Visual pigments of marine carnivores: pinnipeds, polar bear, and sea otter

Rod and cone visual pigments of 11 marine carnivores were evaluated. Rod, middle/long-wavelength sensitive (M/L) cone, and short-wavelength sensitive (S) cone opsin (if present) sequences were obtained from retinal mRNA. Spectral sensitivity was inferred through evaluation of known spectral tuning residues. The rod pigments of all but one of the pinnipeds were similar to those of the sea otter, polar bear, and most other terrestrial carnivores with spectral peak sensitivities (λ_max) of 499 or 501 nm. Similarly, the M/L cone pigments of the pinnipeds, polar bear, and otter had inferred λ_max of 545 to 560 nm. Only the rod opsin sequence of the elephant seal had sensitivity characteristic of adaptation for vision in the marine environment, with an inferred λ_max of 487 nm. No evidence of S cones was found for any of the pinnipeds. The polar bear and otter had S cones with inferred λ_max of ∼440 nm. Flicker-photometric ERG was additionally used to examine the in situ sensitivities of three species of pinniped. Despite the use of conditions previously shown to evoke cone responses in other mammals, no cone responses could be elicited from any of these pinnipeds. Rod photoreceptor responses for all three species were as predicted by the genetic data.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Effects of sea water on thermal insulation of the otter, Lutra lutra

Otters Lutra lutra L. which feed in the sea in Scotland frequently wash in fresh water. Experiments were carried out with otter pelts and with captive otters, to study the biological function of this behaviour. In vitro , the fur of otters lost much of its thermal insulation after five soakings in sea water and subsequent drying. Otters were fed in sea water or fresh water, with or without simultaneous access to alternative fresh water. When fed in sea water, otters used the alternative fresh water much more than when fed in fresh water, they were more reluctant to enter sea water if no alternative fresh water was present, and without this alternative fresh water they showed signs of hypothermia. After swimming in sea water the animals spent more time grooming and rolling. Without fresh water present the otters' fur lost its capacity for retaining air under water. These observations suggest an explanation for the restricted distribution of otters living along the coast, and for the lack of use of marine habitats by small mammals in general.     

Jaguar mobbing by giant otter groups

Group-living in carnivores is mostly associated with cooperative hunting and anti-predator defense. Giant otters (Pteronura brasiliensis) live in monogamous and cooperative breeding groups, where mechanisms other than cooperative foraging may be driving group maintenance in the species. We herein describe three interactions between giant otters and jaguars (Panthera onca) observed in the wild, two of which involved groups of otters and one, a lone individual. In the two group instances, the otters mobbed the jaguar until it left the area. The mobbing behavior displayed in these instances likely reinforces the advantages of living in groups, reducing predation risk and promoting group cohesion, with resulting territorial and fitness benefits.     

Genetic evaluation of an otter translocation program

The translocation of individuals from onepopulation to another is a common technique inwildlife conservation. However, the outcome oftranslocation programs is not always properlyevaluated and the relative contribution ofreleased individuals to the resident populationoften remains unknown. We used mitochondrialDNA and autosomal genetic markers to evaluatethe success of a translocation program ofEurasian otters (Lutra lutra) in Sweden.The program is regarded as successful becauseof subsequent population growths. Norwegianotters used for the restocking program could begenetically differentiated from Swedish otters.The releases took place at two sites. In anarea south of the first site, where 47 otterswere released, no genetic contribution of theintroduced animals to the population could beobserved and the genetic diversity was lowerthan before the releases. At the second site,the release of seven otters led to a change ingenetic composition of the resident population.The results of this study suggest that thegrowth of the otter population after therestocking may not be as dependent on thereleases as initially suspected. The geneticeffects of the translocations appear to berestricted to areas in the immediate vicinityof the release sites.     

Mechanical properties of river otter limb bones

The determination of the bone strengths of wild animals has many potential advantages, which include the ability to estimate age of animals; monitor strengths of bones as influenced by contaminants, particularly lead; provide appropriate data for design of capture, handling, and holding equipment to minimize the possibility for bone fracture in captured animals; and measure effects of nutrition on bone strength. The objectives of of this study were to provide data on the mechanical properties of limb bones of river otters and to consider effects of age and sex on the properties. Three-point bending and shear tests were conducted on the radius, ulna, tibia, and fibula. The three-point bending tests were first conducted on the bones loaded within their elastic limit. These tests were used to evaluate the modulii of elasticity of the bones. The data on the modulii indicated that age and sex did not have significant effects on the values. The four different bones tested had approximately the same modulus of elasticity, with an average value of 14. 1 gigapascal (GPa). The shear tests were conducted on the limb bones to failure in order to determine the maximum breaking force and strength of the bones. The shear force of the radius tended to increase with age and there was a significant (P < .001) age effect. The shear force of the ulna for males was significantly (P < .002) higher than that of the females. A similar trend was observed for the fibula (P < .03). The shear strength of the radius increased with age and there was a significant (P < .005) age effect. There was also a significant (P < .001) effect of sex on shear strength of the radius; values for females were higher. There were no significant effects of sex or age found on shear strengths of the ulnae, tibia, and fibulae.     

Oestrus and the vaginal smear cycle of the river otter, Lutra canadensis

Vaginal smears of river otters contained specific cellular associations which can be used to monitor their reproductive cycle. The anoestrous period was identified by the presence of large intermediate epithelial cells while the onset of pro-oestrus was gradual and the duration difficult to determine. Oestrus was indicated by an influx of nucleated and non-nucleated cornified cells which continue after mating. The metoestrous smear was characterized by large quantities of leucocytes and mucus.     

Evolutionary history and identification of conservation units in the giant otter, Pteronura brasiliensis

The giant otter, Pteronura brasiliensis, occupies a range including the major drainage basins of South America, yet the degree of structure that exists within and among populations inhabiting these drainages is unknown. We sequenced portions of the mitochondrial DNA (mtDNA) cytochrome b (612bp) and control region (383 bp) genes in order to determine patterns of genetic variation within the species. We found high levels of mtDNA haplotype diversity (h = 0.93 overall) and support for subdivision into four distinct groups of populations, representing important centers of genetic diversity and useful units for prioritizing conservation within the giant otter. We tested these results against the predictions of three hypotheses of Amazonian diversification (Pleistocene Refugia, Paleogeography, and Hydrogeology). While the phylogeographic pattern conformed to the predictions of the Refugia Hypothesis, molecular dating using a relaxed clock revealed the phylogroups diverged from one another between 1.69 and 0.84 Ma, ruling out the influence of Late Pleistocene glacial refugia. However, the role of Plio-Pleistocene climate change could not be rejected. While the molecular dating also makes the influence of geological arches according to the Paleogeography Hypothesis extremely unlikely, the recent Pliocene formation of the Fitzcarrald Arch and its effect of subsequently altering drainage pattern could not be rejected. The data presented here support the interactions of both climatic and hydrological changes resulting from geological activity in the Plio-Pleistocene, in shaping the phylogeographic structure of the giant otter.     

Genetic diversity and population structure in the endangered giant otter, Pteronura brasiliensis

We assessed levels of genetic diversity and investigated patterns of population structure in three remnant populations of the endangered giant otter, Pteronura brasiliensis, using microsatellite loci. All populations displayed moderate to low levels of heterozygosity and allelic richness (H _O 0.56–0.57, A _R 4.00–5.15) and effective population sizes were low (N _E 10.8–54) although only the Iténez population exhibited the signature of a genetic bottleneck. Population structure analyses revealed a pattern in which the populations of the Upper Amazon, Orinoco and Essequibo drainages comprised partially differentiated segments of a northern South American metapopulation, whereas the population of the Iténez appeared isolated. The observed patterns are congruent with previous mitochondrial DNA analysis which suggested the Iténez and northern South American groups constitute two evolutionary significant units. The results presented here should be considered in planning future policies aiming to manage the recovery of the giant otter across its range.     

Status,trends, and equilibrium abundance estimates of the translocated sea otter population in Washington State

Sea otters (Enhydra lutris kenyoni) historically occurred in Washington State, USA, until their local extinction in the early 1900s as a result of the maritime fur trade. Following their extirpation, 59 sea otters were translocated from Amchitka Island, Alaska, USA, to the coast of Washington, with 29 released at Point Grenville in 1969 and 30 released at La Push in 1970. The Washington Department of Fish and Wildlife has outlined 2 main objectives for sea otter recovery: a target population level and a target geographic distribution. Recovery criteria are based on estimates of population abundance, equilibrium abundance (K), and geographic distribution; therefore, estimates of these parameters have important management implications. We compiled available survey data for sea otters in Washington State since their translocation (1977–2019) and fit a Bayesian state-space model to estimate past and current abundance, and equilibrium abundance at multiple spatial scales. We then used forward projections of population dynamics to explore potential scenarios of range recolonization and as the basis of a sensitivity analysis to evaluate the relative influence of movement behavior, frontal wave speed, intrinsic growth, and equilibrium density on future population recovery potential. Our model improves upon previous analyses of sea otter population dynamics in Washington by partitioning and quantifying sources of estimation error to estimate population dynamics, by providing robust estimates of K, and by simulating long-term population growth and range expansion under a range of realistic parameter values. Our model resulted in predictions of population abundance that closely matched observed counts. At the range-wide scale, the population size in our model increased from an average of 21 independent sea otters (95% CI = 13–29) in 1977 to 2,336 independent sea otters (95% CI = 1,467–3,359) in 2019. The average estimated annual growth rate was 12.42% and varied at a sub-regional scale from 6.42–14.92%. The overall estimated mean K density of sea otters in Washington was 1.71 ± 0.90 (SD) independent sea otters/km² of habitat (1.96 ± 1.04 sea otters/km², including pups), and estimated densities within the current range correspond on average to 87% of mean sub-regional equilibrium values (range = 66–111%). The projected value of K for all of Washington was 5,287 independent sea otters (95% CI = 2,488–8,086) and 6,080 sea otters including pups (95% CI = 2,861–9,300), assuming a similar range of equilibrium densities in currently un-occupied habitats. Sensitivity analysis of simulations of sea otter population growth and range expansion suggested that mean K density estimates in currently occupied sub-regions had the largest impact on predicted future population growth (r² = 0.52), followed by the rate of southward range expansion (r² = 0.26) and the mean K density estimate of currently unoccupied sub-regions to the south of the current range (r² = 0.04). Our estimates of abundance and sensitivity analysis of simulations of future population abundance and geographic range help determine population status in relation to population recovery targets and identify the most influential parameters affecting future population growth and range expansion for sea otters in Washington State.     

The otter (Lutra lutra) in Tunisia

The otter is common and widespread in northern Tunisia and the Oued Medjerda effectively represents a southern limit for the species. The distribution of otters is largely coincident with dense bankside cover, provided mainly by Nerium oleander. Rivers south of the O. Medjerda offer little shelter for the animals.