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Excessive adiposity is associated with altered oxygen tension and comorbidities in humans. In contrast, marine mammals have high adiposity with no apparent detrimental effects. However, partial pressure of oxygen (Po2) in their subcutaneous adipose tissue (blubber) and its relationship with fatness have not been reported. We measured Po2 and temperature at different blubber depths in 12 healthy juvenile grey seals. Fatness was estimated from blubber thickness and morphometric parameters. Simultaneously, we monitored breathing pattern; heart rate and arterial blood saturation with a pulse oximeter; and relative changes in total hemoglobin, deoxyhemoglobin, and oxyhemoglobin in blubber capillaries using near‐infrared spectroscopy (NIRS) as proxies for local oxygenation changes. Blubber Po2 ranged from 14.5 to 71.4 mmHg (39.2 ± 14.1 mmHg), which is similar to values reported in other species. Blubber Po2 was strongly and negatively associated with fatness (LME: p < 0.0001, R2marginal = 0.53, R2conditional = 0.64, n = 10), but not with blubber depth. No other parameters explained variability in Po2, suggesting arterial blood and local oxygen delivery did not vary within and between measurements. The fall in blubber Po2 with increased fatness in seals is consistent with other animal models of rapid fat deposition. However, the Po2 levels at which blubber becomes hypoxic and consequences of low blubber Po2 for its health and function, particularly in very fat individuals, remain unknown. How seals avoid detrimental effects of low oxygen tension in adipose tissue, despite their high and fluctuating adiposity, is a fruitful avenue to explore. [ABSTRACT FROM AUTHOR]

Microplastics (plastic particles <5 mm in size) are highly available for ingestion by a wide range of organisms, either through direct consumption or indirectly, via trophic transfer, from prey to predator. The latter is a poorly understood, but potentially major, route of microplastic ingestion for marine top predators.We developed a novel and effective methodology pipeline to investigate dietary exposure of wild top predators (grey seals; Halichoerus grypus) to microplastics, by combining scat‐based molecular techniques with a microplastic isolation method. We employed DNA metabarcoding, a rapid method of biodiversity assessment, to garner detailed information on prey composition from scats, and investigated the potential relationship between diet and microplastic burden.Outcomes of the method development process and results of both diet composition from metabarcoding analysis and detection of microplastics are presented. Importantly, the pipeline performed well and initial results suggest the frequency of microplastics detected in seal scats may be related to the type of prey consumed.Our non‐invasive, data‐rich approach maximizes time and resource–efficiency, while minimizing costs and sample volumes required for analysis. This pipeline could be used to underpin a much‐needed increase in understanding of the relationship between diet composition and rates of microplastic ingestion in high trophic level species. [ABSTRACT FROM AUTHOR]

Persistent organic pollutants (POPs) remain a risk to marine ecosystem health. POPs accumulate in fat tissue and are biomagnified up through food webs, generating high concentrations in apex predators, including marine mammals. Seals are thus often cited as sentinels of marine environment POP levels. Measuring changes across decadal timescales in these animals is key to understanding the effectiveness of regulations controlling POPs, predicting health, population, and ecosystem level impacts, and informing conservation and management strategies. Information on recent changes in legacy POPs in seals is relatively sparse, however, and datasets are not always continuous in the absence of dedicated POP monitoring programmes.Here, POP concentrations in the blubber of weaned grey seal pups from the Isle of May, Scotland, were compared between studies investigating POP impacts on survival and energy balance in 2002, and in 2015–17. By 2017, the total dioxin‐like polychlorinated biphenyls (ΣDL‐CBs) and the total non‐dioxin‐like polychlorinated biphenyls (ΣNDL‐CBs) had decreased to ~75% of 2002 levels.The organochlorine pesticides (OCPs), dichlorodiphenyltrichoroethane (ΣDDT), dichlorodiphenyldichloroethylene (DDE), and dichlorodiphenyldichoroethane (DDD), and some CB congeners, did not fall over the 15‐year period; however, the power to detect small changes at low concentrations was limited.High DDE and a lack of change in DDD are likely to reflect the low excretion of DDT metabolites, rather than recent exposure.The limited change in many POPs over 15 years suggest that risks remain for energy balance, endocrine status, and immune function in grey seal pups, with contingent effects on conservation and management objectives for this species.These data highlight the need for long‐term datasets and parity in sampling and analytical methods to evaluate continuing impacts of POPs in grey seals and on marine ecosystems more widely. [ABSTRACT FROM AUTHOR]

Investigation of marine mammal dive-by-dive blood distribution and oxygenation has been limited by a lack of noninvasive technology for use in freely diving animals. Here, we developed a noninvasive near-infrared spectroscopy (NIRS) device to measure relative changes in blood volume and haemoglobin oxygenation continuously in the blubber and brain of voluntarily diving harbour seals. Our results show that seals routinely exhibit preparatory peripheral vasoconstriction accompanied by increased cerebral blood volume approximately 15 s before submersion. These anticipatory adjustments confirm that blood redistribution in seals is under some degree of cognitive control that precedes the mammalian dive response. Seals also routinely increase cerebral oxygenation at a consistent time during each dive, despite a lack of access to ambient air. We suggest that this frequent and reproducible reoxygenation pattern, without access to ambient air, is underpinned by previously unrecognised changes in cerebral drainage. The ability to track blood volume and oxygenation in different tissues using NIRS will facilitate a more accurate understanding of physiological plasticity in diving animals in an increasingly disturbed and exploited environment. [ABSTRACT FROM AUTHOR]

Plastic and plasticiser pollution of marine environments is a growing concern. Although phthalates, one group of plasticisers, are rapidly metabolised by mammals, they are found ubiquitously in humans and have been linked with metabolic disorders and altered adipose function. Phthalates may also present a threat to marine mammals, which need to rapidly accumulate and mobilise their large fat depots. High molecular weight (HMW) phthalates may be most problematic because they can accumulate in adipose. We used blubber explants from juvenile grey seals to examine the effects of overnight exposure to the HMW, adipogenic phthalate, benzyl butyl phthalate (BBzP) on expression of key adipose-specific genes and on phosphorylation of Akt in response to insulin. We found substantial differences in transcript abundance of Pparγ, Insig2, Fasn, Scd, Adipoq and Lep between moult stages, when animals were also experiencing differing mass changes, and between tissue depths, which likely reflect differences in blubber function. Akt abundance was higher in inner compared to outer blubber, consistent with greater metabolic activity in adipose closer to muscle than skin, and its phosphorylation was stimulated by insulin. Transcript abundance of Pparγ and Fasn (and Adipoq in some animals) were increased by short term (30 min) insulin exposure. In addition, overnight in vitro BBzP exposure altered insulin-induced changes in Pparγ (and Adipoq in some animals) transcript abundance, in a tissue depth and moult stage-specific manner. Basal or insulin-induced Akt phosphorylation was not changed. BBzP thus acted rapidly on the transcript abundance of key adipose genes in an Akt-independent manner. Our data suggest phthalate exposure could alter seal blubber development or function, although the whole animal consequences of these changes are not yet understood. Knowledge of typical phthalate exposures and toxicokinetics would help to contextualise these findings in terms of phthalate-induced metabolic disruption risk and consequences for marine mammal health. [Display omitted] • Examined juvenile grey seal blubber response to benzyl butyl phthalate (BBzP). • Gene expression and total Akt differed by tissue depth and moult stage/mass change. • Signalling through Akt was initiated by insulin and unaffected by BBzP. • BBzP altered basal and insulin-induced PPARγ expression independent of Akt. • Phthalates may disrupt blubber function in seals in a life-stage specific way. [ABSTRACT FROM AUTHOR]