Evaluating morphometric and metabolic markers of body condition in a small cetacean, the harbor porpoise (Phocoena phocoena)

Physiological welfare indicators in wild cetaceans: Epidermal cortisol and oxytocin concentrations in stranded striped dolphins

Anthropogenic pressures and climate change present growing challenges for cetaceans, as the combined effects of multiple stressors can jeopardize their welfare and survival. In this context, validating reliable individual welfare indicators is crucial for quantifying these impacts. This study aimed to validate a method for measuring cortisol and oxytocin from the epidermis of stranded striped dolphins (Stenella caeruleoalba) using enzyme immunoassays, while accounting for confounding factors such as epidermal layer and body location. The effects of different causes of death-'Peracute Underwater Entrapment' and 'Distress Associated'- along with biological factors, were examined in relation to epidermal hormone levels. Furthermore, the relationship between these hormone levels and markers suggesting an impaired welfare, was explored. Validation tests indicated that the method was effective in quantifying both epidermal cortisol and oxytocin concentrations. Specifically, epidermal cortisol levels showed strong correlations with both serum and blubber levels and were 6 times higher in emaciated individuals and 14 times higher in those with distress-associated deaths, supporting its use in assessing hypothalamic-pituitary-adrenal activity. Interestingly, results supported the validity of epidermal cortisol levels as markers of impaired welfare in dolphins, as they consistently increased across conditions assumed to negatively affect welfare but varying in terms of severity and duration. In contrast, epidermal oxytocin levels could not be validated as an indicator of the general oxytocin system nor as an indicator of welfare in this species. In conclusion, this study successfully validated epidermal cortisol as a reliable physiological indicator of welfare in striped dolphins, providing a promising tool for assessing individual and population-level welfare impacts. However, further research is needed to fully explore the potential role of oxytocin as a welfare biomarker in cetaceans.

Emaciated enigma: Decline in body conditions of common dolphins in the Celtic Seas ecoregion

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.

Relationship between nutritional condition and causes of death in beluga whales Delphinapterus leucas from the St. Lawrence estuary, Quebec, Canada

Carcasses of endangered beluga whales Delphinapterus leucas from the St. Lawrence Estuary, Canada, have been examined consistently since 1983 to determine causes of death. The objective of this study is to compare the nutritional condition of belugas that died of different causes. Previously published categories of death were refined to discriminate acute from chronic pathological processes. Bayesian linear models were used to predict cause of death from the scaled mass index (SMI). Causes of death were as follows: 'bacterial diseases', 'verminous pneumonia', 'toxoplasmosis', 'other parasitic diseases', 'other infectious diseases', 'trauma-entrapment', 'other noninfectious diseases', 'dystocia-postpartum complications', 'neonatal mortality', 'cancer', 'primary starvation' and 'undetermined'. The models predicted a lower nutritional condition for the 'neonatal mortality' in belugas <290 cm in length and for 'primary starvation' and 'verminous pneumonia' categories for belugas ≥290 cm. Belugas that died from 'dystocia-postpartum complications' or from 'undetermined causes' had a higher-than-average SMI. Animals in the 'trauma-entrapment' category did not exhibit the highest nutritional condition, which was unexpected since individuals that died from trauma or entrapment are often used as references for optimal nutritional condition in other cetacean populations. Females that died from dystocia and postpartum complications were in similar nutritional condition as females dead from other causes during, or shortly after, pregnancy. This suggests that these females are not obese, ruling out a possible cause of dystocia. Although studying dead animals biases results toward low nutritional condition, our findings support the link between chronic pathological processes and poorer nutritional condition in belugas.

Validating a Non-Invasive Method for Assessing Cortisol Concentrations in Scraped Epidermal Skin from Common Bottlenose Dolphins and Belugas

Society is showing a growing concern about the welfare of cetaceans in captivity as well as cetaceans in the wild threatened by anthropogenic disturbances. The study of the physiological stress response is increasingly being used to address cetacean conservation and welfare issues. Within it, a newly described technique of extracting cortisol from epidermal desquamation may serve as a non-invasive, more integrated measure of a cetacean's stress response and welfare. However, confounding factors are common when measuring glucocorticoid hormones. In this study, we validated a steroid hormone extraction protocol and the use of a commercial enzyme immunoassay (EIA) test to measure cortisol concentrations in common bottlenose dolphin (Tursiops truncatus) and beluga (Delphinapterus leucas) epidermal samples. Moreover, we examined the effect of sample mass and body location on cortisol concentrations. Validation tests (i.e., assay specificity, accuracy, precision, and sensitivity) suggested that the method was suitable for the quantification of cortisol concentrations. Cortisol was extracted from small samples (0.01 g), but the amount of cortisol detected and the variability between duplicate extractions increased as the sample mass decreased. In common bottlenose dolphins, epidermal skin cortisol concentrations did not vary significantly across body locations while there was a significant effect of the individual. Overall, we present a contribution towards advancing and standardizing epidermis hormone assessments in cetaceans.

Skin Cortisol and Acoustic Activity: Potential Tools to Evaluate Stress and Welfare in Captive Cetaceans

As people's focus broadens from animals on farms to zoos and aquaria, the field of welfare science and the public's concern for animal welfare continue to grow. In captive animals, stress and its causes are topics of interest in welfare issues, and the identification of an objective method that can be used to assess animals' stress as a physiological state is essential. Both behavioral and physiological parameters can be used as indicators in order to assess animal stress quantitatively. To validate this approach, acoustic activity and the sloughed scrape skin cortisol concentration were used to evaluate the animal welfare of captive beluga whales (Delphinapterus leucas). The acoustic activity (5 min at 10:00 am) of three captive D. leucas was routinely recorded by a transducer and analyzed using audio editing software. The calls were separated into three main categories: whistles, pulses, and combo calls. The sloughed scrape skin samples were collected non-invasively once a week from all three animals' fluke and/or flipper. Cortisol was extracted using a modified skin steroid extraction technique, and detected via commercially available enzyme immunoassays. The results showed that the cortisol concentration increased by varying levels when the whales encountered the same event. In addition, the number and distribution of the calls changed along with the events. This indicated that the changes in the cortisol concentration and acoustic behavior may have reflected the fluctuations in the environment and body condition. Therefore, the scrape cortisol measurement and acoustic recordings could be used to monitor stress levels in captive beluga whales. We recommend that aquaria consider incorporating skin scrape cortisol and acoustic activity monitoring into their standards for animal welfare.

Variation in blubber thickness and histology metrics across the body topography of a false killer whale (Pseudorca crassidens)

Blubber is a multifunctional tissue essential to the survival of cetaceans. Histological assessment of blubber may be useful in determining odontocete nutritional state but a greater understanding of specific variation across the body is needed. We report on morphological variation of the blubber according to girth axes and sampling planes in a sub-adult male, bycaught false killer whale (Pseudorca crassidens) using metrics of blubber thickness (BT), adipocyte area (AA), and adipocyte index (AI). 48 full depth blubber samples were taken along 6 girth axes at 5 equidistant sampling points on both sides of the body. At these sampling locations BT was recorded, and AA and AI were determined for three distinct blubber layers. Linear mixed effect models were used to assess variation of the blubber across layers and body topography. BT was somewhat non-uniform across the body but was generally thicker in the dorsal region and thinner laterally. AA was greater cranially and AI was greater caudally. The middle and inner layer blubber showed significant differences dorsoventrally with larger AA and smaller AI in the ventral region of the body. Variation of the blubber metrics across the body are indicative of variable functions of the blubber within an individual. Due to the variability observed, we expect that AI of the dynamic inner layer blubber is most informative of overall body condition and that biopsy samples of the outer and middle blubber may still be useful in determining the nutritional status of live false killer whales.

Evaluation of a marine mammal status and trends contaminants indicator for European waters

Marine mammals are vulnerable to the bioaccumulation, biomagnification and lactational transfer of specific types of pollutants, such as industrial polychlorinated biphenyls (PCBs), due to their long-life spans, feeding at a high trophic level and unique fat stores that can serve as depots for these lipophilic contaminants. Currently, European countries are developing indicators for monitoring pollutants in the marine environment and assessing the state of biodiversity, requirements under both Regional Seas Conventions and European legislation. As sentinel species for marine ecosystem and human health, marine mammals can be employed to assess bioaccumulated contaminants otherwise below current analytical detection limits in water and lower trophic level marine biota. To aid the development of Regional Seas marine mammal contaminants indicators, as well as Member States obligations under descriptor 8 of the EU Marine Strategy Framework Directive, the current study aims to further develop appropriate methodological standards using data collected by the established UK marine mammal pollutant monitoring programme (1990 to 2017) to assess the trends and status of PCBs in harbour porpoises. Within this case study, temporal trends of PCB blubber concentration in juvenile harbour porpoises were analysed using multiple linear regression models and toxicity thresholds for the onset of physiological (reproductive and immunological) endpoints were applied to all sex-maturity groups. Mean PCB blubber concentrations were observed to decline in all harbour porpoise Assessment Units and OSPAR Assessment Areas in UK waters. However, a high proportion of animals were exposed to concentrations deemed to be a toxicological threat, though the relative proportion declined in most Assessment Units/Areas over the last 10 years of the assessment. Recommendations were made for improving the quality of the assessment going forward, including detailing monitoring requirements for the successful implementation of such an indicator.

Comprehensive molecular and morphological resolution of blubber stratification in a deep-diving, fasting-adapted seal

Blubber is a modified subcutaneous adipose tissue in marine mammals that provides energy storage, thermoregulation, hydrodynamic locomotion, and buoyancy. Blubber displays vertical stratification by lipid content, fatty acid composition, and vascularization, leading to the assumption that deeper blubber layers are metabolically active, while superficial layers are mainly structural and thermoregulatory. However, few studies have examined functional stratification of marine mammal blubber directly, especially in pinnipeds. We characterized morphological and transcriptional differences across blubber layers in the northern elephant seal, a deep-diving and fasting-adapted phocid. We collected blubber from seals early in their fasting period and divided blubber cores into three similarly sized portions. We hypothesized that the innermost blubber portion would have higher 1) heterogeneity in adipocyte size, 2) microvascular density, and 3) expression of genes associated with metabolism and hormone signaling than outer blubber. We found that adipocyte area and variance increased from outermost (skin-adjacent) to innermost (muscle-adjacent) blubber layers, suggesting that inner blubber has a higher capacity for lipid storage and turnover than outer blubber. Inner blubber had a higher proportion of CD144+ endothelial cells, suggesting higher microvascular density. In contrast, outer blubber had a higher proportion of CD4+ immune cells than inner blubber, suggesting higher capacity for response to tissue injury. Transcriptome analysis identified 61 genes that were differentially expressed between inner and outer blubber layers, many of which have not been studied previously in marine mammals. Based on known functions of these genes in other mammals, we suggest that inner blubber has potentially higher 1) adipogenic capacity, 2) cellular diversity, and 3) metabolic and neuroendocrine signaling activity, while outer blubber may have higher 1) extracellular matrix synthesis activity and 2) responsiveness to pathogens and cell stressors. We further characterized expression of nine genes of interest identified by transcriptomics and two adipokines with higher precision across blubber layers using targeted assays. Our study provides functional insights into stratification of blubber in marine mammals and a molecular key, including CD144, CD4, HMGCS2, GABRG2, HCAR2, and COL1A2, for distinguishing blubber layers for physiological and functional studies in seals.

Morphometrics of Xenopus laevis Kept as Laboratory Animals

Morphometric data that provide information on body conditions can be used to monitor the health and well-being of animals. In laboratory animals, they can help to evaluate the stress due to experiments or treatments, following the 3R principles. The aim of the present study was to obtain morphometric data of male and female African clawed frogs, Xenopus laevis, as the bases for body condition evaluations. Adult frogs (n = 198) were weighed and standardized photographs were taken. The photographs were used to determine several measurements (length, cranial width, caudal width, thigh width). In addition, a triangle was drawn to outline each frog’s simplified body form, and the triangle surface was calculated. In conclusion, the triangle surface drawn on the dorsal plane of each frog correlated with the body weight of the females. There were significant differences between the body weights and sizes of male and female frogs, with males being smaller (p < 0.001). Based on the morphometric data, females could be assigned to five groups in which an assessment of the animal’s well-being is feasible.

Key questions in marine mammal bioenergetics

Bioenergetic approaches are increasingly used to understand how marine mammal populations could be affected by a changing and disturbed aquatic environment. There remain considerable gaps in our knowledge of marine mammal bioenergetics, which hinder the application of bioenergetic studies to inform policy decisions. We conducted a priority-setting exercise to identify high-priority unanswered questions in marine mammal bioenergetics, with an emphasis on questions relevant to conservation and management. Electronic communication and a virtual workshop were used to solicit and collate potential research questions from the marine mammal bioenergetic community. From a final list of 39 questions, 11 were identified as 'key' questions because they received votes from at least 50% of survey participants. Key questions included those related to energy intake (prey landscapes, exposure to human activities) and expenditure (field metabolic rate, exposure to human activities, lactation, time-activity budgets), energy allocation priorities, metrics of body condition and relationships with survival and reproductive success and extrapolation of data from one species to another. Existing tools to address key questions include labelled water, animal-borne sensors, mark-resight data from long-term research programs, environmental DNA and unmanned vehicles. Further validation of existing approaches and development of new methodologies are needed to comprehensively address some key questions, particularly for cetaceans. The identification of these key questions can provide a guiding framework to set research priorities, which ultimately may yield more accurate information to inform policies and better conserve marine mammal populations.

Blubber and serum cortisol concentrations as indicators of the stress response and overall health status in striped dolphins

The impacts of environmental changes and anthropogenic threats in marine mammals are a growing concern for their conservation. In recent years, efforts have been directed to understand how marine mammals cope with stressors and to assess and validate stress biomarkers, mainly levels of glucocorticoid hormones (e.g. cortisol) in certain body tissues. The aims of this study were to assess the impact of different causes of stranding (chronically affected and bycaught striped dolphins) on cortisol concentrations in serum and in blubber; and to evaluate the association between cortisol levels in these tissues. Blubber and blood samples were collected from striped dolphins (n = 42) stranded on the Mediterranean coast between 2012 and 2018. Cortisol concentrations were measured by using enzyme immunoassay. A high correlation was found between circulating and blubber cortisol concentrations (R² = 0.85, p < 0.01). Necropsies and pathological studies concluded that a third of the dolphins were bycaught in fishing nets and released by fishermen (Bycaught animals group), while the other two thirds were euthanized, or died, due to a disease or chronic condition (e.g. calves separated from the mother or animals infected with dolphin morbillivirus or Brucella ceti) that impeded survival (Chronically affected animals group). Cortisol concentrations (mean ± SD) were six times higher in chronically affected animals (35.3 ± 23 ng cortisol/g blubber and 6.63 ± 3.22 μg cortisol/dl serum) compared to those bycaught in fishing nets (6.2 ± 4.3 ng cortisol/g blubber and 1.15 ± 1.51 μg cortisol/dl serum). Results suggests that serum and blubber cortisol concentrations can contribute in inferring the overall health and welfare of free-ranging cetaceans. However, further research is required to understand better the kinetics of blubber cortisol incorporation and removal, the factors involved in these processes, and the local conversion of cortisol in the blubber.

Climate change and cetacean health: impacts and future directions

Climate change directly impacts the foraging opportunities of cetaceans (e.g. lower prey availability), leads to habitat loss, and forces cetaceans to move to other feeding grounds. The rise in ocean temperature, low prey availability and loss of habitat can have severe consequences for cetacean survival, particularly those species that are already threatened or those with a limited habitat range. In addition, it is predicted that the concentration of contaminants in aquatic environments will increase owing to Arctic meltwater and increased rainfall events leading to higher rates of land-based runoff in downstream coastal areas. These persistent and mobile contaminants can bioaccumulate in the ecosystem, and lead to ecotoxicity with potentially severe consequences on the reproductive organs, immune system and metabolism of marine mammals. There is a need to measure and assess the cumulative impact of multiple stressors, given that climate change, habitat alteration, low prey availability and contaminants do not act in isolation. Human-caused perturbations to cetacean foraging abilities are becoming a pervasive and prevalent threat to many cetacean species on top of climate change-associated stressors. We need to move to a greater understanding of how multiple stressors impact the metabolism of cetaceans and ultimately their population trajectory. This article is part of the theme issue 'Nurturing resilient marine ecosystems'.

Cyp17a effected by endocrine disruptors and its function in gonadal development of Hyriopsis cumingii

Estrogens and androgens that coexist in the aquatic environment could potentially affect shellfish, however, endocrine disrupting effects of them in shellfish are significant. As an important aquaculture shellfish in China, Hyriopsis cumingii has remarkable economic benefits. In this study, the effects of endocrine disrupting chemicals on the steroid synthase Hc-Cyp17a in the male and female gonads of the H. cumingii were assessed by exposing juvenile mussels to cultured waters containing 17β-Estradiol (E2) and 17α-Methyltestosterone (MT) for 28 days. At the same time, the E2 content in the four stages of gonadal development, the expression changes of Hc-Cyp17a in gonadal development and its localization in the mature gonad were measured to explore the relationship between genes and hormones. The results showed that both E2 and MT at 50 ng/L and 200 ng/L could affect the transcription level of Hc-Cyp17a, which was inhibited initially and promoted in post-development. E2 content was positively correlated with gonadal development stage, which was in mussel. By tracing the expression of Hc-Cyp17a, difference was found during different developmental periods. The expression level in ovary was higher than that in testis during gonadal development of 1/ 2/ 3-year-old mussels and showed an increasing trend with age. Furthermore, the expression levels in 6 tissues of mature individuals were measured and it showed that there was a significant difference between male and female in the gonads (p < 0.01). In situ hybridization, it suggested that Hc-Cyp17a was significantly signaled in the follicular wall and oocyte of female and in the follicular membrane of testis, respectively. These results could play a vital role in assessing and understanding the effects of aquatic environment on the endocrine system of H. cumingii.

Untargeted plasma metabolomic analysis of wild bottlenose dolphins (Tursiops truncatus) indicate protein degradation when in poorer health

Cumulative exposure to sub-lethal anthropogenic stressors can affect the health and reproduction of coastal cetaceans and hence their population viability. To date, we do not have a clear understanding of the notion of health for cetaceans in an ecological context; that is, how health status affects the ability of individuals to survive and reproduce. Here, we make use of a unique health-monitoring programme of estuarine bottlenose dolphins in South Carolina and Florida to determine de novo changes in biological pathways, using untargeted plasma metabolomics, depending on the health status of individuals obtained from veterinary screening. We found that individuals that were in a poor health state had lower circulating amino acids pointing towards increased involvement of gluconeogenesis (i.e., new formation of glucose). More mechanistic work is needed to disentangle the interconnection between health and energy metabolism in cetaceans to mediate potential metabolic constraints they may face during periods of stress.

Steroid hormone profiles and body conditions of migrating male humpback whales (Megaptera novaeangliae)

Simultaneous analysis of multiple steroid hormones from remotely obtained blubber biopsies has the potential to concurrently provide information regarding stress and reproductive status from free-swimming cetaceans, while also investigating correlations between hormone concentrations and other health biomarkers. In this study we measured blubber concentration profiles of eight reproductive and adrenal steroid hormones (17α-hydroxy-progesterone, testosterone, androstenedione, progesterone, cortisol, 11-deoxy-corticosterone, oestrone, and oestradiol) together with body condition, as determined by the inverse Adipocyte Index, of 101 male humpback whales. Whales were sampled randomly at two time points, while migrating to and from their northeast Australian breeding grounds, allowing for intra- and inter-seasonal profile analysis. Testosterone, progesterone and cortisol together with androstenedione 17α-hydroxyprogesterone, and oestrone concentrations (the latter quantified for the first time in live biopsied male humpback whales) decreased between the northward and southward migrations. Decreasing testosterone levels during the height of humpback whale conceptions suggests asynchronicity between blubber testosterone levels and the expected peak of male fertility. Statistically significant relationships between levels of certain steroid analytes were observed and appeared to change between the early and late breeding seasons. During the northward migration, testosterone, progesterone, androstenedione, oestrone and 17α-hydroxyprogesterone levels were positively correlated. Cortisol concentrations correlated positively with those of testosterone during the northward migration, but negatively during the southward migration. Androstenedione and testosterone were positively correlated with adiposity during the late breeding season. These hormone-hormone and hormone-adiposity correlations may be reflective of the activation of certain steroid hormone synthesis pathways, or alternatively, of concomitant physiological stimuli. As steroid hormones work in concert, information on multiple steroid hormones is needed to interpret endocrinological status and understand the relationships between these compounds and ancillary health markers. This study provides steroid hormone profiles of wild male humpback whales, as well as the first insight into seasonal male endocrinology as a function of adiposity.

Blubber endocrine profiles provide insights into reproductive biology in blue whales from the eastern North Pacific Ocean

The goal of the present study was to complement existing data of testosterone and progesterone in blue whale (Balaenoptera musculus) blubber from the eastern North Pacific Ocean to evaluate effects of seasonality and location on these hormones and to better assess reproductive status of individuals. Physiological parameters regarding reproduction are fundamental for describing population dynamics, and hormones can be a valid tool to estimate those for wildlife populations. In this study, blubber tissue was validated for testosterone and progesterone assays. Hormone concentrations were measured in 69 (35 males and 34 females) blubber samples from live (n = 66) and stranded (n = 3) animals collected between 2002 and 2016 from a known winter reproductive ground in the Gulf of California (GoC) and summer feeding areas along the United States West Coast (USWC), specifically off the states of California and Oregon. Results were combined with sighting histories as a tool to determine reproductive status of individual whales. Testosterone concentrations in adult male blue whales were significantly higher (p < 0.05) in blubber biopsies sampled off the USWC between the months of June and November compared to those sampled in the GoC between February and April. Elevated testosterone concentrations likely indicate physiological preparation for reproductive activity while the animals were present off the USWC. Progesterone concentrations were significantly elevated in pregnant females, confirming progesterone as an indicator of pregnancy in blue whales. Probabilities of being pregnant were estimated for adult females with unknown sighting histories based on progesterone concentrations. Testosterone in females was detected and measured only in pregnant whales suggesting its biosynthesis or metabolism is altered during gestation. These results provide updated and new information on the reproductive cycle of blue whales in the eastern North Pacific, posing new milestones to better estimate the timing of the mating season for this endangered population.

Predicting consequences of POP-induced disruption of blubber glucose uptake, mass gain rate and thyroid hormone levels for weaning mass in grey seal pups

Persistent organic pollutants (POPs) are endocrine disruptors that alter adipose tissue development, regulation and function. Top marine predators are particularly vulnerable because they possess large fat stores that accumulate POPs. However, links between endocrine or adipose tissue function disruption and whole animal energetics have rarely been investigated. We predicted the impact of alterations to blubber metabolic characteristics and circulating thyroid hormone (TH) levels associated with polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs) on suckling mass gain and weaning mass in wild grey seal pups. Glucose uptake by inner blubber was a strong predictor of whole animal mass gain rate, which in turn, resulted in heavier weaning mass. Weaning mass was predicted to increase by 3.7 ± 1.59 (sem) %, through increased mass gain rate, in the absence of the previously reported suppressive effect of dioxin-like PCB (DL-PCBs) on blubber glucose uptake. PBDEs were, conversely, associated with faster mass gain. Alleviation of this effect was predicted to reduce weaning mass by 6.02 ± 1.86% (sem). To better predict POPs effects on energy balance, it is crucial to determine if and how PBDEs promote mass gain in grey seal pups. Weaning mass was negatively related to total T3 (TT3) levels. A 20% (range = 9.3-31.7%) reduction in TT3 by DL-PCBs partially overcame the effect of DL-PCB -mediated reduction in blubber glucose uptake. Overall, DL-PCBs were thus predicted to reduce weaning mass by 1.86 ± 1.60%. Organohalogen impacts on whole-animal energy balance in grey seal pups appear to partially offset each other through opposing effects on different mechanisms. POP effects were generally minor, but the largest POP-induced reductions in weaning mass were predicted to occur in pups that were already small. Since weaning mass is positively related to first-year survival, POPs may disproportionately affect smaller individuals, and could continue to have population-level impacts even when levels are relatively low compared to historical values. Our findings show how in vitro experiments combined with measurements in vivo can help elucidate mechanisms that underpin energy balance regulation and help to quantify the magnitude of disruptive effects by contaminants and other stressors in wildlife.

Topographic Variations in Mobilization of Blubber in Relation to Changes in Body Mass in Short-Finned Pilot Whales (Globicephala macrorhynchus)

AbstractFat-level measurements used to indicate individual body condition and fitness are useful only when taken at a region along the body where fat responds to variations in caloric intake. Investigations to identify appropriate species-specific regions are limited, especially for cetaceans that have a specialized fat (blubber) that serves as an energy reserve and provides insulation. Over 18 mo, body mass of six pilot whales varied (range: 50-172 kg), and although caloric intake increased when water temperatures were lower, generally the best-fitting state-space model for length-adjusted mass was based on a single factor, caloric intake. After correcting for body length (range: 330-447 cm), the slope for blubber thickness and "blubber ring" thickness (average blubber thickness along a girth) in relation to body mass was positive and had a P value of <0.10 at six of 16 blubber measurement sites and one of five girth measurement sites, respectively. The slope for body girth (a reflection of changes in underlying blubber thickness) in relation to body mass was positive and had a lower P value ([Formula: see text]) at three of five girth measurement sites. Results indicate that blubber from the anterior insertion of the pectoral fins to the posterior insertion of the dorsal fin is the most metabolically active region. This region includes the midflank site, a location where blubber thickness measurements have historically been taken to monitor cetacean body condition. Conversely, blubber in the peduncle region was comparatively inert. These findings must be considered when measuring blubber thickness and body width (i.e., photogrammetry) to monitor the condition of free-ranging cetaceans.

Polychlorinated biphenyls are associated with reduced testes weights in harbour porpoises (Phocoena phocoena)

Polychlorinated biphenyls (PCBs) are highly toxic and persistent aquatic pollutants that are known to bioaccumulate in a variety of marine mammals. They have been associated with reduced recruitment rates and population declines in multiple species. Evidence to date documents effects of PCB exposures on female reproduction, but few studies have investigated whether PCB exposure impacts male fertility. Using blubber tissue samples of 99 adult and 168 juvenile UK-stranded harbour porpoises (Phocoena phocoena) collected between 1991 and 2017, here we show that PCBs exposures are associated with reduced testes weights in adults with good body condition. In animals with poor body condition, however, the impact of PCBs on testes weights was reduced, conceivably due to testes weights being limited by nutritional stress. This is the first study to investigate the relationship between PCB contaminant burden and testes weights in cetaceans and represents a substantial advance in our understanding of the relationship between PCB exposures and male reproductive biology in cetaceans. As testes weight is a strong indicator of male fertility in seasonally breeding mammals, we suggest the inclusion of such effects in population level impact assessments involving PCB exposures. Given the re-emergent PCB threat our findings are globally significant, with potentially serious implications for long-lived mammals. We show that more effective PCB controls could have a substantial impact on the reproductive health of coastal cetacean species and that management actions may need to be escalated to ensure adequate protection of the most vulnerable cetacean populations.

Rapid weight loss in free ranging pygmy killer whales (Feresa attenuata) and the implications for anthropogenic disturbance of odontocetes

Understanding the impacts of foraging disruptions to odontocete body condition is fundamental to quantifying biological effects of human disturbance and environmental changes on cetacean populations. Here, reductions in body volume of free-ranging pygmy killer whales (Feresa attenuata) were calculated using repeated measurements of the same individuals obtained through Unoccupied Aerial System (UAS)-photogrammetry during a prolonged disruption in foraging activity arising from a 21-day stranding event. Stranded individuals were used to verify UAS-derived volume and length estimates through 3D-imaging, water displacement, and post-mortem measurements. We show that (a) UAS estimates of length were within 1.5% of actual body length and UAS volume estimates were within 10-13% of actual volume, (b) foraging disruption resulted in a daily decrease of 2% of total body mass/day, and (c) pygmy killer whales can lose up to 27% of their total body weight within 17 days. These findings highlight the use of UAS as a promising new method to remotely monitor changes in body condition and animal health, which can be used to determine the potential effects of anthropogenic disturbance and environmental change on free-ranging odontocetes.

Declining reproductive success in the Gulf of St. Lawrence's humpback whales (Megaptera novaeangliae) reflects ecosystem shifts on their feeding grounds

Climate change has resulted in physical and biological changes in the world's oceans. How the effects of these changes are buffered by top predator populations, and therefore how much plasticity lies at the highest trophic levels, are largely unknown. Here endocrine profiling, longitudinal observations of known individuals over 15 years between 2004 and 2018, and environmental data are combined to examine how the reproductive success of a top marine predator is being affected by ecosystem change. The Gulf of St. Lawrence, Canada, is a major summer feeding ground for humpback whales (Megaptera novaeangliae) in the North Atlantic. Blubber biopsy samples (n = 185) of female humpback whales were used to investigate variation in pregnancy rates through the quantification of progesterone. Annual pregnancy rates showed considerable variability, with no overall change detected over the study. However, a total of 457 photo-identified adult female sightings records with/without calves were collated, and showed that annual calving rates declined significantly. The probability of observing cow-calf pairs was related to favourable environmental conditions in the previous year; measured by herring spawning stock biomass, Calanus spp. abundance, overall copepod abundance and phytoplankton bloom magnitude. Approximately 39% of identified pregnancies were unsuccessful over the 15 years, and the average annual pregnancy rate was higher than the average annual calving rate at ~37% and ~23% respectively. Together, these data suggest that the declines in reproductive success could be, at least in part, the result of females being unable to accumulate the energy reserves necessary to maintain pregnancy and/or meet the energetic demands of lactation in years of poorer prey availability rather than solely an inability to become pregnant. The decline in calving rates over a period of major environmental variability may suggest that this population has limited resilience to such ecosystem change.

Leger J, Noren DP, Burek Huntington K, Rotstein DS, Gulland FMD, Ford JKB, Hanson MB, Lambourn DM, Huggins J, Delaney MA, Spaven L, Rowles T, Barre L, Cottrell P, Ellis G, Goldstein T, Terio K, Duffield D, Rice J, Gaydos JK. Pathology findings and correlation with body condition index in stranded killer whales (Orcinus orca) in the northeastern Pacific and Hawaii from 2004 to 2013

Understanding health and mortality in killer whales (Orcinus orca) is crucial for management and conservation actions. We reviewed pathology reports from 53 animals that stranded in the eastern Pacific Ocean and Hawaii between 2004 and 2013 and used data from 35 animals that stranded from 2001 to 2017 to assess association with morphometrics, blubber thickness, body condition and cause of death. Of the 53 cases, cause of death was determined for 22 (42%) and nine additional animals demonstrated findings of significant importance for population health. Causes of calf mortalities included infectious disease, nutritional, and congenital malformations. Mortalities in sub-adults were due to trauma, malnutrition, and infectious disease and in adults due to bacterial infections, emaciation and blunt force trauma. Death related to human interaction was found in every age class. Important incidental findings included concurrent sarcocystosis and toxoplasmosis, uterine leiomyoma, vertebral periosteal proliferations, cookiecutter shark (Isistius sp.) bite wounds, excessive tooth wear and an ingested fish hook. Blubber thickness increased significantly with body length (all p < 0.001). In contrast, there was no relationship between body length and an index of body condition (BCI). BCI was higher in animals that died from trauma. This study establishes a baseline for understanding health, nutritional status and causes of mortality in stranded killer whales. Given the evidence of direct human interactions on all age classes, in order to be most successful recovery efforts should address the threat of human interactions, especially for small endangered groups of killer whales that occur in close proximity to large human populations, interact with recreational and commercial fishers and transit established shipping lanes.

Evaluating cetacean body condition; a review of traditional approaches and new developments

The ability to accurately gauge the body condition of free-swimming cetaceans is invaluable in population and conservation biology, due to the direct implications that this measure has on individual fitness, survival, and reproductive success. Furthermore, monitoring temporal change in body condition offers insight into foraging success over time, and therefore the health of the supporting ecosystem, as well as a species' resilience. These parameters are particularly relevant in the context of widespread and accelerated, climate-induced habitat change. There are, however, significant logistical challenges involved with research and monitoring of large cetaceans, which often preclude direct measure of body condition of live individuals. Consequently, a wide variety of indirect approaches, or proxies, for estimating energetic stores have been proposed over past decades. To date, no single, standardized, approach has been shown to serve as a robust estimation of body condition across species, age categories, and in both live and dead individuals. Nonetheless, it is clear that streamlining and advancing body condition measures would carry significant benefits for diverse areas of cetacean research and management. Here, we review traditional approaches and new applications for the evaluation of cetacean energetic reserves. Specific attention is given to the criteria of measure performance (sensitivity and accuracy), level of invasiveness, cost and effort required for implementation, as well as versatility e.g. applicability across different species, age groups, as well as living versus deceased animals. Measures have been benchmarked against these criteria in an effort to identify key candidates for further development, and key research priorities in the field.

Levels of Polychlorinated Biphenyls Are Still Associated with Toxic Effects in Harbor Porpoises (Phocoena phocoena) Despite Having Fallen below Proposed Toxicity Thresholds

Polychlorinated biphenyls (PCBs) are toxic, persistent, and lipophilic chemical compounds that accumulate to high levels in harbor porpoises (Phocoena phocoena) and other cetaceans. It is important to monitor PCBs in wildlife, particularly in highly exposed populations to understand if concentrations are declining and how levels relate to toxicological thresholds and indices of health like infectious disease mortality. Here we show, using generalized additive models and tissue samples of 814 U.K.-stranded harbor porpoises collected between 1990 and 2017, that mean blubber PCB concentrations have fallen below the proposed thresholds for toxic effects. However, we found they are still associated with increased rates of infectious disease mortality such that an increase in PCB blubber concentrations of 1 mg kg^-1 lipid corresponds with a 5% increase in risk of infectious disease mortality. Moreover, rates of decline and levels varied geographically, and the overall rate of decline is slow in comparison to other pollutants. We believe this is evidence of long-term preservation in the population and continued environmental contamination from diffuse sources. Our findings have serious implications for the management of PCB contamination in the U.K. and reinforce the need to prevent PCBs entering the marine environment to ensure that levels continue to decline.

Bottlenose dolphin calves have multi-year elevations of plasma oxytocin compared to all other age classes

Providing for infants nutritionally via lactation is one of the hallmarks of mammalian reproduction, and infants without motivated mothers providing for them are unlikely to survive. Mothers must maintain regular contact with infants both spatially and temporally while utilising their environment to forage, avoid threats and find shelter. However, mothers can only do this and maximise their reproductive success with some degree of co-operation from infants, despite their developing physical and cognitive capabilities. The neuropeptide hormone oxytocin (OT) triggers proximity-seeking behaviour and acts in a positive feedback loop across mother-infant bonds, stimulating appropriate pro-social behaviour across the pair. However, data on infant OT levels is lacking, and it is unclear how important infants are in maintaining mother-infant associations. The bottlenose dolphin (Tursiops truncatus) is a mammalian species that is fully physically mobile at birth and has multi-year, but individually variable, lactation periods. We investigated OT concentrations in mother-infant pairs of wild individuals compared to other age and reproductive classes. An ELISA to detect OT in dolphin plasma was successfully validated with extracted plasma. We highlight a statistical method for testing for parallelism that could be applied to other ELISA validation studies. OT concentrations were consistently elevated in calves up to at least 4 years of age with lactating mothers (12.1 ± 0.9 pg/ml), while all mothers (4.5 ± 0.4 pg/ml) had OT concentrations comparable to non-lactating individuals (5.9 ± 0.5 pg/ml). Concentrations within infants were individually variable, and may reflect the strength of the bond with their mother. The OT system likely provides a physiological mechanism for motivating infants to perform behaviours that prevent long-term separation from their mothers during this crucial time in their life history. Elevated infant OT has also been linked to energetic and developmental advantages which may lead to greater survival rates. Environmental or anthropogenic disturbances to OT release can occur during bond formation or can disrupt the communication methods used to reinforce these bonds via OT elevation. Variation in OT expression in infants, and its behavioural and physiological consequences, may explain differences in reproductive success despite appropriate maternal behaviour expression.

Blubber steroid hormone profiles as indicators of physiological state in free-ranging common bottlenose dolphins (Tursiops truncatus)

Blubber has been proposed as a possible alternative to blood in the assessment of endocrine physiology in marine mammals because it can be collected via remote biopsy, which removes some of the confounding variables and logistical constraints associated with blood collection. To date, few studies have directly assessed the relationships between circulating versus blubber steroid hormone profiles in marine mammals, and these studies have been limited to a small subset of steroid hormones, which collectively limit the current utility of blubber steroid hormone measurements. In this study, we used liquid-chromatography tandem-mass spectrometry (LC-MS/MS) to screen for 16 steroid hormones in matched blood and blubber samples from free-ranging common bottlenose dolphins (Tursiops truncatus). Seven steroid hormones were detected and quantified, including two progestogens, two androgens, and three corticosteroids. Using principal components analysis (PCA), we explored relationships between hormones in both matrices and three physiological states: sexual maturity, pregnancy, and acute stress response. Plasma and blubber testosterone and its precursors, 17-hydroxyprogesterone and androstenedione, loaded to the first principal component (PC1), and PC1 scores were higher in mature males. Plasma and blubber progesterone loaded to PC2, and pregnant/probable pregnant females had significantly higher PC2 scores. Pregnant females also had higher PC1 scores than other females, suggesting differences in androgen profiles between these groups. There was disagreement between plasma and blubber corticosteroid profiles, as indicated by their loading to different PCs; plasma corticosteroids loaded to PC3 and blubber corticosteroids to PC4. PC3 scores were significantly predicted by elapsed time to blood collection (i.e., time between initiating the capture process and blood collection), while elapsed time to blubber collection significantly predicted PC4 scores, indicating that corticosteroid profiles shift in both tissues during acute stress. Corticosteroid profiles were not related to demographic group, site-month, body mass index, water temperature, or time spent outside of the water on the processing boat. Overall, these results demonstrate that blubber steroid hormone profiles reflect changes in endocrine function that occur over broad temporal scales.

Evaluation of body mass index as a prognostic indicator from two rough-toothed dolphin (Steno bredanensis) mass strandings in Florida

Rough-toothed dolphins (Steno bredanensis) are a common mass stranding species in Florida. These large stranding events typically include a small number of sick or injured individuals and a much larger number of healthy individuals, making rapid triage essential. Little data exist on rehabilitation outcomes, and historically, successful outcomes are limited. Furthermore, very little data exist on the feeding habits and dietary needs of this species. This study compared morphology and body mass index (BMI) in two rough-toothed dolphin mass stranding events in Florida: August 2004 (n = 36) and March 2005 (n = 32). The two groups were significantly different in morphologic measurements, with age and gender-adjusted intake BMI significantly (p < .01) different (2004 = 0.34 ± 0.02; 2005 = 0.41 ± 0.02) between groups. Ten animals from 2005 had weights tracked throughout the rehabilitation process and demonstrated an initial drop in BMI followed by an increase and a plateau prior to release. When comparing initial BMI by stranding outcome, individuals that were rehabilitated and released had a significantly (p = .03) higher BMI than individuals who were euthanized. However, there was no difference between dolphins that died of natural causes (p = .56) and animals successfully rehabilitated. Analysis of BMI can be a useful marker in triage during a stranding, when resources are limited to identify individuals most likely to survive, as well as in determining the appropriate body condition for release. The data reported here can provide guidance on evaluating the nutritive status on this uncommon species that would otherwise be difficult to obtain among wild populations.

Liquid chromatography tandem mass spectrometry for the quantification of steroid hormone profiles in blubber from stranded humpback whales (Megaptera novaeangliae)

Marine mammal blubber is known to have quantifiable concentrations of steroid hormones and is increasingly chosen as a matrix for the detection of these reproductive and stress biomarkers. Steroid hormones act through complex cascades, often in concert, yet studies conducted on cetaceans have rarely measured more than two steroids simultaneously. Due to the role of steroid hormones in multiple physiological processes, and variability in concentration among individuals, data on single compounds are often difficult to interpret. Here a liquid chromatography tandem mass spectrometry method for the simultaneous analyses of multiple steroid hormones in cetacean blubber was validated and applied to samples from 10 stranded humpback whales (Megaptera novaeangliae). Progesterone, 17α-hydroxyprogesterone, testosterone, androstenedione, oestrone, oestradiol, cortisone, cortisol, corticosterone and 11-deoxycorticosterone were reliably (relative standard deviation on six replicates <15%) and accurately (recovery of an amended sample between 70% and 120%) quantified, but not 11-deoxycortisol. With the exception of progesterone, testosterone, oestradiol and cortisol, these compounds were quantified for the first time in humpback whales. Given that blubber is frequently collected from free-swimming cetaceans in ongoing research programs, the technique developed here could substantially strengthen understanding and monitoring of the physiological condition of these species.

Comprehensive endocrine response to acute stress in the bottlenose dolphin from serum, blubber, and feces

Several hormones are potential indicators of stress in free-ranging animals and provide information on animal health in managed-care settings. In response to stress, glucocorticoids (GC, e.g. cortisol) first appear in circulation but are later incorporated into other tissues (e.g. adipose) or excreted in feces or urine. These alternative matrices can be sampled remotely, or by less invasive means, than required for blood collection and are especially valuable in highly mobile species, like marine mammals. We characterized the timing and magnitude of several hormones in response to a stressor in bottlenose dolphins (Tursiops truncatus) and the subsequent incorporation of cortisol into blubber, and its metabolites excreted in feces. We evaluated the endocrine response to an acute stressor in bottlenose dolphins under managed care. We used a standardized stress protocol where dolphins voluntarily beached onto a padded platform and remained out of water for two hours; during the stress test blood samples were collected every 15 min and blubber biopsies were collected every hour (0, 60, and 120 min). Each subject was studied over five days: voluntary blood samples were collected on each of two days prior to the stress test; 1 and 2 h after the conclusion of the out-of-water stress test; and on the following two days after the stress test. Fecal samples were collected daily, each afternoon. The acute stressor resulted in increases in circulating ACTH, cortisol, and aldosterone during the stress test, and each returned to baseline levels within 2 h of the dolphin's return to water. Both cortisol and aldosterone concentrations were correlated with ACTH, suggesting both corticosteroids are at least partly regulated by ACTH. Thyroid hormone concentrations were generally unaffected by the acute stressor. Blubber cortisol increased during the stress test, and fecal GC excretion was elevated on the day of the stress test. We found that GCs in bottlenose dolphins can recover within hours of acute stress, and that cortisol release can be detected in alternate matrices within a few hours-within 2 h in blubber, and 3.5-5 h in fecal samples.

Not just fat: investigating the proteome of cetacean blubber tissue

Mammalian adipose tissue is increasingly being recognized as an endocrine organ involved in the regulation of a number of metabolic processes and pathways. It responds to signals from different hormone systems and the central nervous system, and expresses a variety of protein factors with important paracrine and endocrine functions. This study presents a first step towards the systematic analysis of the protein content of cetacean adipose tissue, the blubber, in order to investigate the kinds of proteins present and their relative abundance. Full depth blubber subsamples were collected from dead-stranded harbour porpoises (Phocoena phocoena) (n = 21). Three total protein extraction methods were trialled, and the highest total protein yields with the lowest extraction variability were achieved using a RIPA cell lysis and extraction buffer based protocol. Extracted proteins were separated using 1D Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE), and identified using nanoflow Liquid Chromatography Electrospray Ionization in tandem with Mass Spectrometry (nLC-ESI-MS/MS). A range of proteins were identified (n = 295) and classed into eight functional groups, the most abundant of which were involved in cell function and metabolism (45%), immune response and inflammation (15%) and lipid metabolism (11%). These proteins likely originate both from the various cell types within the blubber tissue itself, and from the circulation. They therefore have the potential to capture information on the cellular and physiological stresses experienced by individuals at the time of sampling. The importance of this proteomic approach is two-fold: Firstly, it could help to assign novel functions to marine mammal blubber in keeping with current understanding of the multi-functional role of adipose tissue in other mammals. Secondly, it could lead to the development of a suite of biomarkers to better monitor the physiological state and health of live individuals though remote blubber biopsy sampling.

Evaluating morphometric and metabolic markers of body condition in a small cetacean, the harbor porpoise (Phocoena phocoena)

Mammalian body condition is an important individual fitness metric as it affects both survival and reproductive success. The ability to accurately measure condition has key implications for predicting individual and population health, and therefore monitoring the population‐level effects of changing environments. No consensus currently exists on the best measure to quantitatively estimate body condition in many species, including cetaceans. Here, two measures of body condition were investigated in the harbor porpoise (Phocoena phocoena). First, the most informative morphometric body condition index was identified. The mass/length² ratio was the most appropriate morphometric index of 10 indices tested, explaining 50% of the variation in condition in stranded, male porpoises with different causes of death and across age classes (n = 291). Mass/length² was then used to evaluate a second measure, blubber cortisol concentration, as a metabolic condition marker. Cortisol is the main glucocorticoid hormone involved in the regulation of lipolysis and overall energy balance in mammals, and concentrations could provide information on physiological state. Blubber cortisol concentrations did not significantly vary around the girth (n = 20), but there was significant vertical stratification through the blubber depth with highest concentrations in the innermost layer. Concentrations in the dorsal, outermost layer were representative of concentrations through the full blubber depth, showed variation by sex and age class, and were negatively correlated with mass/length². Using this species as a model for live cetaceans from which standard morphometric measurements cannot be taken, but from which blubber biopsy samples are routinely collected, cortisol concentrations in the dorsal, outermost blubber layer could potentially be used as a biomarker of condition in free‐ranging animals.