Karen A. Stockin

Aggressive and affiliative interactions shape resource allocation, social structure and reproduction in social species. In delphinids, rake marks (parallel scars from tooth raking) indicate social interactions. When examined alongside ontogeny, demographic traits and scar position, rake marks can inform social dynamics. We assessed rake marks on common dolphins (Delphinus delphis) in Aotearoa New Zealand (2006–2024; n = 102) during post-mortem examinations to explore drivers of social behaviour. Using a zero-inflated generalized linear mixed model, we assessed rake mark occurrence (probability of rake density > 0) and prevalence (rake density, rake marks dm−2) across the body (n = 101; dorsal/ventral, cranial/caudal, left/right) in relation to sex, age, total body length (TBL), sexual maturity, body condition (n = 101) and female reproductive status (n = 51), to infer confrontation, avoidance and lateralization. Females showed higher rake mark prevalence but lower occurrence than males, suggesting infrequent but prolonged interactions, possibly sexual coercion. Rake prevalence and occurrence increased with TBL, potentially related to increased social interactions and surface area in larger individuals. Age, sexual maturity, body condition, and female reproductive status were not strong predictors of rake mark occurrence or prevalence. Our findings highlight rake marks as potential indicators of social dynamics.

Metals and per- and polyfluoroalkyl substances (PFAS) represent a significant environmental concern, yet their association with epigenetic age acceleration (EAA) remain largely understudied in marine mammals. Here, associations between EAA in common dolphins ( Delphinus delphis ) and life history (sex and sexual maturity), trace metals, and PFAS were investigated. EAA was calculated as the residual in the regression of epigenetic age vs chronological age, hence providing a direct measure of the deviation of the epigenetic age of an organism (positive or negative) by comparison with expectation, given their actual chronological age. Sixteen trace elements were quantified in hepatic and renal tissues (n = 53). In addition, 28 PFAS were quantified in hepatic tissue (n = 58). Associations between EAA and explanatory variables were assessed using regression-based and multivariate modelling approaches (linear models and canonical analysis of principal coordinates). No effect of sex was observed, although sexual maturity did significantly increase EAA. Exposure to metals was significantly associated with variation in EAA, explaining 55.4% of the variation, with hepatic metals (Se, Zn, Cu, Al, Mn) driving this relationship. Although EAA was not significantly related to the total PFAS exposure overall, a subset of PFAS variables (PFBA, PFDA, PFHxS-B, PFNA) showed significant association with EAA after adjusting for sex and sexual maturity. Together, these subsets of metal and PFAS variables, in addition to the selenium-to-mercury (Se:Hg) molar ratio, explained 66.7% of the variation in EAA. Our results identify sexual maturity and specific contaminant mixtures as key potential drivers of EAA in common dolphins, highlighting the possible use of EAA as a biomarker of environmental and physiological stress in marine mammals.

Chronic contaminant exposure may impose hidden physiological costs long before obvious demographic or health effects become detectable in wildlife populations. Epigenetic clocks quantify biological ageing and may provide sensitive biomarkers of cumulative toxicological stress. Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants that bioaccumulate in marine food webs, yet their long-term physiological consequences for wildlife remain poorly understood. Here, we tested whether PFAS exposure is associated with accelerated biological ageing in common dolphins (Delphinus delphis). We analysed liver PFAS concentrations and skin DNA methylation profiles from 30 stranded or bycaught dolphins from New Zealand waters. Epigenetic age was estimated using a recently developed species-specific epigenetic clock, and age acceleration was calculated as the residual deviation between epigenetic and chronological age. Using an information-theoretic modelling framework, we assessed the effects of total PFAS burden, sex, and their interactions on epigenetic age acceleration. Total PFAS concentrations were positively associated with epigenetic age acceleration, indicating that dolphins with higher PFAS burdens were biologically older than expected for their chronological age. Each 1 ng/g increase in total PFAS was associated with an average increase of 0.031 years in biological age. Sex did not significantly influence age acceleration, suggesting that PFAS-associated ageing effects occur across both sexes. Although modest, this effect is consistent with PFAS acting as a chronic physiological stressor influencing molecular ageing processes. Our findings provide the first evidence linking PFAS exposure to accelerated biological ageing in a wild mammal, highlighting epigenetic ageing as an integrative biomarker of long-term contaminant effects in wildlife.

A juvenile bottlenose dolphin (Tursiops truncatus) was first observed among a group of approximately 12 dolphins on 10 December 2024, repeatedly breaching off Riverhead, Auckland, New Zealand. On subsequent observations, material consistent with fishing debris was seen entangled around the dorsal fin and tail flukes. While most conspecifics departed the area, a larger dolphin remained in close association with the entangled individual. The pair remained within the local area for at least 29 days prior to human intervention efforts to disentangle the animal. During the interim period, the entangled dolphin exhibited progressive deterioration in body condition and reduced activity compared with the free-swimming conspecific. The animal was found dead shortly thereafter. Within 48 hours of death, post-mortem MRI and necropsy were conducted on the cadaver, which was scored as decomposition carcass code 1 (within rigor mortis). These identified an emaciated, sexually immature female bottlenose dolphin. Gross examination revealed severe, multifocal to coalescing lacerations and abrasions affecting the dorsal fin and caudal peduncle, with associated soft-tissue loss and irregular wound margins. Histologically, sections from the dorsal fin laceration showed evidence of severe, subacute to chronic, ulcerative necrosuppurative dermatitis with secondary bacterial infection. Pulmonary tissue samples revealed an acute, severe bacterial pneumonia characterised by neutrophilic infiltration and short bacilli. The liver and spleen showed findings of hepatitis and splenitis, suggestive of bacterial septicaemia. Swab isolates from these pooled tissues identified moderate growth of Erysipelothrix rhusiopathiae and Pseudomonas spp. Collectively, in vivo evidence and post-mortem gross and histopathological findings were consistent with poor body condition resulting from a progressive wasting disease primarily associated with chronic entanglement, leading to chronic active deep infectious necrosuppurative dermatitis and subsequent fatal bacterial septicaemia. Bacterial septicaemia. This case highlights the importance of timely intervention in entanglement events to reduce the risk of secondary complications, including impaired foraging, progressive loss of body condition, and infection. Based on post-mortem findings, death was consistent with bacterial septicaemia in the context of a deep skin lesion to the dorsal fin caused by fishing gear and its subsequent pathological effects. From an animal welfare perspective, the prolonged duration of entanglement, progressive debilitation, and evidence of systemic wasting disease support a period of substantial and sustained welfare compromise prior to death. This incident would be classified as high-intensity, long-duration suffering.

We present the first radiographic ageing framework for common dolphins ( Delphinus delphis ), based on ossification and epiphyseal fusion patterns in the pectoral flipper, demonstrating higher reliability for chronological age estimation than currently available epigenetic approaches for this species. Using individuals of known dental age, we calibrated two modelling approaches to predict dental age from radiographic bone scores: 1) a univariate polynomial regression using a total bone score (sum of 16 scores across all assessed flipper bones), and 2) a multivariate canonical analysis of principal coordinates (CAP) incorporating 16 individual bone-score variables. Both approaches successfully predicted dental age from skeletal ossification patterns. For an age range of 0 to 24 years, polynomial regression demonstrated high predictive accuracy with median absolute errors (MAEs) of 1.25 years in females (Spearman’s ρ = 0.93, R² = 0.90) and 1.08 years in males (ρ = 0.95, R² = 0.86). The CAP model yielded MAEs of 1.35 years in females (ρ = 0.90, R² = 0.85) and 1.80 years in males (ρ = 0.94, R² = 0.84). Notably, both radiographic bone ageing models achieved equal or lower median absolute errors and higher coefficients of determination than a recently developed epigenetic clock for common dolphins derived from the same population (MAE = 1.80, Pearson’s correlation ( r ) = 0.91, R² = 0.82). When applying the bone ageing models to individuals of unknown dental age, both models produced age estimates consistent with expected life-history stages (foetus, neonate, juvenile, subadult, adult), although accuracy declined in dolphins above 20 years, likely as a consequence of subtle age-related variation in skeletal changes in this species. Radiographic ageing provides an accurate non-invasive tool for demographic assessment to support conservation management of common dolphins.

Radiographic evaluation of flipper ossification is a reliable technique for age estimation in bottlenose dolphins (Tursiops truncatus), although its applicability to other odontocetes remains untested. Interspecific differences in flipper morphology and bone development may limit transferability or require adjustments for robust application. This study applies the bottlenose dolphin framework to common dolphins (Delphinus delphis) to characterise developmental patterns, describe morphological differences and evaluate the interspecies application of this method. Radiographs from 137 common dolphins aged 0–31 years were examined, with bone maturation scored at 16 anatomical sites on the pectoral flipper. Several differences were identified, including bilateral asymmetry between left and right flippers and the need to adjust long and delta bone scoring systems due to interspecific variation in bone maturation. Despite these differences, reproducibility between observers was high, and ossification scores correlated strongly with age, underscoring the reliability of the method. This study provides the groundwork for a species-specific bone ageing model for common dolphins by addressing interspecific variation in skeletal maturation. One caveat concerns the subtle expression of degenerative changes in this species compared with bottlenose dolphins, which may limit age estimation precision in older individuals but is unlikely to affect accuracy across most of the lifespan. Thus, our findings provide the first evidence that, despite morphological differences, the method can be successfully applied to common dolphins.

Per- and polyfluoroalkyl substances (PFAS) are globally recognised as emerging contaminants of concern due to their persistence, toxicity, endocrine-disrupting and immunosuppressive effects. Because of their extensive industrial use, PFAS are now widespread across ecosystems and accumulate in marine environments. Despite their ubiquity, the extent and drivers of PFAS contamination remain poorly characterised, particularly in marine systems. Odontocetes (toothed whales) are effective bioindicators of marine pollution, integrating contamination across regions, time, and trophic levels. Here, we present the first global assessment of factors influencing PFAS contamination in marine ecosystems by analysing standardised PFAS concentrations of PFNA, PFDA, PFUnDA, PFDoDA and PFOS reported for 713 liver samples across 33 odontocete species spanning 13 countries from 2000 to 2023. Using generalised linear mixed models, we evaluated the effects of genus, location, sex, life stage, and sampling year on PFAS concentrations, combining published datasets with new samples from Australia. Genus and location were the strongest predictors, suggesting that interspecific ecological and physiological traits likely contribute to PFAS accumulation. Concentrations were highest in males and younger individuals, consistent with maternal offloading and possible age-related dilution. Spatio-temporal trends indicate that PFAS contamination is widespread and increasing globally, with highest concentrations reported in the Pacific. This study provides a critical baseline for understanding global PFAS exposure in marine mammals, which underscores the need for coordinated monitoring and further research to address regional data gaps and potential unrecognised biological effects. Highlights: High genus-specific and spatial differences in PFAS contamination across odontocetes globally. Increased contamination in younger/smaller individuals. Sex-specific trends, including higher PFAS levels in male odontocetes. Spatio-temporal trends suggesting increased PFAS concentration despite global regulatory efforts, with highest concentrations in the Pacific Ocean.

Determining exact age in wild odontocetes is essential for understanding population dynamics, survival, and reproduction, yet remains logistically challenging. Although epigenetic ageing is emerging as a valuable approach, only nine species‐specific clocks currently exist. Most have been calibrated using known‐age animals in human care or well‐studied wild populations. Only three previous studies have used dental ages from stranded or bycaught individuals. This is due to concerns that dental age inaccuracies, especially in older animals, may affect epigenetic clock performance. To explore this, we developed the first species‐specific epigenetic clock for common dolphins ( Delphinus delphis ), analysing DNA methylation at 37,492 cytosine‐phosphate‐guanine sites in skin samples from stranded and bycaught dolphins with estimated dental ages. Elastic net models with Leave‐One‐Out Cross‐Validation were applied to three subsets: the ‘ relaxed ’ subset (all individuals; n = 75, median absolute error (MAE) = 2.02, r = 0.81, R ² = 0.66), the ‘ strict ’ subset (excluding individuals with minimum dental age estimates only; n = 73, MAE = 2.29, r = 0.81, R ² = 0.66), and the ‘ restricted ’ subset (excluding outliers with prediction errors > 6 years; n = 63, MAE = 1.80, r = 0.91, R ² = 0.82) to compare performance. Our models consistently underestimated the age of dolphins > 16 years, even when minimum dental ages were applied, suggesting that absolute errors between dental and epigenetic estimates are unlikely to reflect the dental ageing error. Additionally, post‐mortem decomposition condition code (DCC 1 to 3) did not affect age prediction, signalling promise for future epigenetic clocks calibrated with strandings and bycaught individuals.

The anatomical description of the hourglass dolphin ( Cephalorhynchus cruciger ) and the spectacled porpoise ( Phocoena dioptrica ) remains largely unexplored, due to limited specimen availability and preservation challenges. This study employed digital imaging techniques, conventional histology, and computed tomography to provide visualization of anatomical structures for a detailed analysis. We present a comprehensive analysis of the gross macroscopical and microscopical morphology of two hourglass dolphins and four spectacled porpoises. Morphometric measurements and skeletal characteristics aligned with the literature, while internal anatomy (organs and systems) was similar to other odontocetes. Precise and consistent lung measurements were challenging; qualitative assessments indicated relatively large lungs with respect to body size. The spectacled porpoise dorsal fin was uniquely large with a well‐developed blood supply; this is hypothesized to act as a thermoregulatory window, though it may also play a role in sexual display in the case of males. Overall, this study provides new data on the anatomy of the hourglass dolphin and spectacled porpoise, contributing insights that may influence future research on these rare species. The findings highlight the importance of anatomical studies as a basis for explaining evolutionary relationships within cetaceans and their ecological roles in the Southern Ocean ecosystems.