Sea Otters Research Articles

Recent surveys of the sea otter (Enhydra lutris) population on Kuril Islands

Context Sea otters, an endangered species, require regular assessments of their distribution and abundance. These animals inhabit the coastal waters of the North Pacific, traversing from Japan through the Kurils, southern Kamchatka, Commander and Aleutian Islands, and the coasts of North America, to California. Although populations in America and the Commander Islands have been consistently monitored over recent decades, the same cannot be said for the Kuril Islands. Aim This study aims to estimate the state of sea otter populations on the Kuril Islands. Methods The study area encompassed a section of the Kuril archipelago, including Iturup, Urup, Broughton, Chirpoy, and Simushir Islands, surveyed from 2019 to 2023. Sea otters were counted along sections of the coastline, and published sources on other Kuril Islands were analysed. Key results There are several hundred sea otters within surveyed area, whereas in 1960–1980 ~2000 were reported. The total number of sea otters on the archipelago hardly exceeds 3000. The initial or normal number is not known, but the information on hunting indicates that it was much bigger. Up to the end of 19th century, at least ‘one thousand individuals’ had been harvested annually over several decades; this means that the total number was at least several tens of thousands. Conclusions Sea otter populations on the Kuril Islands are in decline, with poaching in the recent past identified as significant contributing factor in a part of the archipelago. Implications Urgent conservation measures are imperative to address the decline of sea otter populations.

A novel comparison of southern sea otter (Enhydra lutris nereis) fur buoyancy across ontogeny.

Sea otters are extremely positively buoyant and spend most of their time resting at the water surface. It is understood that some of this buoyancy comes from the air layer that sea otters maintain in their pelage, with the lungs providing an additional source of positive buoyancy. Past studies have investigated the fur buoyant force in adult sea otters; however, little is known about the fur buoyant force in younger age classes. This study compared ontogenetic changes in the fur buoyant force of southern sea otter (Enhydra lutris nereis) pelage. We measured the fur buoyant force of pelt samples, scaled that to the whole animal, and calculated mass-specific fur buoyant force for six age classes: neonates (<1 month), small pups (1-2 months), large pups (3-5 months), juveniles (6months-1 year), subadults (1-3 years) and adults (4-9 years). Each pelt sample was measured under three conditions: control, oiled and washed with Dawn® dish soap. Oiled and washed pelts had a lower fur buoyant force compared with the control pelts across all age classes. When oiled, the air layer of the pelt is ruined and no longer provides sufficient positive buoyancy. Pelts washed with Dawn® had higher variability in buoyant force compared with other conditions, and the air layer was not restored consistently. When we scaled up, we found that younger age classes were more buoyant because of their larger surface area to volume ratio. These differences in buoyancy may underlie variations in energetic costs and behavior among sea otters across development.

Crude oil destroys sea otter buoyancy

Crude oil destroys sea otter buoyancy

Novel Sea Otter Optimization Algorithm for WSN Coverage Intelligence Optimization

Novel Sea Otter Optimization Algorithm for WSN Coverage Intelligence Optimization

Foraging ecology of southern sea otters at the northern range extent informs regional population dynamics

Sea otters Enhydra lutris are vital keystone predators throughout the North Pacific that were nearly extirpated during the maritime fur trade. Recovery of southern sea otters E. l. nereis has proceeded slowly, with much of their historical range remaining unoccupied, resulting in reduced ecosystem functioning. Numerous studies have used foraging metrics to assess the population status of southern sea otters throughout their current range, but little is known about the northern range extent, where a stall in expansion has limited recovery. Thus, we collected census and foraging data of sea otters at Año Nuevo State Park, California, from 2019 to 2021 to determine sea otter abundance, diet composition, diet diversity, and average energy intake rate at the northern range edge. We then assessed regional population status by comparing values from Año Nuevo with previously collected data from other locations in California, including high-density, range center sites and low-density, range periphery sites. We found that sea otter density at Año Nuevo was greater than surrounding areas at the northern range periphery, and the average (±95% CI) energy intake (9.51 ± 0.91 kcal min-1) more closely resembled values observed at high-density sites. Further, dietary diversity (using the Shannon-Wiener index, H) was intermediate between previously studied high- and low-density populations (H = 1.81), with crabs making up the largest proportion of the diet (~56%). Overall, this study highlights possible effects of occupation time and range stagnation, identifies unique aspects of the prey resource base at Año Nuevo, and provides insight into the ongoing lack of northern range expansion.

Articulating the Pacific Economy: Chinese Mercury, American Silver, and Californian Sea Otters

Articulating the Pacific Economy: Chinese Mercury, American Silver, and Californian Sea Otters

From Individual Calcifiers to Ecosystem Dynamics: Ocean Acidification Effects on Urchins and Abalone.

A central question in ecology is to what extent do trophic interactions govern the structure and function of communities? This question is becoming more pressing as trophic interactions shift with rapid climate change. Sea urchins and abalone are key invertebrates in the habitats where they reside. Sea urchins are critical members of exemplar trophic cascades in kelp forests due to their impact on kelp establishment and maintenance; yet their populations are controlled by predators, such as sea otters and sunflower sea stars. Abalone compete with urchins for macroalgal food resources and therefore can help regulate urchin populations in kelp forests. Given that both urchin tests and abalone shells used for predator defense are comprised of calcium carbonate, much research has been conducted on the impacts of ocean acidification (OA) on these calcified structures. A growing body of literature has shown that urchin tests are less calcified and break with less force under OA conditions. Less is known about abalone, but their shells also appear to respond negatively to OA. Using kelp forest communities as exemplar ecosystems, we discuss the morphological, biomechanical, and physiological responses to OA in urchins and abalone and consider how these individual level responses scale to trophic interactions and ultimately whole ecosystem processes. Although the impacts of OA on the calcified structures used for defense have been well studied, calcified mechanisms for food consumption, such as the Aristotle's lantern of urchins, are much less understood. Thus, examining both the feeding and defense sides of trophic interactions would greatly improve our understanding of OA responses across individual to ecosystem scales. More generally, measurements of morphological, biomechanical, and physiological responses to OA can be made in individuals to help predict higher level ecological responses, which would greatly contribute to broader predictions of whole ecosystem responses to OA.

Biological and Conservation Aspects of Otter Mortality: A Review

The post mortem exam is important in diagnosing and investigating wildlife diseases. It is even more important to monitor the population of species that are not easily observed in the wild, such as otters. Of the 13 otter species, 11 are endangered due to many factors, such as climate change, pollution, or urbanisation. The authors present a review of the patterns of mortality of free-ranging otters worldwide, aiming to improve the knowledge of otter mortality and the role of mortality studies in their conservation. The main cause of death in aquatic otters is vehicle collision; hence, sea otter deaths are associated with shark attacks and imprisonment in fishing gear. It is possible to conclude that humans and human activity play a significant role in the mortality of these animals. In the future, a more standardised analysis of otter carcasses is necessary to understand their threats and diseases and design significant measures to protect these species.

THE MANAGEMENT OF LYMPHOPROLIFERATIVE NEOPLASIA IN FOUR NORTHERN SEA OTTERS (ENHYDRA LUTRIS KENYONI).

Lymphoproliferative neoplasia has been reported in both free-ranging sea otters and those in managed care, but little information is available on the management of this neoplastic disease in this species. This case series describes clinical lymphoma in four northern sea otters (Enhydra lutris kenyoni) in managed care. Two otters presented with Stage 5 lymphoma with evidence of hematologic spread resulting in leukemia. Two additional otters presented with Stage 3 disease. Immunophenotypes in these cases included disseminated large B-cell lymphoma and lymphoblastic lymphoma of potential T-cell origin. Cases were managed with multiagent chemotherapy protocols including prednisone, L-asparaginase, cyclophosphamide, vincristine, cytosine arabinoside, lomustine, and doxorubicin. Unique approaches included the use of a vascular access port in one case and development of an autologous vaccine in another. Survival time ranged from 81 to 409 days. Diagnosis, staging, and treatment with multiagent protocols is recommended for the management of lymphoma in sea otters.

Tool use increases mechanical foraging success and tooth health in southern sea otters (Enhydra lutris nereis).

Although tool use may enhance resource utilization, its fitness benefits are difficult to measure. By examining longitudinal data from 196 radio-tagged southern sea otters (Enhydra lutris nereis), we found that tool-using individuals, particularly females, gained access to larger and/or harder-shelled prey. These mechanical advantages translated to reduced tooth damage during food processing. We also found that tool use diminishes trade-offs between access to different prey, tooth condition, and energy intake, all of which are dependent on the relative prey availability in the environment. Tool use allowed individuals to maintain energetic requirements through the processing of alternative prey that are typically inaccessible with biting alone, suggesting that this behavior is a necessity for the survival of some otters in environments where preferred prey are depleted.

Tool use promotes dental health.

Using tools increases foraging success in sea otters and protects their teeth from damage.

Red Blood Cell Hemoglobin Oxygen Transfer in Deep-Diving Marine Mammals

Objective: Some marine mammals of the order pinniped and cetacean can dive for long durations to forage for food and travel over distances. During these extended dives both pinnipeds and cetaceans experience extreme tissue hypoxia. Numerous adaptations have evolved to allow these species to effciently deliver and utilize oxygen (O2). One genetic difference, which our laboratory has proposed to play an important role in O2 transport effciency in modern hominids, is the inactivation of the CMP-Neu5AC hydroxylase (CMAH) gene. Pinnipeds inactivated Cmah ~ 40 million years ago but, cetaceans still express this N-glycan modifying enzyme. CMAH converts the sialic acid, N-acetylneuraminic acid (Neu5Ac), to its hydroxylated form, N-glycolylneuraminic acid (Neu5Gc). These sialic acids are located at the end of branched sugar chains on the surface of cell membranes. As a result, a change in composition could affect cell membrane charge and hydrophobicity, as well as potentially alter O2 diffusion laterally or across cell membranes. Hypothesis: In this study we hypothesized that O2 transfer from hemoglobin (Hb) in red blood cells (RBCs) to myoglobin (Mb) would differ between cetaceans (CMAH+) and pinnipeds (CMAH-). Methods: This hypothesis was tested using optical absorption spectroscopy to measure O2 exchange between oxygenated Hb in RBC and deoxygenated Mb collected in several species of mustelids and pinniped (CA sea otter, CA sea lion, and walrus) and cetaceans (Bottlenose Dolphin, Beluga, and Orca). Measurements of cell diameters (diffusion length) were also measured. Results: The mean oxygen transfer (O2D/A410) was 47% lower in pinnipeds than cetaceans (p&lt;0.01). The amount of O2 transferred in cetaceans increased with longer reported maximal dive durations. There was a trend for overall RBC diameters to be larger in cetaceans than pinnipeds (p=0.054). Summary: The RBC O2 transfer data in these hypoxia tolerant marine mammals suggest a transfer mechanism that is more effcient in cetaceans in a normoxic environment. Conclusions: More effcient oxygen transfer in cetaceans, who retained the Cmah gene, compared to pinnipeds and mustelids, who did not retain the Cmah gene, suggests that the gene knockout may not be the only factor that facilitates delivery of O2 in these marine mammals. A trend for larger RBC diameters in cetaceans than pinnipeds also suggests that diffusion length is not a main contributing factor. Future experiments to measure oxygen transfer from RBC O2-Hb to Mb under different O2 environments are needed to more closely model what may occur during long duration dives. NSF1929325. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Local and regional variation in kelp loss and stability across coastal British Columbia

Kelp forests are among the most abundant coastal marine habitats but are vulnerable to climate change. The Northeast Pacific has experienced recent large-scale changes in kelp abundance and distribution, but little is known about changes north of the British Columbia (BC)-Washington border. Here, we assessed whether and how floating canopy kelp (Macrocystis pyrifera, Nereocystis luetkeana) distributions have changed in recent decades along the extensive coast of BC. We assembled and analysed available kelp distributional data, comparing snapshots of kelp linear extent from 1.5-3 decades ago (1994-2007) to recently collected data (2017-2021) across 11 different subregions spanning the province. We then leveraged timeseries, where available (n = 7 data sets), to contextualise patterns of change. In aggregate, the data suggest that kelp forests have declined considerably in some parts of the province, but with variable patterns of change across BC. In the warmest areas (southern BC), kelp persistence was negatively correlated with mean summer sea surface temperatures, which at times exceeded known thermal tolerances. In contrast, in northern subregions, top-down control by sea urchins and otters appeared to modulate kelp dynamics, with declines occurring in 2 subregions despite cool ocean temperatures. Timeseries data suggest that many declines occurred around the 2014-2016 marine heatwave, an event associated with sustained warming and altered trophic dynamics. Our results suggest that the extent of BC’s kelp forests has declined in some places in recent decades, but that regional and local-scale factors influence their responses to environmental change.

The origin, connectivity, and individual specialization of island wolves after deer extirpation.

Wolves are assumed to be ungulate obligates, however, a recently described pack on Pleasant Island, Alaska USA, is persisting on sea otters and other marine resources without ungulate prey, violating this long-held assumption. We address questions about these wolves regarding their origin and fate, degree of isolation, risk of inbreeding depression, and diet specialization by individual and sex. We applied DNA metabarcoding and genotyping by amplicon sequencing using 957 scats collected from 2016 to 2022, and reduced representation sequencing of tissue samples to establish a detailed understanding of Pleasant Island wolf ecology and compare them with adjacent mainland wolves. Dietary overlap was higher among individual wolves on Pleasant Island (Pianka's index mean 0.95 ± 0.03) compared to mainland wolves (0.70 ± 0.21). The individual diets of island wolves were dominated by sea otter, ranging from 40.6% to 63.2% weighted percent of occurrence (wPOO) (mean 55.5 ± 8.7). In contrast, individual mainland wolves primarily fed on ungulates (42.2 ± 21.3) or voles during a population outbreak (31.2 ± 23.2). We traced the origin of the Pleasant Island pack to a mainland pair that colonized around 2013 and produced several litters. After this breeding pair was killed, their female offspring and an immigrant male became the new breeders in 2019. We detected 20 individuals of which 8 (40%) were trapped and killed while two died of natural causes during the 6-year study. Except for the new breeding male, the pedigree analysis and genotype results showed no additional movement to or from the island, indicating limited dispersal but no evidence of inbreeding. Our findings suggest wolves exhibit more flexible foraging behavior than previously believed, and hunting strategies can substantially differ between individuals within or between packs. Nevertheless, anthropogenic and natural mortality combined with limited connectivity to the mainland may inhibit the continued persistence of Pleasant Island wolves.

Sea Otters’ Appetite for Crab Is Helping Strengthen Estuary Banks

Apex predators can have a powerful impact on coastal erosion rates by keeping grazer populations down, but their influence has been largely overlooked.

Species distribution modeling of northern sea otters (Enhydra lutris kenyoni) in a data-limited ecosystem.

Species distribution models (SDMs) are used to map and predict the geographic distributions of animals based on environmental covariates. Typically, SDMs require high-resolution habitat data and time series information on animal locations. For data-limited regions, defined as having scarce habitat or animal survey data, modeling is more challenging, often failing to incorporate important environmental attributes. For example, for sea otters (Enhydra lutris), a federally protected keystone species with variable population trends across the species' range, predictive modeling of distributions has been successfully conducted in areas with robust sea otter population and habitat data. We used open-access data and employed a presence-only model, maximum entropy (MaxEnt), to investigate subtidal habitat associations (substrate and algal cover, bathymetry, and rugosity) of northern sea otters (E. lutris kenyoni) for a data-limited ecosystem, represented by Kachemak Bay, Alaska. Habitat association results corroborated previous findings regarding the importance of bathymetry and understory kelp as predictors of sea otter presence. Novel associations were detected as filamentous algae and shell litter were positively and negatively associated with northern sea otter presence, respectively, advancing existing knowledge of sea otter benthic habitat associations useful for predicting habitat suitability. This study provides a quantitative framework for conducting species distribution modeling with limited temporal and spatial animal distribution and abundance data. Utilizing drop camera information, our novel approach allowed for a better understanding of habitat requirements for a stable northern sea otter population, including bathymetry, understory kelp, and filamentous algae as positive predictors of sea otter presence in Kachemak Bay, Alaska.

Novel lambdapapillomavirus in northern sea otters Enhydra lutris kenyoni, associated with oral hyperplastic nodules.

A novel papillomavirus (PV) associated with hyperplastic nodules scattered over the muco-cutaneous border of the oral cavity of a dead, wild, subadult northern sea otter Enhydra lutris kenyoni (NSO) in 2004 in Homer, Alaska, USA, was genetically characterized. Primers for the amplification of 2 large overlapping DNA fragments that contained the complete genome of the NSO PV were designed. Sanger methodology generated sequences from which new specific primers were designed for the primer-walking approach. The NSO PV genome consists of 8085 nucleotides and contains an early region composed of E6, E7, E1, and E2 open reading frames (ORFs), an E4 ORF (contained within E2) lacking an in-frame proximal ATG start codon, an unusually long (907 nucleotide) stretch lacking any ORFs, a late region that contains the capsid genes L2 and L1, and a non-coding regulatory region (ncRR). This NSO PV has been tentatively named Enhydra lutris kenyoni PV2 (ElkPV2). Pairwise and multiple sequence alignments of the complete L1 ORF nucleotides and concatenated E1-E2-L1 amino acid sequences showed that the NSO PV is a novel PV, phylogenetically most closely related to southern sea otter PV1. The carboxy end of the E6 oncoprotein does not contain the PDZ-binding motif with a strong correlation with oncogenicity, suggesting a low-risk PV, which is in agreement with histopathological findings. However, the ElkPV2 E7 oncoprotein does contain the retinoblastoma (pRb) binding domain LXCXE (LQCYE in ElkPV2), associated with oncogenicity in some high-risk PVs. Further studies on the prevalence and clinical significance of ElkPV2 infections in NSO are needed.

Dynamic structural equation models synthesize ecosystem dynamics constrained by ecological mechanisms

Abstract Ecological analyses typically involve many interacting variables. Ecologists often specify lagged interactions in community dynamics (i.e. vector‐autoregressive models) or simultaneous interactions (e.g. structural equation models), but there is less familiarity with dynamic structural equation models (DSEM) that can include any simultaneous or lagged effect in multivariate time‐series analysis. We propose a novel approach to parameter estimation for DSEM, which involves constructing a Gaussian Markov random field (GMRF) representing simultaneous and lagged path coefficients, and then fitting this as a generalized linear mixed model to missing and/or non‐normal data. We provide a new R‐package dsem, which extends the ‘arrow interface’ from path analysis to represent user‐specified lags when constructing the GMRF. We also outline how the resulting nonseparable precision matrix can generalize existing separable models, for example, for time‐series and species interactions in a vector‐autoregressive model. We first demonstrate dsem by simulating a two‐species vector‐autoregressive model based on wolf–moose interactions on Isle Royale. We show that DSEM has improved precision when data are missing relative to a conventional dynamic linear model. We then demonstrate DSEM via two contrasting case studies. The first identifies a trophic cascade where decreased sunflower starfish has increased urchin and decreased kelp densities, while sea otters have a simultaneous positive effect on kelp in the California Current from 1999 to 2018. The second estimates how declining sea ice has decreased cold‐water habitats, driving a decreased density for fall copepod predation and inhibiting early‐life survival for Alaska pollock from 1963 to 2023. We conclude that DSEM can be fitted efficiently as a GLMM involving missing data, while allowing users to specify both simultaneous and lagged effects in a time‐series structural model. DSEM then allows conceptual models (developed with stakeholder input or from ecological expertise) to be fitted to incomplete time series and provides a simple interface for granular control over the number of estimated time‐series parameters. Finally, computational methods are sufficiently simple that DSEM can be embedded as component within larger (e.g. integrated population) models. We therefore recommend greater exploration and performance testing for DSEM relative to familiar time‐series forecasting methods.

Assessment of mercury concentrations in fur, liver, and brain tissue from necropsied southern sea otters (Enhydra lutris nereis)

AbstractSouthern sea otters (Enhydra lutris nereis) are a federally listed threatened keystone species of the California kelp forest ecosystem and a sentinel species, indicating environmental health. Mercury (Hg) is a bioaccumulative neurotoxin that poses a threat to high trophic‐level species such as marine mammals. We quantified total Hg (THg) concentrations in fur, brain, and liver tissues of necropsied southern sea otters (n = 44) that stranded along the California coast from 2010 to 2019. THg concentrations differed significantly between fur and brain, and between liver and brain. Tissue type explained 64%, and sex explained only 3.3% of overall THg variability (0.48–46.1 μg/g dry weight). All individuals had liver Hg concentrations measuring well under the proposed lower‐limit low risk guideline for harp seals, Pagophilus groenlandicus. However, six sea otters exceeded the liver THg moderate risk threshold for terrestrial furbearers to which sea otters are closely related. These data represent baseline THg concentrations in fur, brain, and liver of the southern sea otter and build upon previous studies in various sea otter subspecies. Research on sea otter Hg tolerance and continued monitoring are needed to clarify potential health risks associated with the tissue concentrations observed in this study.

Complex dental wear analysis reveals dietary shift in Triassic placodonts (Sauropsida, Sauropterygia)

Placodonts were durophagous reptiles of the Triassic seas with robust skulls, jaws, and enlarged, flat, pebble-like teeth. During their evolution, they underwent gradual craniodental changes from the Early Anisian to the Rhaetian, such as a reduction in the number of teeth, an increase in the size of the posterior palatal teeth, an elongation of the premaxilla/rostrum, and a widening of the temporal region. These changes are presumably related to changes in dietary habits, which, we hypothesise, are due to changes in the type and quality of food they consumed. In the present study, the dental wear pattern of a total of nine European Middle to Late Triassic placodont species were investigated using 2D and 3D microwear analyses to demonstrate whether there could have been a dietary shift or grouping among the different species and, whether the possible changes could be correlated with environmental changes affecting their habitats. The 3D analysis shows overlap between species with high variance between values and there is no distinct separation. The 2D analysis has distinguished two main groups. The first is characterised by low number of wear features and high percentage of large pits. The other group have a high feature number, but low percentage of small pits. The 2D analysis showed a correlation between the wear data and the size of the enlarged posterior crushing teeth. Teeth with larger sizes showed less wear feature (with higher pit ratio) but larger individual features. In contrast, the dental wear facet of smaller crushing teeth shows more but smaller wear features (with higher scratch number). This observation may be related to the size of the food consumed, i.e., the wider the crown, the larger food it could crush, producing larger features. Comparison with marine mammals suggests that the dietary preference of Placochelys, Psephoderma and Paraplacodus was not exclusively hard, thick-shelled food. They may have had a more mixed diet, similar to that of modern sea otters. The diet of Henodus may have included plant food, similar to the modern herbivore marine mammals and lizards.