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Reliable age estimation is an essential tool to assess the status of wildlife populations and inform successful management. Aging methods, however, are often limited by too few data, skewed demographic representation, and by single or uncertain morphometric relationships. In this study, we synthesize age estimates in southern sea otters Enhydra lutris nereis from 761 individuals across 34 years of study, using multiple noninvasive techniques and capturing all life stages from 0 to 17 years of age. From wild, stranded, and captive individuals, we describe tooth eruptions, tooth wear, body length, nose scarring, and pelage coloration across ontogeny and fit sex‐based growth functions to the data. Dental eruption schedules provided reliable and identifiable metrics spanning 0.3–9 months. Tooth wear was the most reliable predictor of age of individuals aged 1–15 years, which when combined with total length, explained >93% of observed age. Beyond age estimation, dental attrition also indicated the maximum lifespan of adult teeth is 13‒17 years, corresponding with previous estimates of life expectancy. Von Bertalanffy growth function model simulations of length at age gave consistent estimates of asymptotic lengths (male Loo = 126.0‒126.8 cm, female Loo = 115.3‒115.7 cm), biologically realistic gestation periods (t 0 = 115 days, SD = 10.2), and somatic growth (male k = 1.8, SD = 0.1; female k = 2.1, SD = 0.1). Though exploratory, we describe how field radiographic imaging of epiphyseal plate development or fusions may improve aging of immature sea otters. Together, our results highlight the value of integrating information from multiple and diverse datasets to help resolve conservation problems., By synthesizing more than two decades of southern sea otter physical examination data from strandings, captive‐rearing for release, and field studies, we provide strong support for adopting minimally invasive aging techniques based on metrics obtainable during brief field capture. These techniques provide the means to gather age‐specific information from a living, wild population to inform management decisions focused on restoring sea otters and their ecosystems throughout California. Our results also highlight the value of integrating information from multiple and diverse datasets to help resolve conservation problems.

Southern sea otters (Enhydra lutris nereis) rely on intact pelage for thermoregulation, and thus clinically significant demodicosis and associated alopecia can cause morbidity and death.This study aimed to describe lesions associated with follicular Demodex sp. infestation, estimate the prevalence and intensity of infestation, describe mite distribution across key anatomical regions, and assess mite presence or absence in relation to lesions and host risk factors.Twenty necropsied, wild southern sea otters that stranded along the central California coast from 2005 to 2018.Grossly normal and abnormal integument from the head, perineum, genitals, mamillary papillae and limbs was assessed microscopically for mites and mite-associated pathological findings.Intrafollicular mites were observed in the integument of 55% of otters and 20% had clinical demodicosis. Demodicosis was considered to be contributory to death or euthanasia in two cases. Although Demodex sp. mites often were observed microscopically in grossly normal skin, the presence of multiple densely-packed intrafollicular mites generally was associated with pigmentary incontinence, ectatic follicles, lymphoplasmacytic perifolliculitis, and neutrophilic and lymphoplasmacytic, dermal inflammation. Other findings included epidermal hyperplasia, orthokeratotic hyperkeratosis of epidermis and follicular epithelium, concurrent pyoderma and cell necrosis. Perioral integument, especially of the chin, had the highest prevalence of mites and the highest mite density, suggesting facial contact as a means of mite transmission.Our research confirmed demodectic mange as a contributor to morbidity and mortality in sea otters, with important implications for clinical care, rehabilitation and conservation.La loutre de mer de Californie (Enhydra lutris nereis) utilise son pelage intact pour sa thermorégulation et ainsi, une démodécie cliniquement significative et l’alopécie associée peuvent causer une morbidité et la mort. HYPOTHÈSES/OBJECTIFS: Cette étude a pour but de décrire les lésions associées à une infestation folliculaire de Demodex sp., estimer la prévalence et l’intensité de l’infestation, décrire la distribution des acariens à l’aide de régions anatomiques clés et déterminer la présence ou l’absence d’acariens et les facteurs de risque des hôtes.Vingt loutres de mer de Californie sauvages ont été autopsiées après s’être échouées le long de la côte californienne de 2005 à 2018. MATÉRIELS ET MÉTHODES: La peau macroscopiquement normale et anomale de la tête, du périnée, des zones génitales, des papilles mammaires et des membres a été évaluée microscopiquement pour les acariens et les lésions pathologiques liées aux acariens. RÉSULTATS: Les acariens intrafolliculaires ont été observés dans la peau de 55% des loutres et 20% avaient une démodécie clinique. La démodécie a été considérée comme contribuant à la mort ou à l’euthanasie dans deux cas. Bien que les acariens Demodex sp. soient souvent observées dans la peau macroscopiquement normale, la présence multiple d’acariens intrafolliculaires regroupés en amas denses était généralement associée avec de l’incontinence pigmentaire, des follicules ectatiques, une périfolliculite lymphoplasmocytaire et une inflammation dermique neutrophilique et lymphoplasmocytaire. Les autres données regroupent une hyperplasie épidermique, une hyperkératose orthokératosique de l’épiderme et de l’épithélium folliculaire, une pyodermite concomitante et une nécrose cellulaire. La peau péri-orale, en particulier le menton, avait la prévalence la plus élevée d’acariens et la densité en acarien la plus élevée suggérant un contact facial comme mode de transmission.Nos recherches confirment que la démodécie participe à la morbidité et à la mortalité des loutres de mer avec implications importantes pour les soins de cliniques, de réhabilitation et de conservation.INTRODUCCIÓN: las nutrias marinas del sur (Enhydra lutris nereis) dependen de un pelaje en buenas condiciones para la termorregulación y, por lo tanto, la demodicosis clínicamente significativa y la alopecia asociada pueden causar morbilidad y muerte. HIPÓTESIS/OBJETIVOS: Este estudio tuvo como objetivo describir las lesiones asociadas con la infestación folicular por Demodex sp., estimar la prevalencia e intensidad de la infestación, describir la distribución de ácaros en regiones anatómicas clave y evaluar la presencia o ausencia de ácaros en relación con las lesiones y los factores de riesgo del huésped. ANIMALES: Veinte nutrias marinas salvajes del sur necropsiadas que quedaron varadas a lo largo de la costa central de California entre 2005 y 2018. MÉTODOS Y MATERIALES: Se evaluó microscópicamente el tegumento macroscópicamente normal y anormal de la cabeza, el perineo, los genitales, las papilas mamilares y las extremidades para detectar ácaros y hallazgos patológicos asociados a los ácaros. RESULTADOS: Se observaron ácaros intrafoliculares en el tegumento del 55% de las nutrias y el 20% presentó demodicosis clínica. Se consideró que la demodicosis contribuyó a la muerte o la eutanasia en dos casos. Aunque ácaros de Demodex sp. a menudo se observaron microscópicamente en piel macroscópica normal, la presencia de múltiples ácaros intrafoliculares densamente empaquetados generalmente se asoció con incontinencia pigmentaria, folículos ectásicos, perifoliculitis linfoplasmocítica e inflamación dérmica neutrofílica y linfoplasmacítica. Otros hallazgos incluyeron hiperplasia epidérmica, hiperqueratosis ortoqueratósica de epidermis y epitelio folicular, pioderma concurrente y necrosis celular. El tegumento perioral, especialmente del mentón, tuvo la mayor prevalencia de ácaros y la mayor densidad de ácaros, lo que sugiere el contacto facial como medio de transmisión de ácaros. CONCLUSIONES E IMPORTANCIA CLÍNICA: Nuestra investigación confirmó que la sarna demodécica contribuye a la morbilidad y mortalidad en las nutrias marinas, con importantes implicaciones para la atención clínica, la rehabilitación y la conservación.Der Seeotter des Südpazifiks (Enhydra lutris nereis) benötigt zur Thermoregulierung zwingend ein intaktes Haarkleid und daher kann eine klinisch signifikante Demodikose und eine damit einhergehende Alopezie Erkrankung und Tod verursachen.Diese Studie zielte darauf ab, Veränderungen, die mit einer follikulären Demodex sp. Infektion einhergehen, zu beschreiben, die Prävalenz und die Intensität des Befalls abzuschätzen, die Milbenverteilung an den anatomischen Schlüsselregionen zu beschreiben, und die Milbenpräsenz oder deren Fehlen in Relation zu den Veränderungen und den Risikofaktoren des Wirtes zu beurteilen.Es wurden zwanzig wilde südliche Seeotter, die entlang der Küste Zentralkaliforniens zwischen 2005 und 2018 gestrandet waren, autopsiert.Makroskopisch normale und abnormale Haut von Kopf, Perineum, den Genitalien, der Brustwarzen und der Extremitäten wurden mikroskopisch auf Milben und auf pathologische Befunde im Zusammenhang mit Milben untersucht.Es wurden intrafollikuläre Milben in der Haut von 55% der Otter gefunden, wobei 20% von ihnen eine klinische Demodikose aufwiesen. Die Demodikose wurde als ursächlich für den Tod und die Euthanasie in zwei Fällen angesehen. Obwohl Demodex sp. Milben oft mikroskopisch in mit freiem Auge normaler Haut gefunden wurden, wurde das Vorkommen von multiplen dicht gepackten intrafollikulären Milben generell mit Pigmentinkontinenz, ektatischen Follikeln, lymphoplasmazytischer Perifollikulitis, und neutrophiler und lymphoplasmazytischer, dermaler Entzündung gesehen. Die Haut rundum den Mund, vor allem am Kinn, zeigte die höchste Prävalenz von Milben und die höchste Milbendichte, was auf einen Gesichtskontakt als Übertragungsweg für die Milben hinweist.Unsere Forschung bestätigte die Demodexmilbe als Beitragende zur Morbidität und Mortalität der Seeotter, was wichtige Implikationen für ihre klinische Versorgung, Rehabilitation und Erhaltung darstellt.背景: 南方ラッコ (Enhydra lutris nereis)の体温調節は無傷の毛に依存するため、臨床的に著しいニキビダニ症およびそれに伴う脱毛症は、病的疾患や死亡の原因となることがある。 仮説/目的: 本研究の目的は、毛包寄生性ニキビダニ属に関連する病変の記述、寄生の有病率および強度の推定、主要な解剖学的領域におけるダニの分布の記述、病変および宿主の危険因子との関連におけるダニの有無を評価することであった。 被験動物: 2005年から2018年までカリフォルニア中央海岸で座礁した野生の南方ラッコ20頭を剖検した。 材料と方法: 頭部、会陰部、生殖器、乳頭および四肢の総じて正常または異常な皮膚を顕微鏡的に評価し、ダニおよびダニに関連した病理学的所見を調査した。 結果: ラッコの55%の皮膚には毛包内にダニが観察され、20%には臨床的にニキビダニ症が認められた。そのうち2例は死亡または安楽死の原因と考えられた。正常な皮膚においてしばしばニキビダニが顕微鏡下で観察されたが、毛包内に密に詰まった複数のダニの存在は、一般的に色素脱、拡張性毛包、リンパ球形質細胞性毛包周囲炎、好中球性およびリンパ球形質細胞性の真皮の炎症と関連していた。その他の所見としては、表皮過形成、表皮および毛包漏斗部の正角化性角化亢進、膿皮症および細胞壊死を併発していた。口周囲の皮膚、特に顎部でダニの有病率が最も高く、ダニ密度も最も高かったことから、顔面接触がダニの感染手段であることが示唆された。 結論と臨床上の重要性: 本研究は、ラッコの罹患率および死亡率の一因であるニキビダニを確認し、臨床ケア、リハビリテーション、管理に重要な意味を持つことを示した。.背景: 方海獭依赖于被毛完整来进行体温调节, 因此具有临床意义的蠕形螨病和造成的脱毛可导致其发病和死亡。 假设/目的: 本研究旨在描述毛囊蠕形螨侵染造成的病变, 评估侵染的流行率和严重程度, 描述关键解剖区域的螨虫分布, 并评估是否存在造成病变的螨虫, 以及宿主风险因素。 动物: 2005年至2018年, 在加利福尼亚中部海岸搁浅并进行尸检的20只野生南方海獭。 方法和材料: 采自外观正常和异常的头部、会阴、生殖器、乳头和四肢皮肤, 评估显微镜下螨虫及螨虫相关的病理学结果。 结果: 在55%的水獭皮肤中观察到毛囊内螨虫, 20%患有临床蠕形螨病。在2个病例中, 蠕形螨病导致了死亡或因此而人道处死。尽管在外观正常的皮肤中, 通过显微镜经常能观察到蠕形螨虫体, 多处毛囊内出现的密集螨虫, 通常造成色素失禁、毛囊扩张、淋巴浆细胞性毛囊周炎以及中性粒细胞和淋巴浆细胞性真皮炎症。其他结果包括表皮增生、表皮和毛囊上皮的正角化性过度角化、并发脓皮病和细胞坏死。口周皮肤, 尤其是颏部, 螨虫侵染率最高, 螨虫密度最高, 这提示面部接触是螨虫传播的一种途径。 结论和临床重要性: 我们的研究证实蠕形螨是海獭发病和死亡的因素, 临床护理、康复和保护具有重要意义。.As lontras do mar do Sul (Enhydra lutris nereis) dependem da pelagem intacta para termorregulação e, portanto, demodiciose clinicamente significativa e alopecia associada podem causar morbidade e morte. HIPÓTESE/OBJETIVOS: Este estudo teve como objetivo descrever lesões associadas à infestação folicular por Demodex sp., estimar a prevalência e intensidade da infestação, descrever a distribuição de ácaros nas principais regiões anatômicas e avaliar a presença ou ausência de ácaros em relação a lesões e fatores de risco do hospedeiro.Vinte lontras do mar do Sul selvangens necropsiadas que ficaram presas ao longo da costa central da Califórnia de 2005 a 2018. MÉTODOS E MATERIAIS: Tegumento grosseiramente normal e anormal da cabeça, períneo, genitais, papilas mamilares e membros foram avaliados microscopicamente para pesquisa de ácaros ácaros e achados patológicos associados aos ácaros.Observou-se ácaros intrafoliculares no tegumento de 55% das lontras e 20% apresentaram demodiciose clínica. A demodiciose foi considerada como contribuinte para a morte ou eutanásia em dois casos. Embora os ácaros Demodex sp. tenham sido frequentemente observados microscopicamente na pele grosseiramente normal, a presença de múltiplos ácaros intrafoliculares densamente compactados geralmente estava associada a incontinência pigmentar, folículos ectáticos, perifoliculite linfoplasmocitária e inflamação dérmica neutrofílica e linfoplasmocitária. Outros achados incluíram hiperplasia epidérmica, hiperceratose ortoqueratótica da epiderme e epitélio folicular, pioderma concomitante e necrose celular. O tegumento perioral, principalmente do mento, apresentou a maior prevalência de ácaros e a maior densidade de ácaros, sugerindo o contato facial como meio de transmissão dos ácaros. CONCLUSÕES E IMPORTÂNCIA CLÍNICA: Nossa pesquisa confirmou a sarna demodécica como contribuinte para a morbidade e mortalidade em lontras marinhas, com implicações importantes para o atendimento clínico, reabilitação e conservação.

The sea otter (Enhydra lutris) is a marine mammal hunted to near extinction during the 1800s. Despite their well‐known modern importance as a keystone species, we know little about historical sea otter ecology. Here, we characterize the ecological niche of ancient southern sea otters (E. lutris nereis) using δ13C analysis and δ15N analysis of bones recovered from archaeological sites spanning ~7,000 to 350 years before present (N = 112 individuals) at five regions along the coast of California. These data are compared with previously published data on modern animals (N = 165) and potential modern prey items. In addition, we analyze the δ15N of individual amino acids for 23 individuals to test for differences in sea otter trophic ecology through time. After correcting for tissue‐specific and temporal isotopic effects, we employ nonparametric statistics and Bayesian niche models to quantify differences among ancient and modern animals. We find ancient otters occupied a larger isotopic niche than nearly all modern localities; likely reflecting broader habitat and prey use in prefur trade populations. In addition, ancient sea otters at the most southerly sites occupied an isotopic niche that was more than twice as large as ancient otters from northerly regions. This likely reflects greater invertebrate prey diversity in southern California relative to northern California. Thus, we suggest the potential dietary niche of sea otters in southern California could be larger than in central and northern California. At two sites, Año Nuevo and Monterey Bay, ancient otters had significantly higher δ15N values than modern populations. Amino acid δ15N data indicated this resulted from shifting baseline isotope values, rather than a change in sea otter trophic ecology. Our results help in better understanding the contemporary ecological role of sea otters and exemplify the strength of combing zooarchaeological and biological information to provide baseline data for conservation efforts., We measured the dietary niche of modern and ancient Southern sea otters in California using stable isotope analysis. We find the size of the realized niche in southern California has decreased over time. These results should be considered for effective management and conservation efforts of this threatened species.

Despite its recent invasion into the marine realm, the sea otter (Enhydra lutris) has evolved a suite of adaptations for life in cold coastal waters, including limb modifications and dense insulating fur. This uniquely dense coat led to the near-extinction of sea otters during the 18th–20th century fur trade and an extreme population bottleneck. We used the de novo genome of the southern sea otter (E. l. nereis) to reconstruct its evolutionary history, identify genes influencing aquatic adaptation, and detect signals of population bottlenecks. We compared the genome of the southern sea otter with the tropical freshwater-living giant otter (Pteronura brasiliensis) to assess common and divergent genomic trends between otter species, and with the closely related northern sea otter (E. l. kenyoni) to uncover population-level trends. We found signals of positive selection in genes related to aquatic adaptations, particularly limb development and polygenic selection on genes related to hair follicle development. We found extensive pseudogenization of olfactory receptor genes in both the sea otter and giant otter lineages, consistent with patterns of sensory gene loss in other aquatic mammals. At the population level, the southern sea otter and the northern sea otter showed extremely low genomic diversity, signals of recent inbreeding, and demographic histories marked by population declines. These declines may predate the fur trade and appear to have resulted in an increase in putatively deleterious variants that could impact the future recovery of the sea otter.

Sea otters (Enhydra lutris) have the highest mass-specific metabolic rate of any marine mammal, which is superimposed on the inherently high costs of reproduction and lactation in adult females. These combined energetic demands have been implicated in the poor body condition and increased mortality of female sea otters nearing the end of lactation along the central California coast. However, the cost of lactation is unknown and currently cannot be directly measured for this marine species in the wild. Here, we quantified the energetic demands of immature sea otters across five developmental stages as a means of assessing the underlying energetic challenges associated with pup rearing that may contribute to poor maternal condition. Activity-specific metabolic rates, daily activity budgets and field metabolic rates (FMR) were determined for each developmental stage. Mean FMR of pre-molt pups was 2.29±0.81 MJ day−1 and increased to 6.16±2.46 and 7.41±3.17 MJ day−1 in post-molt pups and dependent immature animals, respectively. Consequently, daily energy demands of adult females increase 17% by 3 weeks postpartum and continue increasing to 96% above pre-pregnancy levels by the average age of weaning. Our results suggest that the energetics of pup rearing superimposed on small body size, marine living and limited on-board energetic reserves conspire to make female sea otters exceptionally vulnerable to energetic shortfalls. By controlling individual fitness, maternal behavior and pup provisioning strategies, this underlying metabolic challenge appears to be a major factor influencing current population trends in southern sea otters (Enhydra lutris nereis).

The existence of individual prey specializations has been reported for an ever-growing number of taxa, and has important ramifications for our understanding of predator–prey dynamics. We use the California sea otter population as a case study to validate the use of archival time–depth data to detect and measure differences in foraging behaviour and diet. We collected observational foraging data from radio-tagged sea otters that had been equipped with Mk9 time depth recorders (TDRs, Wildlife Computers, Redmond, WA). After recapturing the study animals and retrieving the TDRs it was possible to compare the two data types, by matching individual dives from the TDR record with observational data and thus examining behavioural correlates of capture success and prey species. Individuals varied with respect to prey selection, aggregating into one of three distinct dietary specializations. A number of TDR-derived parameters, particularly dive depth and post-dive surface interval, differed predictably between specialist types. A combination of six dive parameters was particularly useful for discriminating between specialist types, and when incorporated into a multivariate cluster analysis, these six parameters resulted in classification of 13 adult female sea otters into three clusters that corresponded almost perfectly to the diet-based classification (1 out of 13 animals was misclassified). Thus based solely on quantifiable traits of time–depth data that have been collected over an appropriate period (in this case 1 year per animal), it was possible to assign female sea otters to diet type with >90% accuracy. TDR data can thus be used as a tool to measure the degree of individual specialization in sea otter populations, a conclusion that will likely apply to other diving marine vertebrates as well. Our ultimate goals must be both to understand the causes of individual specialization, and to incorporate such variation into models of population- and community-level food web dynamics.

Summary 1 Growth models for body mass and length were fitted to data collected from 1842 sea otters Enhydra lutris shot or live-captured throughout south-west Alaska between 1967 and 2004. Growth curves were constructed for each of two main year groups: 1967–71 when the population was at or near carrying capacity and 1992–97 when the population was in steep decline. Analyses of data collected from animals caught during 2004, when the population density was very low, were precluded by a small sample size and consequently only examined incidentally to the main growth curves. 2 Growth curves demonstrated a significant increase in body mass and body length at age in the 1990s. Asymptotic values of body mass were 12–18% higher in the 1990s than in the 1960s/70s, and asymptotic values for body length were 10–11% higher between the same periods. Data collected in 2004 suggest a continued increase in body size, with nearly all data points for mass and length falling significantly above the 1990s growth curves. 3 In addition to larger asymptotic values for mass and length, the rate of growth towards asymptotic values was more rapid in the 1990s than in the 1960s/70s: sea otters reached 95% of asymptotic body mass and body length 1–2 years earlier in the 1990s. 4 Body condition (as measured by the log mass/log length ratio) was significantly greater in males than in females. There was also an increasing trend from the 1960s/70s through 2004 despite much year-to-year variation. 5 Population age structures differed significantly between the 1960s/70s and the 1990s with the latter distribution skewed toward younger age classes (indicating an altered lx function) suggesting almost complete relaxation of age-dependent mortality patterns (i.e. those typical of food-limited populations). 6 This study spanned a period of time over which the population status of sea otters in the Aleutian archipelago declined precipitously from levels at or near equilibrium densities at some islands in the 1960s/70s to

Recently published data demonstrated a sea otter population collapse across theAleutian archipelago (Doroff et al. 2003). This assessment, undertaken in responseto earlier reports of precipitous declines at several islands (Estes et al. 1998), wasbased on archipelago-wide aerial surveys conducted in 1965, 1992, and 2000, andskiff surveys of particular islands or small island groups during various years fromthe early 1990s through 2000. To summarize the main findings: (1) aerial countsdeclined by about 70% from 1992 to 2000, (2) populations at those islandsthought by Kenyon (1969) to be at or near carrying capacity in 1965 had declined88% by 2000, (3) most of the overall decline occurred after the late 1980s or early1990s, and (4) sea otters had reached a uniformly low population density (numbersper unit length of shoreline) throughout the Aleutian archipelago by 2000. Doroffet al. (2003) interpreted this latter finding to mean that the factors responsible forthe decline were density-dependent, thus implying that a steady state may havebeen attained between killer whale predation, the purported cause of the decline(Estes et al. 1998), and the reduced availability of sea otters. If that conjecture is

Summary 1. Longitudinal records of prey selection by 10 adult female sea otters on the Monterey Peninsula, California, from 1983 to 1990 demonstrate extreme inter-individual variation in diet. Variation in prey availability cannot explain these differences as the data were obtained from a common spatial-temporal area. 2. Individual dietary patterns persisted throughout our study, thus indicating that they are life-long characteristics. 3. Individual dietary patterns in sea otters appear to be transmitted along matrilines, probably by way of learning during the period of mother‐young association. 4. Efficient utilization of different prey types probably requires radically different sensory/motor skills, each of which is difficult to acquire and all of which may exceed the learning and performance capacities of any single individual. This would explain the absence of generalists and inertia against switching, but not the existence of alternative specialists. 5. Such individual variation might arise in a constant environment from frequencydependent effects, whereby the relative benefit of a given prey specialization depends on the number of other individuals utilizing that prey. Additionally, many of the sea otter’s prey fluctuate substantially in abundance through time. This temporal variation, in conjunction with matrilineal transmission of foraging skills, may act to mediate the temporal dynamics of prey specializations. 6. Regardless of the exact cause, such extreme individual variation in diet has broad ramifications for population and community ecology. 7. The published literature indicates that similar patterns occur in many other species.

After nearly a century of recovery from overhunting, sea otter populations are in abrupt decline over large areas of western Alaska. Increased killer whale predation is the likely cause of these declines. Elevated sea urchin density and the consequent deforestation of kelp beds in the nearshore community demonstrate that the otter's keystone role has been reduced or eliminated. This chain of interactions was probably initiated by anthropogenic changes in the offshore oceanic ecosystem.

1. Growth models for body mass and length were fitted to data collected from 1842 sea otters Enhydra lutris shot or live-captured throughout south-west Alaska between 1967 and 2004. Growth curves were constructed for each of two main year groups: 1967-71 when the population was at or near carrying capacity and 1992-97 when the population was in steep decline. Analyses of data collected from animals caught during 2004, when the population density was very low, were precluded by a small sample size and consequently only examined incidentally to the main growth curves. 2. Growth curves demonstrated a significant increase in body mass and body length at age in the 1990s. Asymptotic values of body mass were 12-18% higher in the 1990s than in the 1960s/70s, and asymptotic values for body length were 10-11% higher between the same periods. Data collected in 2004 suggest a continued increase in body size, with nearly all data points for mass and length falling significantly above the 1990s growth curves. 3. In addition to larger asymptotic values for mass and length, the rate of growth towards asymptotic values was more rapid in the 1990s than in the 1960s/70s: sea otters reached 95% of asymptotic body mass and body length 1-2 years earlier in the 1990s. 4. Body condition (as measured by the log mass/log length ratio) was significantly greater in males than in females. There was also an increasing trend from the 1960s/70s through 2004 despite much year-to-year variation. 5. Population age structures differed significantly between the 1960s/70s and the 1990s with the latter distribution skewed toward younger age classes (indicating an altered lx function) suggesting almost complete relaxation of age-dependent mortality patterns (i.e. those typical of food-limited populations). 6. This study spanned a period of time over which the population status of sea otters in the Aleutian archipelago declined precipitously from levels at or near equilibrium densities at some islands in the 1960s/70s to5% of estimated carrying capacity by the late 1990s. The results of this study indicate an improved overall health of sea otters over the period of decline and suggest that limited nutritional resources were not the cause of the observed reduced population abundance. Our findings are consistent with the hypothesis that the decline was caused by increased killer whale predation.

The defect microstructure of NiO scales, formed by oxidation of pure Ni substrates at 1275 K in 3 kPa p(O2) for times between 5 s and 25 h, has been studied by transmission electron microscopy (TEM) of sections cut and thinned parallel and transverse to the NiO/Ni interface. It has proven possible in both sectioning techniques to preserve portions of the Ni substrate, so that the NiO/Ni interface itself could be studied. The NiO/oxygen interface was additionally retained in transverse sections by electroplating a Ni layer onto the NiO scale surface before sectioning and thinning by argon ion bombardment. The microstructure of scales invariably comprises a submicron layer of fine-grained NiO topotactically related to the substrate in several orientation relationships and overlaid by thick columnar-grained oxide resulting from subsequent renucleation and competitive growth. Enhanced oxidation is observed at the emergence of NiO grain boundaries at the scale surface. Interface structure is observed ...

In the study of oxidation, the microstructure and microchemistry of oxide scales can readily be examined via transverse sections. This necessitates the preparation of transversely sectioned specimens that possess electron transparent oxide scales. Another method for transverse sectioning of oxidized nickel has been previously reported, These specimens were produced from techniques similar to those of Tuck, Sheng and Marcus and Katz and Evans. In this method, two oxidized metal strips are placed adjacent to each other and the strips encased within an epoxy-resin setting. The specimens are then transversely sectioned and ion-beam thinned. Unfortunately, this technique results in inadequate success rates, mostly because of the relatively fast ion-thinning of the epoxy resin.

There is considerable technological interest in oxidation of nickel because of the importance of nickel-base superalloys in high-temperature oxidizing environments. NiO scales on nickel grow classically, by outward diffusion of nickel through the scale, and are among the most studied of oxidation systems. We report here the first extensive characterization by transmission electron microscopy of nickel oxide scales formed on bulk nickel substrates and sectioned both parallel and transversely to the Ni/NiO interface.Electrochemically-polished nickel sheet of 99.995% purity was oxidized at 1273 K in 0.1 MPa oxygen partial pressure for times between 5 s and 25 h. Parallel sections were produced using a combination of electropolishing of the nickel substrate and ion-beam thinning of the scale to any desired depth in the scale. Transverse sections were prepared by encasing stacked strips of oxidized nickel sheet in epoxy resin, sectioning transversely and ion-beam thinning until thin area spanning one or more interfaces was obtained.