Heartworms in Halichoerus grypus: first records of Acanthocheilonema spirocauda (Onchocercidae; Filarioidea) in 2 grey seals from the North Sea.

The assumed definitive host of the heartworm Acanthocheilonema spirocauda (Onchocerdidae; Filarioidea) is the harbour seal (Phoca vitulina). This filaroid nematode parasitizing in cardiac ventricles and blood vessel lumina of harbour seals (P. vitulina) has a low prevalence and seldom causes severe health impacts. The seal louse (Echinophthirius horridus) is the assumed intermediate host for transmission of A. spirocauda filariae between seals, comprising a unique parasite assembly conveyed from the terrestrial ancestors of pinnipeds. Although grey seals (Halichoerus grypus) are infected by seal lice, heartworm infection was not verified. Analysing a longterm dataset compiled over decades (1996­2021) of health monitoring seals along the German coasts comprising post mortem investigations and archived parasites, 2 cases of A. spirocauda infected male grey seals were detected. Tentative morphological identification was confirmed with molecular tools by sequencing a section of mtDNA COI and comparing nucleotide data with available heartworm sequence. This is the first record of heartworm individuals collected from the heart of grey seals at necropsy. It remains puzzling why heartworm infection occur much less frequently in grey than in harbour seals, although both species use the same habitat, share mixed haul-outs and consume similar prey species. If transmission occurs directly via seal louse vectors on haul-outs, increasing seal populations in the North- and Baltic Sea could have density dependent effects on prevalence of heartworm and seal louse infections. It remains to be shown how species-specificity of filarial nematodes as well as immune system traits of grey seals influence infection patterns of A. spirocauda.

Masking release at 4 and 32 kHz in harbor seals associated with sinusoidal amplitude-modulated masking noise.

Masking can reduce the efficiency of communication and prey and predator detection. Most underwater sounds fluctuate in amplitude, which may influence the amount of masking experienced by marine mammals. The hearing thresholds of two harbor seals for tonal sweeps (centered at 4 and 32 kHz) masked by sinusoidal amplitude modulated (SAM) Gaussian one-third octave noise bands centered around the narrow-band test sweep frequencies, were studied with a psychoacoustic technique. Masking was assessed in relation to signal duration, (500, 1000, and 2000 ms) and masker level, at eight amplitude modulation rates (1-90 Hz). Masking release (MR) due to SAM compared thresholds in modulated and unmodulated maskers. Unmodulated maskers resulted in critical ratios of 21 dB at 4 kHz and 31 dB at 32 kHz. Masked thresholds were similarly affected by SAM rate with the lowest thresholds and the largest MR being observed for SAM rates of 1 and 2 Hz at higher masker levels. MR was higher for 32-kHz maskers than for 4-kHz maskers. Increasing signal duration from 500 ms to 2000 ms had minimal effect on MR. The results are discussed with respect to MR resulting from envelope variation and the impact of noise in the environment on target signal detection.

Normal pre- and post-prandial bile acids and protein C values vary by age in harbor seal pups (Phoca vitulina richardsi) undergoing rehabilitation.

OBJECTIVE: To establish normal values for pre- and post-prandial bile acids and protein C in Pacific harbor seal (Phoca vitulina richardsi) pups. ANIMALS: 45 harbor seals undergoing rehabilitation at the Vancouver Aquarium Marine Mammal Rescue Centre, 0 to 16 weeks, and deemed healthy aside from malnutrition or maternal separation. PROCEDURES: Venous blood was collected from the intervertebral extradural sinus in fasted seals and again 2 hours after a fish meal. RESULTS: The reference interval (90% CL, confidence limit) for pre-prandial (fasting) bile acids was 17.2 µmol/L to 25.4 µmol/L, post-prandial bile acids were 36.9 µmol/L to 46.4 µmol/L, and protein C was 72.3% to 85.4%, across ages. For comparison between developmental ages, pups were grouped into 3 age classes: < 14 days, 5 to 8 weeks, and 10 to 16 weeks. Age affected pre- and post-prandial bile acids; pups < 14 days had significantly higher pre-prandial bile acids (36.0 µmol/L ± 16.5 µmol/L; P < .0001) than other age groups and pups 5 to 8 weeks had significantly higher post-prandial bile acids (50.4 µmol/L ± 21.9 µmol/L; P < .001). Protein C was also affected by age, with seals < 14 days having significantly lower values (mean, 51.8% ± 16.7%; P < .0001). CLINICAL RELEVANCE: This study established normal reference intervals for bile acids in harbor seal pups and offered a preliminary investigation into protein C in pinnipeds. The bile acid values from 0- to 16-week-old seal pups were well above established normal ranges for domestic species, highlighting the utility of age- and species-specific reference ranges. The values presented here and the differences across age classes will aid clinicians in accurately diagnosing hepatobiliary disease in harbor seal pups.

Occurrence and tissue distribution of 33 legacy and novel per- and polyfluoroalkyl substances (PFASs) in Baikal seals (Phoca sibirica).

Per- and polyfluoroalkyl substances (PFASs) are bioaccumulative and associated with adverse effects in both wildlife and humans. The occurrence of 33 PFASs was assessed in the plasma, liver, blubber, and brain of 18 Baikal seals (Phoca sibirica) (16 pups and 2 adult females) from Lake Baikal, Russia (in 2011). Of the 33 congeners analysed for: perfluorooctanosulfonic acid (PFOS), 7 long chain perfluoroalkyl carboxylic acids (C8-C14 PFCAs) and 1 branched PFCA (perfluoro-3,7-dimethyloctanoic acid; P37DMOA) were most frequently detected. The PFASs in plasma and liver with the highest median concentrations were legacy congeners: perfluoroundecanoic acid (PFUnA; plasma: 11.2 ng/g w.w.; liver: 7.36 ng/g w.w.), PFOS (plasma: 8.67 ng/g w.w.; liver: 9.86 ng/g w.w.), perfluorodecanoic acid (PFDA; plasma: 5.13 ng/g w.w.; liver: 6.69 ng/g w.w.), perfluorononanoic acid (PFNA; plasma: 4.65 ng/g w.w.; liver: 5.83 ng/g w.w.) and perfluorotridecanoic acid (PFTriDA; plasma: 4.29 ng/g w.w.; liver: 2.55 ng/g w.w.). PFASs were detected in the brain of Baikal seals, indicating that PFASs cross through the blood-brain barrier. In blubber, the majority of PFASs were detected in low abundance and concentrations. In contrast to legacy PFASs, novel congeners (e.g., Gen X) were either detected infrequently or not found in Baikal seals. The worldwide occurrence of PFASs in pinnipeds was compared and lower median concentrations of PFOS were observed in Baikal seals relative to other pinnipeds. Conversely, similar concentrations of long chain PFCAs were found in Baikal seals compared to other pinnipeds. Furthermore, human exposure was assessed by estimating weekly intakes (EWI) of PFASs through Baikal seal consumption. Although PFASs concentrations were comparatively low relative to other pinnipeds, consumption of Baikal seal could exceed current regulatory guidelines.

Bone mineral density and microarchitecture change during skeletal growth in harbor seals (Phoca vitulina) from the German coast.

Across species, the skeletal system shares mutual functions, including the protection of inner organs, structural basis for locomotion, and acting as an endocrine organ, thus being of pivotal importance for survival. However, insights into skeletal characteristics of marine mammals are limited, especially in the growing skeleton. Harbor seals (Phoca vitulina) are common marine mammals in the North and Baltic Seas and are suitable indicators of the condition of their ecosystem. Here, we analyzed whole-body areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) and lumbar vertebrae by high-resolution peripheral quantitative computed tomography (HR-pQCT) in neonate, juvenile, and adult harbor seals. Along skeletal growth, an increase in two-dimensional aBMD by DXA was paralleled by three-dimensional volumetric BMD by HR-pQCT, which could be attributed to an increasing trabecular thickness while trabecular number remained constant. Strong associations were observed between body dimensions (weight and length) and aBMD and trabecular microarchitecture (R2 = 0.71-0.92, all p < 0.001). To validate the results of the DXA measurement (i.e., the standard method used worldwide to diagnose osteoporosis in humans), we performed linear regression analyses with the three-dimensional measurements from the HR-pQCT method, which revealed strong associations between the two imaging techniques (e.g., aBMD and Tb.Th: R2 = 0.96, p < 0.0001). Taken together, our findings highlight the importance of systematic skeletal investigations in marine mammals during growth, illustrating the high accuracy of DXA in this context. Regardless of the limited sample size, the observed trabecular thickening is likely to represent a distinct pattern of vertebral bone maturation. As differences in nutritional status, among other factors, are likely to affect skeletal health, it appears essential to routinely perform skeletal assessments in marine mammals. Placing the results in the context of environmental exposures may allow effective measures to protect their populations.

Movements and spatial usage of harbour seals in the Elbe estuary in Germany.

Harbour seals are top predators in the North Sea and regarded as sentinels for ecosystem health. A few hundred also occur in adjacent estuaries, such as the Elbe estuary, Germany. However, only little is known about how these animals use this dynamic tidally influenced habitat, which has been under high anthropogenic pressure for decades. In this context, nine harbour seals (Phoca vitulina) from the Elbe estuary were equipped with biotelemetry devices to track their movements over multiple months. Harbour seal movements were characterised by short trips (trip length outside pupping season for females: 9.0 ± 1.12 km, males: 7.0 ± 1.24 km) as well as small home ranges (median 50% home range for females: 16.3 km2, males: 36.1 km2) compared to harbour seals from marine regions. Within the estuary, the animals utilised the fairway, river branches and tributaries. During the pupping season in June and July, four seals showed strongly reduced trip lengths and durations, increased daily haul out durations as well as smaller home ranges. Even though a continuous exchange with harbour seals from the Wadden Sea likely occurs, most individuals in this study spent the entire deployment duration inside the estuary. This indicates that the Elbe estuary provides a suitable habitat for harbour seals, despite extensive anthropogenic usage, calling for further studies on the consequences of living in such an industrialised habitat.

Vessel noise exposures of harbour seals from the Wadden Sea.

The North Sea faces intense ship traffic owing to increasing human activities at sea. As harbour seals (Phoca vitulina) are abundant top predators in the North Sea, it is hypothesised that they experience repeated, high-amplitude vessel exposures. Here, we test this hypothesis by quantifying vessel noise exposures from deployments of long-term sound and movement tags (DTAGs) on nine harbour seals from the Wadden Sea. An automated tool was developed to detect intervals of elevated noise in the sound recordings. An assessment by multiple raters was performed to classify the source as either vessels or other sounds. A total of 133 vessel passes were identified with received levels > 97 dB re 1µPa RMS in the 2 kHz decidecade band and with ambient noise > 6 dB below this detection threshold. Tagged seals spent most of their time within Marine Protected Areas (89 ± 13%, mean ± SD) and were exposed to high-amplitude vessel passes 4.3 ± 1.6 times per day. Only 32% of vessel passes were plausibly associated with an AIS-registered vessel. We conclude that seals in industrialized waters are exposed repeatedly to vessel noise, even in areas designated as protected, and that exposures are poorly predicted by AIS data.

Exposure to legacy and alternative flame retardants in two harbor seal populations and the association with blubber fatty acid profiles.

Flame retardants (FRs) are ubiquitously present in various environmental compartments due to widespread application. However, there have been few reports on the alternative FRs in harbor seals, and their relationship with fatty acid (FA) profiles have largely been overlooked. Here, we investigated the levels of legacy and alternative FRs and FA profiles in the blubber of harbor seals from the coasts of South Sweden (2009-2016) and Northeastern US (NE US) (1999-2010). We observed different proportions of mono- and poly-unsaturated FAs (MUFAs and PUFAs) between the two populations, which may reflect variations in the diet. Significantly higher concentrations of ΣPBDE were also observed in harbor seals from US compared to those from Sweden, both dominated by BDE 47. By comparison, the levels of alternative FRs, noticeably HBBZ and PBEB were much lower compared to those of PBDEs. Moreover, we found a positive correlation between BDE 99 and Σn-6/Σn-3 PUFA in harbor seals from Sweden. In addition, BDE 153 and BDE 154 were positively correlated with ΣUFA/ΣSFA in seals from Sweden and US, respectively. Our results imply the influence of diet in FA profiles and FR concentrations in top predators, as well as the importance of blubber FA characteristics in indicating FR exposure. Further investigations are required to assess the risk of exposure in these harbor seals, as well as to elucidate the underlying mechanisms associating FA profiles with FR exposure.

Measuring rhythms of vocal interactions: a proof of principle in harbour seal pups.

Rhythmic patterns in interactive contexts characterize human behaviours such as conversational turn-taking. These timed patterns are also present in other animals, and often described as rhythm. Understanding fine-grained temporal adjustments in interaction requires complementary quantitative methodologies. Here, we showcase how vocal interactive rhythmicity in a non-human animal can be quantified using a multi-method approach. We record vocal interactions in harbour seal pups (Phoca vitulina) under controlled conditions. We analyse these data by combining analytical approaches, namely categorical rhythm analysis, circular statistics and time series analyses. We test whether pups' vocal rhythmicity varies across behavioural contexts depending on the absence or presence of a calling partner. Four research questions illustrate which analytical approaches are complementary versus orthogonal. For our data, circular statistics and categorical rhythms suggest that a calling partner affects a pup's call timing. Granger causality suggests that pups predictively adjust their call timing when interacting with a real partner. Lastly, the ADaptation and Anticipation Model estimates statistical parameters for a potential mechanism of temporal adaptation and anticipation. Our analytical complementary approach constitutes a proof of concept; it shows feasibility in applying typically unrelated techniques to seals to quantify vocal rhythmic interactivity across behavioural contexts. This article is part of a discussion meeting issue 'Face2face: advancing the science of social interaction'.

Urinary glucocorticoids in harbour seal (Phoca vitulina) pups during rehabilitation.

The glucocorticoid (GC) hormone cortisol is often measured in seals to indicate their stress levels, although other endogenous GCs are usually overlooked. We investigated concentrations of four endogenous GCs in the urine of "orphan" harbour seal pups in rehabilitation. We hypothesised that the GC levels would be elevated if pups were socially isolated, without water access, and with low body mass. Ninety-six samples were collected from 32 pups at four different rehabilitation centres and were analysed by Ultra Performance Liquid Chromatography and Tandem Mass Spectrometry. Median urinary creatinine (Cr) concentrations of endogenous prednisolone (31.6 ng/mg/Cr) and prednisone (31.1 ng/mg/Cr) occurred in similar magnitude to cortisol (37.0 ng/mg/Cr), while median cortisone concentrations were higher (390 ng/mg/Cr). Prednisolone and prednisone concentrations were more strongly inversely related to pup growth rate and pup mass than cortisol and cortisone. Concentrations of all four GCs decreased with mass gain for pups with water access but did not decrease for pups without water; linear mixed models indicated the interaction between these trends was significant for cortisol and cortisone, but not for prednisolone or prednisone. These results indicate the potential value of measuring all four of these endogenous GC hormones in phocid seal pups.

Hidden variable models reveal the effects of infection from changes in host survival.

The impacts of disease on host vital rates can be demonstrated using longitudinal studies, but these studies can be expensive and logistically challenging. We examined the utility of hidden variable models to infer the individual effects of infectious disease from population-level measurements of survival when longitudinal studies are not possible. Our approach seeks to explain temporal deviations in population-level survival after introducing a disease causative agent when disease prevalence cannot be directly measured by coupling survival and epidemiological models. We tested this approach using an experimental host system (Drosophila melanogaster) with multiple distinct pathogens to validate the ability of the hidden variable model to infer per-capita disease rates. We then applied the approach to a disease outbreak in harbor seals (Phoca vituline) that had data on observed strandings but no epidemiological data. We found that our hidden variable modeling approach could successfully detect the per-capita effects of disease from monitored survival rates in both the experimental and wild populations. Our approach may prove useful for detecting epidemics from public health data in regions where standard surveillance techniques are not available and in the study of epidemics in wildlife populations, where longitudinal studies can be especially difficult to implement.

RETROSPECTIVE REVIEW OF NEUROLOGIC DISEASE IN STRANDED ATLANTIC HARBOR SEALS (PHOCA VITULINA CONCOLOR) ALONG THE NEW ENGLAND COAST.

Harbor seals (Phoca vitulina) are a common species admitted to marine mammal rehabilitation facilities. As important indicators of marine ecosystem health, monitoring trends of disease in harbor seal populations is critical. However, few studies have evaluated neurologic disease in this species. The general objective of this study was to retrospectively review and delineate neurologic disease in free-ranging Atlantic harbor seals (P. vitulina concolor) that stranded along the New England (United States) coast and entered a rehabilitation facility between 2006 and 2019. Any Atlantic harbor seal that stranded live along the New England coast during the study period and was diagnosed with neurologic disease on either antemortem or postmortem evaluation was included; medical records and pathologic reports were reviewed. From 211 records, 24 animals met the inclusion criteria. Prevalence of neurologic disease was 11% in the study population and six major categories of neurologic disease were identified including: inflammatory (54%), idiopathic (33%), trauma (4%), congenital (4%), and degenerative (4%). Of the seals diagnosed with neurologic disease, 13 (54%) seals died during rehabilitation, 10 (42%) seals were euthanized, and 1 (4%) seal survived to release. Unique cases seen included a seal with Dandy-Walker-like malformation and another seal with histopathologic findings compatible with neuroaxonal dystrophy, a degenerative process that has not been previously reported in marine mammals. This study contributes to the overall knowledge of the health of free-ranging Atlantic harbor seals and may aid clinicians in characterizing neurologic conditions that may be present in seals undergoing rehabilitation.

BARIUM SULFATE GELATIN AS A NOVEL APPROACH TO FACILITATE GASTROINTESTINAL TRACT POSITIVE CONTRAST STUDIES IN A CAPTIVE HARBOR SEAL (PHOCA VITULINA) AND CALIFORNIA SEA LIONS (ZALOPHUS CALIFORNIANUS) WITHOUT RESTRAINT.

Gastrointestinal tract contrast medium studies are a valuable diagnostic modality to evaluate gastrointestinal anatomy, motility, and pathology. Four positive contrast medium studies were performed twice on a harbor seal (Phoca vitulina) and once each on two California sea lions (Zalophus californianus) to evaluate for gastrointestinal abnormalities by using barium-impregnated gelatin. Because marine mammals in human care routinely receive plain gelatin as a component of their diet and as secondary reinforcement, feeding a barium gelatin mitigates the need for tube feeding or restraint. Operant conditioning was used to position the pinnipeds for voluntary radiographs. The barium gelatin permitted adequate evaluation of gastric emptying and intestinal transit times and good evaluation of the structure of the intestinal tract. Full evaluation of gastric anatomy was limited due to the gelatin blocks not conforming to the stomach in their solid form and the barium quickly exiting the stomach as barium gelatin blocks disintegrated and because orthogonal views could not always be acquired. Even with these limitations, barium gelatin resulted in diagnostically valuable contrast imaging in a stress-free patient setting with reduced risk of aspiration and eliminated the effects that anesthesia can have on gastric motility as well as other anesthesia-associated risks.

Occurrence and tissue-specific partitioning of alternative brominated flame retardants in northwest Atlantic harbor seal pups (Phoca vitulina vitulina).

Brominated flame retardants such as polybrominated diphenyl ethers (PBDEs) have been used for decades until evidence of negative health effects led to bans in many countries. PBDEs have since been replaced by alternative legacy compounds or newly developed chemicals. In this study, eight alternative brominated flame retardants were analyzed in blubber and liver of harbor seal pups (≤6 months) from the Northwest Atlantic collected during 2001-2010 to elucidate concentrations, patterns, contamination trends, potential maternal transfer, and tissue partitioning. All compounds were detected in liver and blubber tissues with hexabromocyclododecane (HBCD) isomers and 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) predominating. Overall, α-HBCD was the dominant HBCD isomer in both tissues although the concentrations of γ-HBCD exceeded those of α-HBCD in seven pups, indicating their mothers may have had alternative dietary patterns or recent exposure to the commercial mixture. Although it was detected in less than half of the samples, to our knowledge, this is the first study to report tetrabromobisphenol A (TBBPA) concentrations in multiple tissues of a top marine predator. For the brominated components of Firemaster® flame retardants, TBB concentrations exceeded bis-(2-ethylhexyl)-tetrabromophthalate (TBPH). This pattern may result from recent exposure to commercial mixtures in which TBB exceeds TBPH 4:1 or from differences in perinatal or lactational transfer efficiency of the two compounds. Between the two tissues, lipid-normalized ß-HBCD, γ-HBCD, TBB and decabromodiphenyl ethane (DBDPE) concentrations were significantly higher in liver than blubber. This indicates that the bioaccumulation of these chemicals is not simply related to lipid dynamics but may be linked to blood proteins. This study demonstrates that harbor seal pups from this region are contaminated with alternative flame retardants passed to them via placental or lactational transfer. Given the evidence for negative health effects of these chemicals, this contamination adds additional pressure on the first year survival of these young, developing animals.

Hoover the talking seal.

Diandra Duengen and colleagues introduce Hoover, a male harbor seal famous for his imitation of human speech.

Maintaining control: metabolism of molting Arctic seals in water and when hauled out.

Seals haul out of water for extended periods during the annual molt, when they shed and regrow their pelage. This behavior is believed to limit heat loss to the environment given increased peripheral blood flow to support tissue regeneration. The degree to which time in water, particularly during the molt, may affect thermoregulatory costs is poorly understood. We measured the resting metabolism of three spotted seals (Phoca largha), one ringed seal (Pusa hispida) and one bearded seal (Erignathus barbatus) during and outside the molting period, while resting in water and when hauled out. Metabolic rates were elevated in spotted and ringed seals during molt, but comparable in water and air for individuals of all species, regardless of molt status. Our data indicate that elevated metabolism during molt primarily reflects the cost of tissue regeneration, while increased haul out behavior is driven by the need to maintain elevated skin temperatures to support tissue regeneration.

Arcanobacterium buesumense sp. nov., isolated from an anal swab of a male harbour seal (Phoca vitulina).

A polyphasic taxonomic study was performed on an unidentified previously described Arcanobacterium-like Gram-positive strain 2701T isolated from an anal swab of a dead male harbour seal. Comparative 16S rRNA sequencing showed that the bacterium belonged to the genus Arcanobacterium in the family Arcanobacteriaceae. The genome sequence of the strain was obtained by Borowiak et al. [1]. The genome had a G+C content of 49 mol% and a total length of 1.94 Mb. The presence of the major menaquinone MK-9(H4) supported the affiliation of the isolate with the genus Arcanobacterium. The polar lipid profile consisted of diphosphatidylglycerol and an unidentified phospholipid as major components and two unidentified lipids, a further unidentified phospholipid, two unidentified phosphoglycolipids as well as phosphatidylglycerol. The major fatty acids were C16 : 0, C18 : 1 and C18 : 0. Biochemical and phylogenetic analyses clearly distinguished the isolate from other members of the genus Arcanobacterium and closely related other species. Based on these results, it is proposed that the unknown Arcanobacterium sp. strain 2701T should be classified as representing a novel species with the name Arcanobacterium buesumense sp. nov. The type strain is 2701T (=DSM 112952T=LMG 32446T).

Feeding and contaminant patterns of sub-arctic and arctic ringed seals: Potential insight into climate change-contaminant interactions.

To provide insight into how climate-driven diet shifts may impact contaminant exposures of Arctic species, we compared feeding ecology and contaminant concentrations in ringed seals (Pusa hispida) from two Canadian sub-Arctic (Nain at 56.5°N, Arviat at 61.1°N) and two Arctic sites (Sachs Harbour at 72.0 °N, Resolute Bay at 74.7 °N). In the sub-Arctic, empirical evidence of changing prey fish communities has been documented, while less community change has been reported in the Arctic to date, suggesting current sub-Arctic conditions may be a harbinger of future Arctic conditions. Here, Indigenous partners collected tissues from subsistence-harvested ringed seals in 2018. Blubber fatty acids (FAs) and muscle stable isotopes (δ15N, δ13C) indicated dietary patterns, while measured contaminants included heavy metals (e.g., total mercury (THg)), legacy persistent organic pollutants (e.g., dichlorodiphenyltrichloroethanes (DDTs)), polybrominated diphenyl ethers (PBDEs), and per-/polyfluoroalkyl substances (PFASs). FA signatures are distinct between sub-Arctic and Resolute Bay seals, likely related to higher consumption of southern prey species including capelin (Mallotus villosus) in the sub-Arctic but on-going feeding on Arctic species in Resolute Bay. Sachs Harbour ringed seals show FA overlap with all locations, possibly consuming both southern and endemic Arctic species. Negative δ13C estimates for PFAS models suggest that more pelagic, sub-Arctic type prey (e.g., capelin) increases PFAS concentrations, whereas the reverse occurs for, e.g., THg, ΣPBDE, and ΣDDT. Inconsistent directionality of δ15N estimates in the models likely reflects baseline isotopic variation not trophic position differences. Adjusting for the influence of diet suggests that if Arctic ringed seal diets become more like sub-Arctic seals due to climate change, diet-driven increases may occur for newer contaminants like PFASs, but not for more legacy contaminants. Nonetheless, temporal trends studies are still needed, as are investigations into the potential confounding influence of baseline isotope variation in spatial studies of contaminants in Arctic biota.

Tissue distribution and trophic magnification of trace elements in typical marine mammals in Bohai and north Yellow Seas.

A total of 20 stranded spotted seals (Phoca largha) and 9 stranded minke whales (Balaenoptera acutorostrata) were collected from Liaodong Bay and the northern part of the Yellow Sea to investigate the tissue distribution (liver, kidney, heart, lung, and muscle), risk, and trophic magnification of 13 trace elements (TEs, Hg, As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, Sn, V, Zn). The 13 TEs were all detected in all spotted seal and minke whale tissue samples, with mean concentrations ranging from 0.041 to 136.3 mg kg-1 dry weight (dw) and 0.022 to 152.6 mg kg-1 dw, respectively. Zn was the dominant contaminant in all tissues for both spotted seals and minke whales. There was tissue-specific distribution of TEs in both marine mammals, and the TEs tended to accumulate in internal organs. Significant positive correlations were found in the body length of the spotted seals and minke whales among some of the TEs, especially for Cd in the internal organs. Gender-dependent distribution of the TEs was not obtained for the spotted seal. Ecological risk evaluation for spotted seals and minke whales suggested that greater concern should be given to Hg, As, and Se. Based on the TE concentrations detected in this study and trophic levels determined by stable carbon and nitrogen isotopes, trophic level-associated biodilution was obtained for As, Cd, Co, Cu, Mn, Pb, Se, Sn, and V in the spotted seal, while Zn displayed a significant biomagnification trend with increasing trophic levels. In the case of the minke whale, As, Cd, Co, Mn, Pb, Se, and V displayed significant biomagnification trends with increasing trophic levels.

Age as a primary driver of the gut microbial composition and function in wild harbor seals.

Dietary changes are the major variation cause in the composition of the gut microbiota. The short lactation phase in phocids provides an exceptional opportunity to explore the microbiota's response to a quick transition from a milk-based to a solid diet. We investigated the effects of age and sex on the gut microbiota of harbor seals in Mexico using rectal and fecal samples from pups and adults. 16S gene sequencing revealed age explains most of the observed variations in microbial composition. Individuals with frequent contact (pups-female adults) have major microbial similarities than those with little or no contact (pups-male adults). Overall, adults and females (regardless of sex and age, respectively) have a greater microbial richness; as seals grow, the core microbiome shrinks, and microbial diversity increases. We found pathways related to milk and chitin digestion in pups' microbiomes, indicating pups were transitioning to a solid diet. An enrichment of routes related to dramatic weight loss and body mass indicated higher metabolic stress in pups in late breeding season, when they are weaned and start intermittent fasting. Our findings highlight the host-microbiome interaction in harbor seals during late breeding season in response to food shifts and metabolic stress.