Body growth in Atlantic walruses (Odobenus rosmarus rosmarus) from Greenland

Morphometric data were collected from 105 Atlantic walruses ( Odobenus rosmarus rosmarus ) in northwestern Greenland in the periods 1977–78 and 1989–91. Of these 21 walruses were subjected to a detailed study on body composition.
The asymptotic maximum standard body length of Atlantic walruses in NW Greenland was 269 cm for females and 314 cm for males. This is similar to Pacific walruses, but significantly longer than Atlantic walruses from Hudson Bay. Despite this, walruses from NW Greenland apparently do not attain the same total body mass as Pacific walruses ( O.r.divergens ).
The asymptotic maximum body weights for walruses in NW Greenland were estimated to be 720 kg for females and 1114 kg for males.
Total body surface area was proportional to the two-thirds power of total body weight.
The percentage proportion of blubber and viscera were both negatively correlated to body mass, while skin and muscles constituted a nearly fixed proportion. On average, blubber constituted 19% of total body mass of adult females, 15% of adult males and 24% of subadults of both genders. The average walrus consisted of 18% blubber, 12% skin, 12% viscera and 58% blood, muscle and skeleton. Muscles were estimated to constitute 44% of total body weight.
Allometric functions for weight of internal organs relative to body mass are presented.     

Body size of male Atlantic walruses (Odobenus rosmarus rosmarus) from Svalbard

Morphometric data are given for 41 adult male Atlantic walruses ( Odobenus rosmarus rosmarus) immobilized at Svalbard. Total body weight ranged from 960 to 1450 kg. Standard body length ranged from 258 to 380 cm, while curvilinear tusk length ranged from 17 to 65 cm. Immobilized animals were selected for their large size. The sample is therefore biased towards larger animals. Based on regression equations developed for walruses caught in Greenland, the weights of Svalbard walruses were estimated from standard body length and axillary girth. Estimated weights ranged from 632 to 1883 kg. The present data suggest that Atlantic walruses at Svalbard can attain the same body size as Pacific ( O. r. divergens ) and Laptev walruses (O. r. laptevi).     

Haul-out and diving activity of male Atlantic walruses (Odobenus rosmarus rosmarus) in NE Greenland

During August-September 1989 and 1990, movements, haul out and dive activity of male Atlantic walruses ( Odobenus rosmarus rosmarus L.) were studied at a terrestrial haul-out site situated in an inshore foraging area in NE Greenland at 76± 30' N. Data were collected from direct observations of a group of about 50 males during August, including walruses that could be individually identified from natural markings, and from tracking of 8 adults equipped with satellite-linked radio transmitters during August-September. In both years, instrumented walruses hauled out for a total of 29.3% of the sampling time. In 1989, when ice floes were available for hauling out, the walruses spent 11% of the time on ice, whereas in 1990, when ice was absent from the study area, they only hauled out on land. Duration of haul-out periods, which did not differ between months or years, averaged 11 h (0.46 d) on ice (S.D. = 5.9, range: 1–29 h, n = 19 periods), and 38 h (1.6 d) on land (S.D. = 11.7, range: 13–64 h, n = 43). The walruses mainly hauled out during the afternoon and evening. Numbers hauling out on land during August were negatively correlated with wind direction, precipitation (rain) and wind-chill. In 1989, the duration of periods of absence from the terrestrial haul-out site (i.e. presumed foraging trips) averaged 206 h or 8.5 d (S.D. = 106.9, range: 48–412 h, n = 13), whereas, in 1990, such trips averaged only 81 h or 3.4 d (S.D. = 37.9, range: 24-156 h, n = 24), reflecting that walruses used the haul-out site more frequently when ice was absent. Direct observations of foraging walruses showed that they were submerged about 81% of the time.     

Aerial survey of Atlantic walruses (Odobenus rosmarus rosmarus) in the Pechora Sea, August 2011

Basic knowledge of the population biology of Atlantic walruses throughout the eastern parts of their range, including the Pechora Sea, is scarce or nonexistent. Herein, we present the first estimate of walrus numbers from the Pechora Sea based on an aerial survey of 2,563?km of coastline, using a combination of infrared techniques and digital imagery. Hauled out walruses were found at three sites (Vaygach Island and two sites on Matveyev Island). A total of 968 animals were counted on aerial photographs; all of the animals appeared to be males. Crude measurements of dorsal curvilinear lengths of a subset of the photographed animals (N?=?504) showed that many were adults, but 14.5?% belonged to younger age classes (shorter than 225?cm). Using an adjustment factor developed for male walruses in Svalbard, to account for animals at sea during the survey, the number of walruses occupying this area was estimated to be 3,943 (95?% CI, 3,605–4,325). No females with calves were seen in this survey, implying that the population that uses the Pechora Sea during summer has a distributional area that is larger than the survey area. Extensive oil exploration, development and production are currently taking place in the Pechora Sea. Risks posed to walruses and their prey by these industrial activities should be assessed immediately, and the genetic delineations of this population should be clarified.     

Underwater observations of foraging free-living Atlantic walruses (Odobenus rosmarus rosmarus) and estimates of their food consumption

Food consumption of Atlantic walruses (Odobenus rosmarus rosmarus L.) was quantified by combining underwater observations of feeding with satellite-telemetry data on movement and diving activity. The study was conducted between 31 July and 7 August 2001 in Young Sound (74°N-20°W) in Northeast Greenland. On ten occasions, divers were able to accompany foraging walruses to the sea floor and collect the shells of newly predated bivalves (Mya truncata, Hiatella arctica, Serripes groenlandicus) for determination of number of prey and biomass ingested per dive. Simultaneously, the activity of a 1,200-kg adult male walrus was studied by use of satellite-telemetry during an entire foraging cycle that included 74 h at sea followed by a 23-h rest on land. An average of 53.2 bivalves (SE=5.2, range: 34-89, n=10) were consumed per dive, corresponding to 149.0 g shell-free dry matter (SE=18.9, range: 62.4-253.1 g), or 2,576 kJ per dive (SE=325.2, range: 1,072-4,377 kJ). During the foraging trip, the walrus spent 57% of the time diving to depths of between 6 and 32 m, and it made a total of 412 dives that lasted between 5 and 7 min (i.e. typical foraging dives). If the entire feeding cycle is considered (97 h), the estimated daily gross energy intake was 214 kJ per kg body mass (95% CI: 153-275 kJ), corresponding to the ingestion of 57 kg (95% CI: 41-72 kg) wet weight bivalve biomass per day, or 4.7 (95% CI: 3.3-5.9%) of total walrus body mass. Due to ice cover, walrus access to the plentiful inshore bivalve banks in the area is restricted to the short summer period, where walruses rely on them for replenishing energy stores. It is hypothesised that the documented decrease in the extent and duration of Arctic sea ice may increase food availability for walruses in eastern Greenland in the future.     

A review of the genetic relationships of Atlantic walrus (Odobenus rosmarus rosmarus) east and west of Greenland

Studies of the genetic variation involving allozymes, mitochondrial and nuclear DNA (microsatellites) in walruses (Odobenus rosmarus) were reviewed. In addition, the genetic relationships of a total of 211 Atlantic walruses, O. r. rosmarus, from 5 sampling areas west and east of Greenland were studied using 12 nuclear DNA-microsatellite loci and restriction fragment length polymorphism obtained from the ND1, ND2 and ND3/4 segments of the mitochondrial DNA (mtDNA). At the mtDNA level, no divergence was observed among the three sampling areas east of Greenland (i.e. East Greenland, Svalbard and Franz Josef Land), whereas areas west of Greenland (i.e. Northwest and West Greenland) showed some differentiation. The genetic variation at the microsatellite loci grouped the individuals into four sub-populations: Northwest Greenland, West Greenland, East Greenland and a common Svalbard-Franz Josef Land sub-population. A significant correlation between genetic distance and geographic distance between the sampling areas (isolation-by-distance effect) was detected, especially at the mtDNA level. At a small-scale phylo-geographical level, the mtDNA data indicated that Atlantic walruses have diverged into two major groups: one northwest (i.e. in the North Water) and one east of Greenland (i.e. an East Greenland-Svalbard-Franz Josef Land group), whereas the haplotype distribution in the West Greenland sample reflected a mixture of both these groups. The microsatellite data supported a general grouping of walruses to the west and east of Greenland.     

Levels of cadmium and mercury in the hair of Atlantic walruses (Odobenus rosmarus rosmarus) from Svalbard,Norway

Hair samples of 15 adult male Atlantic walruses (Odobenus rosmarus rosmarus) collected from anaesthetized individuals at Svalbard, Norway, were analysed for cadmium and total mercury. The mean level of cadmium was 0.860 ± 0.321 μg/g dry weight (median = 0.811, range = 0.349–1.51 μg/g dry weight) and the mean level of mercury was 0.235 ± 0.100 μg/g dry weight (median = 0.251, range = 0.121–0.424 μg/g dry weight). Levels of cadmium and mercury in hair of walruses from other areas are not known. Both cadmium and mercury levels in hair of walruses from Svalbard are relatively low compared to the levels found in the hair of other marine mammal species. It has been documented from a number of marine species, including marine mammals such as ringed seals and polar bears, that both cadmium and mercury levels at Svalbard are lower than in other areas. It is uncertain as to what degree levels in hair reflect levels in internal organs in walruses. In rare and highly endangered species or populations tissue samples can be difficult to collect. In walruses, it is possible to collect hair from anaesthetized individuals or at the haul-out sites during moult, to monitor heavy metal levels of the population. Accepted: 6 December 1998     

Diving and haul-out patterns of walruses Odobenus rosmarus on Svalbard

Nine male walruses were equipped with dive recording devices in Svalbard to investigate walrus diving and haul-out behaviour in late summer. Dive information on 6,018 dives was collected by 3 satellite linked dive recorders. Additional dive information on 7,769 dives was obtained from 3 time depth recorders. The deepest dive recorded was 67 m, but mean depth of foraging dives was 22.5 m. The longest-lasting dive recorded was 24 min, but mean duration of foraging dives was 6 min. The walruses, on average, spent 56 h in the water followed by 20 h hauled out on land.     

Population structure and gene flow of the Atlantic walrus (Odobenus rosmarus rosmarus) in the eastern Atlantic Arctic based on mitochondrial DNA and microsatellite variation

The population structure of the Atlantic walrus, Odobenus rosmarus rosmarus , was studied using 11 polymorphic microsatellites and restriction fragment length polymorphism detected in the NADH-dehydrogenase ND1, ND2 and ND3/4 segments in mtDNA. A total of 105 walrus samples were analysed from northwest (NW) Greenland, east (E) Greenland, Svalbard and Franz Joseph Land. Two of the 10 haplotypes detected in the four samples were diagnostic for the NW Greenland sample, which implied that the group of walruses in this area is evolutionary distinct from walruses in the other three areas. One individual sampled in E Greenland exhibited a Pacific haplotype, which proved a connection between the Pacific walrus and walruses in eastern Greenland. The Franz Joseph Land, Svalbard and E Greenland samples shared the most common haplotype, indicating very little differentiation at the mtDNA level. Gene flow ( Nm ) estimates among the four areas indicated a very restricted exchange of female genes between NW Greenland and the more eastern Atlantic Arctic samples, and a closer relationship between the three samples composing the eastern Atlantic Arctic. The genetic variation at 11 polymorphic microsatellite loci grouped individuals into three populations, NW Greenland, E Greenland and a common Franz Joseph Land–Svalbard population, which were connected by moderate gene flow.     

Faecal DNA amplification in Pacific walruses (Odobenus rosmarus divergens)

Dietary information is critical for assessing the population status of seals, sea lions and walruses—and is determined for most species of pinnipeds using non-invasive methods. However, diets of walruses continue to be described from the stomach contents of dead individuals. Our goal was to assess whether DNA could be extracted from the faeces of Pacific walruses (Odobenus rosmarus divergens) collected at haulout sites, and whether potential prey species or taxa could be amplified from that DNA. We extracted DNA from 70 faecal samples collected from ice pans in the Bering Sea during the spring of 2008 and 2009 (with between 4.6 and 308.9 ng/μl of DNA in every sample). We also extracted DNA from 12 potential prey species or taxa collected by bottom-grabs in 2009 to identify positive controls for primers and to test the ability of previously published taxon-specific and species-specific primers to correctly identify the prey using conventional PCR. We tested primers that successfully amplified DNA from the tissue of at least one potential prey species or taxon on all 70 walrus faecal samples. We found that two sets of primers successfully amplified many of the potential prey species or taxa using DNA from their tissue, and that one of these primer sets produced positive amplification in 4 of the 70 faecal samples. The band size that was produced for prey organisms and in the faecal samples was consistent with expectations, although prey identities were not verified with sequencing. Our pilot study demonstrates that DNA can be successfully extracted and amplified from walrus faeces, providing a stepping stone towards describing the diets of walruses from faecal DNA.     

Models of tongue movement in the walrus (Odobenus rosmarus)

Three hypothetical models of tongue movement of the walrus during suction feeding are examined. These models encompass the entire range of simple tongue retraction movements possible by examining 1) movement of the tongue directly to the rear following the curvature of the palate, 2) to the rear and ventrally in a straight line, and 3) ventrally in a straight line. The percent of muscular force available from the hyoglossus, genioglossus, and styloglossus that could be applied toward retraction as predicted by each model is calculated. The resistance that the tongue would provide during retraction is calculated using projected tongue areas and is combined with the above data from the muscles to provide an estimate of the percent of the total available force that is needed to retract the tongue for each model. A separate examination of the direction of tongue-induced wear striations on the palatal and lingual aspects of the teeth is used to help support or reject the three models. The model where the tongue is moved directly to the rear is supported by studies of both muscle force and tooth wear. In the mammalian groups that were compared to the walrus, there is a great deal of interspecific variation in movements of the tongue during suction feeding; no two groups can be considered to have identical stereotyped tongue movements.     

Towards a Better Understanding of the Effects of UV on Atlantic Walruses,Odobenus rosmarus rosmarus: A Study Combining Histological Data with Local Ecological Knowledge

Walruses, Odobenus rosmarus, play a key role in the Arctic ecosystem, including northern Indigenous communities, which are reliant upon walruses for aspects of their diet and culture. However, walruses face varied environmental threats including rising sea-water temperatures and decreasing ice cover. An underappreciated threat may be the large amount of solar ultraviolet radiation (UV) that continues to reach the Arctic as a result of ozone loss. UV has been shown to negatively affect whales. Like whales, walrus skin is unprotected by fur, but in contrast, walruses spend long periods of time hauled-out on land. In this study, we combined the results of histological analyses of skin sections from five Atlantic walruses, Odobenus rosmarus rosmarus, collected in Nunavik (Northern Quebec, Canada) with qualitative data obtained through the interviews of 33 local walrus hunters and Inuit Elders. Histological analyses allowed us to explore UV-induced cellular lesions and interviews with experienced walrus hunters and Elders helped us to study the incidences and temporal changes of UV-induced gross lesions in walruses. At the microscopic scale, we detected a range of skin abnormalities consistent with UV damage. However, currently such UV effects do not seem to be widely observed at the whole-animal level (i.e., absence of skin blistering, erythema, eye cataract) by individuals interviewed. Although walruses may experience skin damage under normal everyday UV exposure, the long-term data from local walrus hunters and Inuit Elders did not report a relation between the increased sun radiation secondary to ozone loss and walrus health.     

The Laptev Sea walrus Odobenus rosmarus laptevi: an enigma revisited

The walrus ( Odobenus rosmarus ) is in some current systematic schemes divided into three subspecies: O. r. rosmarus in the North Atlantic, O.   r. divergens in the North Pacific and O.   r. laptevi in the Laptev Sea. These three subspecies have been described as differing in body size, but the taxonomic status of O.   r. laptevi is disputed. The current study applies molecular and morphometric methods to assess the taxonomic status of O.   r. laptevi and to analyse the systematic and phylogeographic relationships between the three purported walrus subspecies. Tusk length and tusk circumference were measured from the few skulls available of O.   r. laptevi , and the obtained values were within the ranges reported for Pacific walruses. Thus, morphologically, subspecies status for O.   r. laptevi is not supported according to the Amadon–Mayr '75% rule'. Phylogenetic analyses and haplotype networks based on mitochondrial nucleotide sequence data of NADH dehydrogenase 1, 16S rRNA, cytochrome oxidase I and the d -loop of the control region of the historic O.   r. laptevi bone material and contemporary O.   r. rosmarus and O.   r. divergens showed that the Laptev Sea walrus groups with individuals from the North Pacific. Thus, the mitochondrial sequence data do not support the recognition of three walrus subspecies as reciprocally monophyletic evolutionary units with independent evolutionary histories. Only O.   r. rosmarus and O.   r. divergens meet this criterion with the present sampling. Accordingly, we recommend that Odobenus r. laptevi be abandoned and the Laptev walrus instead be recognized as the westernmost population of the Pacific walrus, Odobenus r. divergens. However, further research is recommended to assess whether the Laptev walrus could be considered as a significant unit in terms of conservation and management, since it is unique in several ecological parameters.     

Social vocal communication in captive Pacific walruses Odobenus rosmarus divergens

Walrus are highly gregarious pinnipeds that can form herds of several hundreds or thousands of individuals when hauling out on ice or on land. They produce vocalisations in almost all social interactions, from aggressive vocalisations, contact calls involved in mother–calf bond to adult–adult communication to stereotyped courtship display during the mating season. The knowledge on walrus’ vocal behaviour and its perceptual abilities is limited due to the extreme difficulty of studying these animals in their natural environment. In the present study, we reported the results of a pilot experimental work on group/social vocal communication in captive Pacific Walruses (Odobenus rosmarus divergens). By analysing the main vocalisations produced by females and males during social interactions, we found some differences in their call characteristics compared to the Atlantic subspecies. In a second step, we experimentally demonstrated the abilities of females and mature males to discriminate between vocalizations of individuals from their own group and those of unknown individuals. In spite of the low sample size of animals, these findings on captive walruses improved knowledge of the cognitive abilities of this endemic Arctic species.     

Resting and swimming metabolic rates in juvenile walruses (Odobenus rosmarus)

Changes in Arctic ice conditions have raised concerns regarding potential impacts on energy expenditure and food requirements of walruses. Modeling the repercussions of environmental changes requires accurate species-specific measures of bioenergetic expenditures. This is particularly true for walruses, who have a unique anatomy and foraging ecology from other pinnipeds. This study measured resting metabolic rate (RMR) and subsurface swimming metabolism in two juvenile walruses over a 13-month period. The walruses had relatively low RMR compared to studies of other young pinnipeds. RMR was greater for the male than the female, as expected given its larger size; the reverse was true on a mass-specific basis. There was also considerable variability in RMR for each walrus during the year that could not be accounted for by changes in body mass. Metabolism while swimming was about twice RMR, and locomotor costs were higher than generally predicted for other marine mammals. The lower calculated swimming efficiency may reflect the fact that walruses are not “high velocity” pursuit predators. The estimates of metabolic expenditure obtained in this study for young walruses are invaluable for quantifying the energetic consequences of behavioral changes induced by environmental shifts in the wild.     

The number of walruses (Odobenus rosmarus) in Svalbard in summer

Walruses were on the verge of extinction in Svalbard prior to becoming totally protected in 1952. The present study attempts to determine the number of walruses in Svalbard in summer based on aerial, ground and boat surveys. In 1993, 741 walruses were observed, almost all of which were males. This population, which is shared with the neighbouring Russian archipelago Franz Joseph Land, is believed to consist of an equal number of females. We therefore conclude that the shared population consists of a minimum of about 1450 walruses older than 2 years and an unknown number of calves.     

Dentition in Pacific walrus (Odobenus rosmarus divergens) calves of the year

The oral cavity and teeth were examined in Pacific walrus calves of the year that died or were harvested on Cape Vancarem and Koluchin Island, the Chukchi Sea, in September to October 2010. The order of gingival eruption of teeth, the resultant dental formula in calves of the year and 1.5-year-old animals, and the dental formula after alveolar eruption of teeth were determined. The number of teeth after gingival eruption in calves of the year did not depend on their body length and sex. The loss of some teeth, mainly incisors, was recorded in individuals aged 5?C6 months. Already at early developmental stages, functional teeth were found to differ significantly from other (rudimentary) teeth in their weight, total size, and the size of apical foramen. Some individuals had milk teeth, which were either gingivally erupted or partly remained within soft tissues. Cases of aberration in dentition that require additional studies were recorded.