Bacular and testicular growth and allometry in the ringed seal (Pusa hispida): evidence of polygyny?

Winter behavior of Saimaa ringed seals: Non-overlapping core areas as indicators of avoidance in breeding females

Climate change, together with increasing human activity, poses a threat to the breeding success of endangered landlocked ringed seals (Phoca hispida saimensis). In this study, we estimated the spatial ecology of Saimaa ringed seals during the breeding season in the ice-covered period of December-April. The telemetry data on tagged seals (n = 20), with a total of 25 separate tracking periods and birth lair locations (n = 59) of non-tagged seals, were studied to estimate the movement ecology and breeding density. The movements of the ringed seals were more restricted during the ice-covered season; the total home range size (average 7.4 km²) in winter was 13 times smaller than that in summer. Individual tagged seals occupied an average of 5 ± 3 SD subnivean haul outs (snow lairs or ice cavities), and the mean distance between the haul outs was 1.6 ± 1.1 SD km (range 0.2–5.9 km). Moreover, our data indicated that ringed seal females likely exhibited breeding time avoidance of each other’s core areas, which may indicate some degree of territoriality. This was supported by the findings that the core areas (mean 1.2 km²) of tagged adult females (n = 9), did not overlap with each other. Also data on non-tagged seals showed that females did not give birth to pups within the core area radius of other parturient females. This study, together with earlier findings on the home ranges of nursed pups and perinatal mortality rates, has implications into land usage planning in Lake Saimaa by highlighting the need of undisturbed area between seal lairs and anthropogenic disturbances.

Geographic variation in ringed seal (Pusa hispida) growth rate and body size

We summarize geographical patterns in ringed seal (Pusa hispida (Schreber, 1775)) body length and girth growth using 3012 samples collected by Inuit hunters in the eastern Canadian Arctic from 1990 to 2016. Spatial structure was detected using cluster analysis of environmental variables separating a northern region in the eastern Canadian High Arctic and a southern region in Hudson Bay. The north was characterized by more fast ice, multiyear ice, greater snow depth, colder temperatures, and greater sea-ice concentration in the spring seal breeding season. Hierarchical Bayesian models described length and axillary girth growth of northern seals as slower than in the south, reaching asymptotic size 5–7 years later. Northern females were larger than males (asymptotic length of 149 versus 140 cm, respectively) and both were larger than southern seals (males and females 126 cm). We conclude that environmental variation was best represented by regions rather than latitude, regional body size differences were driven by differential growth rates, and northern ringed seals may be characterized by reverse sexual size dimorphism.

How small could a pup sound? The physical bases of signaling body size in harbor seals

Vocal communication is a crucial aspect of animal behavior. The mechanism which most mammals use to vocalize relies on three anatomical components. First, air overpressure is generated inside the lower vocal tract. Second, as the airstream goes through the glottis, sound is produced via vocal fold vibration. Third, this sound is further filtered by the geometry and length of the upper vocal tract. Evidence from mammalian anatomy and bioacoustics suggests that some of these three components may covary with an animal's body size. The framework provided by acoustic allometry suggests that, because vocal tract length (VTL) is more strongly constrained by the growth of the body than vocal fold length (VFL), VTL generates more reliable acoustic cues to an animal's size. This hypothesis is often tested acoustically but rarely anatomically, especially in pinnipeds. Here, we test the anatomical bases of the acoustic allometry hypothesis in harbor seal pups Phoca vitulina. We dissected and measured vocal tract, vocal folds, and other anatomical features of 15 harbor seals post-mortem. We found that, while VTL correlates with body size, VFL does not. This suggests that, while body growth puts anatomical constraints on how vocalizations are filtered by harbor seals' vocal tract, no such constraints appear to exist on vocal folds, at least during puppyhood. It is particularly interesting to find anatomical constraints on harbor seals' vocal tracts, the same anatomical region partially enabling pups to produce individually distinctive vocalizations.

Patterns of cetacean vaginal folds yield insights into functionality

Complex foldings of the vaginal wall are unique to some cetaceans and artiodactyls and are of unknown function(s). The patterns of vaginal length and cumulative vaginal fold length were assessed in relation to body length and to each other in a phylogenetic context to derive insights into functionality. The reproductive tracts of 59 female cetaceans (20 species, 6 families) were dissected. Phylogenetically-controlled reduced major axis regressions were used to establish a scaling trend for the female genitalia of cetaceans. An unparalleled level of vaginal diversity within a mammalian order was found. Vaginal folds varied in number and size across species, and vaginal fold length was positively allometric with body length. Vaginal length was not a significant predictor of vaginal fold length. Functional hypotheses regarding the role of vaginal folds and the potential selection pressures that could lead to evolution of these structures are discussed. Vaginal folds may present physical barriers, which obscure the pathway of seawater and/or sperm travelling through the vagina. This study contributes broad insights to the evolution of reproductive morphology and aquatic adaptations and lays the foundation for future functional morphology analyses.

Seasons of the ringed seal: pelagic open-water hyperphagy, benthic feeding over winter and spring fasting during molt

Context The ringed seal (Phoca hispida), a small phocid seal with a circumpolar Arctic distribution and a strong association with sea ice, occurs at the southern limit of its range in Hudson and James Bays: an area that experiences complete ice cover in winter and complete open water in summer. Because of the high seasonal variability in environmental conditions, it is expected that ringed seals experience seasonal changes in diet and foraging habitat, which will be reflected in body condition and biomarkers of stable isotopes and fatty acids. Aims The purpose of the present study was to investigate intra-annual variation in the feeding habits and body condition of the ringed seal. Methods Tissue samples and morphological measurements from south-eastern Hudson Bay ringed seals were obtained every month during the Inuit subsistence hunt from November 2009 to May 2011 (n = 192). Muscle samples were used for δ15N and δ13C stable isotope analysis, blubber was used for analysis of fatty acid composition, bodyweight and sculp weight were used to estimate percentage blubber, and lower right canines were used to determine age. Key results Fatty acid composition, δ15N, and δ13C varied significantly by season, suggesting seasonal changes in foraging habitat and diet. Variation in percentage blubber indicated that poorest body condition occurs following the molting and fasting period, followed by a gradual increase from late summer through fall, with the highest body condition occurring in time for freeze-up in December. Key conclusions Patterns of δ13C indicate pelagic feeding during the open-water season (August–December) when fat and energy stores are replenished, increased benthic foraging during the period of ice cover (January–May), followed by a period of fasting during the spring molt (June–July). Fatty acid composition suggested seasonal changes in diet that could include increased importance of pelagic fish in the fall during the period of positive energy balance. Implications The first continuous collection of ringed seal tissue samples provided a comprehensive seasonal pattern of biomarker composition, which is baseline data that have important applications for short-term management and ecology studies as well as long-term conservation and monitoring programs.