Sea Otters Enhydra Research Articles

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.

Occurrence of killer whales Orcinus orca off the Commander Islands and Avacha Gulf from 2008�2021 and its relation to the sea otter Enhydra lutris population decline

Occurrence of killer whales Orcinus orca off the Commander Islands and Avacha Gulf from 2008�2021 and its relation to the sea otter Enhydra lutris population decline

The historical and contemporary status of the sea otter Enhydra lutris population on Urup Island, southern Kuril Islands

AbstractWe describe the population of the Еndangered sea otter Enhydra lutris on Urup Island, one of the main wildlife refuges in the southern Kuril Islands of Russia. We reviewed historical and local reports of the sea otter, identified its habitat around the island, and surveyed the coastal waters of the island in 2019. Sea otters were numerous on Urup Island in the past but were hunted excessively and almost exterminated by the 1950s. Since then, sea otter populations have increased, and as the island is almost uninhabited we expected otters to be numerous. This was not the case, and we estimated the total population to be 363 ± SE 126 individuals. Our observation of two skinned carcasses on the shore suggests the low numbers are a result of poaching for the illegal fur trade. The case of Urup Island demonstrates that sea otters require active conservation, as even on a remote island they remain threatened. Establishment of protected areas would be an effective conservation measure for this species, although the suppression of demand for sea otter fur is of the greatest importance.

Biological correlates of sea urchin recruitment in kelp forest and urchin barren habitats

Shifts between the alternate stable states of sea urchin barren grounds and kelp forests correspond to sea urchin density. In the Aleutian Archipelago, green sea urchins Strongylocentrotus polyacanthus are the dominant herbivores that graze kelp forests. Sea urchin recruitment is an important driver that influences sea urchin density, particularly in the absence of top-down control from a keystone predator such as the sea otter Enhydra lutris. To understand how the biological community may influence patterns of sea urchin recruitment, we compared sea urchin recruit (size ≤20 mm) densities with biomass of other benthic organisms in both barren ground and kelp forest habitats at 9 islands across the Aleutian Archipelago. Patterns of biological community structure between the 2 habitats did not explain patterns of sea urchin recruits; however, the same 10 specific taxa were found to correlate with sea urchin recruits in each habitat. Taxa that showed strong positive correlations included Codium, Constantinea, Schizymenia, and hydrozoans, while strong negative correlations were observed with Pachyarthron and Pugettia. Weak positive correlations were observed with Alcyonidium and ascidiaceans in both habitats, while weak variable relationships were detected with Polysiphonia and Corallina between habitats. The observed species-specific relationships may be due to small sea urchin displacement by larger conspecifics, larval responses to settlement cues, post-settlement survival via biogenic refugia, or potentially predation. These potential species-specific interactions were apparent, regardless of habitat, and it can be inferred that they would be preserved in the presence or absence of keystone predation.

Characterizing the impact of recovering sea otters on commercially important crabs in California estuaries

Protective legislation and management have led to an increase in California’s sea otter Enhydra lutris nereis population. While sea otter recovery has been linked to ecosystem benefits, sea otter predation may negatively affect commercially valuable species. Understanding the potential influence of sea otters is of particular importance as their range expands into estuaries that function as nurseries for commercially valuable species like Dungeness crab Metacarcinus magister. We consider how sea otter predation has affected the abundance and size of juvenile Dungeness crab in Elkhorn Slough, California, USA, and analyzed cancrid crab abundance and size across 4 California estuaries with and without sea otters to understand how biotic and abiotic factors contribute to observed variation in crab size and abundance. We compared trends in southern sea otters relative to Dungeness crab landings in California to assess whether increasing sea otter abundance have negatively impacted landings. In Elkhorn Slough, juvenile Dungeness crab abundance and size have declined since 2012, coinciding with sea otter population growth. However, the impact of sea otters on juvenile Dungeness crab size was habitat-specific and only significant in unvegetated habitat. Across estuaries, we found that cancrid crab abundance and size were negatively associated with sea otter presence. While abiotic factors varied among estuaries, these factors explained little of the observed variation in crab abundance or size. Although we found evidence that sea otters can have localized effects on cancrid crab populations within estuaries, we found no evidence that southern sea otters, at recent population sizes, have negatively impacted Dungeness crab landings in California from 2000-2014.

Surrogate rearing a keystone species to enhance population and ecosystem restoration

AbstractTranslocation and rehabilitation programmes are critical tools for wildlife conservation. These methods achieve greater impact when integrated in a combined strategy for enhancing population or ecosystem restoration. During 2002–2016 we reared 37 orphaned southern sea otter Enhydra lutris nereis pups, using captive sea otters as surrogate mothers, then released them into a degraded coastal estuary. As a keystone species, observed increases in the local sea otter population unsurprisingly brought many ecosystem benefits. The role that surrogate-reared otters played in this success story, however, remained uncertain. To resolve this, we developed an individual-based model of the local population using surveyed individual fates (survival and reproduction) of surrogate-reared and wild-captured otters, and modelled estimates of immigration. Estimates derived from a decade of population monitoring indicated that surrogate-reared and wild sea otters had similar reproductive and survival rates. This was true for males and females, across all ages (1–13 years) and locations evaluated. The model simulations indicated that reconstructed counts of the wild population are best explained by surrogate-reared otters combined with low levels of unassisted immigration. In addition, the model shows that 55% of observed population growth over this period is attributable to surrogate-reared otters and their wild progeny. Together, our results indicate that the integration of surrogacy methods and reintroduction of juvenile sea otters helped establish a biologically successful population and restore a once-impaired ecosystem.

Gaps in kelp cover may threaten the recovery of California sea otters

Despite more than a century of federal protection, the California sea otterEnhydra lutris nereisremains threatened under the U.S. Endangered Species Act (ESA), and the population has not appreciably expanded its range in two decades. Here, we examine a novel dataset of 725 sea otter live strandings from 1984–2015 to gain insights into demographic and environmental factors underlying threats to sea otter recovery. Using multinomial logistic regression to evaluate spatiotemporal patterns of stranding causes, we demonstrate that increases in stranding rates, particularly outside the range center, are related to a substantial increase in shark bites. By contrast, trauma linked to human activities has declined dramatically, and now accounts for less than 5% of stranding cases. Within the range core, where the sea otter population seems regulated by prey availability, symptoms of energetic stress represent more than 63% of all strandings and are strongly associated with high sea otter density. Conversely, in range peripheries, the majority of strandings are caused by shark bite and neurological disease. Notably, these threats are virtually absent where nearshore habitat is characterized by at least 10% kelp canopy cover. Our analyses reveal that declining kelp cover may therefore constrain the population's spatial expansion and recovery in two key ways. Absence of kelp intensifies density‐independent threats in the range peripheries, and likely limits dispersal of reproductive females, which depend on kelp canopy for nursery habitat. These results highlight the significance of both top‐down and bottom‐up processes in population dynamics, and inform an ecosystem‐based approach to conservation planning.

Discovery of the fossil otter Enhydritherium terraenovae (Carnivora, Mammalia) in Mexico reconciles a palaeozoogeographic mystery.

The North American fossil otter Enhydritherium terraenovae is thought to be partially convergent in ecological niche with the living sea otter Enhydra lutris, both having low-crowned crushing teeth and a close association with marine environments. Fossil records of Enhydritherium are found in mostly marginal marine deposits in California and Florida; despite presence of very rich records of fossil terrestrial mammals in contemporaneous localities inland, no Enhydritherium fossils are hitherto known in interior North America. Here we report the first occurrence of Enhydritherium outside of Florida and California, in a land-locked terrestrial mammal fauna of the upper Miocene deposits of Juchipila Basin, Zacatecas State, Mexico. This new occurrence of Enhydritherium is at least 200 km from the modern Pacific coastline, and nearly 600 km from the Gulf of Mexico. Besides providing further evidence that Enhydritherium was not dependent on coastal marine environments as originally interpreted, this discovery leads us to propose a new east-to-west dispersal route between the Florida and California Enhydritherium populations through central Mexico. The proximity of the fossil locality to nearby populations of modern neotropical otters Lontra longicaudis suggests that trans-Mexican freshwater corridors for vertebrate species in riparian habitats may have persisted for a prolonged period of time, pre-dating the Great American Biotic Interchange.

Gross intestinal morphometry and allometry in Carnivora

Although typical anatomical features of the digestive tract of carnivores are well known, such as the presence or absence of a caecum in various carnivore taxa, and although a large number of length measurements have been published, the body mass measurement of the corresponding specimens has mostly not been reported. Here, we add original mass and intestine length measurements for 36 carnivore species to literature data. Using Phylogenetic Generalized Least Squares, we demonstrate that marine Carnivora (pinnipeds and the sea otter Enhydra lutris) have significantly longer total and small intestines relative to body mass than terrestrial Carnivora, and both pinnipeds and mustelids in general have particularly long total intestines amongst terrestrial Carnivora. The natural diet explains little about variation in relative intestinal length measures. However, amongst species that do have a caecum, a higher proportion of plant material in the diet might be associated with a longer caecum. In particular, a diet with higher proportions of plant material provided by humans could have led to a particularly long caecum in the domestic dog.

Harmful algal bloom toxins protect bivalve populations from sea otter predation

We demonstrate how harmful algal bloom (HAB) toxins can mediate the strength of consumer-prey interactions, and thus ecosystem level patterns and processes, by altering the foraging behavior of a keystone marine predator (sea otter Enhydra lutris). Our approach was to com- pare sea otter foraging behavior, diet, prey abundance and paralytic shellfish poisoning toxins (PSPT) across a range of sites within the Inside Passage of southeast Alaska recently occupied by sea otters. Sea otters in southeast Alaska modified their foraging behaviors depending on concentrations of PSPT in bivalve prey, especially their preferred prey, butter clams Saxidomus giganteus. At sites of intermediate prey toxicity (200 to 500 µg saxitoxin (STX) eq · 100 g -1 ), otters continued to forage on butter clams while discarding the most toxic body parts. At highly toxic sites (prey toxicity > 500 µg STX eq · 100 g -1 ) otters avoided butter clams and other large and abundant but toxic bivalve prey, and consumed smaller and/or less abundant non-toxic species. Butter clams were larger and more abundant in highly toxic feeding areas, supporting the hypothesis that PSPT toxicity provides a refuge from sea otter predation.

Helminth parasites of the southern sea otter Enhydra lutris nereis in central California: abundance, distribution and pathology.

From October 1997 to May 2001, the gastrointestinal tracts from 162 beach-cast southern sea otters Enhydra lutris nereis were examined for helminth parasites and associated lesions. Carcasses were collected opportunistically in central California between Pt. San Pedro and Pt. Arguello. The primary goals of this study were to examine spatial and temporal variability in mortality due to parasite infection, identify factors associated with increased risk of infection, and illustrate the process of intestinal perforation by Profilicollis spp. Two genera and 4 species of acanthocephalans (Profilicollis altmani, P. kenti, P. major, Corynosoma enhydri) were found in 46.3% (Profilicollis spp.) and 94.4% (C. enhydri) of the carcasses examined. Three species of Digenea (Microphallus pirum, M. nicolli, Plenosoma minimum) were found in 47% of carcasses, at times in massive numbers (> 3000 per cm2). This is the first report of the latter 2 species from the sea otter. Mortality resulting from infection by Profilicollis spp. occurred in 13.0% (n = 21) of sampled carcasses, either directly, due to perforation of the intestinal wall and peritonitis (9.9%, n = 16), or indirectly, due to inhibition of host nutrient uptake or depletion of host energy reserves to fight chronic infections (3.1%, n = 5). The most massive infections (< 8760 parasites), and all cases of intestinal perforation occurred in carcasses infected by P. altmani and/or P. kenti. Mortality due to infection by Profilicollis spp. occurred more frequently among juvenile and old-adult females (chi2 = 17.479, df = 9, p = 0.045) from sand and mixed habitats in Monterey and Santa Cruz in the north of the sea otter range (chi2 = 9.84, df = 4, p = 0.045). Spatial differences in sea otter mortality coincided with the relative distributions of Profilicollis altmani, P. kenti, and P. major, and may reflect differences in sea otter diet, or differences in intensity of infection in intermediate hosts. Mortality rate due to infection by Profilicollis spp. decreased between 1998 and 2001, though differences were not significant (chi2 = 3.983, df = 3, p = 0.40), and may vary on multi-year cycles due to environmental factors such as density of definitive hosts (e.g. the surf scoter Melanitta perspicillata), or El Niño. Corynosoma enhydri did not cause significant damage to the intestine of the host, even when present in great numbers.

Sea otter population status and the process of recovery from the 1989 'Exxon Valdez' oil spill

Sea otter Enhydra lutris populations were severely affected by the 1989 'Exxon Valdez' oil spill in western Prince William Sound, AK, and had not fully recovered by 2000. Here we present results of population surveys and incorporate findings from related studies to identify current population status and factors affecting recovery. Between 1993 and 2000, the number of sea otters in the spill-area of Prince William Sound increased by about 600 to nearly 2700. However, at Knight Island, where oil exposure and sea otter mortality in 1989 was most severe, no increase has been observed. Sea otter reproduction was not impaired, and the age and sex composition of captured otters are consistent with both intrinsic reproduction and immigration contributing to recovery. However, low resighting rates of marked otters at Knight Island compared to an unoiled reference area, and high proportions of young otters in beach cast carcasses through 1998, suggest that the lack of recovery was caused by relatively poor survival or emigration of potential recruits. Significantly higher levels of cytochrome P4501A (CYP1A), a biomarker of hydrocarbons, were found in sea otters at Knight Island from 1996 to 1998 compared to unoiled Montague Island, implicating oil effects in the lack of recovery at Knight Island. Delayed recovery does not appear to be directly related to food limitation. Although food availability was relatively low at both oiled and unoiled areas, we detected significant increases in sea otter abundance only at Montague Island, a finding inconsistent with food as a principal limiting factor. Persistent oil in habitats and prey provides a source of continued oil exposure and, combined with relatively low prey densities, suggests a potential interaction between oil and food. However, sea otters foraged more successfully at Knight Island and young females were in better condition than those at Montague Island. We conclude that progress toward recovery of sea otters in Prince William Sound is evident, but that in areas where initial oil effects were greatest, recovery may be constrained by residual spill effects, resulting from elevated mortality and emigration. It is evident that internal reproduction and immigration of juveniles has been the primary means of population recovery, as opposed to broad scale redistribution of adults from outside affected areas. The result is a recovery period protracted by long-term spill effects on survival and emigration and intrinsic limits to population growth.

Functional significance of bone ballastin in the evolution of buoyancy control strategies by aquatic tetrapods

The primary function of pachyostosis, pachyosteo‐sclerosis, and osteosclerosis may be to act as ballast, not so much (as previously suggested) to neutralise the buoyancy of existing lungs, but to allow enlargement of the lungs. Enlarged lungs cause an animal to lose buoyancy more rapidly with depth. They also provide a larger oxygen store. These features are useful for slow swimmers and shallow divers, such as feeders on benthic plants and invertebrates. Examples are sirenians, primitive sauropterygians ("not‐hosaurs"), placodonts, and the sea otter Enhydra. These last two show convergent evolution of adaptations to feeding on hard‐shelled invertebrate prey in shallow water. Mesosaurids are problematical. Bone ballast uses body mass and volume less efficiently than other buoyancy control strategies. Theoretical analysis predicts that bone ballast should not occur in semiaquatic forms, fast swimmers or deep divers. It does not usually occur in such organisms. Marine iguanas of the Galápagos, desmostylians, and the aquatic sloth Thalassocnus are all littoral feeders and all lack bone ballast as predicted. Plesiosaurs adopted varied strategies: some used bone ballast, and others used gastroliths. Biomechanical considerations lead to the prediction that a new marine tetrapod clade will typically evolve bone ballast as part of its adaptation to life in water. Slow swimmers and grazers on sessile food, like sirenians and placodonts, develop it more strongly, but active predators like ichthyosaurs and cetaceans secondarily lose this character.

The osteology and paleoecology of the giant otter Enhydritherium terraenovae

ABSTRACT The giant otter Enhydritherium terraenovae, a New World taxon thought to be related to both the Old World otter Enhydriodon and the extant sea otter Enhydra, was originally described on the basis of relatively limited material, mostly dental. However, an incomplete skeleton of E. terraenovae recovered from the early Hemphillian Moss Acres Racetrack site in northern Florida includes a skull, mandible, part of the axial skeleton, and most of both the fore- and hindlimbs, adding greatly to knowledge of this animal. On the basis of this new material, the osteology of this species is described in detail for the first time, with its diagnosis revised accordingly. This new osteological information, along with information about the nature of the Moss Acres Racetrack site, allows such paleoecological and functional aspects of E. terraenovae as habitat preference, mode of swimming, and diet to be inferred or interpreted in a detail previously impossible. E. terraenovae: 1) was a habitat generalist rather than a marine specialist, as previously thought; 2) was reasonably competent for terrestrial locomotion; 3) extensively used its forelimbs during swimming like living otariid seals, in contrast to the hindlimb-specialized Enhydra; and 4) had a generalized diet, potentially including soft items such as fish, as well as hard items, such as thick-shelled molluscs.

Contribution of Specific Dynamic Action to Heat Balance and Thermoregulation in the Sea Otter Enhydra lutris

Specific dynamic action (SDA), measured in three sea otters using indirect calorimetry, is 10.0%-13.2% of the ingested clam or squid energy. Sea otter SDA is intermediate in magnitude and shorter in duration than reported for marine mammals that were fed fish. The postprandial peak increase in resting $\dot{V}O_{2}$, was 54% higher than postabsorptive values. This peak occurred 82 min after the otter ate 0.84 kg of squid or clam. The $\dot{V}O_{2}$ returned to postabsorptive levels 4-5 h after feeding. The short duration rise in metabolism attributable to SDA may contribute to thermoregulation at rest and correlates with field observations of resting and foraging behavior.

Changes in Subtidal Community Structure Associated with British Columbia Sea Otter Transplants

Sea otters Enhydra Iutris were re-introduced into coastal waters of British Columbia, Canada, in 1969-1972, after being hunted to extinction In the previous 2 centuries. In 1979, we visited an area where 55 individuals had been seen in 1978, and we made subtidal observations of the abundance and distribution of red sea urchins, other grazers, and kelps. Earlier observations, made in the area before sea otters were re-introduced, confirmed that changes have taken place in subtidal communities since the re-introduction. Where sea otters had been observed feeding, sea urchins Strongylocentrotus franciscanus were scarce and restricted to crevices or beneath boulders, other grazers were scarce, and kelps colonized the bottom to 10-m depths. The algal communities in these areas appeared to be simple downward extensions of sublittoral fringe communities. Where sea otters had not fed, kelps were limited to shallow water by abundant sea urchins. The observed differences between the 2 types of areas are concluded to have been caused by early ellmlnation of sea urchins by sea otters, as reported in Alaska and California. From the pattern of sea urchin abundance in the general area of the transplant, we were able to delineate the feeding range of this small population of sea otters.

Energy, Nitrogen, and Electrolyte Flux and Sea Water Drinking in the Sea Otter Enhydra Lutris

An elevated metabolism requires the sea otter, Enhydra lutris, to include large quantities of invertebrate prey in its diet. This necessitates processing large quantities of energy, nitrogen, electrolytes, and water. Feeding studies were conducted to document these high material and energy fluxes and the dilution of tritiated water through time was used to measure total water flux. Total energy influx on a diet of clam and squid was 234 ± 19 (X ± SE) kcal/kg-day with an assimilation efficiency of 82% and an estimated metabolic efficiency of 72%. Material influx from food was 5.22 ± 0.41 (X ± SE) g/kg-day nitrogen and 166 meq/kg-day electrolytes (Cl, Na, K, Mg). The presence of large lobulate kidneys may allow for the production of large volumes of urine at elevated concentrations. Urine samples from wild and captive animals had a mean osmotic pressure of 1,627 ± 91 mOsm/kg (range, 910-2,130), which was composed of 647 meq/L Na, K, Cl and 698 ± 67 mmol/L urea. Total water flux was 269 ± 25 mL/kg-day. Mean ...