic that also increased markedly during the UME. Surface feeding and feeding in shallow waters may have been contributing factors. We found no evidence that offshore wind development contributed to strandings or mortalities. This work highlights the need to consider behavioral, ecological, and anthropogenic factors to determine the drivers of mortality and serious injury in large whales and to provide informed guidance to decision‐makers. [ABSTRACT FROM AUTHOR]

Background: The life cycle of most baleen whales involves annual migrations from low-latitude breeding grounds to high latitude feeding grounds. In most species, these migrations are traditionally considered to be carried out according to information acquired through vertical social learning during the first months of life and made individually. However, some recent studies have suggested a more complex scenario, particularly for the species of the Balaenoptera genus. Methods: Here, we studied the variation of δ15N and δ13C values along the growth axis of the baleen plate from 24 fin whales feeding off western Iceland to delve into their pattern of movements and to identify potential associations between individuals. The segment of baleen plate analyzed informed about at least two complete migratory cycles. We performed cluster analyses through two different methodologies and, whenever possible, we genotyped 20 microsatellite loci to determine potential existence of kinship. Results: Results of the of δ15N and δ13C values agree with a dispersion strategy in the winter breeding grounds. However, and despite the overall large variability, several pairs or groups of individuals with no kinship showed highly similar isotopic patterns for two consecutive years for both δ15N and δ13C values. Conclusions: Our results suggest that, notably, some whales without kinship share the same migratory regime and destinations. We hypothesize that this could reflect either: (i) the sharing of particularly beneficial migratory regimes, and/or (ii) long-term association between individuals. [ABSTRACT FROM AUTHOR]

The south-east Indian Ocean population of pygmy blue whales (Balaenoptera musculus brevicauda) forages in habitats between temperate foraging grounds off southern Australia and breeding grounds in Indonesian waters. With the opportunity to forage during migration, limited seasonal variation in body condition would be expected. However, increasing numbers of individuals in poor body condition with prominent spinal columns and other features of emaciation have been sighted during their southern migration. This study aimed to measure the morphology and body condition (relative body volume to body length) of pygmy blue whales during their northbound and southbound migration. Unmanned aerial vehicles were used to obtain images of 42 pygmy blue whales (one calf, five juveniles and 36 adults, including one lactating female) in 2021 and 2022. The body lengths ranged from 15.32 to 24.32 m, and the mean relative head length, length to blowhole, width of eyes, fluke width and length of peduncle were 21.8, 18.1, 12.8, 22.9 and 21.3% respectively. There was a significant decrease in body condition of 15.3% between north and southern migrating adult whales. Given the importance of body condition for reproductive success, understanding if this loss is due to natural seasonal variation, or habitat or prey disturbance from environmental environmental or anthropogenic sources, has implications for the future management of the species. Body condition is important for successful migration, reproductive success and survival. Knowledge surrounding nutritional health of south-east Indian Ocean (SEIO) pygmy blue whales is currently lacking. We aimed to quantify and compare the body condition of SEIO pygmy blue whales at two points during northbound and southbound migration between south-west Australia and Indonesian waters. Results indicate the poorer condition of southbound migrating individuals and highlight the need to learn more about the nutritional health of this endangered species. Photograph by Grace Russell. [ABSTRACT FROM AUTHOR]

Migratory humpback whales (Megaptera novaeangliae) cover the cost of reproduction in low‐latitude breeding grounds with stored energy accumulated from polar feeding grounds. The ability to accumulate sufficient energy reserves during feeding periods is vital for key life history stages during migration, including mating, calving, and lactation. This study aimed to investigate the relationship between migration timing and body condition of Western Australian humpback whales. We used unmanned aerial vehicles to measure body condition (residual of body volume vs. length) in 2017 and 2021. Morphometric measurements were obtained from 460 individuals (71 calves, 83 juveniles, 235 adults, and 71 lactating females) during the northbound (toward breeding grounds) and southbound (toward feeding grounds) migration between May and November. Body condition decreased by 23 and 13 percentage points for juveniles and adults, respectively. The body condition of juveniles was shown to be correlated with migration timing for their northern migration, with individuals in better body condition migrating to the breeding grounds earlier. While stored energy is vital for humpback whales to successfully complete their vast migration to‐and‐from breeding grounds, we found no evidence that body condition affects the migration timing for adults, lactating females, and calves. [ABSTRACT FROM AUTHOR]

Baleen whales are key consumers in marine ecosystems and can serve as ecosystem sentinels. Body condition, defined as an individual’s energy stores relative to its structural size, can provide a useful proxy for health in baleen whales. As capital breeders, important life history events in baleen whales such as seasonal migrations and reproduction depend on having sufficient energy stores. Spatiotemporal variability of body condition of baleen whales can reflect differences in energy accumulated during the foraging season. Here we assess and compare the body condition and mass of humpback whales (Megaptera novaeangliae) across four different foraging areas from the West Indies distinct population segment in the Northwest Atlantic. Morphometric measurements of humpback whales were obtained using unoccupied aerial systems (UAS, or drones) from the New York Bight, the Gulf of Maine, Iceland, and Greenland. Uncertainty in morphometric estimates was incorporated and propagated using a bootstrapping approach. Measurements were used to estimate body volume and calculate a body condition index (BCI) for each individual whale. Since body mass is a key parameter for understanding animal physiology and bioenergetics, we further compared whale body mass to body size between foraging areas by converting body volume to body mass using estimates of tissue density from tagging studies. BCI showed significant differences between foraging areas with a large effect size (ANCOVA: mean η2 = 0.168; all p< 0.001) when incorporating day of year and year as covariates. Humpback whales in the Gulf of Maine showed significantly higher BCI than those in the New York Bight, Iceland, and Greenland. Standardized Major Axis (SMA) regressions comparing log-log relationships of both body volume and body mass, respectively, to total length reinforced these results. Humpback whales in the Gulf of Maine showed significantly higher elevation in the SMAs than those in the other study regions (p

Marine predators face the challenge of reliably finding prey that is patchily distributed in space and time. Predators make movement decisions at multiple spatial and temporal scales, yet we have a limited understanding of how habitat selection at multiple scales translates into foraging performance. In the ocean, there is mounting evidence that submesoscale (i.e. less than 100 km) processes drive the formation of dense prey patches that should hypothetically provide feeding hot spots and increase predator foraging success. Here, we integrated environmental remote-sensing with high-resolution animal-borne biologging data to evaluate submesoscale surface current features in relation to the habitat selection and foraging performance of blue whales in the California Current System. Our study revealed a consistent functional relationship in which blue whales disproportionately foraged within dynamic aggregative submesoscale features at both the regional and feeding site scales across seasons, regions and years. Moreover, we found that blue whale feeding rates increased in areas with stronger aggregative features, suggesting that these features indicate areas of higher prey density. The use of fine-scale, dynamic features by foraging blue whales underscores the need to take these features into account when designating critical habitat and may help inform strategies to mitigate the impacts of human activities for the species.

Eomysticetidae (Chaeomysticeti clade) is an archaic family of baleen whales that originated and diversified during the Oligocene epoch. The fossil record of this family is represented by at least 11 formally described species, including records in Baja California Sur (Mexico), Kaiserswerth (Germany), Kitakyushu (Japan), South Carolina (United States), and South Island (New Zealand). Baja California Sur (BCS) possesses important marine deposits from the upper Oligocene, which document a rich diversity of fossil mysticetes, including members of the family Eomysticetidae. In this work, we report a whale specimen collected in the upper Oligocene San Juan Member, El Cien Formation, from the so-called "Ten Minute locality", San Hilario, about 100 km NW of La Paz, Baja California Sur. The studied specimen consists of an incomplete skull, in which most of the rostrum and part of the occipital shield are missing but preserving one tympanic bulla in situ. This specimen is identified as belonging to the family Eomysticetidae based on both an elongated skull and nasals and transversely narrow and long intertemporal region with a wide exposure of parietals and frontals. The lack of more diagnostic regions precludes its identification at generic/specific levels. The specimen represents the first description of an eomysticetid for the San Hilario area, increasing our knowledge of the evolution of this group of mysticetes and its record in the Pacific basin from the late Oligocene of BCS. [ABSTRACT FROM AUTHOR]

Context. The east and west coasts of Australia form the breeding grounds for two of the world’s largest and fastest-growing populations of humpback whales (Megaptera novaeangliae). These populations show differences in mean lipid content, fatty acid profiles, and stable isotope values. Aims. To determine whether these differences result in variation in nutritional health and physiology between populations, we quantified and compared the morphology, body condition and energetic requirements between the two populations. Methods. We used unmanned aerial vehicles to measure body morphometrics (residual of body volume vs length) of humpback whales from May to November in 2017, 2020 and 2021. Key results. Morphometric measurements were obtained from 973 humpback whales (119 calves, 249 juveniles, 486 adults, and 119 lactating females). Results showed that the two populations did not differ significantly in their morphology. The average body condition was significantly different for sexually mature reproductive classes, with adults and lactating females on the west coast having a lower body condition, by an average of 7.7 and 11.1 percentage points below the east coast population respectively. All reproductive classes, with the exception of calves followed a similar pattern in body condition loss through the breeding season. Calves on the east coast exhibited a curvilinear relationship with days post-partum, with early and late-migrating calves being in poorer body condition than were those migrating midseason. In contrast, west coast calves did not significantly change their condition through the breeding season. Conclusions. The poorer body condition of sexually mature individuals in the west coast population is concerning, given the overall condition loss during a breeding season. This difference could be influenced by variations in sampling time; however, differences in feeding opportunities, climatic regimes and/or environmental variables may influence the ability of one population to acquire similar amounts of energy. Implications. The difference in body condition between these two humpback whale populations highlighted the need to assess populations individually, so as to develop representative levels that can be used for future conservation monitoring and management. [ABSTRACT FROM AUTHOR]

Knowledge of lampreys during their marine phase is limited, and for the southern hemisphere species was gleaned from their predators (albatrosses) in the 1970s. Taking advantage of new methodologies and long-term data on predator diet and distributions, we infer diverse aspects of lamprey distribution and ecology. DNA analyses indicated that albatrosses at South Georgia prey on Patagonian lamprey Geotria macrostoma, originating from Argentina. Their core pelagic distribution when free swimming appears to be the Antarctic Polar Frontal zone (APFZ), and not South Georgia waters as assumed previously. If so, the APFZ would be the first known hotspot in abundance of an anadromous lamprey in oceanic waters. We could not identify a teleost fish that would be a likely host. Instead, we infer that the lamprey may prey on baleen whales, based on comparison of stable isotope ratios in lamprey with candidate host species, timing of appearance in albatross diets coincident with whale migrations, and circumstantial evidence (unexplained scarring recorded during the whaling era). We suggest that the lamprey do not tolerate cold Antarctic waters, and detach from southerly-migrating whales at the thermal boundary of the APFZ, where they become accessible to albatrosses in surface waters. Given strong evidence that relative importance of prey in seabird diets reflects availability in foraging areas, the steep decrease in the annual consumption of lamprey by albatrosses at South Georgia from > 550 tonnes in 1975–1976 and 1986, to very low levels in most years since 2012, is likely to indicate a major population decrease. Despite our unconventional means of assessing the population trend, there is a compelling case for listing of Patagonian lamprey at least as Near threatened by the International Union for the Conservation of Nature, and an urgent need to better understand anthropogenic threats in Argentina. [ABSTRACT FROM AUTHOR]

Background: Satellite tags were deployed on 50 east Australian humpback whales (breeding stock E1) between 2008 and 2010 on their southward migration, northward migration and feeding grounds in order to identify and describe migratory pathways, feeding grounds and possible calving areas. At the time, these movements were not well understood and calving grounds were not clearly identified. To the best of our knowledge, this dataset details all long-term, implantable tag deployments that have occurred to date on breeding stock E1. As such, these data provide researchers, regulators and industry with clear and valuable insights into the spatial and temporal nature of humpback whale movements along the eastern coastline of Australia and into the Southern Ocean. As this population of humpback Background Satellite tags were deployed on 50 east Australian humpback whales (breeding stock E1) between 2008 and 2010 on their southward migration, northward migration and feeding grounds in order to identify and describe migratory pathways, feeding grounds and possible calving areas. At the time, these movements were not well understood and calving grounds were not clearly identified. To the best of our knowledge, this dataset details all long-term, implantable tag deployments that have occurred to date on breeding stock E1. As such, these data provide researchers, regulators and industry with clear and valuable insights into the spatial and temporal nature of humpback whale movements along the eastern coastline of Australia and into the Southern Ocean. As this population of humpbackwhales navigates an increasingly complex habitat undergoing various development pressures and anthropogenic disturbances, in addition to climate-mediated changes in their marine environment, this dataset may also provide a valuable baseline. New information: At the time these tracks were generated, these were the first satellite tag deployments intended to deliver long-term, detailed movement information on east Australian (breeding stock E1) humpback whales. The tracking data revealed previously unknown migratory pathways into the Southern Ocean, with 11 individuals tracked to their Antarctic feeding grounds. Once assumed to head directly south on their southern migration, five individuals initially travelled west towards New Zealand. Six tracks detailed the coastal movement of humpback whales migrating south. One tag transmitted a partial southern migration, then ceased transmissions only to begin transmitting eight months later as the animal was migrating north. Northern migration to breeding grounds was detailed for 13 individuals, with four tracks including turning points and partial southern migrations. Another 14 humpback whales were tagged in Antarctica, providing detailed Antarctic feeding ground movements. Broadly speaking, the tracking data revealed a pattern of movement where whales were at their northern limit in July and their southern limit in March. Migration north was most rapid across the months of May and June, whilst migration south was most rapid between November and December. Tagged humpback whales were located on their Antarctic feeding grounds predominantly between January and May and approached their breeding grounds between July and August. Tracking distances ranged from 68 km to 8580 km and 1 to 286 days. To the best of our knowledge, this dataset compiles all of the long-term tag deployments that have occurred to date on breeding stock E1. [ABSTRACT FROM AUTHOR]

Copepods of the genus Calanus are a critical source of food for the North Atlantic right whale (NARW), Eubalaena glacialis. We quantified variations in depth-integrated abundance and vertical distribution of Calanus spp. in the southern Gulf of St. Lawrence (sGSL) in August 2019. While Calanus finmarchicus was the most abundant species of Calanus , the larger C. hyperboreus was prominent in the Shediac Valley, a NARW high-use area, contributing a median of 55% estimated depth-integrated biomass of Calanus spp. during the first leg of the field mission. Near-bottom aggregations of Calanus spp. with concentrations exceeding 1000 ind m−3 occurred primarily at depths ranging from 70 to 90 m. Ontogenetic and diel vertical migrations likely contributed to development of these subsurface aggregations. During the day, Calanus spp. and euphausiids occurred in a compact near-bottom layer, indicating enhanced foraging conditions for NARW. We observed considerable variation in abundance and vertical distribution of Calanus spp. highlighting the dynamic nature of NARW prey distribution at scales of weeks and tens of kilometers in the sGSL. [ABSTRACT FROM AUTHOR]

Fin whales Balaenoptera physalus were hunted unsustainably across the globe in the 19th and 20th centuries, leading to vast reductions in population size. Whaling catch records indicate the importance of the Southern Ocean for this species; approximately 730,000 fin whales were harvested during the 20th century in the Southern Hemisphere (SH) alone, 94% of which were at high latitudes. Genetic samples from contemporary whales can provide a window to past population size changes, but the challenges of sampling in remote Antarctic waters limit the availability of data. Here, we take advantage of historical samples in the form of bones and baleen available from ex-whaling stations and museums to assess the pre-whaling diversity of this once abundant species. We sequenced 27 historical mitogenomes and 50 historical mitochondrial control region sequences of fin whales to gain insight into the population structure and genetic diversity of Southern Hemisphere fin whales (SHFWs) before and after the whaling. Our data, both independently and when combined with mitogenomes from the literature, suggest SHFWs are highly diverse and may represent a single panmictic population that is genetically differentiated from Northern Hemisphere populations. These are the first historic mitogenomes available for SHFWs, providing a unique time series of genetic data for this species. [ABSTRACT FROM AUTHOR]

On 5 September 2022, a dead baleen whale was found stranded at Laem Phak Bia, Phetchaburi, the Gulf of Thailand, Thailand but could not be identified because it was in an advanced stage of decomposition. It was first suspected to be Omura's whale (Balaenoptera Omurai), as that is a common species in the Gulf of Thailand. However, the cranium morphology was different from B. omurai and more similar to the common minke whale (Balaenoptera acutorostrata) from the North Pacific Ocean, which has never been reported in Thai territorial waters. The mitochondrial DNA control region (D-loop) was then used to identify the species through the Basic Local Alignment Search Tool (BLAST) available at the National Center for Biotechnology Information (NCBI) GenBank, which resulted in a high percent identity, 96.49 to 98.84, with B. acutorostrata. A Bayesian phylogenetic tree was further used to confirm the species, which grouped with B. acutorostrata from the North Pacific Ocean. This study provides evidence of the first stranding event of B. acutorostrata in the Gulf of Thailand. It is new information that extends previous knowledge on the distribution of the common minke whale and raises the need for more active surveys of cetaceans in the South China Sea going forward. [ABSTRACT FROM AUTHOR]

Abstract The Lower St. Lawrence Seaway (LSLS), in eastern Canada, is an important habitat for several species of endangered baleen whale. As we seek to reduce the hazards that these endangered species face from human activity, there is increasing demand for detailed knowledge of their habitat use. Only a sparse network of hydrophones exists in the LSLS to remotely observe whales. However, there is also a network of onshore seismometers, designed to monitor earthquakes, that have sufficiently high sample rates to record fin and blue whale calls. We present a simple method for detecting band‐limited, regularly repeating calls, such as the 20 Hz calls of fin and blue whales, and apply the method to build a catalog of fin and blue whale detections at 14 onshore seismometers across the LSLS, over approximately a 4‐year period. The resulting catalog contains over 600 000 fin whale calls and almost 60 000 blue whale calls. Individual calls are rarely detected at more than one seismometer. Fin whale calls recorded onshore often consist of multiple seismic phases arriving as a ∼2 sequence. Onshore seismometers provide a valuable, previously unused source of data for monitoring baleen whales. However, in the LSLS, the current seismometer network cannot provide high‐precision whale tracking alone, so a denser deployment of onshore and/or offshore seismometers is required.

Long‐term distribution data for cetaceans are lacking, inhibiting the ability of management bodies to assess trends and react appropriately. Such is true even along the US Atlantic Outer Continental Shelf (OCS) where previous passive acoustic monitoring programs have laid the groundwork for monitoring cetacean occurrence over a multidecadal scale. Here, we continue and expand the scope of previous acoustic programs, providing a synopsis of the monthly cetacean acoustic occurrence from late 2017 to late 2020. Acoustic data were collected using bottom‐mounted autonomous recorders located at seven stations along the OCS in depths of 212–900 m. Automated cetacean vocalization detector‐classifiers were applied, and the resulting automated detections directed the manual review of a subset of the data by analysts. Only manual detections informed the occurrence results. Six baleen whale species and at least eight toothed whale species occurred in the region with diversity increasing in winter. In considering previous monitoring program results, we found evidence that some mysticete whales are spending less time in the region annually, confirmed that some species occur farther offshore than previously reported, and identified two previously unreported areas utilized by beaked whales. For effective species management, these findings must be considered, and monitoring programs continued. [ABSTRACT FROM AUTHOR]

Cetaceans in the eastern South Atlantic Ocean are poorly studied. We present results from a 2 week ship-based survey from Cape Town to Vema Seamount (980 km to the west) during October–November 2019, including visual and towed-hydrophone observations from the vessel, and 10 days of acoustic monitoring on the seamount. Fifty-two hours of visual surveys resulted in 39 encounters of whale groups including seven of humpback, six of fin and one sei whale, as well as four unidentified baleen whales, 18 unidentified balaenopterid whales and four unidentified odontocetes. Two humpback whales at the seamount were engaged in possible feeding behaviour. A large aggregation of mostly fin whales was observed near the continental shelf edge (22 encounters over a 70 × 50 km2 area, six fin, one sei whale, 15 not confirmed to species), an historic whaling ground for both fin and sei whales. Towed-hydrophone data (78.7 h) detected five groups of sperm whales, 45 of delphinids, one beaked whale and no Kogiids. Acoustic data from the seamount detected calls from several baleen whale species including humpback whale non-song calls, Antarctic minke 'bioduck' calls, sei whale down-sweep calls and a likely Bryde's whale call. Two call types could not be assigned to species, including the most detected – a simple frequency-modulated call with peak power around 130 Hz. This study contributes to an improved understanding of cetacean occurrence in the eastern South Atlantic Ocean and highlights the need for more research to improve identification of cetacean vocalizations in the region. [ABSTRACT FROM AUTHOR]

The debate concerning the mechanisms that drive population-level song evolution in humpback whales rests on evidence that social learning mechanisms contribute to variations in song elements. In the following dialogue, Eduardo Mercado addresses points raised in support of claims that song evolution in humpbacks arises from social learning, and Heidi Lyn further challenges the idea that recent evidence argues against this interpretation.

We constructed annual abundance of a migratory baleen whale at an oceanic stopover site to elucidate temporal changes in Bermuda, an area with increasing anthropogenic activity. The annual abundance of North Atlantic humpback whales visiting Bermuda between 2011 and 2020 was estimated using photo-identification capture-recapture data for 1,204 whales, collected between December 2009 and May 2020. Owing to a sparse data set, we combined a Cormack-Jolly-Seber (CJS) model, fit through maximum likelihood estimation, with a Horvitz-Thompson estimator to calculate abundance and used stratified bootstrap resampling to derive 95% confidence intervals (CI). We accounted for temporal heterogeneity in detection and sighting rates via a catch-effort model and, guided by goodness-of-fit testing, considered models that accounted for transience. A model incorporating modified sighting effort and time-varying transience was selected using (corrected) Akaike’s Information Criterion (AICc). The survival probability of non-transient animals was 0.97 (95% CI 0.91-0.98), which is comparable with other studies. The rate of transience increased gradually from 2011 to 2018, before a large drop in 2019. Abundance varied from 786 individuals (95% CI 593-964) in 2016 to 1,434 (95% CI 924-1,908) in 2020, with a non-significant linear increase across the period and interannual fluctuations. These abundance estimates confirm the importance of Bermuda for migrating North Atlantic humpback whales and should encourage a review of cetacean conservation measures in Bermudian waters, including area-based management tools. Moreover, in line with the time series presented here, regional abundance estimates should be updated across the North Atlantic to facilitate population monitoring over the entire migratory range.

Humpback whales (Megaptera novaeangliae) use vocalizations during diverse social interactions or activities such as foraging or mating. Unlike songs produced only by males, social calls are produced by all types of individuals (adult males and females, juveniles and calves). Several studies have described social calls in the humpback whale's breeding and the feeding grounds and from different geographic areas. We aimed to investigate for the first time the vocal repertoire of humpback whale mother-calf groups during the breeding season off Sainte Marie island, Madagascar, South Western Indian Ocean using data collected in 2013, 2014, 2016, and 2017. We recorded social calls using Acousonde tags deployed on the mother or the calf in mother-calf groups. A total of 21 deployments were analyzed. We visually and aurally identified 30 social call types and classified them into five categories: low, medium, high-frequency sounds, amplitude-modulated sounds, and pulsed sounds. The aural-visual classifications have been validated using random forest (RF) analyses. Low-frequency sounds constituted 46% of all social calls, mid-frequency 35%, and high frequency 10%. Amplitude-modulated sounds constituted 8% of all vocalizations, and pulsed sounds constituted 1%. While some social call types seemed specific to our study area, others presented similarities with social calls described in other geographic areas, on breeding and foraging grounds, and during migrating routes. Among the call types described in this study, nine call types were also found in humpback whale songs recorded in the same region. The 30 call types highlight the diversity of the social calls recorded in mother-calf groups and thus the importance of acoustic interactions in the relationships between the mother and her calf and between the mother-calf pair and escorts. [ABSTRACT FROM AUTHOR]

The Lower St. Lawrence Seaway (LSLS), in eastern Canada, is an important habitat for several species of endangered baleen whale. As we seek to reduce the hazards that these endangered species face from human activity, there is increasing demand for detailed knowledge of their habitat use. Only a sparse network of hydrophones exists in the LSLS to remotely observe whales. However, there is also a network of onshore seismometers, designed to monitor earthquakes, that have sufficiently high sample rates to record fin and blue whale calls. We present a simple method for detecting band‐limited, regularly repeating calls, such as the 20 Hz calls of fin and blue whales, and apply the method to build a catalog of fin and blue whale detections at 14 onshore seismometers across the LSLS, over approximately a 4‐year period. The resulting catalog contains over 600 000 fin whale calls and almost 60 000 blue whale calls. Individual calls are rarely detected at more than one seismometer. Fin whale calls recorded onshore often consist of multiple seismic phases arriving as a ∼2 sequence. Onshore seismometers provide a valuable, previously unused source of data for monitoring baleen whales. However, in the LSLS, the current seismometer network cannot provide high‐precision whale tracking alone, so a denser deployment of onshore and/or offshore seismometers is required. [ABSTRACT FROM AUTHOR]

Humpback whales (Megaptera novaeangliae) use vocalizations during diverse social interactions or activities such as foraging or mating. Unlike songs produced only by males, social calls are produced by all types of individuals (adult males and females, juveniles and calves). Several studies have described social calls in the humpback whale’s breeding and the feeding grounds and from different geographic areas. We aimed to investigate for the first time the vocal repertoire of humpback whale mother-calf groups during the breeding season off Sainte Marie island, Madagascar, South Western Indian Ocean using data collected in 2013, 2014, 2016, and 2017. We recorded social calls using Acousonde tags deployed on the mother or the calf in mother-calf groups. A total of 21 deployments were analyzed. We visually and aurally identified 30 social call types and classified them into five categories: low, medium, high-frequency sounds, amplitude-modulated sounds, and pulsed sounds. The aural-visual classifications have been validated using random forest (RF) analyses. Low-frequency sounds constituted 46% of all social calls, mid-frequency 35%, and high frequency 10%. Amplitude-modulated sounds constituted 8% of all vocalizations, and pulsed sounds constituted 1%. While some social call types seemed specific to our study area, others presented similarities with social calls described in other geographic areas, on breeding and foraging grounds, and during migrating routes. Among the call types described in this study, nine call types were also found in humpback whale songs recorded in the same region. The 30 call types highlight the diversity of the social calls recorded in mother-calf groups and thus the importance of acoustic interactions in the relationships between the mother and her calf and between the mother-calf pair and escorts.

Marine ecosystems are experiencing rapid shifts under climate change scenarios and baleen whales are vulnerable to environmental change, although not all impacts are yet clear. We identify how the migration behaviour of the Chagos whale, likely a pygmy blue whale (Balaenoptera musculus brevicauda), has changed in association with shifts in environmental factors. We used up to 18 years of continuous underwater acoustic recordings to analyse the relationships between whale acoustic presence and sea surface temperature (SST), chlorophyll-a concentration, El-Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). We compared these relationships between two independent sites Diego Garcia southeast (DGS) and Diego Garcia northwest (DGN) where Chagos whales are detected and are suspected to move interannually across the Chagos-Laccadive ridge. We showed that the number of whale songs detected increased on average by 7.7% and 12.6% annually at DGS and DGN respectively. At the DGS site, Chagos whales shifted their arrival time earlier by 4.2 ± 2.0 days/year ± SE and were detected for a longer period by 7.3 ± 1.2 days/year ± SE across 18 years. A larger number of songs were detected during periods of higher chlorophyll-a concentration, and with positive IOD phases. At the DGN site, we did not see an earlier shift in arrival and songs were not detected for a longer period across the 13 years. Whale presence at DGN had a weaker but opposite relationship with chlorophyll-a and IOD. The oceanic conditions in the Indian Ocean are predicted to change under future climate scenarios and this will likely influence Chagos whale migratory behaviour. Understanding how environmental factors influence whale movement patterns can help predict how whales may respond to future environmental change. We demonstrate the value of long-term acoustic monitoring of marine fauna to determine how they may be affected by changing environmental conditions.

On 5 September 2022, a dead baleen whale was found stranded at Laem Phak Bia, Phetchaburi, the Gulf of Thailand, Thailand but could not be identified because it was in an advanced stage of decomposition. It was first suspected to be Omura’s whale (Balaenoptera Omurai), as that is a common species in the Gulf of Thailand. However, the cranium morphology was different from B. omurai and more similar to the common minke whale (Balaenoptera acutorostrata) from the North Pacific Ocean, which has never been reported in Thai territorial waters. The mitochondrial DNA control region (D-loop) was then used to identify the species through the Basic Local Alignment Search Tool (BLAST) available at the National Center for Biotechnology Information (NCBI) GenBank, which resulted in a high percent identity, 96.49 to 98.84, with B. acutorostrata. A Bayesian phylogenetic tree was further used to confirm the species, which grouped with B. acutorostrata from the North Pacific Ocean. This study provides evidence of the first stranding event of B. acutorostrata in the Gulf of Thailand. It is new information that extends previous knowledge on the distribution of the common minke whale and raises the need for more active surveys of cetaceans in the South China Sea going forward.

The cost of reproduction greatly affects a species' life history strategy. Baleen whales exhibit some of the fastest offspring growth rates in the animal kingdom. We quantified the energetic cost of gestation for southern right whales (Eubalaena australis) by combining whaling catch records of pregnant females with photogrammetry data on southern right whale mothers and calves from two breeding grounds in Argentina and Australia. The relationship between calf birth size and maternal length was determined from repeated measurements of individual females before and after giving birth. Fetal growth was determined from generalized linear models fitted to fetal length data from whaling operations between 1961 and 1967. Fetal length was converted to volume and mass, using the volume‐to‐length relationship of newborn southern right whales calves, and published tissue composition and energy content estimates. Fetal maintenance costs (heat of gestation) and the energy content of the placenta were predicted from published relationships and added to the fetal growth cost to calculate the total cost of gestation. Our findings showed that fetal growth rates and birth size increased linearly with maternal length, with calves being born at ∼35% maternal length. Fetal length increased curvilinearly through gestation, which resulted in an exponential increase in fetal volume and mass. Consequently, the cost of gestation was very low during the first (0.1% of total cost) and second trimester (4.9%), but increased rapidly during the last trimester (95.0%). The heat of gestation incurred the highest cost for pregnant females (73.8%), followed by fetal growth (21.2%) and the placental energy content (5.0%). Key points: Baleen whales exhibit some of the fastest fetal growth rates in the animal kingdom. Despite this, the energetic cost of gestation is largely unknown, as well as the influence of maternal body size on fetal growth rates and calf birth sizes.We combined historical whaling records and drone photogrammetry data to determine fetal growth rates and birth sizes in southern right whales (Eubalaena australis), from which we estimated the cost of gestation.Calf birth size, and consequent fetal growth rates, increased positively with maternal body size.The cost of gestation was negligible for southern right whale females during the first two trimesters, but increased rapidly during the last trimester.These results show that late gestation incurs a significant cost for baleen whale females, and needs to be accounted for in bioenergetic models. [ABSTRACT FROM AUTHOR]

The relative energetic benefits of foraging on one type of prey rather than another are not easily measured, particularly for large free‐ranging predators. Nonetheless, assumptions about preferred and alternative prey are frequently made when predicting how a predator may impact its environment, adapt to environmental change or interact with human activities.We developed and implemented a process‐based model to investigate the potential energetic benefit (PEB) of in situ foraging opportunities in rorqual whales. The model integrates and evaluates the energetic importance of measured prey patch characteristics (prey distribution, energy content and predator avoidance) and predator characteristics (morphometrics, foraging tactics and feeding rates). We applied the model to test the assumption that hatchery‐released juvenile salmon are an 'easy meal' for humpback whales compared to more common prey: herring and krill.In 11 out of the 13 foraging situations considered, whales were found to be feeding in a manner where net energy gain was greater than the energetic costs of non‐foraging swimming. Humpback whale PEB for hatchery‐released juvenile salmon fell within the range of the PEB for krill and herring but varied by species, from relatively high PEB for chum salmon to relatively low for coho salmon. Our model provides behavioural insight as well, indicating that shallow feeding may be more important for reducing energy expenditure through slower lunge speeds than for increasing prey capture. The model also provides a means of identifying prey patch characteristics, with prey aggregation playing the largest role in determining PEB despite being a poor overall proxy for PEB, supporting the use of the complex model framework.Modelling approaches are especially valuable where they can use reasonable assumptions to substitute for lack of reliable observations, thereby integrating a range of interacting factors into a single framework. Additionally, because process‐based models can be used to make predictions outside the range of previously observed conditions, they will be increasingly useful in a changing climate. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The Antarctic blue whale Balaenoptera musculus intermedia was hunted to near extinction in the twentieth century. Current data on the abundance and distribution of the species are lacking owing to the difficulty and expense of surveys under adverse weather conditions in open-ocean habitats, and to the small population size. The most recently accepted global abundance estimate, based on the middle survey (1997/1998) of three circumpolar Antarctic surveys conducted between 1991/1992 and 2003/2004, was less than 1% of the original pre-whaling population size. The present study used a visual line-transect survey off the Queen Maud Land coast of Antarctica, in an area between 0° and 18° E and south of 67° S, in January 2014, to estimate the abundance of Antarctic blue whales in this area. Effort-accounted densities of sightings averaged 13.3 individuals per 1 000 nautical miles of survey effort (CV = 0.26) and reinforce recent findings that the area has significantly higher densities than averaged in circumpolar surveys (0.17–1.48 per 1 000 nautical miles). Distance sampling resulted in a population density estimate of 0.019 whales nautical-mile−2 (CV = 0.24) and an estimated abundance of 1 026 Antarctic blue whales (CV = 0.20, 95% CI 632–1 450) in the surveyed area. Obtaining such current estimates of abundance is crucial for assessment of the conservation status of the Antarctic blue whale population and for monitoring its recovery. [ABSTRACT FROM AUTHOR]

Interactions between whale-watching boats and cetaceans can lead to changes in their behavior. From a management perspective, it is important to understand how this type of disturbance can be translated into physiological effects, such as changes in their energetic metabolism. Humpback whales (Megaptera novaeangliae) typically do not feed while in breeding grounds, thus they depend on finite energy reserves. The effect of whale-watching boats on the energetic metabolism of humpback whales, in the breeding ground of northern Peru (4°10′35″S, 81°08′03″W) was evaluated. Groups of humpback whales were tracked from land, under the following scenarios: with, without, and before-during-after the presence of whale-watching boats. Mass-specific cost of transport (COT) was used as a proxy of energetic efficiency and calculated from swimming speed and breath frequency estimations. No differences were detected in breath frequency, swimming speed, and COT when comparing whales with and without boats. However, in the presence of boats, swim speed increased, and COT decreased as the number of boats increased. Exponential increment in breathing frequency at higher swimming speed was not detected. The absence of swimming speeds beyond the assumed optimal range suggested no shifts into metabolic inefficiency. Our results suggest optimal swimming speed between 2 and 4.05 m/s, representing COT values between 0.020 and 0.041 J × (kg × m)–1. In light of our results, we encourage the implementation of regulations of the activity, particularly limiting the number of boats interacting with the same group of humpback whales.

We quantified the stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) as well as the total mercury (Hg) concentration in muscle samples from 20 common minke whales (Balaenoptera acutorostrata) stranded along the coast of Hokkaido, Japan. We investigated the relationship between the quantified values and the body length (BL) of the whales to examine the BL at which ontogenetic changes, such as nursing and weaning, occur. The whales investigated consisted of 12 calves (BL ≤ 5 m), including newborns, and eight sexually mature whales (7.2 to 10.2 m BL). The δ15N values in the calves were in the range of 11.2 to 13.8‰ and were fitted to a quadratic function (F10 = 4.588, R² = 0.505, p = 0.0423). The δ15N-enriched peak was calculated to be 4.0 m BL, which may correspond with the onset of weaning. In contrast, the δ15N values of the mature whales showed no particular change regardless of growth (10.8 to 12.4‰). The δ13C values in the calves showed no particular pattern (-18.3 to -20.0‰), probably due to the large variation in the lipid concentration in milk, while those in the mature whales tended to decrease with growth (F6 = 3.400, R² = 0.362, p = 0.115). The Hg concentrations in the muscle samples were trace but increased linearly with an increase in BL (F18 = 87.68, R2 = 0.830, p < 0.0001). The δ15N and Hg levels of mature whales were lower than respective levels observed in odontocetes stranded along the coast of Hokkaido, suggesting that mature whales feed mainly on zooplankton and small fish containing low Hg concentrations at low trophic positions. [ABSTRACT FROM AUTHOR]

Abstract Baleen whales store energy gained on foraging grounds to support reproduction and other metabolic needs while fasting for long periods during migration. Whale body condition can be used to monitor foraging success, and thus better understand and anticipate individual‐ and population‐level trends in reproduction and survival. We assessed the body condition of eastern North Pacific gray whales (Eschrichtius robustus) on their foraging grounds along the Oregon coast, USA, from June to October of three consecutive years (2016–2018). We used drone photogrammetry and applied the body area index (BAI) to measure and compare whale body condition, which is a continuous, unitless metric similar to the body mass index in humans. A total of 289 drone flights were carried out over 106 photo‐identified whales, which were grouped into demographic units by sex, maturity, and female reproductive status. Calves and pregnant females displayed the highest BAIs, followed by resting females, mature males, and, finally, lactating females, reflecting the significant energetic demands on reproductive females. In all three years, gray whale body condition improved with the progression of feeding seasons, demonstrating the accumulation of body energy reserves on the foraging grounds. Yet, body condition was significantly better in 2016 than in 2017 and 2018 when overall body depletion was observed, indicating a difference in prey availability and/or quality between years. We analyzed local upwelling patterns between 2013 and 2018 as an oceanographic proxy for prey and determined significantly greater upwelling between 2013 and 2015 than low upwelling years between 2016 and 2018. We hypothesize that these upwelling patterns created ecosystem shifts in primary productivity and zooplankton prey of gray whales, causing carry‐over effects between foraging success and body condition in subsequent years. This study demonstrates the value of monitoring whale body condition to better understand temporal variation in foraging success, and potentially detect and describe the causes of anomalous changes in whale population health, such as the 2019 gray whale mortality event.

Baleen whales store energy gained on foraging grounds to support reproduction and other metabolic needs while fasting for long periods during migration. Whale body condition can be used to monitor foraging success, and thus better understand and anticipate individual- and population-level trends in reproduction and survival.We assessed the body condition of eastern North Pacific graywhales (Eschrichtius robustus) on their foraging grounds along the Oregon coast, USA, from June to October of three consecutive years (2016-2018). We used drone photogrammetry and applied the body area index (BAI) to measure and compare whale body condition, which is a continuous, unitless metric similar to the body mass index in humans. A total of 289 drone flights were carried out over 106 photo-identified whales, which were grouped into demographic units by sex, maturity, and female reproductive status. Calves and pregnant females displayed the highest BAIs, followed by resting females, mature males, and, finally, lactating females, reflecting the significant energetic demands on reproductive females. In all three years, gray whale body condition improved with the progression of feeding seasons, demonstrating the accumulation of body energy reserves on the foraging grounds. Yet, body condition was significantly better in 2016 than in 2017 and 2018 when overall body depletion was observed, indicating a difference in prey availability and/or quality between years. We analyzed local upwelling patterns between 2013 and 2018 as an oceanographic proxy for prey and determined significantly greater upwelling between 2013 and 2015 than low upwelling years between 2016 and 2018. We hypothesize that these upwelling patterns created ecosystem shifts in primary productivity and zooplankton prey of gray whales, causing carry-over effects between foraging success and body condition in subsequent years. This study demonstrates the value of monitoring whale body condition to better understand temporal variation in foraging success, and potentially detect and describe the causes of anomalous changes in whale population health, such as the 2019 gray whale mortality event. [ABSTRACT FROM AUTHOR]

DNA sequence alignments have provided the majority of data for inferring phylogenetic relationships with both concatenation and coalescent methods. However, DNA sequences are susceptible to extensive homoplasy, especially for deep divergences in the Tree of Life. Retroelement insertions have emerged as a powerful alternative to sequences for deciphering evolutionary relationships because these data are nearly homoplasy-free. In addition, retroelement insertions satisfy the "no intralocus-recombination" assumption of summary coalescent methods because they are singular events and better approximate neutrality relative to DNA loci commonly sampled in phylogenomic studies. Retroelements have traditionally been analyzed with parsimony, distance, and network methods. Here, we analyze retroelement data sets for vertebrate clades (Placentalia, Laurasiatheria, Balaenopteroidea, Palaeognathae) with 2 ILS-aware methods that operate by extracting, weighting, and then assembling unrooted quartets into a species tree. The first approach constructs a species tree from retroelement bipartitions with ASTRAL, and the second method is based on split-decomposition with parsimony. We also develop a Quartet-Asymmetry test to detect hybridization using retroelements. Both ILS-aware methods recovered the same species-tree topology for each data set. The ASTRAL species trees for Laurasiatheria have consecutive short branch lengths in the anomaly zone whereas Palaeognathae is outside of this zone. For the Balaenopteroidea data set, which includes rorquals (Balaenopteridae) and gray whale (Eschrichtiidae), both ILS-aware methods resolved balaeonopterids as paraphyletic. Application of the Quartet-Asymmetry test to this data set detected 19 different quartets of species for which historical introgression may be inferred. Evidence for introgression was not detected in the other data sets. [ABSTRACT FROM AUTHOR]

Body mass is a key life‐history trait in animals. Despite being the largest animals on the planet, no method currently exists to estimate body mass of free‐living whales.We combined aerial photographs and historical catch records to estimate the body mass of free‐living right whales (Eubalaena sp.). First, aerial photogrammetry from unmanned aerial vehicles was used to measure the body length, width (lateral distance) and height (dorso‐ventral distance) of free‐living southern right whales (Eubalaena australis; 48 calves, seven juveniles and 31 lactating females). From these data, body volume was estimated by modelling the whales as a series of infinitely small ellipses. The body girth of the whales was next calculated at three measurement sites (across the pectoral fin, the umbilicus and the anus) and a linear model was developed to predict body volume from the body girth and length data. To obtain a volume‐to‐mass conversion factor, this model was then used to estimate the body volume of eight lethally caught North Pacific right whales (Eubalaena japonica), for which body mass was measured. This conversion factor was consequently used to predict the body mass of the free‐living whales.The cross‐sectional body shape (height–width ratio) of the whales was slightly flattened dorso‐ventrally at the anterior end of the body, almost circular in the mid region, and significantly flattened in the lateral plane across the posterior half of the body. Compared to a circular cross‐sectional model, our body mass model incorporating body length, width and height improved mass estimates by up to 23.6% (mean = 6.1%, SD = 5.27). Our model had a mean error of only 1.6% (SD = 0.012), compared to 9.5% (SD = 7.68) for a simpler body length‐to‐mass model. The volume‐to‐mass conversion factor was estimated at 754.63 kg/m3 (SD = 50.03). Predicted body mass estimates were within a close range of existing body mass measurements.We provide a non‐invasive method to accurately estimate body mass of free‐living whales while accounting for both their structural size (body length) and relative body condition (body width). Our approach can be directly applied to other marine mammals by adjusting the model parameters (body mass model script provided). [ABSTRACT FROM AUTHOR]

Rorqual whales are among the most species rich group of baleen whales (or mysticetes) alive today, yet the monophyly of the traditional grouping (i.e., Balaenopteridae) remains unclear. Additionally, many fossil mysticetes putatively assigned to either Balaenopteridae or Balaenopteroidea may actually belong to stem lineages, although many of these fossil taxa suffer from inadequate descriptions of fragmentary skeletal material. Here we provide a redescription of the holotype of Megaptera miocaena, a fossil balaenopteroid from the Monterey Formation of California, which consists of a partial cranium, a fragment of the rostrum, a single vertebra, and both tympanoperiotics. Kellogg (1922) assigned the type specimen to the genus Megaptera Gray (1846), on the basis of its broad similarities to distinctive traits in the cranium of extant humpback whales (Megaptera novaeangliae (Borowski, 1781)). Subsequent phylogenetic analyses have found these two species as sister taxa in morphological datasets alone; the most recent systematic analyses using both molecular and morphological data sets place Megaptera miocaena as a stem balaenopteroid unrelated to humpback whales. Here, we redescribe the type specimen of Megaptera miocaena in the context of other fossil balaenopteroids discovered nearly a century since Kellogg’s original description and provide a morphological basis for discriminating it from Megaptera novaeangliae. We also provide a new generic name and recombine the taxon as Norrisanima miocaena, gen. nov., to reflect its phylogenetic position outside of crown Balaenopteroidea, unrelated to extant Megaptera. Lastly, we refine the stratigraphic age of Norrisanima miocaena, based on associated microfossils to a Tortonian age (7.6–7.3 Ma), which carries implications for understanding the origin of key features associated with feeding and body size evolution in this group of whales.

Cetotheriidae are a group of small baleen whales (Mysticeti) that evolved alongside modern rorquals. They once enjoyed a nearly global distribution, but then largely went extinct during the Plio-Pleistocene. After languishing as a wastebasket taxon for more than a century, the concept of Cetotheriidae is now well established. Nevertheless, the clade remains notable for its variability, and its scope remains in flux. In particular, the recent referral of several traditional cetotheriids to a new and seemingly unrelated family, Tranatocetidae, has created major phylogenetic uncertainty. Here, we describe a new species of Tranatocetus, the type of Tranatocetidae, from the Late Miocene of the Netherlands. Tranatocetus maregermanicum sp. nov. clarifies several of the traits previously ascribed to this genus, and reveals distinctive auditory and mandibular morphologies suggesting cetotheriid affinities. This interpretation is supported by a large phylogenetic analysis, which mingles cetotheriids and tranatocetids within a unified clade. As a result, we suggest that both groups should be reintegrated into the single family Cetotheriidae.

The sensory mechanisms used by baleen whales (Mysticeti) for locating ephemeral, dense prey patches in vast marine habitats are poorly understood. Baleen whales have a functional olfactory system with paired rather than single blowholes (nares), potentially enabling stereo-olfaction. Dimethyl sulfide (DMS) is an odorous gas emitted by phytoplankton in response to grazing by zooplankton. Some seabirds use DMS to locate prey, but this ability has not been demonstrated in whales. For 14 extant species of baleen whale, nares morphometrics (imagery from unoccupied aerial systems, UAS) was related to published trophic level indices using Bayesian phylogenetic mixed modelling. A significant negative relationship was found between nares width and whale trophic level ( β = -0.08, lower 95% CI = -0.13, upper 95% CI = -0.03), corresponding with a 39% increase in nares width from highest to lowest trophic level. Thus, species with nasal morphology best suited to stereo-olfaction are more zooplanktivorous. These findings provide evidence that some baleen whale species may be able to localize odorants e.g. DMS. Our results help direct future behavioural trials of olfaction in baleen whales, by highlighting the most appropriate species to study. This is a research priority, given the potential for DMS-mediated plastic ingestion by whales.