Search Results (335)

Yangtze finless porpoise (Neophocaena asiaeorientalis) is the only extant cetacean species in the Yangtze River, a national first-class protected wild animal in China, and a key indicator reflecting the health status of the Yangtze River ecosystem. Environmental changes can induce adaptive trophic responses in animal communities; thus, clarifying the dynamic interactions between fish assemblages and dietary shifts in the Yangtze finless porpoise after the fishing moratorium is critically important. In this study, fishery resources in Poyang Lake were surveyed using triple-layer composite gill nets and cage traps, with samples collected and analyzed accordingly. A total of 81 fish species belonging to 8 orders and 16 families were recorded. Following the fishing ban, the abundance of small-bodied fish species (e.g., Hemiculter bleekeri, Carassius auratus) decreased, while the proportion of piscivorous species among the top ten dominant fish increased from 40% to 60%. DNA barcoding was used to analyze gastric contents of 10 dead porpoises found post-moratorium, and the results were compared with pre-ban data. Gastric content analysis identified 11 prey taxa, and comparative analysis demonstrated that prey selectivity was closely correlated with local prey availability. Concomitant with the structural reorganization of the fish community in Poyang Lake during the early stage of the fishing ban, the Yangtze finless porpoise exhibited adaptive dietary shifts toward benthic and small-bodied fish species, suggesting a potential linkage between these ecological responses. These findings provide direct implications for formulating targeted conservation strategies for this endangered cetacean and highlight the necessity of protecting small and benthic fish populations to ensure their long-term survival. Full article

This exploratory study evaluated plasma atrial natriuretic peptide (ANP) concentrations in four species of captive cetaceans and their associations with physiological and environmental factors, including husbandry conditions, diet, and management practices. Twenty-six individuals were voluntarily sampled, and blood samples were analyzed using a human-based chemiluminescent immunoassay. Transthoracic echocardiography was also attempted in several individuals but was technically challenging due to interference from the lung tissue and the sternum. The mean plasma ANP concentration in clinically healthy young animals was 44.12 ± 14.62 pg/mL, with no significant differences observed according to age, sex, species, or the presence of mild chronic disease. ANP was detectable across all species using human reagents. In addition, brain natriuretic peptide (BNP), a commonly used cardiac biomarker in humans and other animals, was evaluated for comparison; however, BNP concentrations remained below the detection threshold, possibly reflecting species-specific differences. Importantly, ANP concentrations were not evaluated in animals with clinically significant disease, and therefore the relevance of these findings to diseased populations remains unknown. These results demonstrate that plasma ANP can be measured using existing clinical assays and provide preliminary baseline data for multiple cetacean species. Overall, ANP may offer preliminary insights into physiological variation in managed cetaceans; however, its utility as a biomarker for cardiovascular or systemic health assessment remains to be determined. Full article

The adrenal glands are central regulators of endocrine function and stress physiology, yet detailed species-specific anatomical baselines remain limited in cetaceans. This study provides a comprehensive gross, histological, morphometric, and ultrastructural characterization of the adrenal glands in 55 short-beaked common dolphins (Delphinus delphis) examined postmortem in the Canary Islands. Adrenal glands were evaluated macroscopically and microscopically, and histological corticomedullary ratios were calculated from mid-transverse sections. Associations with body length, sexual maturity, and cause-of-death category were assessed statistically. Transmission electron microscopy was used to characterize cortical and medullary cellular ultrastructure. Adrenal weight showed a positive correlation with body length. The histological corticomedullary ratio showed no lateral asymmetry but differed significantly between sexually immature and mature individuals, indicating ontogenetic remodeling of adrenal architecture. In contrast, the corticomedullary ratio did not differ significantly between adult dolphins that died from acute events and those that died following more progressive pathological conditions. Ultrastructural analysis identified characteristic steroidogenic cortical cells and two distinct chromaffin cell populations in the medulla. These findings establish the first integrated anatomical baseline for the adrenal gland in Delphinus delphis, providing essential reference data for comparative anatomy, veterinary pathology, and the interpretation of endocrine-related findings in cetaceans. Full article

Candida albicans is currently considered one of the most significant fungal pathogens in cetaceans and pinnipeds and the spread of antifungal-resistant strains pose significant threats to animal health and One Health concerns. Although C. albicans is the most commonly detected species, non-albicans Candida (NAC) species, including C. tropicalis, C. parapsilosis and Nakaseomyces glabratus and the multidrug-resistant C. auris, have been recognized in captive dolphins. This review examines the clinical patterns observed in marine mammal taxa: cetaceans are most commonly vulnerable to respiratory and disseminated mycoses owing to their distinct anatomical characteristics, whereas mucocutaneous infections are the common manifestation in pinnipeds. Localized mucocutaneous infections may progress to fatal systemic disease, with mortality rates approaching 100% in severe cases, despite therapeutic treatment. The most important predisposing factors are immunosuppression, long-term antibiotic treatment, environmental stress factors, and the deterioration of water quality. Diagnostic methods are based on cytology, histopathology, culture, and molecular methods, and treatment is mostly composed of systemic azole antifungals although with high levels of therapeutic failure. Recent results showed that there are high levels of azole resistance in the isolates of marine mammals that had no history of exposure to antifungal agents, which points to the role of aquatic environments as sources of resistance genes. The lack of knowledge remains particularly evident in species-specific pharmacokinetics and the development of evidence-based treatment guidelines. These infections also have broader implications for ecosystem health surveillance and the protection of endangered marine mammal populations. The current review highlights the One Health approach with marine mammals being at the core of ocean health surveillance and identifies the potential for zoonotic transmission. Full article

The Black Sea harbour porpoise (Phocoena phocoena relicta Abel, 1905) is an endemic cetacean with poorly understood spatial ecology in Bulgarian waters. This study aimed to update knowledge on its distribution, abundance, and habitat use throughout the Bulgarian Exclusive Economic Zone (EEZ). We conducted systematic aerial line-transect surveys in all four seasons between October 2022 and October 2023, combined with distance sampling and MaxEnt habitat modelling. Porpoises were present year-round across the EEZ, with marked seasonal shifts in distribution and habitat preferences. Highest densities were observed in spring, while winter distributions were concentrated offshore. Habitat suitability was dynamic, with key high-use areas identified near Cape Emine and in southern offshore waters near the Turkish border. Overall, about 40% of the EEZ represented high-suitability habitat. These findings provide the first comprehensive, year-round baseline for P. p. relicta in Bulgarian waters, highlighting the species’ flexible habitat use and seasonality. The study was conducted under extraordinary conditions due to regional military activity, which may have influenced porpoise behaviour and spatial patterns. The provided results are critical for designing effective conservation and management measures in the face of both natural and anthropogenic pressures and threats. Full article

Parasitism affects nearly half of all animal species and strongly influences ecosystem dynamics. Despite their sentinel value, parasitic infections in cetaceans remain understudied. This study assessed the diversity, prevalence, and burden of gastrointestinal and pulmonary parasites in seventy-five stranded cetaceans from six species along the central and northern Portuguese coastline. Coprological methods included Mini-FLOTAC^®, Willis-flotation, natural sedimentation, modified Ziehl–Neelsen staining, direct immunofluorescence, and adapted spontaneous sedimentation. Overall, 61.3% of samples tested positive for at least one parasitic taxon, with 22.7% showing coinfections. Anisakidae and Ascaridida were the most prevalent (36%), followed by Pseudaliidae larvae (5.3%), unidentified trematode eggs (8.0%), Odhneriella spp. (5.3%), Nasitrema spp. (2.7%), Zalophotrema spp. (2.7%), and Synthesium spp. (1.3%). Nematode eggs exhibited the highest mean burden, with anisakids reaching 4862 eggs per gram of feces (EPG), whereas trematodes showed a markedly lower burden, exemplified by Zalophotrema spp. with 90 EPG. All samples assessed were negative for Cryptosporidium spp. and Giardia spp. Unidentified ovoid structures were present in 76% of samples. Macroscopic sedimentation revealed anisakid larvae, one cestode, over fifty Ogmogaster antarctica specimens, and six marine arthropods. These findings provide baseline data for cetacean parasitology and support future integrative research for conservation and ecosystem health. Full article

The study examined how season, age, sex, and pregnancy outcomes influenced serum total thyroxine (TT4) and triiodothyronine (TT3) levels in killer whales (Orcinus orca). Total T4 and TT3 concentrations were quantified in 1513 serum samples collected voluntarily over ~40 years from 14 males and 24 females (ages 1–54) under managed care. Data were analyzed using LMM to determine the effects of age, sex, season, and pregnancy status (normal vs. abnormal outcomes). Age, season, and pregnancy significantly influenced thyroid hormone concentrations, while sex did not. Juveniles exhibited higher concentrations consistent with increased thermoregulatory needs and growth demands. Seasonal analysis showed TT4 peaked in summer and declined in winter suggesting thermoregulatory adaptation. Pregnancies with abnormal outcomes (abortion, dystocia, stillbirth) were associated with atypical thyroid hormone profiles; specifically, dystocia was linked to consistently low TT3/TT4, while stillbirths correlated with elevated late-term TT3. Females experiencing abortion showed decreased TT3 and TT4 during the late gestation. These findings suggest that in pregnancies with adverse outcomes, metabolic imbalances or transient hyperthyroid-like states may negatively impact fetal health. Consequently, in killer whales, variation in thyroid hormone levels may reflect a complex interplay between environmental adaptation, reproductive status, and underlying evolutionary physiology. Full article

Studies of vocal communication often focus on the messages that calls and songs convey related to reproductive activities, foraging, predator avoidance, social bonding, individual recognition, and conflict resolution. We consider ways in which vocalizations may dynamically mediate social interactions at a more basic level, through collective coordination of movements and the enhancement of spatial perception. From this perspective, animals may vocalize to probe the locations, movements, and intentions of others, to manipulate position changes by listeners, or to increase their own capacity to localize sounds. An animal’s capacity to flexibly adjust vocalizations, both in real-time and over longer periods, can increase their ability to monitor and influence conspecifics independently of any information that may be encoded within those vocalizations. Beyond simply conveying messages, reproductive fitness, or emotional states, an animal’s ability to modulate vocalizations may dynamically affect its future action plans and social roles within a group. Identifying situational, life-history, and sociospatial factors that determine how animals vocally interact in real-time is key to understanding how an animal’s vocalizations relate to its own actions and the actions of others. Full article

Very-high-resolution (VHR) satellite imagery has expanded the scale at which researchers can monitor marine mammals in remote regions and improved monitoring efforts in data-deficient areas. Relatively little is known about beluga whale (Delphinapterus leucas) distribution in their wintering grounds, due partly to the unpredictability of sea ice formation and limited accessibility. VHR satellite imagery has been used successfully to estimate the abundance of summering beluga whales; however, the feasibility of tasking VHR satellite imagery in the winter and determining the detectability of beluga whales amongst sea ice have not been formally assessed. Our objective was to assess the feasibility of acquiring VHR satellite imagery in the winter and whether beluga whales could be reliably distinguished from sea ice in the imagery. Our study focused on beluga whale populations that are winter residents within James Bay and Cumberland Sound, occupying nearshore open water and ice leads in the winter. Two images were collected in Cumberland Sound covering known beluga whale wintering grounds in February and March 2022 encompassing 745 km², with ice covering >75% of the image, and three images were acquired within James Bay from January to March 2024 spanning over 5700 km², with ice covering >86% of the survey area. We observed 0 certain and 294 uncertain detections, suggesting that current satellite imagery resolutions are too low for confidently detecting beluga whales amongst densely packed ice. High-definition sharpening to 15 cm reduced the number of uncertain detections, but we were still unable to identify any certain whales. Continued advancements in imagery resolution are required to distinguish beluga whales from sea ice and improve year-round beluga whale monitoring. Full article

The common dolphin (Delphinus delphis) is one of the most abundant small cetaceans along the Galician coast and a definitive host for the nematode parasite Anisakis, which is transmitted to cetaceans through the food chain. This study aimed to analyse which factors, including dolphin diet, affect the parasitic load. Samples of stomach contents from stranded dolphins along the Galician coast (2004–2024) were examined. The number of parasites was counted, and the contribution of different prey species to the diet was analysed based on hard remains. Generalised Additive Models (GAMs) were used to assess the relationships between parasitic load (number of Anisakis in the stomach) and various putative explanatory variables (e.g., year, month, size, sex, latitude, body condition, cause of death and diet of the dolphins). Results showed an increase in parasitic load over the years and a seasonal pattern, with numbers peaking in the first months of the year. A significant positive relationship was found between dolphin length and Anisakis load. In addition, dolphins that died from bycatch had the lowest parasitic loads. The numbers of Atlantic mackerel (Scomber scombrus) and blue whiting (Micromesistius poutassou) in the stomach had a significant effect on parasite load: parasite abundance decreased as the numbers of these prey species in the stomach increased. This result confirms the influence of diet on Anisakis load, although it does not reveal which species contribute the most to the parasite load. The study offers insights into how diet and other ecological factors influence the parasitic load in D. delphis. Full article

Body condition, the relative amount of energy reserves in an individual, reflects nutritional status and overall health in marine mammals and can indicate the influence of stressors on individuals. Energy in marine mammals is primarily stored as lipids within adipocytes in blubber tissue, making blubber thickness a common proxy for body condition. However, blubber also serves structural roles, complicating its use as a body condition indicator. Our objective was to assess the relationship between adipocyte size, a common measure of cetacean adiposity, and blubber thickness in beluga whales (Delphinapterus leucas). We used mixed-effect generalized linear models to test how sex and blubber layer influenced this relationship. We found a significant positive relationship between adipocyte size and blubber thickness in male but not female beluga whales, suggesting sex-specific differences in fat storage or mobilization. Blubber thickness may be maintained in female beluga whales during periods with low energy reserves, for example during gestation and lactation, to preserve buoyancy, insulation, and hydrodynamism, which may be especially important when supporting swimming calves. Continuing to develop methods to assess beluga whale health will further our understanding of the impact of current and future stressors on beluga whale populations. Full article

The scientific understanding of cetacean pathology has advanced significantly in recent decades. However, data concerning the health status of members of the family Kogiidae remains scarce. This study presents a comprehensive pathological assessment and determination of causes of death in 45 stranded kogiids, comprising 35 Kogia breviceps and 10 K. sima, along the coasts of the Canary Islands between 1999 and 2018. Causes of death (CD) were classified as natural (30/45; 66.6%) or anthropogenic (11/45; 24.4%), while the cause remained undetermined in four cases (9%). Among natural causes, the most prevalent etiologies included trauma (13/30; 43.3%), infectious (7/30; 23.3%), parasitic (5/30; 16.6%), cardiomyopathy (3/30; 10%), malnutrition (1/30; 3.3%), and fetal distress (1/30; 3.3%). Anthropogenic causes were vessel collisions (7/11; 63.6%), interactions with fishing activities (2/11; 18.2%), and foreign body-associated pathology (2/11; 18.2%). Notably, intra- and interspecific traumatic interactions were frequently identified in this cohort, and variable degrees of gross and histologic cardiomyopathic changes were observed in 68.9% of individuals (31/45) without evident sex bias. Septicemia caused by Clostridium perfringens and C. tertium was confirmed in three cases. Additionally, cervical gill slit adenitis by Crassicauda sp. (15/45; 33%) and parasitic gastritis by Anisakis sp. (27/45; 60%) were frequent findings. These findings provide novel insights into the pathologic spectrum affecting kogiids and enhance the current understanding of their health status, with implications for diagnostic protocols, stranding response, and conservation strategies. Full article

This study investigates the effects of physical activity on serum cortisol levels and phagocytic capacity of the innate immune system in eight common bottlenose dolphins under human care. Analysis of 8 pairs (16 samples) revealed a significant increase in cortisol during periods of physical activity (mean increase of 1.27 µg/dL, 122% elevation), accompanied by decreased phagocytosis in granulocytes (92% reduction) and monocytes (52% reduction). Statistical analyses demonstrated consistent negative correlations between cortisol levels and phagocytic function, suggesting that physical activity influences hypothalamic–pituitary–adrenal axis activation and, consequently, innate immune system function. The male showed an attenuated cortisol response, but maintained monocyte sensitivity. These findings highlight the complex interplay between the neuroendocrine cortisol response and immune function in cetaceans, for the management and evaluation of animals under human care. A multi-method statistical framework incorporating Bayesian analysis, bootstrapping, and traditional approaches ensured robust inference despite limited sample size. Full article

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is the only extant freshwater cetacean species inhabiting the Yangtze River in China. Facing significant threats from habitat degradation and human activities, this critically endangered species requires urgent conservation efforts. A thorough understanding of its genetic diversity is fundamental for informing effective conservation strategies. To address the need for stable and reliable molecular markers, this study aimed to develop and validate a set of highly polymorphic single nucleotide polymorphism (SNP) markers. Candidate SNPs were initially identified based on chromosome-level genome and whole-genome resequencing data, yielding a total of 1070 candidate loci. Following the principle of even distribution across chromosomes, 50 SNPs were randomly selected for Sanger sequencing validation, from which 35 polymorphic SNPs were preliminarily confirmed. These 35 SNPs were subsequently genotyped using the Kompetitive allele-specific PCR (KASP) assay, which successfully validated 19 highly polymorphic markers. Genetic diversity analysis using these SNPs successfully captured moderate-to-high polymorphism in the Poyang Lake population, demonstrating the capability of these markers in detecting genetic variation. The SNP markers developed in this study show promising applicability for genetic diversity assessment in the Yangtze finless porpoise. Further validation across broader geographic and demographic samples will be essential to confirm their potential efficiency for detecting spatial heterogeneity and informing region-wide management strategies. Full article

Cetaceans are artiodactyls adapted to live in the marine environment, and this group includes whales, dolphins, and porpoises. Although mitochondrial nucleotide diversity has been reported separately for many cetacean groups, the proportion of deleterious mutations in these populations is unknown. Furthermore, a comparison of mitogenomic diversities across all cetaceans is also lacking. To investigate this, we conducted a comparative genomic analysis of 2244 mitochondrial genomes from 65 populations across 32 cetacean species. We observed a 78-fold variation in mitogenomic diversity among cetacean populations, suggesting a large difference in genetic diversity. We used the ratio of nonsynonymous-to-synonymous diversities (dN/dS) to measure the proportion of deleterious mutations in the mitochondrial exomes. The dN/dS ratio showed a 22-fold difference between the cetacean population. Based on genetic theories, the large differences observed in the two measures could be attributed to differences in the effective sizes of the cetacean populations. Typically, small populations have low heterozygosity and a high dN/dS ratio, and the reverse is true for large populations. This was further confirmed by the negative correlation observed between heterozygosity and dN/dS ratios of cetacean populations. While our analysis revealed similarities in mitogenomic diversity between the endangered and least-concern cetacean species, the dN/dS ratio of the former was found to be higher than that of the latter. The findings of this study are useful for identifying the relative magnitude of reductions in the population sizes of different cetacean species. This will help conservation management efforts prioritise the use of limited resources, time, and effort to protect the cetacean populations that need immediate attention. Full article