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Deep ocean foraging northern elephant seals (Mirounga angustirostris) consume fish and squid in remote depths of the North Pacific Ocean. Contaminants bioaccumulated from prey are subsequently transferred by adult females to pups during gestation and lactation, linking pups to mercury contamination in mesopelagic food webs (200-1000 m depths). Maternal transfer of mercury to developing seal pups was related to maternal mercury contamination and was strongly correlated with maternal foraging behavior (biotelemetry and isotopes). Mercury concentrations in lanugo (hair grown in utero) were among the highest observed worldwide for young pinnipeds (geometric mean 23.01 μg/g dw, range 8.03-63.09 μg/g dw; n = 373); thus, some pups may be at an elevated risk of sub-lethal adverse health effects. Fetal mercury exposure was affected by maternal foraging geographic location and depth; mercury concentrations were highest in pups of the deepest diving, pelagic females. Moreover, pup lanugo mercury concentrations were strongly repeatable among successive pups of individual females, demonstrating relative consistency in pup mercury exposure based on maternal foraging strategies. Northern elephant seals are biosentinels of a remote deep-sea ecosystem. Our results suggest that mercury within North Pacific mesopelagic food webs may also pose an elevated risk to other mesopelagic-foraging predators and their offspring.

Eggshell thickness can be an indicator of environmental pollution in wild birds and shell quality in wild and domestic birds, but it is difficult to measure calcite eggshell thickness due to the presence of the adherent outer eggshell membrane. Eggshells of 13 waterbird species were divided in half longitudinally and the outer membrane was removed from one of the halves. Subsequently, we measured eggshell thickness, both with and without the outer eggshell membrane, using a Hall-effect thickness gauge to the nearest 0.001 mm along the equator of each eggshell half. Outer eggshell membrane thicknesses ranged from 0.014 to 0.073 mm. Caspian Tern (Hydroprogne caspia) and California Gull (Larus californiens) had the thickest eggshell membranes (0.056 and 0.073 mm, respectively), and Green Heron (Butorides virescens) and Killdeer (Charadrius vociferus) had the thinnest membranes (0.014 and 0.022 mm, respectively). The eggshell membrane, as a percent of the total eggshell and membrane thickness, varied among the 13 species and ranged among species from 7.9% to 20.6%. The outer membrane comprised a greater percent of the total eggshell and membrane thickness for Black Skimmer (19.3%; Rynchops niger), California Gull (20.5%), and Forster's Tern (20.6%; Sterna forsteri) than for Green Heron (7.9%), Double-crested Cormorant (10.4%; Phalacrocorax auritus), and Western Grebe (10.6%; Aechmophorus occidentalis). Within species, the outer membrane thickness was not correlated with egg morphometries but, for a subset of species, there was some indication that the calcite eggshell thickness decreases with embryo development (age). We discuss several reasons for conducting future eggshell thickness measurements without removing the membrane. Received 27 February 2023. Accepted 31 December 2023. Key words: eggshell measurement, eggshell membrane, eggshell thickness, Hall-effect thickness gauge. El grosor de la cascara de huevo puede ser indicador de la contaminacion ambiental en aves silvestres y de calidad de la cascara tanto en aves silvestres como domesticas, pero es dificil medir el grosor de la calcita de la cascara de huevo por la presencia de la membrana externa adherente. Cascaras de huevos de 13 especies de aves acuaticas fueron divididas en mitades longitudinales y la membrana externa fue removida de una de las dos mitades. Luego medimos el grosor de las cascaras de huevo, tanto con como sin membrana externa, usando calibrador de grosor de efecto Hall con al 0.001 mm mas cercano, proximo al ecuador de cada mitad de la cascara de huevo. El grosor de la membrana externa vario entre 0.014 to 0.073 mm. El charran Hydroprogne caspia y la gaviota Larus californicus tuvieron las membranas mas gruesas (0.056 and 0.073 mm, respectivamente), mientras que la garcita verde (Butorides virescens) y el chorlo Charadrius vociferus tuvieron las membranas mas delgadas (0.014 y 0.022 mm, respectivamente). La membrana del cascaron como porcentaje de la suma del grosor del cascaron y de la membrana, vario entre las 13 especies de 7.9% a 20.6%. La membrana externa represento un mayor porcentaje del grosor total de cascara de huevo y membrana para rayador Rynchops niger (19.3%), la gaviota (20.5%) y el charran Sterna forsteri (0.6%) que para la garcita verde (7.9%), cormoran Phalacrocorax auritus (10.4%) y archichilique Aechmophorus occidentalis (10.6%). Dentro de las especies, el grosor de la membrana externa no estaba correlacionado con la morfometria del huevo pero, para un subconjunto de especies, hubo algunos indicios de que el grosor de la calcita de la cascara de huevo disminuyo con el desarrollo del embrion (edad). Discutimos varias razones para llevar a cabo mediciones futuras de grosor de cascara de huevo sin remover la membrana. Palabras clave: medida de cascara de huevo, membrana de cascara de huevo, grosor de cascara de huevo, calibrador de grosor de efecto Hall., Eggshell thickness is used as an indicator of environmental pollution in wild birds, eggshell quality in wild and domestic birds (e.g., Blus 2011, Maurer et al. 2012), and to investigate [...]

BACKGROUND: Early identification of dogs with progressive vs stable chronic kidney disease (CKD) might afford opportunity for interventions that would slow progression. However, currently no surrogate biomarker reliably predicts CKD progression. HYPOTHESIS/OBJECTIVES: Urinary cystatin B (uCysB), a novel kidney injury biomarker, predicts progressive disease in International Renal Interest Society (IRIS) CKD Stage 1. ANIMALS: Seventy-two dogs, including 20 dogs from 4 university centers with IRIS CKD Stage 1, with IDEXX symmetric dimethylarginine (SDMA) concentration up to 17 μg/dL and no systemic comorbidities, and 52 clinically healthy staff-owned dogs from a fifth university center. METHODS: A multicenter prospective longitudinal study was conducted between 2016 and 2021 to assess uCysB concentration in IRIS CKD Stage 1 and control dogs. Dogs were followed to a maximum of 3 years (control) or 25 months (CKD). Stage 1 IRIS CKD was classified as stable or progressive using the slope of 1/SDMA, calculated from 3 timepoints during the initial 90-day period. Dogs with slope above or below -0.0007 week × dL/μg were classified as stable or progressive, respectively. Mixed effects modeling was used to assess the association between uCysB and progression rate. RESULTS: Estimates of first visit uCysB results predictive of active ongoing kidney injury based on the mixed effects models were 17 ng/mL for control, 24 ng/mL for stable CKD, and 212 ng/mL for progressive CKD (P

BACKGROUND: Circulating creatinine and symmetric dimethylarginine (SDMA) are biomarkers of kidney function that have been used variously to define stable vs progressive chronic kidney disease (CKD). Slope monitoring of inverse biomarker values (creatinine-1 or SDMA-1 ) has shown promise, but quantitative criteria to distinguish stable vs progressive CKD using this approach are lacking. OBJECTIVE: Assessment of creatinine-1 and SDMA-1 slope cutoffs to distinguish stable vs progressive CKD. ANIMALS: One hundred ten clinically healthy university staff-owned dogs and 29 male colony dogs with progressive X-linked hereditary nephropathy (XLHN). METHODS: Retrospective analysis combining 2 prospective observational studies, 1 tracking kidney function biomarkers in healthy dogs (HDs) to a maximum of 3 years, and 1 tracking kidney function biomarkers in male colony dogs with progressive XLHN to a maximum of 1 year. The minimum slope of creatinine-1 or SDMA-1 as measured using the IDEXX SDMA test from HD was assigned as the slope cutoff for stable kidney function. RESULTS: The stable vs progressive slope cutoff was -0.0119 week × dL/mg for creatinine-1 and -0.0007 week × dL/μg for SDMA-1 . CONCLUSIONS AND CLINICAL IMPORTANCE: In the studied CKD population, progressive dysfunction can be distinguished from stable kidney function by using the slope of creatinine-1 or SDMA-1 . These criteria may serve to characterize CKD in other cohorts of dogs and to establish guidelines for degrees of progression rate in dogs with naturally occurring CKD.

The South Bay Salt Pond Restoration Project aims to restore many former salt production ponds, now managed for wildlife and water quality, to tidal marsh. However, because managed ponds support large densities of breeding waterbirds, reduction of pond habitat may influence breeding waterbird distribution and abundance. We investigated habitat use associated with breeding, feeding, and roosting behaviors during the breeding season for American Avocets (Recurvirostra americana), Black-necked Stilts (Himantopus mexicanus), Forster’s Terns (Sterna forsteri), and Caspian Terns (Hydroprogne caspia) in south San Francisco Bay in 2019 after substantial tidal marsh restoration, and compared results to a 2001 survey (before restoration). In 2019, managed ponds (26% of currently available habitat) were selected by waterbirds engaged in breeding behaviors (> 39% of observations), foraging (> 42%), and roosting (> 73%). Waterbirds avoided tidal habitats (43% of available habitat), comprising

This article examines why and how teachers of refugees enact protection by engaging with local forms of harm facing their refugee students. Through portraits of two classrooms in Jordan, we describe the relationships that form between Jordanian teachers and Syrian students, and the protection practices teachers develop in response. We propose a more comprehensive conceptualization of protection in refugee education that layers socio-political protection on legal and rights-based protection commonly embedded in humanitarian activities.

Environmental contamination is widespread and can negatively impact wildlife health. Some contaminants, including heavy metals, have immunosuppressive effects, but prior studies have rarely measured contamination and disease simultaneously, which limits our understanding of how contaminants and pathogens interact to influence wildlife health. Here, we measured mercury concentrations, influenza infection, influenza antibodies and body condition in 749 individuals from 11 species of wild ducks overwintering in California. We found that the odds of prior influenza infection increased more than fivefold across the observed range of blood mercury concentrations, while accounting for species, age, sex and date. Influenza infection prevalence was also higher in species with higher average mercury concentrations. We detected no relationship between influenza infection and body fat content. This positive relationship between influenza prevalence and mercury concentrations in migratory waterfowl suggests that immunotoxic effects of mercury contamination could promote the spread of avian influenza along migratory flyways, especially if influenza has minimal effects on bird health and mobility. More generally, these results show that the effects of environmental contamination could extend beyond the geographical area of contamination itself by altering the prevalence of infectious diseases in highly mobile hosts.

On August 3rd, 2019, a racially-charged mass shooting occurred at Walmart in El Paso, TX that killed 23 people and injured another 23. Following the Walmart shooting, students in this borderland region wrote essays related to their experiences. We used the themes we identified to inform implications for teaching writing and composition for middle school level instruction. Student themes reflected affective, behavioral and cognitive reactions to violence. Students' proposed actions to address violence included themes at the national/global level and personal level. Essential attributes from "This We Believe" and critical expressivism provide insights for writing pedagogy which encourages students to connect their experiences with violence to their own personal thoughts, emotions, and solutions. Some recommended critical expressivist activities educators can include in their work with students are: low-stakes writing focused on experiences with violence, specific readings connected to experiences of violence, journaling about encounters with violence, poetry, and the creation of a research paper on the effects of violence.

We evaluated external and internal sources of variation in second language (L2) and native language (L1) proficiency among college students. One hundred and twelve native-English L2 learners completed measures of L1 and L2 speaking proficiency, working memory, and cognitive control and provided self-ratings of language exposure and use. When considering learner-external variation, we found that more frequent L2 exposure predicted higher L2 and L1 proficiency, while earlier L2 exposure predicted higher L2 proficiency, but poorer L1 maintenance. L1-L2 distance limited crosslinguistic transfer of print-to-sound mappings. When considering learner-internal variation, we found that L1 and L2 proficiency were highly correlated and that better working memory, but not cognitive control, accounted for additional variance in L2 and L1 proficiency. More frequent L2 exposure was associated with better cognitive control.

Small mesopelagic fishes dominate the world's total fish biomass, yet their ecological importance as prey for large marine animals is poorly understood. To reveal the little-known ecosystem dynamics, we identified prey, measured feeding events, and quantified the daily energy balance of 48 deep-diving elephant seals throughout their oceanic migrations by leveraging innovative technologies: animal-borne smart accelerometers and video cameras. Seals only attained positive energy balance after feeding 1000 to 2000 times per day on small fishes, which required continuous deep diving (80 to 100% of each day). Interspecies allometry suggests that female elephant seals have exceptional diving abilities relative to their body size, enabling them to exploit a unique foraging niche on small but abundant mesopelagic fish. This unique foraging niche requires extreme round-the-clock deep diving, limiting the behavioral plasticity of elephant seals to a changing mesopelagic ecosystem.

BackgroundDetection of urinary casts is difficult due to their intermittent presence and deterioration in urine samples.ObjectiveTo compare the performance of the IDEXX SediVue Dx® Urine Sediment Analyzer (SediVue) with manual microscopy for the detection of urinary casts. We hypothesized that the SediVue analyzer would perform similarly to manual microscopy in cast detection.AnimalsFour hundred forty-three samples from 420 dogs from a hospital population.MethodsThis is a prospective, cross-sectional study. For SediVue analysis (software version [SW] 1.0.1.3), uncentrifuged urine was pipetted into a disposable cartridge. Seventy images were captured and processed by an onboard algorithm. For manual microscopy, urine was centrifuged to obtain sediment. Any cast identified by either method was considered a positive result (>0/low-power field [LPF]). SediVue images were evaluated if casts were detected by either methodology. A revised sensitivity and specificity were calculated after image review and when using a threshold of >1 cast/LPF.ResultsThe sensitivity of the SediVue analysis for the detection of urinary casts was 53.7% (43.85%-63.35%), and specificity was 86.0% (81.78%-89.51%). After image review, the revised sensitivity/specificity was 52.0% (42.89%-61.02%) and 90.6% (86.81%-93.54%), respectively. When using a more clinically relevant threshold of >1/LPF, the sensitivity was 52.6% (35.82%-69.02%) and specificity was 99.3% (97.85%-99.85%).Conclusions and clinical importanceThe SediVue provides moderate agreement to manual methodology for detection of casts in urine.

Availability of wetlands with low salinities during the breeding season can influence waterfowl reproductive success and population recruitment. Salinities as low as 2 ppt (3.6 mScm–1) can impair duckling growth and influence behavior, with mortality occurring above 9 ppt (14.8 mScm–1). We used satellite imagery to quantify the amount of available water, and sampled surface water salinity at Grizzly Island, in the brackish Suisun Marsh, at three time-periods during waterfowl breeding (April, May, July) over 4 years (2016–2019). More water was available and salinity was lower during wetter years (2017, 2019) than during drier years (2016, 2018), and the amount of water in wetlands decreased 73%–86% from April to July. Across all time-periods and years, the majority (64%–100%) of wetland habitat area had salinities above what has been shown to negatively affect ducklings (> 2 ppt), and up to 42% of wetland area had salinities associated with duckling mortality (> 9 ppt). During peak duckling production in May, 81%–95% of available water had salinity above 2 ppt, and 5%–21% was above 9 ppt. In May of the driest year (2016), only 0.5 km2 of low-salinity water (

This mixed methods case study focuses on one school's experiences with Do the Write Thing (DtWT) Challenge, a national violence prevention program for middle schools. Using the theory of planned behavior as a theoretical framework, we examined program impact and learning activities. Students in participating schools demonstrated significantly more positive attitudes toward behaviors to reduce violence and intentions to enact these behaviors than those in nonparticipating schools. Teachers reported that the program had a positive impact on both students and teachers. Classroom discussions about personal experiences with violence were rated as the most helpful activity and predicted several positive outcomes. Teachers used creative learning activities tied to state standards and reported improved relationships with students due to sharing personal experiences. Results offer important implications for program design and continuing research.

Background: This study examined reasons not to drink in young adults in relation to demographics, alcohol use patterns, timing (weekend vs. weekday), and typical drinking motives. Methods: Young adults who reported past 30‐day alcohol use and at least one nondrinking day (n = 614; mean age = 21.5 years ±0.53) completed a survey of alcohol‐related measures (e.g., typical drinking motives) and up to 14 daily surveys that included 12 reasons not to drink assessed on nondrinking days. Multilevel logistic regressions were estimated for each reason not to drink and related covariates. Results: The most common reasons not to drink on a given day were "wasn't interested in drinking" (83.4% of nondrinking days) and "didn't want to get drunk" (81.8% of nondrinking days), with over 96% of participants endorsing each of these at least once. On days (11.6%; by 29.5% of participants) when another drug was used instead of alcohol, 81.8% used cannabis. Sex, race/ethnicity, weekend (vs. weekday), and drinking motives were differentially linked to reasons not to drink. Reporting high‐intensity drinking (i.e., ≥10 drinking on a day) versus binge (5–9 drinks on a day) in the past 2 weeks was linked to "had a hangover recently" (odds ratio = 2.85) as a reason not to drink. Conclusions: Findings suggest that reasons not to drink reflect personal decisions and highlight ways to acknowledge situational barriers (e.g., saving money for food and essentials) that can be emphasized in brief interventions. Furthermore, reasons not to drink and alcohol motives may work in tandem within the motivational model to impact alcohol use behaviors. [ABSTRACT FROM AUTHOR]

Simple Summary: In our study, we looked into finding better ways to diagnose and predict acute kidney injury (AKI) in dogs. To do so, two substances were studied in dog urine, urinary clusterin (uClust) and cystatin B (uCysB), to see if they could be useful as markers for AKI. We compared samples from 18 dogs with different levels of AKI and 10 healthy dogs. Dogs with AKI initially had higher levels of uClust and uCysB than healthy dogs. Also, the level of uCysB was higher in dogs that did not survive. In conclusion, uClust and uCysB seem to be promising markers for diagnosing and predicting the outcome of AKI in dogs. Novel biomarkers are needed in diagnosing reliably acute kidney injury (AKI) in dogs and in predicting morbidity and mortality after AKI. Our hypothesis was that two novel tubular biomarkers, urinary clusterin (uClust) and cystatin B (uCysB), are elevated in dogs with AKI of different etiologies. In a prospective, longitudinal observational study, we collected serum and urine samples from 18 dogs with AKI of different severity and of various etiology and from 10 healthy control dogs. Urinary clusterin and uCysB were compared at inclusion between dogs with AKI and healthy controls and remeasured one and three months later. Dogs with AKI had higher initial levels of uClust (median 3593 ng/mL; interquartile range [IQR]; 1489–10,483) and uCysB (554 ng/mL; 29–821) compared to healthy dogs (70 ng/mL; 70–70 and 15 ng/mL; 15–15; p < 0.001, respectively). Initial uCysB were higher in dogs that died during the one-month follow-up period (n = 10) (731 ng/mL; 517–940), compared to survivors (n = 8) (25 ng/mL; 15–417 (p = 0.009). Based on these results, uClust and especially uCysB are promising biomarkers of AKI. Further, they might reflect the severity of tubular injury, which is known to be central to the pathology of AKI. [ABSTRACT FROM AUTHOR]

We examined experiences of participants in "Do the Write Thing" national violence prevention program for middle-level students. Using mixed methods, we conducted surveys and focus groups with students, parents, and teachers who attended the program's National Recognition Week in Washington, DC. Results revealed important affective, behavioral, and cognitive impacts on participants, including improved relationships, increased understanding of violence, and commitment to reduce violence. Participants from cities where insufficient time and resources were devoted to the project did not experience significant change. Teachers reported developing greater empathy for their students and making substantial changes in their teaching, providing support for students and infusing activities addressing violence into their curriculum. Recommendations are made for increased program support and future research.

This study examines the relationships between school processes and literacy in public schools that serve low-income families in a midsize city in Colombia. We focus on four categories of school processes: instructional practice; school-community engagement; well-being of students, teachers, and parents; and community belonging. We present two key results. First, we find considerable variation in literacy performance across schools, despite serving students with similar family background characteristics. Second, we find community belonging to be the most salient school process for predicting literacy. Among measures of community belonging, higher levels of students' sense of belonging and lower levels of bullying were associated with higher literacy. This study contributes to the field of international and comparative education by highlighting the importance of relational and interpersonal dimensions of school processes for children's learning. Our study also demonstrates the value of adopting an interdisciplinary lens that combines economics, child development, and sociology to better understand the links between school processes and student learning.

Currently, more than 25 million people across the globe live as refugees, having been driven from their countries of origin by crises and conflicts. Although the right to education is articulated in global agreements, national education systems in the host countries are primarily responsible for refugee children's instruction. In one of the first studies of its kind, we assessed all the schools providing lower primary education to refugee children in Kakuma refugee camp in Kenya, one of the largest and oldest refugee camps in the world at the time of data collection. The outcomes for these students were concerningly low, even lower than for those of disadvantaged children in the host community, Turkana County. Literacy outcomes differed among the refugee children, depending on their country of origin, the language of instruction used at the school in Kenya, the languages spoken at home, and the children's self-professed expectation of a return to their country of origin. Our findings point to the urgent need to invest heavily in improving learning among refugee children, rather than focusing solely on their access to education.

In this research article, Sarah Dryden-Peterson explores the concept of researcher positionality, focusing on its malleability over time. The methodological analysis is situated in an empirical study of history teaching and learning in Cape Town, South Africa, schools in 1998 and 2019. Dryden-Peterson argues that researcher positionality is often articulated as static, ignoring temporal shifts. She analyzes the ways shifts in identities, comparative frames, and positions on expertise and vulnerability have implications for how researchers collect and interpret their data.

We examine the ways in which young Syrian refugees perceive and navigate the symbolic boundaries of belonging when displaced in Lebanon. Using portraiture, we identify three dimensions of belonging for refugees -- safety, dignity, and relationships -- and we explore the role of education in cultivating each one. We find that educational spaces, such as formal school and informal volunteering experiences, are places where refugee young people are at times able to blur bright boundaries of belonging. We also find that this belonging is tenuous and serves to reinforce boundaries of citizenship, rights, and everyday practices that exclude refugee young people. Our findings emphasize the need for the field of refugee education to address the question of how schools can actively resist and counter state-established bright boundaries of belonging to instead serve as spaces that blur and redefine those boundaries.

This essay explores the civic education of refugees within the context of a radical global policy shift to include refugees in national education systems. I argue that this shift has promoted structural inclusion of refugees in national schooling but has not adequately engaged with the relational processes of inclusion. I explore two central dilemmas for civic education in this context: the dilemma of nation-state-centric curriculum and national narratives that do not include refugees; and the dilemma of marginalisation of refugees within national education systems and limited spaces for refugees to imagine or enact civic behaviours. I examine these dilemmas through a synthesis of existing literature, both historical and contemporary, that addresses civic dimensions of the educational experiences of refugee children while also drawing on my original research with refugee children and in refugee-hosting schools and from interviews with national and global actors. I conclude with reflections on the implications of these dilemmas for future research to inform school-based practices in refugee education.

This study examines how students of majority and minority ethnic backgrounds in Botswana understand national identity as inclusive of their ethnic groups. Within assimilationist policies and curriculum, we find that the value of national identity rests on its positioning as a path toward higher levels of education and employment. However, for ethnic minority students, enacting this national identity requires sacrifice of other desired dimensions of a future good life, including ethnic identity.

This article explores the understood purposes of refugee education at global, national, and school levels. To do so, we focus on a radical shift in global policy to integrate refugees into national education systems and the processes of vernacularization accompanying its widespread implementation. We use a comparative case study approach; our dataset comprises global policy documents and original interviews (n = 147) and observations in 14 refugee-hosting nation-states. We analyze how the purposes of refugee education are understood and acted upon by actors occupying diverse positions across these nation-states and over time. We demonstrate that the articulated purposes of refugee education are oriented toward possible futures for refugees, and they presuppose refugees' access to quality education, social belonging, and economic opportunities. Yet we find that across nation-states of exile, refugees' access to these resources is tenuous. Our findings suggest reconceptualizing refugee education to reflect how refugees are simultaneously embedded within multiple national contexts and to address the exclusions they face within each one. This study of refugee education has implications for understanding the purposes of education in other ever-more-common contexts of uncertainty, including the rapid economic and social changes brought about by migration, globalization, and technology. Empirically, understanding the purposes of refugee education is critical in a time of unprecedented forced migration.

Intraspecific variability in foraging behavior has been documented across a range of taxonomic groups, yet the energetic consequences of this variation are not well understood for many species. Understanding the effect of behavioral variation on energy expenditure and acquisition is particularly crucial for mammalian carnivores because they have high energy requirements that place considerable pressure on prey populations. To determine the influence of behavior on energy expenditure and balance, we combined simultaneous measurements of at-sea field metabolic rate (FMR) and foraging behavior in a marine carnivore that exhibits intraspecific behavioral variation, the California sea lion (Zalophus californianus). Sea lions exhibited variability in at-sea FMR, with some individuals expending energy at a maximum of twice the rate of others. This variation was in part attributable to differences in diving behavior that may have been reflective of diet; however, this was only true for sea lions using a foraging strategy consisting of epipelagic (

Large fluctuations in animal body mass in relation to life-history events can influence contaminant concentrations and toxicological risk. We quantified mercury concentrations in adult northern elephant seals (Mirounga angustirostris) before and after lengthy at sea foraging trips (n = 89) or fasting periods on land (n = 27), and showed that mercury concentrations in blood and muscle changed in response to these events. The highest blood mercury concentrations were observed after the breeding fast, whereas the highest muscle mercury concentrations were observed when seals returned to land to moult. Mean female blood mercury concentrations decreased by 30% across each of the two annual foraging trips, demonstrating a foraging-associated dilution of mercury concentrations as seals gained mass. Blood mercury concentrations increased by 103% and 24% across the breeding and moulting fasts, respectively, demonstrating a fasting-associated concentration of mercury as seals lost mass. In contrast to blood, mercury concentrations in female's muscle increased by 19% during the post-breeding foraging trip and did not change during the post-moulting foraging trip. While fasting, female muscle mercury concentrations increased 26% during breeding, but decreased 14% during moulting. Consequently, regardless of exposure, an animal's contaminant concentration can be markedly influenced by their annual life-history events.

Little is known about the foraging behavior of top predators in the deep mesopelagic ocean. Elephant seals dive to the deep biota-poor oxygen minimum zone (OMZ) (>800 m depth) despite high diving costs in terms of energy and time, but how they successfully forage in the OMZ remains largely unknown. Assessment of their feeding rate is the key to understanding their foraging behavior, but this has been challenging. Here, we assessed the feeding rate of 14 female northern elephant seals determined by jaw motion events (JME) and dive cycle time to examine how feeding rates varied with dive depth, particularly in the OMZ. We also obtained video footage from seal-mounted videos to understand their feeding in the OMZ. While the diel vertical migration pattern was apparent for most depths of the JME, some very deep dives, beyond the normal diel depth ranges, occurred episodically during daylight hours. The midmesopelagic zone was the main foraging zone for all seals. Larger seals tended to show smaller numbers of JME and lower feeding rates than smaller seals during migration, suggesting that larger seals tended to feed on larger prey to satisfy their metabolic needs. Larger seals also dived frequently to the deep OMZ, possibly because of a greater diving ability than smaller seals, suggesting their dependency on food in the deeper depth zones. Video observations showed that seals encountered the rarely reported ragfish (Icosteus aenigmaticus) in the depths of the OMZ, which failed to show an escape response from the seals, suggesting that low oxygen concentrations might reduce prey mobility. Less mobile prey in OMZ would enhance the efficiency of foraging in this zone, especially for large seals that can dive deeper and longer. We suggest that the OMZ plays an important role in structuring the mesopelagic ecosystem and for the survival and evolution of elephant seals.