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BACKGROUND: Pathogenic Leptospira species are globally important zoonotic pathogens capable of infecting a wide range of host species. In marine mammals, reports of Leptospira have predominantly been in pinnipeds, with isolated reports of infections in cetaceans. CASE PRESENTATION: On 28 June 2021, a 150.5 cm long female, short-beaked common dolphin (Delphinus delphis delphis) stranded alive on the coast of southern California and subsequently died. Gross necropsy revealed multifocal cortical pallor within the reniculi of the kidney, and lymphoplasmacytic tubulointerstitial nephritis was observed histologically. Immunohistochemistry confirmed Leptospira infection, and PCR followed by lfb1 gene amplicon sequencing suggested that the infecting organism was L.kirschneri. Leptospira DNA capture and enrichment allowed for whole-genome sequencing to be conducted. Phylogenetic analyses confirmed the causative agent was a previously undescribed, divergent lineage of L.kirschneri. CONCLUSIONS: We report the first detection of pathogenic Leptospira in a short-beaked common dolphin, and the first detection in any cetacean in the northeastern Pacific Ocean. Renal lesions were consistent with leptospirosis in other host species, including marine mammals, and were the most significant lesions detected overall, suggesting leptospirosis as the likely cause of death. We identified the cause of the infection as L.kirschneri, a species detected only once before in a marine mammal - a northern elephant seal (Mirounga angustirostris) of the northeastern Pacific. These findings raise questions about the mechanism of transmission, given the obligate marine lifestyle of cetaceans (in contrast to pinnipeds, which spend time on land) and the commonly accepted view that Leptospira are quickly killed by salt water. They also raise important questions regarding the source of infection, and whether it arose from transmission among marine mammals or from terrestrial-to-marine spillover. Moving forward, surveillance and sampling must be expanded to better understand the extent to which Leptospira infections occur in the marine ecosystem and possible epidemiological linkages between and among marine and terrestrial host species. Generating Leptospira genomes from different host species will yield crucial information about possible transmission links, and our study highlights the power of new techniques such as DNA enrichment to illuminate the complex ecology of this important zoonotic pathogen.

BACKGROUND: Elephant seals exhibit extreme hypoxemic tolerance derived from repetitive hypoxia/reoxygenation episodes they experience during diving bouts. Real-time assessment of the molecular changes underlying protection against hypoxic injury in seals remains restricted by their at-sea inaccessibility. Hence, we developed a proliferative arterial endothelial cell culture model from elephant seals and used RNA-seq, functional assays, and confocal microscopy to assess the molecular response to prolonged hypoxia. RESULTS: Seal and human endothelial cells exposed to 1% O2 for up to 6 h respond differently to acute and prolonged hypoxia. Seal cells decouple stabilization of the hypoxia-sensitive transcriptional regulator HIF-1α from angiogenic signaling. Rapid upregulation of genes involved in glutathione (GSH) metabolism supports the maintenance of GSH pools, and intracellular succinate increases in seal but not human cells. High maximal and spare respiratory capacity in seal cells after hypoxia exposure occurs in concert with increasing mitochondrial branch length and independent from major changes in extracellular acidification rate, suggesting that seal cells recover oxidative metabolism without significant glycolytic dependency after hypoxia exposure. CONCLUSIONS: We found that the glutathione antioxidant system is upregulated in seal endothelial cells during hypoxia, while this system remains static in comparable human cells. Furthermore, we found that in contrast to human cells, hypoxia exposure rapidly activates HIF-1 in seal cells, but this response is decoupled from the canonical angiogenesis pathway. These results highlight the unique mechanisms that confer extraordinary tolerance to limited oxygen availability in a champion diving mammal.

Maternal age can influence reproductive success and offspring fitness, but the timing, magnitude and direction of those impacts are not well understood. Evolutionary theory predicts that selection on fertility senescence is stronger than maternal effect senescence, and therefore, the rate of maternal effect senescence will be faster than fertility senescence. We used a 36‐year study of northern elephant seals (Mirounga angustirostris) to investigate reproductive senescence. Our dataset included 103,746 sightings of 1203 known‐age female northern elephant seals. We hypothesized that fertility (maternal reproductive success), offspring survival and recruitment into the breeding population, and male offspring production would decline with advanced maternal age. Furthermore, we hypothesized that older females would shorten their moulting haul out to allow for more time spent foraging. We found evidence for both fertility and maternal effect senescence, but no evidence for senescence impacting offspring recruitment or sex ratio. Breeding probability declined from 96.4% (95% CI: 94.8%–97.5%) at 11 years old to 89.7% (81.9%–94.3%) at 19 years old, and the probability of offspring survival declined from 30.3% (23.6%–38.0%) at 11 years old to 9.1% (3.2%–22.9%) at 19 years old. The rates of decline for fertility and maternal effect senescence were not different from each other. However, maternal effect senescence had a substantially greater impact on the number of offspring surviving to age 1 compared to fertility senescence. Compared to a hypothetical non‐senescent population, maternal effect senescence resulted in 5.3% fewer surviving pups, whereas fertility senescence resulted in only 0.3% fewer pups produced per year. These results are consistent with evolutionary theory predicting weaker selection on maternal effect than fertility senescence. Maternal effect senescence may therefore be more influential on population dynamics than fertility senescence in some systems. [ABSTRACT FROM AUTHOR]

AbstractThe bottlenose dolphin is a widely distributed species found in temperate waters, including the Mediterranean and Black Seas. The Black Sea population is recognized as a distinct subspecies, Tursiops truncatus ponticus, due to genetic and morphological differences. This study analyzed mitochondrial DNA (mtDNA) sequences of 73 bottlenose dolphin samples collected between 1999 and 2016 along the Turkish Black Sea coast, Turkish Straits System (TSS), Aegean, and Mediterranean Seas revealing 14 haplotypes, eight of which are reported here for the first time.The haplotype network shows two main nodes with star-like sub-networks, but no apparent geographic pattern. The lack of geographical groupings of haplotypes indicates the high mobility of the species within the sampled area. The northern Black Sea bottlenose dolphins (NBS) appear to be genetically differentiated from those in the southwestern Black Sea (SBS), Mediterranean, and Atlantic Ocean, but not from the TSS and Aegean Sea populations. Besides, SBS bottlenose dolphins were differentiated only from those in the western Mediterranean (WM) and the Atlantic. Therefore, NBS and SBS bottlenose dolphins should at least be categorized as different populations. However, contrary to some previous studies there was no evidence supporting the classification of Black Sea bottlenose dolphins as a separate subspecies.The TSS differs only from the Atlantic and the Aegean, and functions like a migratory ‘melting pot’ for surrounding populations. Despite the largest sample size, NBS bottlenose dolphins exhibited the lowest haplotype and nucleotide diversity. This low genetic diversity and potential isolation from adjacent populations highlight the need for prioritizing the conservation of NBS bottlenose dolphins. [ABSTRACT FROM AUTHOR]

Bycatch is the most significant threat to marine mammals globally. There are increasing requirements for national governments to fulfil their obligations to international agreements and treaties to assess fisheries catch and bycatch of non-target species. Questionnaire surveys represent one low-cost method to collect data to estimate fisheries catch and bycatch of vulnerable species including marine mammals. Questionnaire surveys can be particularly advantageous when bycatch is being investigated on large spatial and temporal scales, or in data-poor areas. This review aims to provide the necessary guidance required to design and conduct questionnaire studies investigating marine mammal bycatch. To do so, a systematic review was conducted of the methods used in 91 peer-reviewed or grey literature questionnaire studies from 1990 to 2023 investigating marine mammal bycatch. Literature was searched, screened, and analysed following the RepOrting standards for Systematic Evidence Syntheses (ROSES) protocols. A narrative synthesis and critical evaluation of the methods used were conducted and best practice recommendations are proposed. The recommendations include suggestions for how to generate representative samples, the steps that should be followed when designing a questionnaire instrument, how to collect reliable data, how to reduce under-reporting and interviewer bias, and how weighting or model-based bycatch estimation techniques can be used to reduce sampling bias. The review's guidance and best practice recommendations provide much-needed resources to develop and employ questionnaire studies that produce robust bycatch estimates for marine mammal populations where they are currently missing. Recommendations can be used by scientists and decision-makers across the globe. Whilst the focus of this review is on using questionnaires to investigate marine mammal bycatch, the information and recommendations will also be useful for those investigating bycatch of any other non-target species. [ABSTRACT FROM AUTHOR]

A growing and increasingly globalised human population, requiring the movement of goods and commodities, is placing increasing demands on the maritime industry, resulting in a concurrent increase in global shipping activities. This has consequences for the marine environment, particularly for species vulnerable to the impacts of vessel traffic. For example, vessel collisions can result in sub‐lethal or fatal injuries for marine mammals, whilst vessel noise can cause acoustic masking that effectively reduces an animal's listening space, potentially impacting their communication, navigation and foraging capacity.While a number of parallel approaches to mapping collision risk to large whales have arisen, these methods vary in their focus, usually on either co‐occurrence, collision probability, or probability of mortality. However, little attention has been given to the implications of methodological choice and data selection on subsequent risk predictions.To assess differences between these approaches, we used a standardised input dataset comprised of telemetry‐point data from tagged bowhead whales, and satellite‐based Automated Identification System (AIS) data of spatial vessel movements covering the Davis‐Baffin Arctic Marine Area. We applied this data to eight different, previously published analyses for deriving areas of vessel risk.We found that the choice of risk mapping approach affected the location, and total area, identified as 'high risk', and that more computationally complex approaches did not necessarily equate to different predictions. There was considerable variation in the total area of 'high risk' predicted within each map (range = 20–42,246 km2).Synthesis and Applications. The results underscore the importance of methodological transparency, informed data selection and careful interpretation when predicting collision risk. We provide practical recommendations for enhancing transparency when predicting risk, and discuss choice of approach suitable for different situations or management applications. It is critical that managers and policy makers are aware of the implications of applying different approaches when interpreting risk evaluation outputs. [ABSTRACT FROM AUTHOR]

The East Asian finless porpoise, Neophocaena asiaeorientalis sunameri, is an endangered species that inhabits the coastal marine environments of East Asia. In the present study, we investigated the overall infection status of anisakid nematodes in East Asian finless porpoises from three sea sectors off the Korean Peninsula. The genetic diversity and population genetic structure of the identified nematode species were evaluated. The prevalence of all stages of anisakid nematodes collected from the stomach was 57.55% (61 among the 106 porpoises examined), and 16 of the hosts were found to have adult worms. The mean number of infected adults was 211 (± 419.54, 5–1455 per host). Only one species of anisakids, Anisakis pegreffii, was identified from randomly selected worms by molecular approaches. Analysis of the mitochondrial (mt) cox2 partial gene in 50 newly generated sequences of A. pegreffii revealed 24 haplotypes, including 14 new haplotypes. We observed below-average levels of nucleotide diversity and haplotype diversity compared to other seas around the world. The mtDNA cox2 haplotypes of the species in the three Korean sea areas showed no genetic structure, suggesting well-connected gene flow within these areas. This study represents the first record of a definitive host of A. pegreffii in Korean waters, providing important information regarding anisakids genetic diversity in the cetacean species inhabiting limited regions. [ABSTRACT FROM AUTHOR]

Beluga whales (Delphinapterus leucas) have a long history of subsistence harvest that has continued into the present and a history of exploitation through commercial harvest. The Eastern High Arctic – Baffin Bay (EHA) population of beluga whales has the northernmost distribution of any beluga whale population in Canada. Beluga whales from the EHA population have a single complete abundance estimate from 1996 and 3 partial abundance estimates in 1981, 2010, and 2012 from aerial surveys; reliable estimates from surveys are lacking in recent years, limiting the ability to determine population dynamics. In 2020 satellite imagery was used to estimate abundance for beluga whales in the EHA population for estuaries in the whales' summering area. We built a stochastic stock production model to estimate population dynamics from the start of reliably compiled harvest history data in 1977 to 2022, using abundance estimates from 1981, 1996, 2010, 2012, and 2020. We also extended the model 10 years into the future under 7 potential annual harvest scenarios (within the range of annual reported harvests) to calculate the probability of decline. We estimated the starting population in 1977 as 29,615 whales (95% CI = 20,765–46,251), and the estimate from 2022 was 16,495 whales (95% CI = 6,731–33,504). Landed catch of 0, 100, 200, 300, 400, 500, and 600 beluga whales annually resulted in <1%, 3%, 23%, 50%, 70%, 83%, and 90% probabilities of decline, respectively. There was a notable decrease in abundance over the time series, likely caused by harvest pressure. Harvest in recent years has ranged from 155–553 catches per year, and our results suggest that 108 landed catches per year equates to a 5% risk of decline, the low risk goal for precautionary fisheries management, which aligns with population conservation goals. Our model is a first step in understanding the EHA beluga whale population dynamics using what data are available and suggests that current harvests in some years may result in a population decline and should be monitored. [ABSTRACT FROM AUTHOR]

Icebreaker vessels in the Canadian Arctic are used to monitor and maintain open shipping lanes during summer and fall. Icebreaker operating routes often overlap with important habitats of endemic Arctic marine mammals, leading to potential interactions and disturbance. In this study, we examined the frequency, proximity, and duration of encounter events between narwhals (Monodon monoceros) and icebreaker vessels in Tasiujaq (Eclipse Sound), Nunavut, an important summering area for this species. We combined tracking data from 25 narwhals equipped with satellite telemetry devices in Tasiujaq between 2016 and 2018 with automatic identification system (AIS) data for the same period from 7 icebreaker vessels. We defined an encounter event between a narwhal and an icebreaker as the total consecutive occurrences of an individual within 50 km of a vessel within 1 hour. For all years combined, 17 out of 25 narwhals had at least 1 encounter with an icebreaker and all 7 icebreakers were involved in at least 1 encounter. The closest distance (closest point of approach) recorded was <1 km and the longest cumulative duration of encounter events for 1 narwhal with 1 icebreaker was 121.6 hours (n = 27 encounter events over 17 days). Proximity and continuous exposure of narwhals to high levels of noise are a key concern when considering short‐ and long‐term effects on behavior and fitness of this species. [ABSTRACT FROM AUTHOR]

Monitoring the nutritional health of cetaceans has become increasingly important in a changing environment, where multiple stressors impact animals. Particularly for those species that require consumption of energy‐dense prey, such as the common dolphin. Thus far, no uniform measure for monitoring body condition has been recommended across cetaceans, and species‐specific measures may need to be developed if employed as a population condition indicator under Descriptor 1 of the Marine Strategy Framework Directive. Here, nine morphometric body condition indices were applied to long‐term common dolphin stranding data sets originating from Ireland and the UK. We report a recent decline in the nutritional health of common dolphins in the Celtic Seas ecoregion comparing animals from 2017 to 2019 to animals from 1990 to 2006, with an increase in cases of animals dying due to starvation. Using ordinal regression trees, ventral blubber thickness (VBT) was identified as the most important index to predict nutritional status, defined at necropsy, followed by the scaled mass index (SMI). Using generalised linear models, both the VBT and SMI indices differentiated individuals that died from chronic and acute causes of death (i.e., bycatch), where animals in chronic conditions had significantly thinner VBT and lower SMI. Both significant temporal and seasonal patterns in VBT were identified, with poorer body conditions observed during the autumn and better body conditions observed during the spring, as well as an overall decline detected in VBT during the study period. While VBT was positively correlated with total body length, SMI showed the opposite trend. The VBT index is recommended for monitoring nutritional health within the species when total body length and season are considered. Further research is needed to understand the underlying causes for the observed decline, including shifts in prey availability and/or quality, to inform targeted conservation management strategies. [ABSTRACT FROM AUTHOR]

Assessing genetic structure and diversity in wildlife is particularly important in the context of climate change. The Arctic is rapidly warming, and endemic species must adapt quickly or face significant threats to persistence. Bowhead whales (Balaena mysticetus) and narwhals (Monodon monoceros) are two long‐lived Arctic species with similar habitat requirements and are often seen together in the Canadian Arctic. Although their ranges overlap extensively, bowhead whales experienced significantly greater commercial whaling mortality than narwhals over several centuries. The similar habitat requirements but different harvest histories of these two species provide an opportunity to examine present‐day genetic diversity and the demographic and genetic consequences of commercial whaling. We whole‐genome resequenced contemporary Canadian Arctic bowhead whales and narwhals to delineate population structure and reconstruct demographic history. We found higher genetic diversity in bowhead whales compared to narwhals. However, bowhead whale effective population size sharply declined contemporaneously with the intense commercial whaling period. Narwhals, in contrast, exhibited recent growth in effective population size, likely reflecting exposure to limited opportunistic commercial harvest. Bowhead whales will likely continue to experience significant genetic drift in the future, leading to the erosion of genetic diversity. In contrast, narwhals do not seem to be at imminent risk of losing their current levels of genetic variation due to their long‐term low effective population size and lack of evidence for a recent decline. This work highlights the importance of considering population trajectories in addition to genetic diversity when assessing the genetics of populations for conservation and management purposes. [ABSTRACT FROM AUTHOR]

The intracellular pathogens Toxoplasma gondii, Brucella spp., and Chlamydia spp. are all known causative agents of abortion in wildlife. Both T. gondii and Brucella spp. have been identified in marine mammal abortions and a limited number of studies have detected their potential presence in Australian fur seals (Arctocephalus pusillus doriferus), but data are sparse for these pathogens in Australian fur seal breeding colonies. Australian fur seals have been shown to have a high degree of third-trimester pregnancy loss in one of their largest breeding colonies. Additionally, pup production has declined at the largest breeding colony for the species. This study surveyed the presence of T. gondii, Brucella spp., and Chlamydia spp. as potential infectious causes of this reproductive loss. Aborted fetuses were collected from two of the largest breeding colonies for the species, Seal Rocks (n=19) and Kanowna Island (n=34). These were examined grossly and through histopathological evaluation, in conjunction with molecular testing for all three pathogens. Placentas were collected from full-term births during the pupping season from Kanowna Island (n=118). These were used to compare the molecular prevalence of the three pathogens in presumed successful pregnancies. Chlamydia spp. was not detected in aborted fetuses in this study. Brucella spp. was detected with PCR in both aborted fetuses (9.4%) and placentas from full-term births (3.4%), and T. gondii was detected using routine histopathology (n=2/53), immunohistochemistry (n=3/4), and PCR (n=4/53) in tissues from aborted fetuses. Toxoplasma gondii was present in 7.5% of third-trimester abortions and absent from all full-term placentas. Brucella spp. was detected in both aborted fetuses and full-term placentas. This is the first description of vertical transmission of T. gondii in a marine mammal from the southern hemisphere. [ABSTRACT FROM AUTHOR]

As sperm whales are important predators that control energy flux in the oceans, changes in their population can be used as a sentinel to measure of ecosystem health. The present study conducted a sperm whale survey of the eastern Midriff Islands Region in the Gulf of California over the course of nine years, recording sightings and collecting photographs of the fluke of sperm whale individuals. A photo-identification catalog was compiled, while individual recapture data were used to estimate the population size in the central portion of the Gulf of California, using a Jolly-Seber POPAN open population model. The results obtained show a yearly population of between 20 and 167 sperm whales, with a super population of 354 sperm whales observed between 2009 and 2015. However, from 2016 to 2018, no sightings of the species were recorded, which coincides with the decline observed in landings of their main prey, the jumbo squid, in the region. General additive model conducted on sperm whale sightings per unit of effort vs jumbo squid landings obtained an adjusted R2 of 0.644 and a deviance explained of 60.3%, indicating a good non-linear relationship between sightings of this odontocete and its prey availability. This evidence suggests that sperm whales departed the region between 2016 and 2018, due to a documented fishery collapse alongside changes of their main prey into its small phenotype, possibly as the result of increase warming conditions in surface and subsurface waters in the Gulf of California in the last three decades. [ABSTRACT FROM AUTHOR]

Understanding reproductive output and success is integral to the conservation and management of threatened species and populations. Little is known about the reproductive parameters of Australian humpback dolphins (Sousa sahulensis), a species subject to cumulative pressures from anthropogenic threats due to their coastal distribution and strong site fidelity. This study assesses several reproductive parameters, including crude birth, recruitment, fecundity, and calf survival rates, in addition to interbirth intervals of Australian humpback dolphins inhabiting the near‐urban embayment of Moreton Bay, Queensland. Between 2014 and 2020, 106 adult females were photographically identified during 222 boat surveys. Of these, 75.5% (n = 80) were observed with calves. Birth seasonality was apparent and coincided with austral autumn and winter months. Interbirth intervals ranged between 1 and >6 years, with an average of 3.1 (SD = 1.1) years if offspring survived. Findings indicate declining fecundity rates (p <.05, M = 0.12, SD = 0.02), relatively low recruitment rates (M = 0.04, SD = 0.01) and calf survival rates to 1 year of age (M = 0.63, SD = 0.15). This study provides a useful baseline that can inform viability assessments and conservation measures, for both this population and others throughout the species range. [ABSTRACT FROM AUTHOR]

Understanding animals' movements is essential to assess habitat use, life‐history strategies, and population dynamics. Here, we investigate the movement and behavior patterns of 153 humpback whales in the Southwest Atlantic Ocean (SWA) using data obtained by satellite telemetry between 2003 and 2019 during the species' breeding season (August–December) off the Brazilian coast. Switching state space models were applied to estimate behavior states (bmode) classified as Area Restricted Search (ARS), Transiting (TRANS), or uncertain. Whales were distributed from 4°S to 24°S, and five clusters of ARS behavior were identified along the Brazilian coast. Generalized linear mixed modeling revealed three main results: (1) a transition towards more sinuous behavioral states with increasing latitude; (2) more sinuous movement behavior around new moons; (3) movement behavior was temporally dynamic throughout the breeding season over the years, particularly in 2019. The results then revealed important regions where humpback whales cluster to engage in mating and nursing behaviors, highlighting the influence of spatial location and environmental cycles on their behavior. Estimated movement behavior presented here improves the knowledge about the habitat use and movement patterns of SWA humpback whales in their breeding ground and can be used to mitigate potential human‐related impacts. [ABSTRACT FROM AUTHOR]

In rapidly changing ocean systems, there is a dual need to engage and educate community members and carry out rapid data acquisition. There is a body of evidence to support community or citizen science projects as successful vehicles for achieving these goals, with a particular need to increase global ocean literacy. The online SealSpotter program is a citizen science initiative aimed at monitoring trends in Australian fur seal (Arctocephalus pusillus doriferus) populations and connecting people to the marine environment. Here we present the findings of five years of monitoring of fur seals using drone surveys counted by citizen scientists via SealSpotter. Over five years, global participants from 23 countries were engaged in counting seals with a focus on the annual breeding season and pup abundance, with an average of 13,479 images and 171,137 seals counted per year. SealSpotter participants presented more conservative (lower) counts than expert counts, however both groups detected similar trends in abundance, emphasizing success of the project aims that included obtaining a precise index of pup abundance; ultimately a more achievable goal than accuracy due to the difficulties in measuring absolute abundance. We reflect on SealSpotter's accomplishments and highlight the potential for marine citizen science programs as important tools for addressing global ocean literacy needs. The SealSpotter program contributes to our understanding of marine ecosystems through a simple but effective citizen science program. [ABSTRACT FROM AUTHOR]

Abstract Clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 virus was detected in the South American sea lions found dead in Santa Catarina, Brazil, in October 2023. Whole genome sequencing and comparative phylogenetic analysis were conducted to investigate the origin, genetic diversity, and zoonotic potentials of the H5N1 viruses. The H5N1 viruses belonged to the genotype B3.2 of clade 2.3.4.4b H5N1 virus, which was identified in North America and disseminated to South America. They have acquired new amino acid substitutions related to mammalian host affinity. Our study provides insights into the genetic landscape of HPAI H5N1 viruses in Brazil, highlighting the continuous evolutionary processes contributing to their possible adaptation to mammalian hosts.

Abstract Background To reduce heat loss underwater, marine mammals cover their bodies with insulation. Cetaceans in particular rely solely on blubber for insulation which has low conductivity. Blubber establishes a great thermal gradient between the warmer body core and cooler body surface, reducing heat transfer to the environment. A temperature gradient within the blubber determines the conductive heat transfer from the body trunk, where conduction and convection are the primary heat transfer mechanisms in cetaceans. Therefore, measuring the temperature at the innermost part of the blubber, i.e., the temperature at the muscle–blubber interface (Tmbi), can enhance our understanding of thermoregulatory mechanisms in cetaceans. In thermoregulation, activity-induced heat produced by increased muscle metabolism is another factor that plays an important role, however, the effects of activity on Tmbi have not been investigated in cetaceans. To assess this relationship in free-swimming cetaceans, we measured Tmbi and activity levels in a captive Risso’s dolphin (Grampus griseus) using an implantable biologging device. Results Tmbi and activity data were analyzed for 11 days. The average Tmbi was 35.1 ± 0.6 ºC and the temperature gradient between Tmbi and the water temperature was 13.0 ± 0.7 ºC. Tmbi was higher during the daytime and lower in the early morning. The variation in Tmbi was best explained by both the activity levels and time of day. Tmbi did not simply increase with activity levels; it appeared to remain relatively constant at most activity levels. However, Tmbi appeared to decrease when the animal was inactive and increase when it was intensely active. Conclusion Our results provide important insights into how a dolphin regulates its body temperature underwater. Thermal insulation by blubber and heat production by activity were suggested to play important roles in thermoregulation. Whole-body heat dissipation might be used to regulate temperature increases when heat production is excessive due to intense activity. During inactive periods, decreasing temperature gradient may help reduce heat loss from the body.

Abstract Background Pathogenic Leptospira species are globally important zoonotic pathogens capable of infecting a wide range of host species. In marine mammals, reports of Leptospira have predominantly been in pinnipeds, with isolated reports of infections in cetaceans. Case presentation On 28 June 2021, a 150.5 cm long female, short-beaked common dolphin (Delphinus delphis delphis) stranded alive on the coast of southern California and subsequently died. Gross necropsy revealed multifocal cortical pallor within the reniculi of the kidney, and lymphoplasmacytic tubulointerstitial nephritis was observed histologically. Immunohistochemistry confirmed Leptospira infection, and PCR followed by lfb1 gene amplicon sequencing suggested that the infecting organism was L. kirschneri. Leptospira DNA capture and enrichment allowed for whole-genome sequencing to be conducted. Phylogenetic analyses confirmed the causative agent was a previously undescribed, divergent lineage of L. kirschneri. Conclusions We report the first detection of pathogenic Leptospira in a short-beaked common dolphin, and the first detection in any cetacean in the northeastern Pacific Ocean. Renal lesions were consistent with leptospirosis in other host species, including marine mammals, and were the most significant lesions detected overall, suggesting leptospirosis as the likely cause of death. We identified the cause of the infection as L. kirschneri, a species detected only once before in a marine mammal – a northern elephant seal (Mirounga angustirostris) of the northeastern Pacific. These findings raise questions about the mechanism of transmission, given the obligate marine lifestyle of cetaceans (in contrast to pinnipeds, which spend time on land) and the commonly accepted view that Leptospira are quickly killed by salt water. They also raise important questions regarding the source of infection, and whether it arose from transmission among marine mammals or from terrestrial-to-marine spillover. Moving forward, surveillance and sampling must be expanded to better understand the extent to which Leptospira infections occur in the marine ecosystem and possible epidemiological linkages between and among marine and terrestrial host species. Generating Leptospira genomes from different host species will yield crucial information about possible transmission links, and our study highlights the power of new techniques such as DNA enrichment to illuminate the complex ecology of this important zoonotic pathogen.

Clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 virus was detected in the South American sea lions found dead in Santa Catarina, Brazil, in October 2023. Whole genome sequencing and comparative phylogenetic analysis were conducted to investigate the origin, genetic diversity, and zoonotic potentials of the H5N1 viruses. The H5N1 viruses belonged to the genotype B3.2 of clade 2.3.4.4b H5N1 virus, which was identified in North America and disseminated to South America. They have acquired new amino acid substitutions related to mammalian host affinity. Our study provides insights into the genetic landscape of HPAI H5N1 viruses in Brazil, highlighting the continuous evolutionary processes contributing to their possible adaptation to mammalian hosts. [ABSTRACT FROM AUTHOR]

Free‐ranging otariids are routinely captured for data and sample collection. To achieve this, anesthesia may be used to facilitate handling, decrease stress, and improve human and animal safety. Injectable anesthetics are widely used for such endeavors; however, certain disadvantages to this approach warrant further exploration of alternative anesthetic techniques. Inhalant anesthesia, commonly utilized for otariids in a clinical setting, is used more sparingly in the field, with few studies assessing safety and efficacy in free‐ranging otariids. During 2016–2020, 175 Guadalupe fur seals were net‐captured and anesthetized with isoflurane and oxygen on Guadalupe Island, Mexico, for satellite telemetry attachment and biological sampling. To contribute to the body of knowledge surrounding the use of inhalants in the field, physiologic and anesthetic parameters (time to induction, total oxygen use, heart rate, respiratory rate, time to recovery, and anesthetic depth) were assessed for effects of biometric and logistical factors (pursuit and holding time, sex, age class, body weight, year, oxygen flow rate, and total anesthesia time). This anesthetic technique provided rapid induction and recovery times and rare side effects in Guadalupe fur seals, serving as a practical means of field immobilization for minimally invasive procedures in this imperiled species. [ABSTRACT FROM AUTHOR]

Southern sea otters (Enhydra lutris nereis) are a federally listed threatened keystone species of the California kelp forest ecosystem and a sentinel species, indicating environmental health. Mercury (Hg) is a bioaccumulative neurotoxin that poses a threat to high trophic‐level species such as marine mammals. We quantified total Hg (THg) concentrations in fur, brain, and liver tissues of necropsied southern sea otters (n = 44) that stranded along the California coast from 2010 to 2019. THg concentrations differed significantly between fur and brain, and between liver and brain. Tissue type explained 64%, and sex explained only 3.3% of overall THg variability (0.48–46.1 μg/g dry weight). All individuals had liver Hg concentrations measuring well under the proposed lower‐limit low risk guideline for harp seals, Pagophilus groenlandicus. However, six sea otters exceeded the liver THg moderate risk threshold for terrestrial furbearers to which sea otters are closely related. These data represent baseline THg concentrations in fur, brain, and liver of the southern sea otter and build upon previous studies in various sea otter subspecies. Research on sea otter Hg tolerance and continued monitoring are needed to clarify potential health risks associated with the tissue concentrations observed in this study. [ABSTRACT FROM AUTHOR]

Few studies have examined the impacts of externally fitted data‐loggers and telemetry tags on pinnipeds. We tested for instrument effects on body mass of lactating female gray seals and their offspring and probability of pupping in the next breeding season. Known‐age adult females (n = 216) were fitted with instruments in winter, spring, and fall from 1992 to 2018 at Sable Island, Nova Scotia. Of those tagged in spring and fall, 61 of 135 returning females and 59 of their offspring were weighed within 5 days postpartum and 79 pups were weighed at weaning. Instrumented females were assigned to treatments based on tag frontal area sums, tag mass, deployment duration, and acoustic tag presence compared to control females without instruments using linear mixed‐effects models. None of the treatment effects were included in the preferred models predicting birth mass of offspring or probability of breeding in the following year. The small negative effect (−3% to −7%) on postpartum maternal mass and pup weaning mass (−4.7%) for females instrumented in fall may be an artifact as longer spring deployments showed no effect. Overall, we found that the instruments deployed had no detectable negative effects on the maternal and offspring variables measured. [ABSTRACT FROM AUTHOR]

Background: Marine mammals, which have evolved independently into three distinct lineages, share common physiological features that contribute to their adaptation to the marine environment. Objective: To identify positively selected genes (PSGs) for adaptation to the marine environment using available genomic data from three taxonomic orders: cetaceans, pinnipeds, and sirenians. Methods: Based on the genomes within each group of Artiodactyla, Carnivora and Afrotheria, we performed selection analysis using the branch-site model in CODEML. Results: Based on the branch-site model, 460, 614, and 359 PSGs were predicted for the cetaceans, pinnipeds, and sirenians, respectively. Functional enrichment analysis indicated that genes associated with hemostasis were positively selected across all lineages of marine mammals. We observed positive selection signals for the hemostasis and coagulation-related genes plasminogen activator, urokinase (PLAU), multimerin 1 (MMRN1), gamma-glutamyl carboxylase (GGCX), and platelet endothelial aggregation receptor 1 (PEAR1). Additionally, we found out that the sodium voltage-gated channel alpha subunit 9 (SCN9A), serine/arginine repetitive matrix 4 (SRRM4), and Ki-ras-induced actin-interacting protein (KRAP) are under positive selection pressure and are associated with cognition, neurite outgrowth, and IP3-mediated Ca2 + release, respectively. Conclusion: This study will contribute to our understanding of the adaptive evolution of marine mammals by providing information on a group of candidate genes that are predicted to influence adaptation to aquatic environments, as well as their functional characteristics. [ABSTRACT FROM AUTHOR]

Marine mammals serve as sentinels for environmental health, offering insights into ecosystem health. Enhancing management and conservation strategies for these species requires a comprehensive understanding of factors contributing to their morbidity and mortality. This review aims to identify reported causes of morbidity and mortality in small Odontoceti within the Southern Hemisphere. A scoping review of literature was conducted, searching Scopus, PubMed, and Web of Science, with additional screening of citations for articles not captured in the search. The review encompassed 198 articles, with a total sample size of 25567 deceased small Odontoceti across 20 genera. A major challenge emerged, with the cause of death undetermined or unspecified in 39% of cases. Known entanglements accounted for 47% of total mortalities. Mass strandings (11%) and infectious disease (1.1%) were also reported. The study identified 14 primary infectious pathogens in 276 animals, spanning viral (CeMV = 214, H5N1 = 1), bacterial (Brucella sp. = 15, Erysipelothrix sp. = 1, Streptococcus iniae = 1, Enterobacter kobei = 1), parasitic (Toxoplasma gondii = 15, Halocercus sp. = 17, Clistobothrium grimaldii = 1, Stenurus globicephalae = 1, Giardia sp. = 1), and fungal (Aspergillus sp. = 2, Paracoccidioides brasiliensis = 5, Cryptococcus sp. = 1) origins. Anthropogenic‐induced mortality emerges as a significant threat to small Odontoceti of the Southern Hemisphere, underscoring the urgent need for enhanced conservation and management strategies. Increased surveillance of infectious pathogens is imperative, aiming to deepen our understanding of pathogen distribution, prevalence, and impact on Odontoceti health. [ABSTRACT FROM AUTHOR]

Background: To reduce heat loss underwater, marine mammals cover their bodies with insulation. Cetaceans in particular rely solely on blubber for insulation which has low conductivity. Blubber establishes a great thermal gradient between the warmer body core and cooler body surface, reducing heat transfer to the environment. A temperature gradient within the blubber determines the conductive heat transfer from the body trunk, where conduction and convection are the primary heat transfer mechanisms in cetaceans. Therefore, measuring the temperature at the innermost part of the blubber, i.e., the temperature at the muscle–blubber interface (Tmbi), can enhance our understanding of thermoregulatory mechanisms in cetaceans. In thermoregulation, activity-induced heat produced by increased muscle metabolism is another factor that plays an important role, however, the effects of activity on Tmbi have not been investigated in cetaceans. To assess this relationship in free-swimming cetaceans, we measured Tmbi and activity levels in a captive Risso's dolphin (Grampus griseus) using an implantable biologging device. Results: Tmbi and activity data were analyzed for 11 days. The average Tmbi was 35.1 ± 0.6 ºC and the temperature gradient between Tmbi and the water temperature was 13.0 ± 0.7 ºC. Tmbi was higher during the daytime and lower in the early morning. The variation in Tmbi was best explained by both the activity levels and time of day. Tmbi did not simply increase with activity levels; it appeared to remain relatively constant at most activity levels. However, Tmbi appeared to decrease when the animal was inactive and increase when it was intensely active. Conclusion: Our results provide important insights into how a dolphin regulates its body temperature underwater. Thermal insulation by blubber and heat production by activity were suggested to play important roles in thermoregulation. Whole-body heat dissipation might be used to regulate temperature increases when heat production is excessive due to intense activity. During inactive periods, decreasing temperature gradient may help reduce heat loss from the body. [ABSTRACT FROM AUTHOR]

Gut bacterial communities play a vital role in a host's digestion and fermentation of complex carbohydrates, absorption of nutrients, and energy harvest/storage. Dugongs are obligate seagrass grazers with an expanded hindgut and associated microbiome. Here, we characterised and compared the faecal bacterial communities of dugongs from genetically distinct populations along the east coast of Australia, between subtropical Moreton Bay and tropical Cleveland Bay. Amplicon sequencing of fresh dugong faecal samples (n=47) revealed Firmicutes (62%) dominating the faecal bacterial communities across all populations. Several bacterial genera (Bacteroides, Clostridium sensu stricto 1, Blautia and Polaribacter) were detected in samples from all locations, suggesting their importance in seagrass digestion. Principal coordinate analysis showed the three southern-most dugong populations having different faecal bacterial community compositions from northern populations. The relative abundances of the genera Clostridium sensu stricto 13 and dgA-11 gut group were higher, but Bacteroides was lower, in the southern dugong populations, compared to the northern populations, suggesting potential adaptive changes associated with location. This study contributes to our knowledge of the faecal bacterial communities of dugongs inhabiting Australian coastal waters. Future studies of diet selection in relation to seagrass availability throughout the dugong's range will help to advance our understanding of the roles that seagrass species may play in affecting the dugong's faecal bacterial community composition. [ABSTRACT FROM AUTHOR]

Harbour porpoises (Phocoena phocoena) are the only cetacean residents found year-round in Swedish waters and they are exposed to numerous natural and anthropogenic threats. Since the in situ monitoring of cetaceans can be difficult, invasive and often expensive, investigation of stranding patterns and examination of stranded animals can be used as a cost-effective source of data to study these elusive animals. The aim of this study was to investigate the spatiotemporal patterns of harbour porpoise stranding reports and the possible underlying causes in Swedish waters over a ten-year period (2014–2023). Additionally, the Swedish stranding network plays a key role in the collection of stranded carcasses for health and disease surveillance, and geographic coverage of the network also was analysed. When making spatial comparisons, the ten-year period was divided into two five-year blocks. Data on 854 stranded harbour porpoises were analysed from the coasts of the Skagerrak, Kattegat, and Baltic Seas. Both significant spatial and temporal patterns could be identified. Strandings peaked in July through September and hotspots occurred along most of the Swedish west coast, with the most frequent hotspots located around Öresund and especially the area around the Kullen peninsula. The spatial patterns of strandings found in this study are consistent with data on porpoise abundance, prey abundance, and gillnet fisheries' efforts. The latter is known to be one of the primary causes of porpoise mortality. Furthermore, the coverage of the Swedish stranding network increased between the two periods, likely reflecting an increased awareness of the carcass-based surveillance program, and gaps requiring network expansion efforts were identified. These results also provide baseline data to enable the continued monitoring of stranding trends, as changes may indicate changes in population distribution, size or mortality rates. [ABSTRACT FROM AUTHOR]

The Arctic is the fastest‐warming region on the planet, and the lengthening ice‐free season is opening Arctic waters to sub‐Arctic species such as the killer whale (Orcinus orca). As apex predators, killer whales can cause significant ecosystem‐scale changes. Setting conservation priorities for killer whales and their Arctic prey species requires knowledge of their evolutionary history and demographic trajectory. Using whole‐genome resequencing of 24 killer whales sampled in the northwest Atlantic, we first explored the population structure and demographic history of Arctic killer whales. To better understand the broader geographic relationship of these Arctic killer whales to other populations, we compared them to a globally sampled dataset. Finally, we assessed threats to Arctic killer whales due to anthropogenic harvest by reviewing the peer‐reviewed and gray literature. We found that there are two highly genetically distinct, non‐interbreeding populations of killer whales using the eastern Canadian Arctic. These populations appear to be as genetically different from each other as are ecotypes described elsewhere in the killer whale range; however, our data cannot speak to ecological differences between these populations. One population is newly identified as globally genetically distinct, and the second is genetically similar to individuals sampled from Greenland. The effective sizes of both populations recently declined, and both appear vulnerable to inbreeding and reduced adaptive potential. Our survey of human‐caused mortalities suggests that harvest poses an ongoing threat to both populations. The dynamic Arctic environment complicates conservation and management efforts, with killer whales adding top‐down pressure on Arctic food webs crucial to northern communities' social and economic well‐being. While killer whales represent a conservation priority, they also complicate decisions surrounding wildlife conservation and resource management in the Arctic amid the effects of climate change. [ABSTRACT FROM AUTHOR]

Rehabilitation of marine mammals is performed throughout the world, yet the impact of rehabilitation on individuals and populations is questionable given the lack of robust information on the rehabilitation process and post-release monitoring in most cases. The goals of this study were to perform a systematic review of existing literature on marine mammal rehabilitation between 2000–2023 to determine the current state of rehabilitation and to evaluate the rehabilitation and conservation factors that could be used to build a framework to assess the health of rehabilitation programs worldwide. A total of 418 publications encompassing 52 species of marine mammal were included in the systematic review. Rehabilitation efforts focused mostly on pinnipeds, and North America was the most represented region. Data are scarce for both short- and long-term post-release survival across species. Reports about species threatened with extinction were significantly more likely to include information about conservation parameters than those species of least concern. A meta-analysis demonstrated a fairly strong fit of the dimensions of the proposed framework for a rehabilitation health index. Further refinement would strengthen the utility of this tool for both rehabilitation and conservation programs. [ABSTRACT FROM AUTHOR]

Abstract Monitoring the nutritional health of cetaceans has become increasingly important in a changing environment, where multiple stressors impact animals. Particularly for those species that require consumption of energy‐dense prey, such as the common dolphin. Thus far, no uniform measure for monitoring body condition has been recommended across cetaceans, and species‐specific measures may need to be developed if employed as a population condition indicator under Descriptor 1 of the Marine Strategy Framework Directive. Here, nine morphometric body condition indices were applied to long‐term common dolphin stranding data sets originating from Ireland and the UK. We report a recent decline in the nutritional health of common dolphins in the Celtic Seas ecoregion comparing animals from 2017 to 2019 to animals from 1990 to 2006, with an increase in cases of animals dying due to starvation. Using ordinal regression trees, ventral blubber thickness (VBT) was identified as the most important index to predict nutritional status, defined at necropsy, followed by the scaled mass index (SMI). Using generalised linear models, both the VBT and SMI indices differentiated individuals that died from chronic and acute causes of death (i.e., bycatch), where animals in chronic conditions had significantly thinner VBT and lower SMI. Both significant temporal and seasonal patterns in VBT were identified, with poorer body conditions observed during the autumn and better body conditions observed during the spring, as well as an overall decline detected in VBT during the study period. While VBT was positively correlated with total body length, SMI showed the opposite trend. The VBT index is recommended for monitoring nutritional health within the species when total body length and season are considered. Further research is needed to understand the underlying causes for the observed decline, including shifts in prey availability and/or quality, to inform targeted conservation management strategies.

Bycatch is the most significant threat to marine mammals globally. There are increasing requirements for national governments to fulfil their obligations to international agreements and treaties to assess fisheries catch and bycatch of non-target species. Questionnaire surveys represent one low-cost method to collect data to estimate fisheries catch and bycatch of vulnerable species including marine mammals. Questionnaire surveys can be particularly advantageous when bycatch is being investigated on large spatial and temporal scales, or in data-poor areas. This review aims to provide the necessary guidance required to design and conduct questionnaire studies investigating marine mammal bycatch. To do so, a systematic review was conducted of the methods used in 91 peer-reviewed or grey literature questionnaire studies from 1990 to 2023 investigating marine mammal bycatch. Literature was searched, screened, and analysed following the RepOrting standards for Systematic Evidence Syntheses (ROSES) protocols. A narrative synthesis and critical evaluation of the methods used were conducted and best practice recommendations are proposed. The recommendations include suggestions for how to generate representative samples, the steps that should be followed when designing a questionnaire instrument, how to collect reliable data, how to reduce under-reporting and interviewer bias, and how weighting or model-based bycatch estimation techniques can be used to reduce sampling bias. The review’s guidance and best practice recommendations provide much-needed resources to develop and employ questionnaire studies that produce robust bycatch estimates for marine mammal populations where they are currently missing. Recommendations can be used by scientists and decision-makers across the globe. Whilst the focus of this review is on using questionnaires to investigate marine mammal bycatch, the information and recommendations will also be useful for those investigating bycatch of any other non-target species.

As sperm whales are important predators that control energy flux in the oceans, changes in their population can be used as a sentinel to measure of ecosystem health. The present study conducted a sperm whale survey of the eastern Midriff Islands Region in the Gulf of California over the course of nine years, recording sightings and collecting photographs of the fluke of sperm whale individuals. A photo-identification catalog was compiled, while individual recapture data were used to estimate the population size in the central portion of the Gulf of California, using a Jolly-Seber POPAN open population model. The results obtained show a yearly population of between 20 and 167 sperm whales, with a super population of 354 sperm whales observed between 2009 and 2015. However, from 2016 to 2018, no sightings of the species were recorded, which coincides with the decline observed in landings of their main prey, the jumbo squid, in the region. General additive model conducted on sperm whale sightings per unit of effort vs jumbo squid landings obtained an adjusted R2 of 0.644 and a deviance explained of 60.3%, indicating a good non-linear relationship between sightings of this odontocete and its prey availability. This evidence suggests that sperm whales departed the region between 2016 and 2018, due to a documented fishery collapse alongside changes of their main prey into its small phenotype, possibly as the result of increase warming conditions in surface and subsurface waters in the Gulf of California in the last three decades.

In rapidly changing ocean systems, there is a dual need to engage and educate community members and carry out rapid data acquisition. There is a body of evidence to support community or citizen science projects as successful vehicles for achieving these goals, with a particular need to increase global ocean literacy. The online SealSpotter program is a citizen science initiative aimed at monitoring trends in Australian fur seal (Arctocephalus pusillus doriferus) populations and connecting people to the marine environment. Here we present the findings of five years of monitoring of fur seals using drone surveys counted by citizen scientists via SealSpotter. Over five years, global participants from 23 countries were engaged in counting seals with a focus on the annual breeding season and pup abundance, with an average of 13,479 images and 171,137 seals counted per year. SealSpotter participants presented more conservative (lower) counts than expert counts, however both groups detected similar trends in abundance, emphasizing success of the project aims that included obtaining a precise index of pup abundance; ultimately a more achievable goal than accuracy due to the difficulties in measuring absolute abundance. We reflect on SealSpotter’s accomplishments and highlight the potential for marine citizen science programs as important tools for addressing global ocean literacy needs. The SealSpotter program contributes to our understanding of marine ecosystems through a simple but effective citizen science program.

Cetacean morbillivirus is an etiologic agent associated with strandings of live and dead cetacean species occurring sporadically or as epizootics worldwide. We report 2 cases of cetacean morbillivirus in humpback whales (Megaptera novaeangliae) in Brazil and describe the anatomopathological, immunohistochemical, and molecular characterization findings in the specimens.

Abstract Background Elephant seals exhibit extreme hypoxemic tolerance derived from repetitive hypoxia/reoxygenation episodes they experience during diving bouts. Real-time assessment of the molecular changes underlying protection against hypoxic injury in seals remains restricted by their at-sea inaccessibility. Hence, we developed a proliferative arterial endothelial cell culture model from elephant seals and used RNA-seq, functional assays, and confocal microscopy to assess the molecular response to prolonged hypoxia. Results Seal and human endothelial cells exposed to 1% O2 for up to 6 h respond differently to acute and prolonged hypoxia. Seal cells decouple stabilization of the hypoxia-sensitive transcriptional regulator HIF-1α from angiogenic signaling. Rapid upregulation of genes involved in glutathione (GSH) metabolism supports the maintenance of GSH pools, and intracellular succinate increases in seal but not human cells. High maximal and spare respiratory capacity in seal cells after hypoxia exposure occurs in concert with increasing mitochondrial branch length and independent from major changes in extracellular acidification rate, suggesting that seal cells recover oxidative metabolism without significant glycolytic dependency after hypoxia exposure. Conclusions We found that the glutathione antioxidant system is upregulated in seal endothelial cells during hypoxia, while this system remains static in comparable human cells. Furthermore, we found that in contrast to human cells, hypoxia exposure rapidly activates HIF-1 in seal cells, but this response is decoupled from the canonical angiogenesis pathway. These results highlight the unique mechanisms that confer extraordinary tolerance to limited oxygen availability in a champion diving mammal.

Abstract The dive response, or the ‘master switch of life’, is probably the most studied physiological trait in marine mammals and is thought to conserve the available O2 for the heart and brain. Although generally thought to be an autonomic reflex, several studies indicate that the cardiovascular changes during diving are anticipatory and can be conditioned. The respiratory adaptations, where the aquatic breathing pattern resembles intermittent breathing in land mammals, with expiratory flow exceeding 160 litres s−1 has been measured in cetaceans, and where exposure to extreme pressures results in alveolar collapse (atelectasis) and recruitment upon ascent. Cardiorespiratory coupling, where breathing results in changes in heart rate, has been proposed to improve gas exchange. Cardiorespiratory coupling has also been reported in marine mammals, and in the bottlenose dolphin, where it alters both heart rate and stroke volume. When accounting for this respiratory dependence on cardiac function, several studies have reported an absence of a diving‐related bradycardia except during dives that exceed the duration that is fuelled by aerobic metabolism. This review summarizes what is known about the respiratory physiology in marine mammals, with a special focus on cetaceans. The cardiorespiratory coupling is reviewed, and the selective gas exchange hypothesis is summarized, which provides a testable mechanism for how breath‐hold diving vertebrates may actively prevent uptake of N2 during routine dives, and how stress results in failure of this mechanism, which results in diving‐related gas emboli.

Harbour porpoises (Phocoena phocoena) are the only cetacean residents found year-round in Swedish waters and they are exposed to numerous natural and anthropogenic threats. Since the in situ monitoring of cetaceans can be difficult, invasive and often expensive, investigation of stranding patterns and examination of stranded animals can be used as a cost-effective source of data to study these elusive animals. The aim of this study was to investigate the spatiotemporal patterns of harbour porpoise stranding reports and the possible underlying causes in Swedish waters over a ten-year period (2014–2023). Additionally, the Swedish stranding network plays a key role in the collection of stranded carcasses for health and disease surveillance, and geographic coverage of the network also was analysed. When making spatial comparisons, the ten-year period was divided into two five-year blocks. Data on 854 stranded harbour porpoises were analysed from the coasts of the Skagerrak, Kattegat, and Baltic Seas. Both significant spatial and temporal patterns could be identified. Strandings peaked in July through September and hotspots occurred along most of the Swedish west coast, with the most frequent hotspots located around Öresund and especially the area around the Kullen peninsula. The spatial patterns of strandings found in this study are consistent with data on porpoise abundance, prey abundance, and gillnet fisheries’ efforts. The latter is known to be one of the primary causes of porpoise mortality. Furthermore, the coverage of the Swedish stranding network increased between the two periods, likely reflecting an increased awareness of the carcass-based surveillance program, and gaps requiring network expansion efforts were identified. These results also provide baseline data to enable the continued monitoring of stranding trends, as changes may indicate changes in population distribution, size or mortality rates.

Abstract Despite being subject to intensive research and public interest many populations of dolphins, porpoises, and other toothed whales (small cetaceans) continue to decline, and several species are on the verge of extinction. We examine small cetacean status, human activities driving extinction risk, and whether research efforts are addressing priority threats. We estimate that 22% of small cetaceans are threatened with extinction, with little signs of improvement in nearly thirty years. Fisheries and coastal habitat degradation are the main predictors of extinction risk. Contrary to popular belief, we show that the causal impact of small-scale fisheries on extinction risk is greater than from large-scale fisheries. Fisheries management strength had little influence on extinction risk, suggesting that the implementation of existing measures have been largely ineffective. Alarmingly, we find research efforts for priority threats to be vastly underrepresented and so a major shift in research focus is required. Small cetaceans are among the lower hanging fruits of marine conservation; continued failure to halt their decline bodes poorly for tackling marine biodiversity loss and avoiding an Anthropocene mass extinction.

Marine mammals play a critical role as sentinels for tracking the spread of zoonotic diseases, with viruses being the primary causative factor behind infectious disease induced mortality events. A systematic review was conducted to document marine mammal mortality events attributed to zoonotic viral infections in published literature across the globe. This rigorous search strategy yielded 2883 studies with 88 meeting inclusion criteria. The studies spanned from 1989 to 2023, with a peak in publications observed in 2020. Most of the included studies were retrospective, providing valuable insights into historical trends. The United States (U.S.) reported the highest number of mortality events followed by Spain, Italy, Brazil and the United Kingdom. Harbor seals were the most impacted species, particularly in regions like Anholt, Denmark and the New England Coast, U.S. Analysis revealed six main viruses responsible for mortality events, with Morbillivirus causing the highest proportion of deaths. Notably, the occurrence of these viral events varied geographically, with distinct patterns observed in different regions. Immunohistochemistry emerged as the most employed detection method. This study underscores the importance of global surveillance efforts in understanding and mitigating the impact of viral infections on marine mammal populations, thereby emphasizing the necessity of collaborative One Health approaches to address emerging threats at the human-animal-environment interface. Additionally, the potential transfer of zoonotic viruses to aquatic organisms used in food production, such as fish and shellfish, highlights the broader implications for food safety, food security and public health.

Growth of structural mass and energy reserves influences individual survival, reproductive success, population and species life history. Metrics of structural growth and energy storage of individuals are often used to assess population health and reproductive potential, which can inform conservation. However, the energetic costs of tissue deposition for structural growth and energy stores and their prioritization within bioenergetic budgets are poorly documented. This is particularly true across marine mammal species as resources are accumulated at sea, limiting the ability to measure energy allocation and prioritization. We reviewed the literature on marine mammal growth to summarize growth patterns, explore their tissue compositions, assess the energetic costs of depositing these tissues and explore the tradeoffs associated with growth. Generally, marine mammals exhibit logarithmic growth. This means that the energetic costs related to growth and tissue deposition are high for early postnatal animals, but small compared to the total energy budget as animals get older. Growth patterns can also change in response to resource availability, habitat and other energy demands, such that they can serve as an indicator of individual and population health. Composition of tissues remained consistent with respect to protein and water content across species; however, there was a high degree of variability in the lipid content of both muscle (0.1-74.3%) and blubber (0.4-97.9%) due to the use of lipids as energy storage. We found that relatively few well-studied species dominate the literature, leaving data gaps for entire taxa, such as beaked whales. The purpose of this review was to identify such gaps, to inform future research priorities and to improve our understanding of how marine mammals grow and the associated energetic costs.