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Ecology and Biology of the Pacific Walrus, Odobenus rosmarus divergens Illiger
Abstract
The distribution, physical development, pelage, dentition, feeding behavior, reproduction, causes of mortality, and population structure of the Pacific walrus (Odobenus rosmarus divergens) were studied intermittently from 1952 to 1979. In winter, these animals tend to concentrate in north-central and southeastern Bering Sea, where sea ice conditions are most favorable for them. In summer, they concentrate mainly in northwestern and northeastern Chukchi Sea, along the edge of the ice. Most of the northward migrants are females and young; a large proportion of the adult males remains in the Bering Sea throughout the summer. Pacific walruses show strong sexual dimorphism; adult males are about 18% longer and 45% heavier and tend to have larger, more divergent tusks, as well as thicker, lighter-colored, and less hairy skin than adult females. As in other sexually dimorphic otarioid pinnipeds, males undergo secondary growth, beginning about the time of puberty and ending in full physical maturity about 15 years of age. The first pelage is a fine, white lanugo, which develops and is shed in utero. The second (natal) pelage, which resembles that of the adult, is shed and replaced 2 to 3 months after birth, in synchrony with the molt of older animals. The full primary and secondary dentitions include 38 and 30 teeth, respectively; 7 pairs of primary and 6 pairs of secondary teeth occur in less than 50 % of the animals. The permanent first upper premolar is a secondary tooth, preceded by an uncalcified primary tooth. The lower premolars appear to be homologues of P2-3-4, rather than P1-2-3. The cheek teeth grow in length very slowly, and the pattern of decrement of their crowns indicates no contact with molluscan shells except in the incisive area at the front of the mouth. The abrasion of the tusks indicates that they are dragged through the bottom sediments, rather than used for digging or raking. Food of the Pacific walrus consists of more than 60 genera of marine organisms, most of which are situated on or just beneath the surface of the sediments. The walrus apparently locates these tactually with its sensitive mystacial vibrissae and by “rooting” with its snout. Soft-bodied organisms are ingested directly, without mastication; the soft parts (siphon, foot) of mollusks probably are separated from the shells by suction. The intake of food is at least 5 to 7% of the total body weight per day. Most females ovulate for the first time at 5 or 6 years; males become fertile at 8 to 10 years but probably do not participate in mating until fully mature at 15 years. Walruses are polygynous; mating takes place mainly in mid-winter. Implantation of the blastocyst takes place about 5 months later, and the calf is born in the following spring, after a pregnancy lasting at least 15 months. Females tend to breed at 2-year intervals or less often and are most productive between the ages of 8 and 15 years. The principal causes of mortality appear to be predation, intraspecific trauma, and microbiological infections. The Pacific walrus population was severely depleted in the late 19th century and again in the mid-20th century by overharvests for commercial purposes. Over the past 20 years, it apparently has recovered rapidly, in response to reduced harvest. The sex ratio of breeding adults appears to be about 1 male:3 or 4 females. The crude birth rate in recent years is estimated at 17 ± 2%, and the survival of young to puberty appears to be very high.
... Additional information can be found via comparison with living sexually dimorphic megafauna with similar features and their inferred ecological roles. Many living mammal megafauna, such as hippopotami, elephants, and walruses, have dimorphic tusks and other facial features that can be classified as weaponry [49,50], which are similar to the caniniforms of Placerias. Some of these taxa (e.g., elephants) also represent species with both SSD and proportional differences in features used as weaponry, while others only differ substantially in proportional size of dimorphic weaponry and not in body size (e.g. ...
... Kinematic work on the jaw of Placerias has posited that it, along with other Late Triassic dicynodonts, was specialized for vertical head movement, based on the distances between occipital muscle attachment points, which correlate to proportions of neck muscles in life [51]. This inferred vertical plane of movement correlates well with multiple speculated behaviors in Placerias, such as rooting using the caniniforms, but also, for large morphs, aiming their ventrally projecting caniniforms anteriorly towards other individuals while holding up their heads, in a similar manner to walruses [49]. Some of the largest Placerias maxillae diverge laterally, a phenomenon also observed in male walruses. ...
... Some of the largest Placerias maxillae diverge laterally, a phenomenon also observed in male walruses. While there has not been much work exploring the advantage of tusk divergence in male walruses, it may be related to the greater use of tusks as social organs in males than in females, both to enhance visual threat displays by increasing apparent tusk size [49], and potentially by increasing physical range of the tips of their tusks in combat with other males. These functions may also apply to the caniniforms in Placerias, both for threat displays and physical confrontations, using the cone shaped tips of the caniniforms to stab at opponents. ...
Placerias hesternus, a Late Triassic dicynodont, is one of the last megafaunal synapsids of the Mesozoic. The species has a tusk-like projection on its maxillary bone, known as the caniniform process. This process has been hypothesized to be sexually dimorphic since the 1950s, however this claim has not been thoroughly investigated quantitatively. Here, we examined maxillae, premaxillae, quadrates, and fibulae from a single population from the Placerias Quarry in the Blue Mesa Member of the Chinle Formation, near St. Johns, Arizona, USA to determine if the caniniform process is dimorphic. We made a total of 25 measurements from the four bones and used a maximum likelihood framework to compare the fit of unimodal versus bimodal distributions for each set of measurements. Our results from complete maxillae reveal that the caniniform process has two distinct morphs, with a shorter and longer form. This interpretation is substantiated both by strong statistical support for bimodal distribution of caniniform lengths, and by clustering analysis that clearly distinguishes two morphs for the maxillae. Clustering analysis also shows support for potential dimorphism in the shape of the quadrate. However, no measurements from elements other than the maxilla have a strong likelihood of bimodal distribution. These results support the long-standing hypothesis that the caniniform in Placerias was dimorphic. Alternative explanations to sexual dimorphism that could account for the dimorphism among these fossils include the presence of juveniles in the sample or time-averaged sampling of a chronospecies, but both have been previously rejected for the Placerias Quarry population. The lack of strong dimorphism in non-maxilla elements and increased variation in caniniform length of the large-caniniform morph suggest that the caniniform is a secondary sexual trait, possibly used in intraspecific competition.
... The Pacific walrus (Odobenus rosmarus divergens) is a prevalent species of Arctic megafauna primarily inhabiting the Bering and Chukchi seas. Among indigenous communities along the coasts of Alaska and Siberia, walruses have also served a key role in diet, culture and economic practices for at least 2000 years [1][2][3][4][5][6]. Like many Arctic species, Pacific walruses are potentially vulnerable to rapid changes in climate and sea ice availability in these regions. ...
... Fish and bivalve prey may act as intermediate hosts for parasites that ultimately infect walruses as their definitive host; therefore, a potential climate-driven shift in prey consumption could alter walrus parasite exposure. Previous studies have identified a variety of parasites in walruses including members of families Brachycladiidae [1], Diphyllobothriidea [29], Anisakidae [1], Trichinellidae [30], Polymorphidae (Corynosoma validum) [31] and Sarcocystidae (Toxoplasma gondii, Neospora cranium and Sarcocystis neurona) [32]. Though these parasite families have distinct life cycles, most use bivalves and/or fish as intermediate hosts and are therefore likely to infect walruses via infected prey. ...
... Fish and bivalve prey may act as intermediate hosts for parasites that ultimately infect walruses as their definitive host; therefore, a potential climate-driven shift in prey consumption could alter walrus parasite exposure. Previous studies have identified a variety of parasites in walruses including members of families Brachycladiidae [1], Diphyllobothriidea [29], Anisakidae [1], Trichinellidae [30], Polymorphidae (Corynosoma validum) [31] and Sarcocystidae (Toxoplasma gondii, Neospora cranium and Sarcocystis neurona) [32]. Though these parasite families have distinct life cycles, most use bivalves and/or fish as intermediate hosts and are therefore likely to infect walruses via infected prey. ...
... The extant walrus Odobenus rosmarus Brisson, 1762 is an iconic pinniped uniquely bearing elongated canine tusks, and is the third largest pinniped after the elephant seals (Mirounga spp. Gray, 1827), weighing 800-1200 kg (females and males, respectively; Fay, 1982). Unlike most pinnipeds belonging to the Otariidae (eared seals) and Phocidae (true seals) families, Odobenus feeds predominantly on mollusks and has no other close living relatives (Boessenecker & Churchill, 2021). ...
... Species of Valenictus also possess a palate that is deeply transversely and longitudinally vaulted, as well as a palate that is extended further posteriorly relative to earlier diverging "imagotariine" walruses (e.g., Neotherium, Proneotherium, Imagotaria). Extant Odobenus possesses teeth including one incisor (but up to three in juveniles; McLaughlin et al., 2022) and 3-4 premolars and molars (Fay, 1982), but the teeth are not used in feeding. Feeding experiments and analysis of gut contents indicate that mollusks are held in place by the lips and that the shell does not enter the oral cavity, nor is ingested as might be expected if shells were masticated; likewise, nonmollusk prey recovered as gut contents lack tooth marks (Fay, 1982). ...
... Extant Odobenus possesses teeth including one incisor (but up to three in juveniles; McLaughlin et al., 2022) and 3-4 premolars and molars (Fay, 1982), but the teeth are not used in feeding. Feeding experiments and analysis of gut contents indicate that mollusks are held in place by the lips and that the shell does not enter the oral cavity, nor is ingested as might be expected if shells were masticated; likewise, nonmollusk prey recovered as gut contents lack tooth marks (Fay, 1982). Soft tissues of mollusks are removed from the shell by suction; negative pressure is generated by the ventral retraction of the tongue from the vaulted palate (Fay, 1982;Kastelein et al., 1997). ...
Currently limited to cold climates near the Arctic circle, living walruses are the sole survivors of a previously much more diverse clade that occupied coastal waters throughout the northern hemisphere during the Mio–Pliocene. Though pinniped faunas have the highest diversity of walruses in the Miocene, the Purisima Formation of California records a moderately diverse assemblage of four walrus species. We report new specimens of tusked walruses (Odobeninae) including the oldest known members of Odobeninae, and Odobenini, and fossils of the specialized toothless odobenine walrus Valenictus Mitchell, 1961. Among these is the new species Valenictus sheperdi sp. nov., represented by a complete skull and referred post-crania from lower Pliocene strata within the Purisima Formation (5.33–4.89 Ma). Additionally, we report a geochronologically younger skull of Valenictus chulavistensis Deméré, 1994 from further up section (4.89–3.59 Ma). Expanded phylogenetic analysis recovers Odobeninae including Ontocetus Leidy, 1859 as the earliest diverging lineage in the Odobenini, and places a monophyletic Valenictus as the sister taxon to Pliopedia, Kellogg, 1921 which is included in a phylogeny for the first time; Odobenus is sister to the Valenictus + Pliopedia clade. Discovery of an isolated metacarpal near the base of the formation provides the oldest known well-dated evidence of odobenines. A diverse assemblage of molluskivores characterized the Neogene eastern North Pacific and their extinction around the Pliocene– Pleistocene boundary coincided with tectonically driven paleogeographic changes on the Pacific coast. The loss of temperate walruses may have provided opportunities for both new molluskivores and the otariid and phocid pinnipeds that make up present North Pacific pinniped communities.
... The stenophagous walruses are an important component of many High Arctic marine ecosystems where they predate on the benthic invertebrate fauna in coastal waters (e.g. Vibe, 1950;Fay, 1982;Oliver et al., 1983). Although walruses may feed on a variety of bottom-dwelling invertebrates, only a few bivalve species -usually Mya sp., Hiatella sp. and Serripes sp. ...
... Although walruses may feed on a variety of bottom-dwelling invertebrates, only a few bivalve species -usually Mya sp., Hiatella sp. and Serripes sp. -make up the bulk of their diet (Vibe, 1950;Fay, 1982;Fay et al., 1984;Sheffi eld et al., 2001). The Young Sound study area has a rich benthic infauna including abundant quantities of potential walrus food items Sejr et al., 2000Born et al., 2003). ...
... We estimated that the average TBM of the walruses in Young Sound is about 1000 kg. This is somewhat higher than the average TBM of 512 kg used by Welch et al. (1992) for calculation of walrus feeding in Lancaster Sound (Canada), and 712 kg used by Fay (1982) in Alaska. However, the walruses that feed in Young Sound are nearly all adult males in contrast to the other two areas where all age classes and both sexes are represented at the summer feeding grounds. ...
The total consumption of bivalve prey by walruses (Odobenus rosmarus) in the important inshore summer feeding area Young Sound (about 74° N) in Northeast Greenland was estimated. To determine relative area use, the movement and activity of three adult male walruses carrying satellite transmitters were studied during the open-water season in 1999 and 2001. Because one of the animals was tracked during both years the study covered a total of four “walrus seasons”. Overall, the animals spent c. 30% of their time in the water inshore in Young Sound between Sandøen and Zackenberg. The remaining time was spent along the coast north and south of Young Sound and offshore in the Greenland Sea. The total amount of bivalve food consumed in Young Sound by the walruses during a total of 1620 “walrus feeding days” was calculated from information on the total number of walruses using the area (n=60), occupancy in the study area, and estimates obtained from satellite telemetry on the number of daily feeding dives (118-181/24 h at sea). Depending on the applied estimator of number of feeding dives, the estimated consumption by walruses of shell-free (SF) bivalve wet weight (WW) during the open-water period ranged between 111 and 171 tons. Based on estimates of mean total body mass (TBM: 1000 kg) of walruses using the area and daily per capita gross food intake (6% of TBM), the corresponding estimate of consumption by walruses is c. 97 tons SF WW. It is suggested that the two lowest estimates of total consumption are the most plausible.
... In this section we characterize Pacific walrus "structural mass" (S t ; i.e., tissue such as bones & organs that cannot be catabolized for energetic needs), whereas "reserve mass" (F t ; i.e., muscle and blubber) is modified in the sections below pertaining to growth, metabolism, and reproduction. Because we require structural mass (as opposed to total mass) for the DEB model, we were unable to directly apply documented mass growth curves (Fay, 1982) and instead relied on the generalized von Bertalanffy growth equation, which provided a reasonable fit to historical, empirical data for Pacific walruses (McLaren, 1993): ...
... We assumed male and female calves grow at the same rate from T 0 (birth day) to TC W (weaning day). Although walruses are sexually dimorphic, sex-specific differences in body length growth curves appear minimal, and mass-length relationships are not significantly different between sexes in the first two years of life (Fay 1982;Garlich-Miller & Stewart, 1998). ...
... We assumed fetuses grow at a constant rate from a length of 0 cm (at implantation) to L 0 (at birth), over the course of active gestation (T P = 310 days; Table 1; Fay 1982). We estimated the structural mass of the fetus using the same mass-length relationship that was used for females. ...
Climate change and anthropogenic disturbance are increasingly affecting wildlife at a global scale. Predicting how varying types and degrees of disturbance may interact to influence population dynamics is a key management challenge. Population Consequences of Disturbance (PCoD) models provide a framework to link effects of anthropogenic disturbance on an individual's behavior and physiology to population-level changes. Bioenergetic models often constitute the basis of these frameworks, wherein an individual's daily energy balance is simulated over the course of its lifetime, allowing many individuals to be subjected to different environmental conditions and ultimately simulate population-level vital rates under varying degrees of disturbance. In the present study, we develop a Pacific walrus (Odobenus rosmarus divergens) PCoD model to encompass the population-level effects of both anthropogenic disturbance and climate change. Pacific walruses are an Arctic/subarctic ice-associated pinniped. As the Arctic has become increasingly ice-free with climate change, walruses spend more time on land-based (rather than ice-based) haulouts from which they must expend more energy to reach foraging areas, and where they have a greater risk of predation and disturbance-based mortalities. Concurrently, sea ice loss is increasing the anthropogenic footprint in Arctic regions (e.g., fisheries, shipping, energy exploration) which creates additional disturbance. We developed a bioenergetic Dynamic Energy Budget (DEB) model for the Pacific walrus and applied it to four scenarios (ranging from optimistic-pessimistic) which incorporate different global sea ice model projections along with varying degrees of anthropogenic disturbance. All scenarios indicated a decline in Pacific walrus carrying capacity and population growth rate (and thus overall abundance) to the end of the 21st century, but demonstrated that the intensity of that decline could be mitigated by global efforts to reduce carbon emissions (i.e., lessening the rate of sea ice loss) and local management and conservation efforts to protect sensitive habitat areas. In summary, we introduced a flexible PCoD modelling framework in a novel context which will prove useful to researchers studying walruses and other species similarly threatened by rapid environmental change.
... Se alimenta de la fauna bentónica de las plataformas continentales. Los individuos viven entre 30-40 años, poseen un ciclo migratorio anual y su periodo de gestación dura aproximadamente 15 meses (Fay, 1982). ...
... En invierno (de diciembre a marzo) la población se encuentra en los bordes helados del mar de Bering, la isla St. Lawrence, la bahía de Bristol (al suroeste de Alaska) y las costas continentales del golfo de Anadyr (Fay, 1982). En esta estación se produce el apareamiento de forma panmíctica, comportándose como una única población (Garlich-Miller y cols., 2011;MacCracken, 2012). ...
... Durante la primavera (de abril a junio), los hielos del mar se van derritiendo y comienza la migración hacia el Norte por el estrecho de Bering. Durante la misma, tiene lugar el nacimiento de las nuevas crías, las cuales se mantienen junto a sus madres durante al menos dos años (Fay, 1982). ...
El presente artículo muestra un ejemplo de trabajo interdisciplinario entre la matemática aplicada, la ecología y la docencia. En el mismo se detalla el proceso de construcción de un modelo poblacional para las morsas del Pacífico (Odobenus rosmarus), a partir de su información biológica y etológica, con el agregado de los efectos del cambio climático sobre su ambiente. Describimos paso a paso el razonamiento en cada etapa del modelado, realizamos una simulación del mismo con el software RStudio e interpretamos los resultados. Consideramos que este trabajo puede servir para ejemplificar las herramientas pedagógicas que se requieren para la enseñanza de la matemática aplicada en relación a las problemáticas ambientales del presente, permitiendo dar un sentido concreto a los resultados teóricos de la matemática.
This article provides an example of interdisciplinary work involving applied mathematics, ecology, and education. It describes the process of developing a population model for Pacific walruses (Odobenus rosmarus) based on biological and ethological data, as well as the effects of climate change on their environment. We describe the reasoning at each stage of the modeling step by step, then simulate it with the RStudio software and interpret the results. We believe that this work can serve as an example of the pedagogical tools required for the teaching of applied mathematics in relation to current environmental problems, allowing theoretical mathematical results to be given concrete meaning.
... Visual observations of feeding behaviors both in captivity and in-situ and analysis of stomach contents revealed that suction is the major mechanism of food ingestion (Fay 1982;Levermann et al. 2003;Dehn et al. 2007). Walruses place the whole burrowed mollusc between their lips, remove the soft tissues (foot and/or siphon) of bivalves using their powerful jaw, and then expulse shells (Gordon 1984). ...
... To our knowledge, this new potential behavior has never been described in the walrus literature. Indeed, previous studies have demonstrated they only use suction to feed on bivalves' soft tissues while leaving the shells intact (Fay 1982;Born et al. 2003;Jones et al. 2013). This new behavior could be directly linked to bivalves emerged from the sand, lying down on the seafloor. ...
... This new behavior could be directly linked to bivalves emerged from the sand, lying down on the seafloor. As a result, walruses cannot use suction mechanism because they are unable of employing their fins to manually move their preys to their mouths (Fay 1982;Levermann et al. 2003;Dehn et al. 2007). The emergence of the bivalves on the bottom was observed via scuba divers during this study (Online Resource 2). ...
The vocal repertoire of walruses has been widely described in the bioacoustic literature. These marine mammals produce several distinct types of vocalizations for intraspecific communication during the breeding season. In this study, we provide the first evidence of walrus-generated sounds during foraging dives when they feed on bivalves. We recorded two types of sounds that we associated to different feeding mechanisms. The first sound type was brief and low in frequency that we relate to the suction of soft parts from the bivalves’ shells through the use of walrus powerful tongues, which is the common feeding behavior reported in the walrus literature. We also recorded a second sound type composed of multiple broadband pulse trains. We hypothesize the latter were associated with bivalve shell cracking by walruses, which would represent a new feeding mechanism in the walrus literature. This new feeding mechanism is either related to bivalves’ ecology or to walruses removing the sediment when searching for food. During this study, we observed bivalves lying on the seafloor instead of being buried in the sediment in walrus feeding areas while scuba diving. As a result, walruses cannot use suction to feed on soft body part of bivalves and have to use another strategy, mastication. Our findings provide a first step towards using passive acoustics to quantify walrus behavior and feeding ecology.
... The Pacific walrus (Odobenus rosmarus divergens) is a prevalent species of Arctic megafauna primarily inhabiting the Bering and Chukchi seas. Among indigenous communities along the coasts of Alaska and Siberia, walruses have also served a key role in diet, culture and economic practices for at least 2000 years [1][2][3][4][5][6]. Like many Arctic species, Pacific walruses are potentially vulnerable to rapid changes in climate and sea ice availability in these regions. ...
... Fish and bivalve prey may act as intermediate hosts for parasites that ultimately infect walruses as their definitive host; therefore, a potential climate-driven shift in prey consumption could alter walrus parasite exposure. Previous studies have identified a variety of parasites in walruses including members of families Brachycladiidae [1], Diphyllobothriidea [29], Anisakidae [1], Trichinellidae [30], Polymorphidae (Corynosoma validum) [31] and Sarcocystidae (Toxoplasma gondii, Neospora cranium and Sarcocystis neurona) [32]. Though these parasite families have distinct life cycles, most use bivalves and/or fish as intermediate hosts and are therefore likely to infect walruses via infected prey. ...
... Fish and bivalve prey may act as intermediate hosts for parasites that ultimately infect walruses as their definitive host; therefore, a potential climate-driven shift in prey consumption could alter walrus parasite exposure. Previous studies have identified a variety of parasites in walruses including members of families Brachycladiidae [1], Diphyllobothriidea [29], Anisakidae [1], Trichinellidae [30], Polymorphidae (Corynosoma validum) [31] and Sarcocystidae (Toxoplasma gondii, Neospora cranium and Sarcocystis neurona) [32]. Though these parasite families have distinct life cycles, most use bivalves and/or fish as intermediate hosts and are therefore likely to infect walruses via infected prey. ...
Arctic species are likely to experience rapid shifts in prey availability under climate change, which may alter their exposure to microbes and parasites. Here, we describe fecal bacterial and macroparasite communities and assess correlations with diet trophic level in Pacific walruses harvested during subsistence hunts by members of the Native Villages of Gambell and Savoonga on St Lawrence Island, Alaska. Fecal bacterial communities were dominated by relatively few taxa, mostly belonging to phyla Fusobacteriota and Firmicutes. Members of parasite-associated phyla Nematoda, Acanthocephala and Platyhelminthes were prevalent in our study population. We hypothesized that high versus low prey trophic level (e.g. fish versus bivalves) would result in different gut bacterial and macroparasite communities. We found that bacterial community structure correlated to diet, with nine clades enriched in walruses consuming higher-trophic-level prey. While no parasite compositional differences were found at the phylum level, the cestode genus Diphyllobothrium was more prevalent and abundant in walruses consuming higher-trophic-level prey, probably because fish are the intermediate hosts for this genus. This study suggests that diet is important for structuring both parasite and microbial communities of this culturally and ecologically important species, with potential implications for population health under climate change.
... Another aquatic mammal that utilizes sensory hairs to forage and feed is the Pacific walrus (Odobenus rosmarus divergens) [10,112,113]. The Pacific walrus forages at night in deep water with low visibility and preys on benthic organisms, such as clams, oysters, and mussels [112,113]. ...
... Another aquatic mammal that utilizes sensory hairs to forage and feed is the Pacific walrus (Odobenus rosmarus divergens) [10,112,113]. The Pacific walrus forages at night in deep water with low visibility and preys on benthic organisms, such as clams, oysters, and mussels [112,113]. Due to the position of its eyes and the width of its snout, the Pacific walrus has reduced visibility in front of its face [113] and therefore takes advantage of sensory hairs located on the face for tactile information from the surroundings. The Pacific walrus has approximately 400 to 700 vibrissae organized into 13 to 18 rows on their mystacial pads [110]. ...
... The Pacific walrus has approximately 400 to 700 vibrissae organized into 13 to 18 rows on their mystacial pads [110]. These vibrissae are extremely mobile and have been observed to be active and move rapidly during the exploration of objects or during feeding [112]. Early research hypothesized that these vibrissae in Pacific walruses serve a sensorimotor function and were responsible for providing crucial tactual information for foraging and feeding. ...
Biological mechanosensation has been a source of inspiration for advancements in artificial sensory systems. Animals rely on sensory feedback to guide and adapt their behaviors and are equipped with a wide variety of sensors that carry stimulus information from the environment. Hair and hair-like sensors have evolved to support survival behaviors in different ecological niches. Here, we review the diversity of biological hair and hair-like sensors across the animal kingdom and their roles in behaviors, such as locomotion, exploration, navigation, and feeding, which point to shared functional properties of hair and hair-like structures among invertebrates and vertebrates. By reviewing research on the role of biological hair and hair-like sensors in diverse species, we aim to highlight biological sensors that could inspire the engineering community and contribute to the advancement of mechanosensing in artificial systems, such as robotics.
... Bivalves are their preferred prey item but their diet can also include large contributions of gastropods and polychaetes in the Chukchi and Bering seas [13,17]. Most of what is known about the Pacific walrus diet has come from fresh stomach content studies, acknowledging that some prey items are underrepresented with this method [13,18]. Uncertainties remain regarding the breadth of their diets and the flexibility that exists to adapt and partition resources with other benthic predators in the region [19]. ...
... As an ice-obligate species [21], the geographic range of the Pacific walrus overlaps with the seasonal ice coverage in the region (Fig 1) [22,23]. However, they are limited to the shallow waters over the continental shelf where they can effectively forage [18]. This adaptation has proven to be an issue in recent years because the ice edge has consistently retreated off of the shelf into the deeper waters of the Arctic Ocean, limiting an important platform for foraging walruses in the late summer [11,24]. ...
... The lack of sea ice inhibits their ability to forage further offshore where benthic biomass is substantially higher than these nearshore locations [11]. The ice-obligate classification of the Pacific walrus is also because sea ice provides a necessary platform for female walruses to give birth and nurse their young [18]. Therefore, females and dependent calves are particularly reliant on the presence of sea ice; they migrate annually with the ice edge into the Chukchi Sea where they remain (when possible) through the fall until the ice begins to re-form [18]. ...
The expected reduction of ice algae with declining sea ice may prove to be detrimental to the Pacific Arctic ecosystem. Benthic organisms that rely on sea ice organic carbon (iPOC) sustain benthic predators such as the Pacific walrus (Odobenus rosmarus divergens). The ability to track the trophic transfer of iPOC is critical to understanding its value in the food web, but prior methods have lacked the required source specificity. We analyzed the H-Print index, based on biomarkers of ice algae versus phytoplankton contributions to organic carbon in marine predators, in Pacific walrus livers collected in 2012, 2014 and 2016 from the Northern Bering Sea (NBS) and Chukchi Sea. We paired these measurements with stable nitrogen isotopes (δ15N) to estimate trophic position. We observed differences in the contribution of iPOC in Pacific walrus diet between regions, sexes, and age classes. Specifically, the contribution of iPOC to the diet of Pacific walruses was higher in the Chukchi Sea (52%) compared to the NBS (30%). This regional difference is consistent with longer annual sea ice persistence in the Chukchi Sea. Within the NBS, the contribution of iPOC to walrus spring diet was higher in females (~45%) compared to males (~30%) for each year (p < 0.001), likely due to specific foraging behavior of females to support energetic demands associated with pregnancy and lactation. Within the Chukchi Sea, the iPOC contribution was similar between males and females, yet higher in juveniles than in adults. Despite differences in the origin of organic carbon fueling the system (sea ice versus pelagic derived carbon), the trophic position of adult female Pacific walruses was similar between the NBS and Chukchi Sea (3.2 and 3.5, respectively), supporting similar diets (i.e. clams). Given the higher quality of organic carbon from ice algae, the retreat of seasonal sea ice in recent decades may create an additional vulnerability for female and juvenile Pacific walruses and should be considered in management of the species.
... Here we examine how 150 years of commercial exploitation impacted genetic variation in the Pacific Walrus (Odobenus rosmarus divergens), a gregarious pinniped hunted extensively for its hide, oil, and ivory tusks 12 . Intensive hunting of this species began in 1867 following the U.S. acquisition of what is now Alaska from Russia, which gave American whalers access to the Bering and Chukchi seas, where they began to hunt walruses in addition to whales 13,14 . ...
... Recovery following a bottleneck is impacted by population substructure both before and after the bottleneck event 32 12 . The extent of population structure present within Pacific Walruses is unclear; previous studies found evidence of only mild structure despite their expansive range and suggested this subspecies is more panmictic than Atlantic Walruses 20,34,35 . ...
Pacific Walruses (Odobenus rosmarus divergens [Illiger 1815]) are gregarious marine mammals considered to be sentinels of the Arctic because of their dependence on sea ice for feeding, molting, and parturition. Like many other marine mammal species, their population sizes were decimated by historical overhunting in the nineteenth and twentieth centuries. Although they have since been protected from nearly all commercial hunting pressure, they now face rapidly accelerating habitat loss as global warming reduces the extent of summer sea ice in the Arctic. To investigate how genetic variation was impacted by overhunting, we obtained mitochondrial DNA sequences from historic Pacific Walrus samples in Alaska that predate the period of overhunting, as well as from extant populations. We found that genetic variation was unchanged over this period, suggesting Pacific Walruses are resilient to genetic attrition in response to reduced population size, and that this may be related to their high vagility and lack of population structure. Although Pacific Walruses will almost certainly continue to decline in number as the planet warms and summer sea ice is further reduced, they may be less susceptible to the ratcheting effects of inbreeding that typically accompany shrinking populations.
... This discrepancy in age is more pronounced in male pinnipeds, perhaps because they must be physically capable of breeding, as well as physically large enough and behaviorally mature enough, to compete for territory/females. For example, walrus (Odobenus rosmarus) reach sexual maturity at 9À10 years of age but may not breed successfully until 13-16 years old (Fay 1982). ...
... A third strategy, the aquatic nursing strategy, is only found in the odobenids. The walrus, having the longest period of maternal care (2-3 years), has adopted a strategy of nursing in the water, as opposed to exclusively on land, and pups are known to accompany their mothers on foraging trips (Boness and Bowen 1996;Fay 1982). Walrus pups are born the least precocious of the pinnipeds, and this lengthy dependence on the mother allows for a longer maturation process of the pup prior to survival on its own. ...
... Proximally, the penis extends beyond the baculum, ending posterior to the pelvis (Figure 3). The baculum appears to be over 50% of the length of the flaccid penis (Figure 3), similar proportions to those in the walrus, Odobenus rosmarus (Fay, 1982). ...
... This seems to be the case for leopard, crabeater, Weddell, and harbor seals (Hamilton, 1939;Harrison et al., 1952). There are few descriptions of the baubellum (os clitoridis) in pinnipeds, the exception being the walrus (Fay, 1982). While some individual female pinnipeds are known to lack a baubellum completely (Lough-Stevens et al., 2018), we have no knowledge of the morphological variation in this structure. ...
... The Pacific walrus (Odobenus rosmarus divergens) is considered an ice-obligate species (Moore & Huntington, 2008) due to its close association with sea ice (Fay, 1982;Jay et al., 2011). Sea ice is used as a platform for resting between foraging bouts and for thermoregulation, molting, pupping, and nursing (Fay, 1982;Jay et al., 2012). ...
... The Pacific walrus (Odobenus rosmarus divergens) is considered an ice-obligate species (Moore & Huntington, 2008) due to its close association with sea ice (Fay, 1982;Jay et al., 2011). Sea ice is used as a platform for resting between foraging bouts and for thermoregulation, molting, pupping, and nursing (Fay, 1982;Jay et al., 2012). During the winter months, Pacific walruses inhabit the Bering Sea and females and young walruses migrate north to the Chukchi Sea in summer following the retreating sea ice. ...
Arctic marine mammals live in a rapidly changing environment due to the amplified effects of global warming. Pacific walruses ( Odobenus rosmarus divergens ) have responded to declines in Arctic sea‐ice extent by increasingly hauling out on land farther from their benthic foraging habitat. Energy models can be useful for better understanding the potential implications of changes in behavior on body condition and reproduction but require behavior‐specific metabolic rates. Here we measured the resting metabolic rates (RMR) of three captive, adult female Pacific walruses through breath‐by‐breath respirometry when fed and fasted resting out of water (sitting and lying down) and while fed resting in water. RMR in and out of water were positively related with pretrial energy intake when not fasted and 25% higher than RMR when walruses were fasted and out of water. Overall, RMR was higher than previously estimated for this species. Fasting RMR out of water was only 25% lower than subsurface swimming metabolic rates suggestive of relatively efficient swimming in adult females. Our results identify the importance of considering feeding status and species‐specific differences in affecting metabolic costs. Further research is needed to better understand potential energetic costs of thermoregulation at temperatures experienced by wild walruses.
... Length of lactation in pinnipeds varies from the shortest lactation of any mammal, 4 days in arctic hooded seals (Cystophora cristata), to 18 months in the temperate to subtropical Australian sea lion (Neophoca cinerea), and 2-3 years in the subarctic walrus (Odobenus rosmarus) (Fay, 1982) although no consistent relationship has been observed between latitude and milk composition (Schulz and Bowen, 2004). Comparison of lactation among diverse species is challenging given differences in duration. ...
... Walruses are the only pinniped species that exhibit this strategy; nursing on demand for more than 2 years (Schulz and Bowen, 2004). Walruses are shallow, benthic foragers; thus, limited diving and foraging abilities of young walrus pups likely do not limit female acquisition of prey facilitating this aquatic lactation strategy (Fay, 1982;Noren et al., 2014). ...
-Marine mammals produce a high fat (>25%‐60%), energy rich milk that facilitates rapid growth of offspring.
-Maternal provisioning in pinnipeds, varies from 4 days (hooded seal) to 24 months (Pacific walrus).
-Marine mammals evolved different lactation strategies, including extended periods of fasting in the mother and the offspring influenced by environment yet tightly associated with phylogeny.
-A mutation in alpha-lactalbumin gene is present in otariids (sea lions and fur seals) that prevents lactose production and is thought to allow for maintenance of lactation even with long (up to 23 days) inter-suckling interval by preventing mammary involution.
-Growth strategies of pinnipeds are partially influenced by milk composition (high percentage of fat) and rate of energy delivery (total calories provided); however, offspring physiology (metabolic hormones) and behavior (increased activity) also impact the rate and composition of mass gain which strongly predict offspring survival.
... Although methods for age determination across all species have evolved toward primary reliance on cemental growth layer counting after tooth sectioning 6,7 , some of the unique morphological differences between the families have resulted in species specific methods being evaluated. For walrus, cemental tooth layer counting was first reported in the 1950s and evidence from known age, captive animals indicate high accuracy until approximately 15 years of age [8][9][10] . The use of mandibular bone growth layers has also been evaluated as an indicator for age assessments, but early reports of this method demonstrated conflicting results 1,11 . ...
... Due to the general unavailability of teeth antemortem, scientists have developed non-invasive methods for age determination of animals within a herd based on the visual assessment of morphometrics 2,19 . However, within most pinniped species, morphometric estimates are generally limited to large age group classes, e.g., neonates, juvenile, and adults 8,17,20 . For walrus, additional resolution of animal ages within eight age categories has been recently demonstrated using a tusk to snout length ratio 2 . ...
Age determination of wild animals, including pinnipeds, is critical for accurate population assessment and management. For most pinnipeds, current age estimation methodologies utilize tooth or bone sectioning which makes antemortem estimations problematic. We leveraged recent advances in the development of epigenetic age estimators (epigenetic clocks) to develop highly accurate pinniped epigenetic clocks. For clock development, we applied the mammalian methylation array to profile 37,492 cytosine-guanine sites (CpGs) across highly conserved stretches of DNA in blood and skin samples (n = 171) from primarily three pinniped species representing the three phylogenetic families: Otariidae, Phocidae and Odobenidae. We built an elastic net model with Leave-One-Out-Cross Validation (LOOCV) and one with a Leave-One-Species-Out-Cross-Validation (LOSOCV). After identifying the top 30 CpGs, the LOOCV produced a highly correlated (r = 0.95) and accurate (median absolute error = 1.7 years) age estimation clock. The LOSOCV elastic net results indicated that blood and skin clock (r = 0.84) and blood (r = 0.88) pinniped clocks could predict age of animals from pinniped species not used for clock development to within 3.6 and 4.4 years, respectively. These epigenetic clocks provide an improved and relatively non-invasive tool to determine age in skin or blood samples from all pinniped species.
... These individuals were highly interactive with one another and with their environment. It is well known that captive walruses orally explore and often damage structural features in their living spaces, presumably as a byproduct of natural suction feeding behavior (Fay, 1982). In this situation, a bolt associated with a window frame was removed by one or more of the walruses, leaving a space in the wall behind the frame where the bolt had been. ...
... It is possible that social learning of complex behavior occurs among walruses in natural situations but has not yet been documented in the field. By sharing this anecdote from our time spent with walruses in a zoological setting, we highlight the unique nature of these marine mammals and add to early descriptive reports of their unusual behavior and sociality (see Fay, 1982). ...
... The Pacific walrus (Odobenus rosmarus divergens) inhabits a region of the Arctic that is experiencing some of the most rapid loss of summer sea ice (Laidre et al., 2015;Markus et al., 2009). The sea ice is a critical habitat for this species as it provides a location for resting between foraging bouts, and immediate access to their benthic offshore foraging habitat (Fay, 1982). The sea ice platform is also used for breeding, and females and young walruses usually haul out onto sea ice throughout the year, while adult males haul out on sea ice primarily during winter and spring (Fay, 1982). ...
... The sea ice is a critical habitat for this species as it provides a location for resting between foraging bouts, and immediate access to their benthic offshore foraging habitat (Fay, 1982). The sea ice platform is also used for breeding, and females and young walruses usually haul out onto sea ice throughout the year, while adult males haul out on sea ice primarily during winter and spring (Fay, 1982). In recent years, sea ice has retreated beyond the continental shelf in the eastern Chukchi Sea in 2020). ...
Walruses rely on sea-ice to efficiently forage and rest between diving bouts while maintaining proximity to prime foraging habitat. Recent declines in summer sea ice have resulted in walruses hauling out on land where they have to travel farther to access productive benthic habitat while potentially increasing energetic costs. Despite the need to better understand the impact of sea ice loss on energy expenditure, knowledge about metabolic demands of specific behaviours in walruses is scarce. In the present study, 3 adult female Pacific walruses (Odobenus rosmarus divergens) participated in flow-through respirometry trials to measure metabolic rates while floating inactive at the water surface during a minimum of 5 min, during a 180-second stationary dive, and while swimming horizontally underwater for ∼90 m. Metabolic rates during stationary dives (3.82±0.56 l O2 min−1) were lower than those measured at the water surface (4.64±1.04 l O2 min−1), which did not differ from rates measured during subsurface swimming (4.91±0.77 l O2 min−1). Thus, neither stationary diving nor subsurface swimming resulted in metabolic rates above those exhibited by walruses at the water surface. These results suggest that walruses minimize their energetic investment during underwater behaviours as reported for other marine mammals. Although environmental factors experienced by free-ranging walruses (e.g., winds or currents) likely affect metabolic rates, our results provide important information for understanding how behavioural changes affect energetic costs and can be used to improve bioenergetics models aimed at predicting the metabolic consequences of climate change on walruses.
... Walruses (Odobenus rosmarus) live throughout much of the circumpolar Arctic, where they use sea ice to meet various biological needs such as giving birth and resting (Fay, 1982;Born et al., 1995). However, sea ice in the Arctic is declining at a rapid rate in terms of extent, thickness and seasonal presence (Meredith et al., 2019). ...
Regular counts of walruses (Odobenus rosmarus) across their pan‐Arctic range are necessary to determine accurate population trends and in turn understand how current rapid changes in their habitat, such as sea ice loss, are impacting them. However, surveying a region as vast and remote as the Arctic with vessels or aircraft is a formidable logistical challenge, limiting the frequency and spatial coverage of field surveys. An alternative methodology involving very high‐resolution (VHR) satellite imagery has proven to be a useful tool to detect walruses, but the feasibility of accurately counting individuals has not been addressed. Here, we compare walrus counts obtained from a VHR WorldView‐3 satellite image, with a simultaneous ground count obtained using a remotely piloted aircraft system (RPAS). We estimated the accuracy of the walrus counts depending on (1) the spatial resolution of the VHR satellite imagery, providing the same WorldView‐3 image to assessors at three different spatial resolutions (i.e., 50, 30 and 15 cm per pixel) and (2) the level of expertise of the assessors (experts vs. a mixed level of experience – representative of citizen scientists). This latter aspect of the study is important to the efficiency and outcomes of the global assessment programme because there are citizen science campaigns inviting the public to count walruses in VHR satellite imagery. There were 73 walruses in our RPAS ‘control’ image. Our results show that walruses were under‐counted in VHR satellite imagery at all spatial resolutions and across all levels of assessor expertise. Counts from the VHR satellite imagery with 30 cm spatial resolution were the most accurate and least variable across levels of expertise. This was a successful first attempt at validating VHR counts with near‐simultaneous, in situ, data but further assessments are required for walrus aggregations with different densities and configurations, on different substrates.
... Bearded seals have the lowest [Mb] of any phocid reported to date. They more closely resemble odobenids (Fay, 1982;Fay et al., 1984) and shallow-diving otariids than other Arctic phocids (Figure 6a). Both bearded seals and walruses (Odobenus rosmarus) are benthic foragers that typically exhibit shallow, short-duration dives. ...
The physiological properties of marine mammal skeletal muscle are foundational in defining diving and foraging capacities. Further, these parameters can be useful when assessing the behavioral flexibility of species faced with environmental change or disturbance. Herein, we define species- and age-specific muscle physiology for three ice-associated seal species experiencing Arctic warming. Specifically, we evaluated myoglobin content ([Mb]), nonbicarbonate buffering capacity (β), and fiber type profiles of a major locomotor muscle, the longissimus dorsi. Muscle samples were obtained from subsistence harvested ringed (Pusa hispida; n = 11), bearded (Erignathus barbatus; n = 41), and spotted (Phoca largha; n = 12) seals of all ages in the Bering and Chukchi Seas. Adult ringed seals had the highest [Mb] (6.67 ± 0.20 g 100 g wet tissue-1), followed by spotted (5.38 ± 0.29 g 100 g wet tissue-1) and bearded (4.55 ± 0.07 g 100 g wet tissue-1) seals. [Mb] increased with age for all species, but rates of increase differed by species. In contrast, β was similar for all species and age classes. We documented higher proportions of fast-twitch relative to slow-twitch fibers in these species, and fiber type proportions did not differ significantly with age. Adult bearded seals exhibited the greatest proportion of fast-twitch fibers (68.7 ± 1.5%), followed by ringed (59.0 ± 4.8%) and spotted (55.1 ± 2.1%) seals. Overall, our data suggest a strong link between muscle physiology, diving behavior, and life history strategies, and provide insight into the physiological capacities of these potentially vulnerable species.
... They can break through ice that is about 20 cm thick, but if the ice cover becomes thicker they must relocate to areas with moving pack ice (e.g. Fay 1982Fay , 1985. Between Nuussuaq (70°45'N) and Inannganeq (Kap York; approx. ...
In the early part of the 20th century Atlantic walruses (Odobenus rosmarus rosmarus) occurred abundantly between approximately 66°N and 70°45'N in Central West Greenland from September until mid June. Between September and December several hundred walruses hauled out on small islands and promontories between the entrance to Nassuttooq (Nordre Strømfjord, approx. 67°30'N) and approximately 67°45'N, south of the settlement of Attu. From 1911, the hunt for walruses at terrestrial haul out sites was intensified, and by the late 1930s the walruses had abandoned the terrestrial haul outs in this area. Between 1911 and the early 1940s, the catches of walruses in western Greenland (excluding the Avanersuaq/Thule area) increased rapidly, reaching a maximum of more than 600 animals reported for 1938 and 1940. Mainly reproductive females were caught and the proportion of unretrieved kills was high. Between the early 1940s and the mid 1960s catches decreased rapidly, apparently reflecting a decrease in the stock of walruses wintering off Central West Greenland. Between 1965 and 1987, the recorded annual catch in western Greenland south of 76°N averaged 56 walruses (SD = 19.7; range 19- 101 animals). It is estimated that during this period the total number of walruses removed by hunting was about 100 per year. Comparisons of the results of systematic aerial surveys conducted in early spring of 1981, 1982, 1984, 1990 and 1991 over the walrus wintering grounds at Central West Greenland revealed no trend in abundance. The line transect methods used in the 1990 and 1991 surveys gave higher and more robust estimates of abundance than the strip censuses used in the previous surveys, and resulted in estimates of abundance of about 500 walruses (not corrected for submerged animals). The stock structure of the total walrus population in the Baffin Bay and Davis Strait regions is obscure. However, this study has shown that the numbers of walruses in Central West Greenland are much lower than historical levels, and that walruses in this area are vulnerable.
... The Uniprot or NCBI entry name for each species included in the study is available in the Supplementary Data file (DataS1). We then supplemented the dataset with a binary measure of social monogamy (present/absent) collected from several sources (Isler and van Schaik, 2012;Cerrito and Spear, 2022;Ågmo et al., 2012;Barnett et al., 2005;Belle and Bicca-Marques, 2015;Bendesky et al., 2017;Berteaux and Micol, 1992;Carp et al., 2016;Carter et al., 1995;Clutton-Brock and Manser, 2016;Debeffe et al., 2015;Delgado-Acevedo et al., 2010;Dubuc et al., 2014;Engstrom and Dowler, 1981;Evans et al., 2012;Fay, 1982;Fernandez-Duque, 2016;Fiore and Fleischer, 2005;Frank, 1986;Fruteau et al., 2010;Gerber et al., 2010;Gibson, 2008;Gottelli et al., 2007;Colquhoun, 1997;Harcourt et al., 2007;Iossa et al., 2008;Kiyota et al., 2008;Laman and Fig. 1. Phylogenetic tree of the species included in this study. ...
Oxytocin (OXT) is a neurohypophyseal hormone that influences a wide range of affiliative behaviors, such as pair-bonding and infant care, across mammals. The effects of OXT depend significantly on an adequate interaction with its receptor, OXTR. OXTR belongs to the G-protein coupled receptor family. The extracellular N-terminal domain of OXTR interacts with the linear C-terminal tail of OXT and is required for OXT binding. Across mammalian species there is a genetic diversity in OXTR terminal sequence. Previous work on primates has shown an association between OXTR phylogeny and monogamy. However, it is not clear whether this variation coevolved with either mating system (monogamy) or infant care behaviors (such as allomaternal care). Here, we take a phylogenetic comparative and evolutionary modeling approach across a wide range of placental mammals (n = 60) to test whether OXTR N-terminal variants co-evolved with either monogamy or allomaternal care behaviors. Our results indicate that the diversity in OXTR N-terminal region is unlikely to provide the underlying genetic bases for variation in mating system and/or allomaternal behavior as we find no evidence for co-evolution between protein sequence and affiliative behaviors. Hence, the role played by OXT in influencing affiliative behaviors is unlikely to be mediated by the genetic diversity of its receptor.
... This species last shared a common ancestor with otariids more than 24 Â 10 6 years ago and is even further removed from the phocid lineage and all other carnivores (Berta et al., 2018;Boessenecker and Churchill, 2018). Compared to otariids-which are found in most temperate oceans in areas of high productivity-walruses have a restricted geographic range limited to the shallow continental shelf areas of Arctic and sub-Arctic seas (Fay, 1982;MacCracken et al., 2017). Walruses lack external pinnae and have small ear openings, as well as significantly enlarged ear drums, middle ear cavities, and ossicles (Kastelein et al., 1996b;Repenning, 1972). ...
As the only living species within the odobenid lineage of carnivores, walruses (Odobenus rosmarus) have no close relatives from which auditory information can be extrapolated. Sea lions and fur seals in the otariid lineage are the nearest evolutionary outgroup. To advance understanding of odobenid and otariid hearing, we conducted behavioral testing with two walruses and one California sea lion (Zalophus californianus). Detection thresholds for airborne sounds were measured from 0.08 to at least 16 kHz in ambient noise conditions and then re-measured in the presence of octave-band white masking noise. Walruses were more sensitive than the sea lion at lower frequencies and less sensitive at higher frequencies. Critical ratios for the walruses ranged from 20 dB at 0.2 kHz to 32 dB at 10 kHz, while critical ratios for the sea lion ranged from 16 dB at 0.2 kHz to 35 dB at 32 kHz. The masking values for these species are comparable to one another and to those of terrestrial carnivores, increasing by about 3 dB per octave with increasing frequency. Despite apparent differences in hearing range and sensitivity, odobenids and otariids have a similar ability to hear signals in noisy conditions.
... If teeth were in contact with abrasive material, this would leave marks as those seen on the tusk-like teeth of O. huata and O. marplesi [9,10]. The delicate nature of the tusk-like teeth in N. matakoi suggests they were not used for intraspecific combat or for fending off predators; this would require robust teeth such as those observed in Ankylorhiza [13], ziphiids [17,71] or walruses [72]. Such combat/defence uses would probably result in prominent fractures without reinforced teeth [73]. ...
All extant toothed whales (Cetacea, Odontoceti) are aquatic mammals with homodont dentitions. Fossil evidence from the late Oligocene suggests a greater diversity of tooth forms among odontocetes, including heterodont species with a variety of tooth shapes and orientations. A new fossil dolphin from the late Oligocene of New Zealand, Nihohae matakoi gen. et sp. nov., consisting of a near complete skull, earbones, dentition and some postcranial material, represents this diverse dentition. Several preserved teeth are horizontally procumbent, including all incisors and canines. These tusk-like teeth suggest adaptive advantages for horizontally procumbent teeth in basal dolphins. Phylogenetic analysis places Nihohae among the poorly constrained basal waipatiid group, many with similarly procumbent teeth. Features of N. matakoi such as its dorsoventrally flattened and long rostrum, long mandibular symphysis, unfused cervical vertebrae, lack of attritional or occlusal wear on the teeth and thin enamel cover suggest the rostrum and horizontally procumbent teeth were used to injure and stun prey though swift lateral head movements, a feeding mode that did not persist in extant odontocetes.
... Males' tusks are slightly thicker and longer and are used for dominance, fighting, and display. The most muscular male with the longest tusks dominates the other group members and leads them 53 . An image of walrus is presented in Fig. 1. ...
This paper introduces a new bio-inspired metaheuristic algorithm called Walrus Optimization Algorithm (WaOA), which mimics walrus behaviors in nature. The fundamental inspirations employed in WaOA design are the process of feeding, migrating, escaping, and fighting predators. The WaOA implementation steps are mathematically modeled in three phases exploration, migration, and exploitation. Sixty-eight standard benchmark functions consisting of unimodal, high-dimensional multimodal, fixed-dimensional multimodal, CEC 2015 test suite, and CEC 2017 test suite are employed to evaluate WaOA performance in optimization applications. The optimization results of unimodal functions indicate the exploitation ability of WaOA, the optimization results of multimodal functions indicate the exploration ability of WaOA, and the optimization results of CEC 2015 and CEC 2017 test suites indicate the high ability of WaOA in balancing exploration and exploitation during the search process. The performance of WaOA is compared with the results of ten well-known metaheuristic algorithms. The results of the simulations demonstrate that WaOA, due to its excellent ability to balance exploration and exploitation, and its capacity to deliver superior results for most of the benchmark functions, has exhibited a remarkably competitive and superior performance in contrast to other comparable algorithms. In addition, the use of WaOA in addressing four design engineering issues and twenty-two real-world optimization problems from the CEC 2011 test suite demonstrates the apparent effectiveness of WaOA in real-world applications. The MATLAB codes of WaOA are available in https://uk.mathworks.com/matlabcentral/profile/authors/13903104.
... Glossowear has only been studied in detail once, namely, in extant walruses, where it arises from piston-like tongue movements used to create a strong oral suction force (Fay 1982;Gordon 1984). The same presumably applies to the other species here shown to exhibit this type of wear, all of which seem to use suction for prey capture (Heyning and Mead 1996;Werth 2000a;Marshall et al. 2008;Kane and Marshall 2009;Hocking et al. 2013). ...
Teeth are the primary tool used by most mammals to capture and process food. Over the lifetime of an individual, they progressively wear through contact with each other (attrition) and with food (abrasion), creating distinctive patterns that reflect function and diet. Unlike their terrestrial cousins, many marine mammals capture prey via suction, which so far has not been associated with a specific wear pattern. Here, we describe two new types of tooth wear across 18 species of modern marine mammal (beaked whales, belugas, killer whales, globicephalines, and various seals) that likely stem from this behaviour: “glossowear”, which primarily affects the lingual side of the crown and plausibly records piston-like tongue movements during suction feeding; and “hydrowear”, which wraps around the sides of the crown and occurs as water is expelled from the mouth. Both wear types differ from attrition and biting-related abrasion in their surface characteristics and location on the crown. Horizontal scratches suggest a physical wear process, rather than dental erosion (acid corrosion) and tooth abfraction (microfracture). Since suction specifically exploits the liquid properties of water, physical evidence of this behaviour may help to elucidate marine mammal feeding ecology and evolution. For example, glossowear is found in the toothed ancestors of baleen whales (mammalodontids, at least one aetiocetid, and likely Mystacodon), where it suggests an important role for suction in the emergence of filter feeding. By contrast, it is absent in most long-snouted toothed whales and dolphins, indicating that these animals mostly bite, rather than suck in, their prey.
... Walruses, Odobenus rosmarus, have a discontinuous circumpolar Arctic and sub-Arctic distribution, and are represented by two subspecies: the Pacific walrus, Odobenus rosmarus divergens, which occurs in the Arctic and sub-Arctic waters of the Chukchi, Bering and Laptev seas (USA and Russia) (Fay 1982;Lindqvist et al. 2009) and its abundance has been estimated above 200,000 (Lowry 2016), and the Atlantic walrus, Odobenus rosmarus rosmarus, which inhabits coastal areas in the north-eastern Canada, Greenland (Denmark), Svalbard (Norway), and the Barents and Kara seas (western part of Arctic Russia) (Born et al. 2001), and its abundance has been estimated above 25,000 (Kovacs 2016;Lowry 2016). Although the IUCN (International Union for Conservation of Nature) and the IUCN SSP (Species Survival Commission) Pinniped Specialist Group has recommended Atlantic walruses to be listed as "Near Threatened" because of uncertainties surrounding future decline in their habitat quality, and because of the lack of data on general walrus abundances and trends (Lowry 2016), Inuit consider Atlantic walruses not at risk (DFO 2013). ...
Environmental changes are affecting the Arctic at an unprecedented rate, but limited scientific knowledge exists on their impacts on species such as walruses (Odobenus rosmarus). Inuit Traditional and Local Ecological Knowledge (Inuit TEK/LEK) held by Inuit walrus harvesters could shed light on walrus ecology and related environmental changes. Our main objective was to study spatial and temporal changes in Atlantic walrus (Odobenus rosmarus rosmarus) distribution in Nunavik (northern Québec, Canada) using Inuit TEK/LEK. To do so, we documented the knowledge and observations of 33 local hunters and Elders as part of a larger project on Atlantic walruses in Nunavik. We first gathered information on changes in Inuit land use patterns and harvesting practices through time and space, which was a crucial step to avoid potential biases in interpreting local observations on walrus distribution. We found that walrus hunters are now covering smaller hunting areas over shorter time periods, reducing in space and time their observations of Atlantic walruses around Nunavik. While clearly taking these limitations into account, we learned from interviews that some areas abandoned by Atlantic walruses in the past were now being re-occupied. Importantly, Atlantic walruses, which migrate following the melting ice, are now traveling along the eastern coast of Nunavik one month earlier, suggesting that Atlantic walrus migration has changed due to variations in sea-ice coverage around Nunavik. Our study not only highlighted important changes in Atlantic walrus distribution and migration in Nunavik, but also sheds light on the importance of documenting temporal and spatial changes in Inuit land use patterns and harvesting practices to understand the ecology of Arctic species using Inuit Knowledge.
Supplementary information:
The online version contains supplementary material available at 10.1007/s00300-021-02920-6.
The goal of the work : to assess the current state of the Pacific walrus population and other marine mammal species in the Chukchi Sea subzone (the area of the Natural sanctuary «Cape Vankarem»).
Problems : obtaining new information about the number, sex and age structure, reproduction rates of walruses in the research area; assessment of the timing and intensity of filling the local rookery; assessment of the level of coastal mortality of marine mammals, age and sex composition of fallen animals; assessment of anxiety factors and the level of their impact on animals; collection of meteorological data in the research area during the research period; scientific support of aboriginal fishing; data collection on other marine mammal species in the research area (cetaceans, real seals); accounting of the number of predators (white and brown bears, killer whales) in the vicinity of the rookery and monitoring their relationship with walruses.
Scientific work on the coastal walrus rookery was carried out in the area of the Cape Vankarem (the Arctic coast of the Chukchi Sea), from August 15 to October 2, 2023.
Practical significance of the research : assessment of the current state of the local grouping of Pacific walruses, the level of natural loss and reproductive ability of the grouping; data for regulating fishing, increasing its efficiency and ensuring the conditions of traditional nature use of the indigenous population of Chukotka.
While the mammalian baculum shows enormous morphological variability, the baculum of canids is highly conserved, with most variation restricted to size. Here, we explore the allometric relationship between baculum length and body size in extant and extinct canids. Examination of 26 species in the extant subfamily Caninae using standard linear regression revealed isometry. Phylogenetic regression also revealed an allometric slope indistinguishable from isometry. This pattern differs from the substantially negative slopes seen in other mammalian clades. The strength of the canid allometric relationship (r2) is also greater than in other clades, suggesting functional constraints on their baculum size. The constraints may be related to the copulatory tie that is characteristic of canids, and/or their monogamous mating system. Complete bacula are known from just four extinct species. The two complete bacula from the extinct subfamily Borophaginae (Aelurodon ferox and Aelurodon stirtoni) fall on the same allometric relationship as the living canids. However, the baculum of the extinct dire wolf (Aenocyon dirus, from the extant subfamily Caninae) and from the extinct subfamily Herperocyoninae, Hesperocyon gregarius, are significantly longer than expected based on their body sizes, suggesting that they may have had a different reproductive biology from that of extant canines.
The walrus, Odobenus rosmarus, is an iconic pinniped and predominant molluscivore that is well adapted to Arctic and subarctic environments. Its circumpolar distribution, large body size and ivory tusks facilitated its vital role as food, raw material (for tools and art), income, and cultural influence on many Arctic Indigenous communities for millennia. Intensification of hunting (often due to the arrival of Europeans, especially between the 16th and 19th centuries) to obtain ivory, hide, blubber and meat, resulted in diminished, sometimes extirpated, walrus populations. Zooarchaeological, artefactual and documentary evidence of walrus material has been collated at local and regional scales and is frequently focused on a specific culture or period of time. Systematic collation of this evidence across the Northern Hemisphere will provide insight into the chronology and circumpolar distribution of walrus hunting and provide a tool to document societal change in walrus resource use. Here, we lay out a systematic review protocol to collate records of archaeological walrus artefacts, tusks and bones that have been documented primarily within published literature to archive when and where (as feasible) walrus extractions occurred between 1 CE and 2000 CE. These data will be openly available for the scientific community. The resulting dataset will be the first to provide spatiotemporal information (including the recognition of knowledge gaps) regarding past walrus populations and extirpations on a circumpolar scale. Our protocol is published to ensure reproducibility and comparability in the future, and to encourage the adoption of systematic review methodology (including pre-published protocols) in archaeology.
Currently, many aquariums and zoos around the world keep walruses in captivity. However, the presence of tusks in walruses creates difficulties in their maintenance and preservation of their health since they wear them down on the structure of the pools. In this study, the morphometric parameters of walrus skulls from captivity and wild of similar age were examined (35 skull measurements and 21 mandible measurements were taken). An examination of the skulls of three female walruses that were kept in the Moscow Zoo for 8, 11, and 22 years, respectively during the period of 1953–2005 was conducted. The tusks of one walrus, at the age of 4 years, were surgically removed, while the tusks of the others were not. There were slight deviations in the skull development of these walruses. The skull of captive walruses is slightly smaller in the mastoid processes and zygomatic arches, and facial part, and the lower jaw is smaller in width and symphysis circumference compared to wild walruses. The surface of the skull and lower jaw is smoother in comparison to wild walruses. Diseases such as odontogenic osteomyelitis, pulpitis, periodontitis, dental calculus and caries are observed. Due to frequent inflammations and surgical interventions, early fusion of sutures is noted, leading to skull deformities.
We examined the ultrastructure of the mammalian os penis at the high‐resolution synchrotron level. Previously, bacular microanatomy had only been investigated histologically. We studied the baculum of the harp seal ( Pagophilus groenlandicus ), in which the baculum varies more in size and shape than does a mechanically constrained bone (humerus). We (1) investigated the microarchitecture of bacula and humeri from the same seal specimens, and (2) described changes in bone micro‐ and macro‐morphology associated with age ( n = 15, age range = 1–35 years) and bone type. We analyzed cross‐sectional geometry non‐destructively through laboratory micro‐computed tomography. We suggest that the midshaft may resist axial compression while the proximal region may resist torsion, based on measurements of cross‐sectional and cortical areas, perimeter, ratio of maximum and minimum moments of inertia, and polar moment of inertia. In addition, midshaft bacula may be less mechanosensitive than humeri, based on microstructural variables (e.g., volume, surface area, diameter associated with lacunae and cortical porosity) analyzed across age groupings. Our findings related to the microarchitecture of the pinniped baculum provide a basis for further studies on development, mechanical properties, functions, and adaptations in this and other pinniped species. Our use of a multi‐modal imaging approach was minimally destructive for reproducible and accurate comparison of three‐dimensional bone ultrastructure. Such methods, coupled with multidisciplinary analyses, enable diverse studies of bone biology, life history, and evolution using museum collections.
The physical environment introduced in the last chapter affects the biological environment. Ocean currents move plankton and krill that feed fishes, sea birds, and whales. Island size affects the quantity of nutrients that reach land, storms that cross the archipelago bring rain that sustain plants. Although not a focus of this chapter, humans are not outsiders but integral components affecting and affected by the natural system. Hunters joined in the melee when fish and sea mammals fed on upwelling plankton, and they gathered plants on shore to make mats, baskets, medicines, and meals. When human populations plummeted with the Russian arrival, and when commercial and industrial animal harvesting occurred, the living environment reacted with extinctions and perturbations felt today.
A fragment of a walrus skull of Neopleistocene age was found at a distance of about 340 km from the mouth of the Pechora River. The skull presumably belonged to a mature male Atlantic walrus 13-14 years old. The radiocarbon date of the walrus bone shows an age outside the method's range (>45 Ka). Nitrogen and carbon isotope data from skull collagen are discussed. The reason for the appearance of the walrus far from the modern sea shore was, presumably, the Rodionovo (Shklov, MIS 7) or boreal Sula (Mikulino, MIS 5e) marine transgression into the area of the latitudinal part of the Pechora River. The relatively good preservation of the bone testifies in favor of the Sula marine transgression. The Rodionovo age of the walrus can be assumed on the basis of the presence of shallow water marine deposits lying between two Middle Pleis-tocene moraines-Pechora (Dnieper, MIS 8) and Vychegda (Moscow, MIS 6).
We describe here a novel peeling skin condition (PSC) in 2 neonatal Pacific walruses ( Odobenus rosmarus subsp. divergens). Macroscopically, calves had various degrees of peeling skin exacerbated by mechanical trauma. Lesions occurred in areas subject to friction: ventrum, fore- and hindflippers, and associated joints. Histopathologic features included pseudocarcinomatous epithelial hyperplasia with orthokeratotic hyperkeratosis. Bacterial cocci were present within the stratum corneum. A few intraepidermal clefts were present. Inflammation, epidermolysis, and vasculopathies were not observed. PCR assays were negative for vesivirus and for Staphylococcus aureus exfoliative and toxic shock syndrome toxins. Tissue samples were cultured and bacteria isolated and identified by MALDI-TOF MS as Carnobacterium maltaromaticum, Psychrobacter phenylpyruvicus, Globicatella sanguinis, Streptococcus phocae, Pseudomonas spp., Rahnella aquatilis, and Escherichia coli. Given the young age of the calves and their clinical presentation, congenital ichthyosis was suspected. No genetic differences were detected for sequenced portions of keratin genes (keratin gene K10) between diseased and normal walrus skin. This rare PSC in neonatal Pacific walruses is recognized as novel by indigenous Alaskan marine mammal hunters of the Bering Strait region. A comprehensive diagnostic work-up of future case materials is needed to characterize the underlying biochemical defect(s).
Left tusk’s fragments of the Pleistocene walrus were studied. Its fossil remains were found on the bank of the Pechora River in 2009. The analyses covered granulometric, chemical and normative-mineral composition of grounds inside the bones; thermal properties, chemical and microelemental composition of the tusk; X-ray diffraction parameters and chemical composition of bone bioapatite; macrostructure, elemental and amino acid composition of bone organic matter; isotopic composition of carbon, oxygen in bioapatite and carbon, nitrogen in bone collagen. Bioapatite was identified for moderately isotopically light carbon, characteristic of extracave fossil bones of the Pleistocene animals, and isotopically heavy oxygen, typical of seawater bicarbonate. The isotopic data for the organic matter of the Pechora walrus correlated with the similar characteristics of marine animals but simultaneously indicated not a mollusk diet, typical of modern walruses, but a fish diet. The latter fact evidenced the habitat and the diet of the Pechora walrus being untypical for marine predators.
Cetaceans are atypical mammals whose tongues often depart from the typical (basal) mammalian condition in structure, mobility, and function. Their tongues are dynamic, innovative multipurpose tools that include the world's largest muscular structures. These changes reflect the evolutionary history of cetaceans' secondary adaptation to a fully aquatic environment. Cetacean tongues play no role in mastication and apparently a greatly reduced role in nursing (mainly channeling milk ingestion), two hallmarks of Mammalia. Cetacean tongues are not involved in drinking, breathing, vocalizing, and other non-feeding activities; they evidently play no or little role in taste reception. Although cetaceans do not masticate or otherwise process food, their tongues retain key roles in food ingestion, transport, securing/positioning, and swallowing, though by different means than most mammals. This is due to cetaceans' aquatic habitat, which in turn altered their anatomy (e.g., the intranarial larynx and consequent soft palate alteration). Odontocetes ingest prey via raptorial biting or tongue-generated suction. Odontocete tongues expel water and possibly uncover benthic prey via hydraulic jetting. Mysticete tongues play crucial roles driving ram, suction, or lunge ingestion for filter feeding. The uniquely flaccid rorqual tongue, not a constant volume hydrostat (as in all other mammalian tongues), invaginates into a balloon-like pouch to temporarily hold engulfed water. Mysticete tongues also create hydrodynamic flow regimes and hydraulic forces for baleen filtration, and possibly for cleaning baleen. Cetacean tongues lost or modified much of the mobility and function of generic mammal tongues, but took on noteworthy morphological changes by evolving to accomplish new tasks.
Arctic marine mammals have had little exposure to vessel traffic and potential associated disturbance, but sea ice loss has increased accessibility of Arctic waters to vessels. Vessel disturbance could influence marine mammal population dynamics by altering behavioral activity budgets that affect energy balance, which in turn can affect birth and death rates. As an initial step in studying these linkages, we conducted the first comprehensive analysis to evaluate the effects of vessel exposure on Pacific walrus (Odobenus rosmarus divergens) behaviors. We obtained >120,000 h of location and behavior (foraging, in‐water not foraging, and hauled out) data from 218 satellite‐tagged walruses and linked them to vessel locations from the marine automatic identification system (AIS). This yielded 206 vessel‐exposed walrus telemetry hours for comparison to unexposed hours, which we used to assess if vessel exposure altered walrus behavior. We developed a filter to account for misclassification of vessel exposure of telemetered walruses. Then we tested for an effect of vessel exposure on walrus behaviors using a combination of exact and propensity score‐based matching to account for confounding covariates, and we conducted statistical power analyses. We did not detect an effect of vessel exposure on walrus behaviors even when statistical power was high (i.e., for foraging walruses), which may have been due to the sample size‐driven need to define vessel presence within a larger than desired distance (15‐km measured radius) around a walrus. Although this study did not determine at what distance vessel exposure affects walrus behaviors, it provided an upper bound on the distance at which the vessels encountered may disturb foraging walruses. When more situation‐specific information is lacking, this distance could be used as a conservative buffer to maintain between vessels and areas of high use by foraging walruses. Studies on behavioral consequences of closer proximities between walruses and vessels are needed, and our assessments of misclassification rates and statistical power can be used for future studies. We demonstrated that analytical approaches such as matching, which are rarely used in wildlife studies, are particularly useful for testing hypotheses with observational data.
Several mammalian lineages, most notably cetaceans, sirenians, and pinnipeds, have independently reverted to the marine environment of their long-ago, pre-mammalian ancestors. Other mammals have also adapted to coastal, estuarine, or freshwater habitats. These include various members of the Carnivora and Rodentia, along with some other living and extinct mammals. Because water is dense, heavy, viscous, and incompressible, feeding in water poses challenges, especially for animals whose ancestors evolved in terrestrial settings. Many secondarily aquatic mammals separately adopted similar functional and structural solutions to acquire, ingest, and process food, particularly suction feeding, filter feeding, raptorial (“seizing”) grasping of prey, or adaptations to remove prey from benthic sediments. This led to striking examples of convergence with other mammals or with other aquatic animals, including sharks, bony fishes, marine reptiles, and birds. Most instances of convergence involve close similarities in jaws, dentition, and musculature, overall shape of the head and mouth, methods for separating food from water, and neural and behavioral adaptations to locate and capture prey. Following discussion of basic principles underlying aquatic mammalian feeding, we outline numerous examples of convergence in extant and extinct taxa.
Reproductive costs represent a significant proportion of a mammalian female's energy budget. Estimates of reproductive costs are needed for understanding how alterations to energy budgets, such as those from environmental variation or human activities, impact maternal body condition, vital rates and population dynamics. Such questions are increasingly important for marine mammals, as many populations are faced with rapidly changing and increasingly disturbed environments. Here we review the different energetic costs that marine mammals incur during gestation and lactation and how those costs are typically estimated in bioenergetic models. We compiled data availability on key model parameters for each species across all six marine mammal taxonomic groups (mysticetes, odontocetes, pinnipeds, sirenians, mustelids and ursids). Pinnipeds were the best-represented group regarding data availability, including estimates of milk intake, milk composition, lactation duration, birth mass, body composition at birth and growth. There were still considerable data gaps, particularly for polar species, and good data were only available across all parameters in 45% of pinniped species. Cetaceans and sirenians were comparatively data-poor, with some species having little or no data for any parameters, particularly beaked whales. Even for species with moderate data coverage, many parameter estimates were tentative or based on indirect approaches, necessitating reevaluation of these estimates. We discuss mechanisms and factors that affect maternal energy investment or prey requirements during reproduction, such as prey supplementation by offspring, metabolic compensation, environmental conditions and maternal characteristics. Filling the existing data gaps highlighted in this review, particularly for parameters that are influential on bioenergetic model outputs, will help refine reproductive costs estimated from bioenergetic models and better address how and when energy imbalances are likely to affect marine mammal populations.
В монографии обобщены результаты исследований роли межполушарной асимметрии в материнско-детских взаимоотношениях млекопитающих из различных таксономических групп.
Приведён обзор и критический анализ односторонних предпочтений (латерализаций) в социальном поведении в целом и в поведении матерей и детёнышей в частности. Подробно описаны методика и результаты многолетних исследований авторов по латерализации пространственных взаимоотношений матерей и детёнышей у шести видов млекопитающих: белухи, косатки, тихоокеанского моржа, сайгака, домашней лошади и серого кенгуру. Рассмотрены гипотезы о причинах возникновения односторонних предпочтений в расположении потомства относительно
матери и приведены свидетельства, подтверждающие сенсорную природу данного типа латерализации. Детально рассмотрено влияние асимметричного зрительного восприятия и ведущей роли правого полушария мозга в обработке социальной информации на материнско-детские взаимоотношения. Описаны различия в поведении детёныша при разном латеральном расположении относительно матери, свидетельствующие о преимуществах латерализованного восприятия матери.
Монография предназначена для специалистов, изучающих поведение животных, асимметрию мозга, психологию материнства, а также студентов и аспирантов биологических и медицинских факультетов вузов.
In addition to companion animals and laboratory species, about 270 carnivore species play fundamental ecological roles in different ecosystems. However, almost 40% of carnivore species are now threatened or endangered in the wild because of human activities. While protection of natural habitats is critical, it is equally important to better understand carnivore reproduction, including a solid knowledge in sperm, oocyte, and embryo biology, to maintain sustainable populations in the wild and in conservation breeding centers. Characterizing gamete and embryo biology is also needed to develop cryopreservation and assisted reproductive technologies to enhance conservation efforts. The objective of this review is to provide the most recent knowledge in the biology of sperm cells, oocytes, and early embryos across all carnivore species. Overall, most data originate from populations maintained in breeding centers or zoos. Characterizations of sperm biology and cryopreservation are far more advanced than for oocytes and embryos. Currently, sperm biology is mainly studied in Canids, Felids, Ursids, and Mustelids, with more emphasis on structural than functional properties. Importantly, fundamental studies of gamete and embryo biology in domestic dogs, cats, and ferrets have paved the way for more precise characterizations in wild counterparts as well as the development of cryopreservation and assisted reproductive technologies. A striking feature of spermatozoa across a wide range of Canids and Felids is the presence of teratospermia (>60% of abnormal sperm cells), which is related to the loss of genetic diversity in some populations. Although sperm structures differ across carnivore families, sperm biology remains difficult to compare because of the small amount of data in many species. Regarding oocyte biology and embryology, data are much scarcer than in sperm cells, with too few studies going beyond structural descriptions. More carnivore species and more individuals (especially from wild populations in addition to captive ones) must be studied to improve our understanding about comparative germplasm biology and develop adequate conservation breeding strategies including the use of cryobanking and assisted reproductive technologies.
The modern walrus Odobenus rosmarus is characterized by marked sexual dimorphism, related to its polygynous behavior and the aggressive competition between males during the breeding season. Previous studies treated skeletal sexual dimorphism in walruses either qualitatively or with basic quantitative measurements. The present study combines a detailed qualitative comparison of male and female walrus mandibles with quantitative two-dimensional geometric morphometrics analysis (principal component analysis, Procrustes ANOVA and a linear discriminant analysis). In addition to identifying previously recognized sexually dimorphic features (e.g., convexity of the anterior margin of the mandible in adult males), our study finds new morphological differences between males and females, such as a relative dorsal expansion of the anterior part of the mandible and an accentuated concavity between the dorsal margin and the coronoid process in adult males. Both our qualitative comparisons and quantitative analyses demonstrate that sexual dimorphism as expressed in the mandible of extant walruses is statistically significant and that (variation in) mandibular morphology can be used as tool to attribute sex with a good degree of accuracy to isolated mandibles or skeletons lacking the cranium. Sexual dimorphism in walruses is directly related to their sexual behavior, characterized as aggressive in males and linked to a polygynous reproduction system. Indeed, the difference in size of the tusks between males and females but also the use of these during intraspecific fights, can reasonably account for this great mandibular morphological disparity between adult males and females, but also among different ontogenetic stages. Finally, the results obtained in the present study may serve as a starting point for assessing sexual dimorphism more in-depth and studying inter-and intraspecific variation in the mandibles of fossil walruses by identifying quantified size and shape mandibular features.
Arctic marine ecosystems are undergoing rapid physical and biological change associated with climate warming and loss of sea ice. Sea ice loss will impact many species through altered spatial and temporal availability of resources. In the Bering and Chukchi Seas, the Pacific walrus Odobenus rosmarus divergens is one species that could be impacted by rapid environmental change, and thus, population assessments are needed to monitor changes in the status of this ecologically and culturally important marine mammal. We conducted a 5 yr genetic mark−recapture study to estimate demographic parameters for the Pacific walrus. We developed a Bayesian multievent mark−recapture model to estimate walrus survival and abundance while accounting for age misclassification. We estimated the probability of juvenile annual survival as 0.63 (95% credible interval [CrI]: 0.39−0.87) and adult female annual survival as 0.90 (95% CrI: 0.74−1.00). We estimated total abundance as 257193 (95% CrI: 171138−366366). We provide the first estimate of total Pacific walrus abundance since an aerial survey in 2006, which generated a substantially less precise total population size estimate (129000; 95% CI: 55000−507000). The emerging ecosystem state in the northern Bering and Chukchi Seas will likely result in a decline in Pacific walrus abundance, but there is substantial uncertainty regarding the magnitude of the anticipated decline. Our demographic estimates provide critical information to evaluate future population trends of this subsistence resource vital to communities that border the Bering and Chukchi Seas in the USA and Russia.
Human activities (e.g., shipping, tourism, oil, gas development) have increased in the Chukchi Sea because of declining sea ice. The declining sea ice itself and these activities may affect Pacific walrus ( Odobenus rosmarus divergens ) abundance; however, previous walrus abundance estimates have been notably imprecise. When sea ice is absent from the eastern Chukchi Sea, walruses in waters of the United States usually rest together onshore at a single Alaska coastal haulout, where they can be surveyed more easily than when they rest on dispersed offshore ice floes. We estimated the number of walruses on land (herd size) at this haulout from 13 unoccupied aircraft system (UAS) surveys flown within a 10‐day period in each of 2018 and 2019. We estimated population size of walruses using the haulout over the course of the surveys by combining herd size data with data from satellite‐linked transmitters that indicated whether tagged walruses were in or out of water during each survey. Our estimates of the population size of walruses using the haulout during each year's survey period were similar to each other and more precise than historical walrus abundance estimates: posterior means (95% credibility intervals) were 166,000 (133,000–201,000) for 2018 and 189,000 (135,000–251,000) for 2019. Auxiliary observations support using these estimates to represent the size of the population using the eastern Chukchi Sea in autumn during the surveyed years. Our study site was the only substantial Chukchi Sea coastal haulout in the United States during the survey periods and study‐specific tracking data (consistent with known distribution and movement patterns) indicated tagged walruses remained in eastern Chukchi waters during the survey periods. In addition, the imagery, telemetry, and analytical methods developed for this study advance the prospect for precise range‐wide walrus population size estimates.
Mammalian dental formulae often are highly conserved, at least at a generic level. In walruses (Odobenus rosmarus), the constraints of dentition in light of documented high variability in tooth counts among walrus are examined. We propose that walruses do not have a constrained dental formula in terms of tooth position or tooth count. Instead, while walrus tooth counts vary, total occlusal area (TOA) is constrained relative to body mass, independent of tooth position or count. Nearly three-fourths of the 70 individuals sampled here had dentitions deviating from the previously reported dental formula of 1/1, 1/0, 3/3, 0/0, but there is a strong relationship between body size and total occlusal area. While the positive correlation between body size and TOA is consistent between sexes, the slope of the relationship differs significantly, suggesting an important sexual dimorphism in more than just walrus body size or tusk morphology. It is unclear if walrus teeth are involved at all in feeding, so TOA may impact positioning of prey during feeding or be completely independent of prey acquisition or feeding. Limited field observations support the hypothesis that dentition may play some role in prey positioning, with males feeding on both larger species and larger individuals of bivalves than females. Differences in food availability to individuals of differing body size have implications for conservation of walruses in the face of climate change and interactions with human fisheries, as well as diagnosing fossil taxa frequently defined in part by dental count. Extant walruses also may present an example of linking increased trait variability with the relaxation of functional constraints in response to shifting ecological roles.
Behavioral adaptations for maintaining breathing holes in sea ice and lairs in the overlying snow cover allow ringed seals to occupy sea ice environments from which other marine mammals are excluded for much of the year. The broad distribution of ringed seals in the ice-covered seas of the northern hemisphere created a niche for an apex predator, and polar bears have evolved as specialists preying on ringed seals. The earliest occupation of the Arctic by people, likewise, depended heavily on the year-round availability of ringed seals. Reliance on breathing holes limits ringed seal movements for as much as 9 months of the year, with implications for foraging and reproductive behaviors as well as for predator avoidance. Ringed seals forage throughout the year with the greatest intake during a brief foraging period between the breakup and subsequent formation of sea ice. Predator avoidance appears to explain the allocation of time better than optimal foraging, at least during ice-bound periods. The under-ice behavior of breeding adults is more consistent with mate or resource guarding than with territoriality as a mating strategy. Feeding through lactation requires a trade-off between time spent foraging and attendance of pups vulnerable to predation. Ringed seals are becoming more vulnerable to predators in the water and on the ice as refuge on ice and under snow diminishes in a warming Arctic.Keywords
Pusa hispida
Sea iceSnow coverSite fidelityMate guardingNavigationForagingPredator avoidanceTrade-offs
Crabeater seals Lobodon carcinophaga breed on the Antarctic pack ice. The body composition of seven crabeater seals of various age classes was reported by Bryden and Erickson (J Zool 179:235–247, 1976); weights of internal organs and sculps (skin with blubber attached) are reported here for four animals from East Antarctica. They died under sedation, two in late April 1993 and one each in late September and early October of 1995. Sculp weights in this study averaged 32% of total body weight, 11.8% higher than the average from the previous study. The difference most likely results from the condition of seals. Those in the previous study were likely to have been in poor condition (moulting or recently moulted). In this study, the animals were likely to have been in good condition (pre-moult or post-moult). Weights of five internal organs are reported; stomach and kidneys expressed as a percentage of total body weight were about 20% lighter in the current study and data for the intestines and liver were about 20% heavier, with little difference for heart weight. This study provides estimates of sculp weight of four crabeater seals and extends the knowledge of weights of five of their visceral organs (stomach, intestines, liver, kidney and heart).
The purpose of the research is study of pinniped helminth fauna in Chukotka, and the analysis of the fish of the main commercial families infected with pathogens of helminthozoonoses based on modern literature.
Materials and methods . The helminths were collected in autumn of 2019 from pinnipeds caught in the Mechigmenskaya Guba of the Bering Sea in the Chukotka Autonomous Okrug by the method of partial helminthological dissection per Skryabin (gastrointestinal tract). Samples were examined from 6 walruses and 26 seals (13 spotted seals and 13 ringed seals). The helminths found were fixed in 70% alcohol. The helminth species were identified at the Department of Parasitology and Veterinary and Sanitary Examination of the MVA named after K. I. Skryabin using reference literature.
Results and discussion . All pinnipeds were infected with nematodes of the family Anisakidae. Mature Pseudoterranova desipiens were found in the walrus (Infection Prevalence = 16.7% with Infection Intensity = 3 specimens/animal), mature Ps. desipiens, as well as Contracoecum osculatum and Anisakis simplex larvae (IP = 30.8% with II from 5 to 57 specimens) were found in the spotted seal, and Ps. desipiens larvae and mature Ps. desipiens were found in the ringed seal (IP = 15.4% with II from 1 to 4 specimens). Thus, only Ps. desipiens were represented by mature stages (females and males), and two other species of anisakids, C. osculatum and A. simplex, were found in the seals in the larval stage.
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