Phocid Seals Research Articles

Variation, Sexual Dimorphism, and Allometry in Molar Size of the Black Bear

We investigated molar-crown–size variation, sexual dimorphism, and allometry in the black bear (Ursus americanus), using hunter-shot specimens (n ¼ 429) from the island of Newfoundland, and museum specimens from elsewhere in Canada and the continental United States (n ¼ 502). We predicted higher variation in and weaker correlations among molar size in this omnivorous species than in other species of Carnivora with dentition more specialized for carnivory, because of relatively weak normalizing selection on food-processing mechanisms in U. americanus. Molar-size variation in Newfoundland bears (mean coefficient of variation ; 5.6%) was intermediate between species of Carnivora with simpler (e.g., pinnipeds) and more complex (e.g., canids) postcanine dentition. There was negligible size variation within the molar teeth, unlike some mammals. Bilateral symmetry was strong, especially in mandibular length (r ; 1.0 between left and right sides; r ; 0.95 for other mandibular and maxillary variables and molar size); symmetry in molar size was higher than in phocid seals. Size was positively correlated across molars, especially between adjacent (but not occluding) molars; patterns were similar between sexes and geographic regions, and correlation levels did not differ from other species of Carnivora. We also predicted (and found) smaller sexual differences (¼ 100[(male/female) � 1]) in molar size than in body size, because definitive molar size is attained early in life: differences in molar size averaged ;5.5% in Newfoundland (higher in continental subsamples), which is less than differences in cranial size (7–9%) or body mass 1/3 (21%). Sexes did not differ in relative molar size. Molar size was mainly isometric

Resource partitioning by sympatric pagophilic seals in Alaska: monitoring effects of climate variation with fatty acids

Four species of pagophilic phocid seals in the Western Arctic—bearded (Erignathus barbatus), ringed (Phoca hispida), ribbon (Phoca fasciata), and spotted (Phoca largha)—are particularly vulnerable to arctic warming trends. Documenting diet composition over time is one way in which the flexibility of a species, in the face of broad ecosystem changes, can be measured. Because the fatty acid (FA) composition of depot lipids has long been known to reflect diet, we analysed the FA composition of blubber samples collected from bearded (n = 30), ringed (n = 15), ribbon (n = 32) and spotted seals (n = 24). All animals were taken near Little Diomede Island in May and June 2003, providing a unique opportunity to study interspecies differences with minimal effects of spatial and temporal variation. Bearded seal FA composition was significantly different from all other seals (P < 0.001 in all cases), ringed seal FA composition was significantly different from that of both ribbon and spotted seals (P < 0.001), but ribbon and spotted seal FA compositions could not be distinguished from each other. Overall, the blubber FA compositions of ribbon, ringed and spotted seals implied diets dominated by pelagic prey. Inferences we made about current diets of bearded and ringed seals suggest that certain prey important to them in this area in the 1970s remain important today, despite notable changes in the ecosystem. We believe that blubber FA analysis will be a useful tool in assessing the response of ice-associated pinnipeds and their ecosystem to changes associated with arctic warming.

Seasonal energetics of northern phocid seals

The metabolic rate of harp ( Pagophilus groenlandicus), harbor ( Phoca vitulina), and ringed seals ( Pusa hispida) was measured at various temperatures in air and water to estimate basal metabolic rates (BMRs) in these species. The basal rate and body composition of three harp seals were also measured throughout the year to examine the extent to which they vary seasonally. Marine mammalian carnivores generally have BMRs that are over three times the rates expected from body mass in mammals generally, both as a response to a cold-water distribution and to carnivorous food habits with the basal rates of terrestrial carnivores averaging about 1.8 times the mean of mammals. Phocid seals, however, have basal rates of metabolism that are 30% lower than other marine carnivores. Captive seals undergo profound changes in body mass and food consumption throughout the year, and after accounting for changes in body mass, the lowest rate of food intake occurs in summer. Contrary to earlier observations, harp seals also have lower basal rates during summer than during winter, but the variation in BMR, relative to mass expectations, was not associated with changes in the size of fat deposits. The summer reduction in energy expenditure and food consumption correlated with a reduction in BMR. That is, changes in BMR account for a significant portion of the seasonal variation in energy expenditure in the harp seal. Changes in body mass of harp seals throughout the year were due not only to changes in the size of body fat deposits, but also to changes in lean body mass. These results suggest that bioenergetics models used to predict prey consumption by seals should include time-variant energy requirements.

Terrestrial apnoeas and the development of cardiac control in Australian fur seal (Arctocephalus pusillus doriferus) pups

The development of cardiac control in association with terrestrial respiration patterns was examined throughout the period of maternal dependence in Australian fur seal pups. Resting eupnoic heart rate and respiration rate were significantly correlated (r (2) = 0.49) and both decreased with age (P < 0.05 in both cases). From an early age (1 month), pups displayed terrestrial apnoeas (18.1 +/- 0.5 s) accompanied by substantial bradycardia (127 beats min(-1), a 13% decrease from eupnoic HR). Terrestrial apnoea duration increased significantly with age reaching a mean of 41 s just prior to weaning, slightly lower than the mean dive duration (52 s) previously recorded for pups of the same age. Correspondingly, mean apnoic heart rate decreased with age to 74 beats min(-1) just prior to weaning, representing a 25% decrease on eupnoic heart rate. Importantly, concomitant with the decrease in mean apnoic heart rate with age, an increase in the control of bradycardia was evident with the variability in instantaneous apnoic heart decreasing such that older pups were able to maintain a low steady heart rate for the duration of the apnoea. The changes seen in these parameters are similar to those reported during postnatal development in elephant seals (Mirounga spp.) and harbour seals (Phoca vitulina), and are considered indicative of the development of cardiac control. These findings suggest a common strategy for the development of bradycardia control in both otariid and phocid seals.

Genetic relationships among species ofContracaecumRailliet &amp; Henry, 1912 andPhocascarisHöst, 1932 (Nematoda: Anisakidae) from pinnipeds inferred from mitochondrialcox2sequences, and congruence with allozyme data

The genetic relationships among 11 taxa, belonging to the genus Contracaecum (C. osculatum A, C. osculatum B, C. osculatum (s.s.), C. osculatum D, C. osculatum E, C. osculatum baicalensis, C. mirounga, C. radiatum, C. ogmorhini (s.s.), C. margolisi) and Phocascoris (Phocoscris cystophorae), parasites as adults of seals, were inferred from sequence analysis 1519 bp) of the mitochondrial cytochrome c oxidase subunit II (mtDNA cox2) gene. Phylogenetic analyses obtained from Parsimony (MP) and Neighbour-Joining (NJ) K2P distance values generated similar topologies, each well supported at major nodes. All analyses delineated two main clades: the first encompassing the parasites of the phocid seals, i.e. the C. osculatum species complex, C. osculatum boicolensis, C. mirounga and C. radiatum, with the latter two species forming a separate subclade; the second including the parasites of otarids, i.e. C. ogmorhini (s.s.) and C. margolisi. An overall high congruence between mtDNA inferred tree topologies and those produced from nuclear data sets (20 allozyme loci) was observed. Comparison of the phylogenetic hypothesis here produced for Controcaecum spp. plus Phocascaris with those currently available for their definitive hosts (pinnipeds) suggests parallelism between hosts and parasite phylogenetic tree topologies.

Population structure of ice‐breeding seals

The development of population genetic structure in ice-breeding seal species is likely to be shaped by a combination of breeding habitat and life-history characteristics. Species that return to breed on predictable fast-ice locations are more likely to exhibit natal fidelity than pack-ice-breeding species, which in turn facilitates the development of genetic differentiation between subpopulations. Other aspects of life history such as geographically distinct vocalizations, female gregariousness, and the potential for polygynous breeding may also facilitate population structure. Based on these factors, we predicted that fast-ice-breeding seal species (the Weddell and ringed seal) would show elevated genetic differentiation compared to pack-ice-breeding species (the leopard, Ross, crabeater and bearded seals). We tested this prediction using microsatellite analysis to examine population structure of these six ice-breeding species. Our results did not support this prediction. While none of the Antarctic pack-ice species showed statistically significant population structure, the bearded seal of the Arctic pack ice showed strong differentiation between subpopulations. Again in contrast, the fast-ice-breeding Weddell seal of the Antarctic showed clear evidence for genetic differentiation while the ringed seal, breeding in similar habitat in the Arctic, did not. These results suggest that the development of population structure in ice-breeding phocid seals is a more complex outcome of the interplay of phylogenetic and ecological factors than can be predicted on the basis of breeding substrate and life-history characteristics.

Foraging while breeding: alternative mating strategies by male Weddell seals?

1. In terrestrially breeding phocid seals males are significantly larger than females with their large size conferring advantage in male–male competition, and increasing their ability to fast during the breeding season, prolonging tenure and hence mating opportunities. 2. For aquatically breeding seals, the opportunity to feed during the breeding season may offset the need for large size and the ability to fast. 3. Individual differences in male breeding success, behaviour and mass changes for Weddell seals (Leptonychotes weddellii) at Turtle Rock, McMurdo Sound (77.727S, 166.85E) during 1997, 1998 and 1999 were recorded. 4. Males were tracked under the ice through each breeding season using an acoustic array (n=15). Mass changes were measured for 30 males, all of which were successfully genotyped and were aged between 6 and 20 years (mean 13.7). 5. Territory use was dynamic, with some males spending most of the time either at or near the surface, others diving deep and others switching from regular diving to near surface behaviour. 6. Rate of mass loss varied more than three-fold (mean 2.1 ± 0.53 kg day−1, range 0.0 to 4.1) as did mass-specific loss (mean 0.53 ± 0.23). 7. Maximum dive depth for the individuals also varied dramatically (10 to 518 m) and was inversely related to the rate of mass-specific loss, suggesting that the deep diving males may offset the costs of breeding by foraging. 8. Males that stayed near the surface successfully sired pups as did males that continued to dive. Both strategies therefore seemed to be equally successful. 9. Foraging during the breeding season may be a male strategy that may potentially prolong tenure, but appears to be facultative rather than obligative. Copyright © 2008 John Wiley & Sons, Ltd.

Variation in blubber fatty acid composition among marine mammals in the Canadian Arctic

AbstractThe composition of predator adipose stores can provide important insights into foraging patterns and the ecological relationships among species. We determined the fatty acid (FA) composition of 843 blubber samples from 80 bearded seals (Erignathus barbatus), 33 harbor seals (Phoca vitulina), 239 harp seals (Pagophilus groenlandicus), 32 hooded seals (Cystophora cristata), 281 ringed seals (Phoca hispida), 53 walruses (Odobenus rosmarus rosmarus), 105 beluga whales (Delphinapterus leucas), and 20 narwhals (Monodon monoceros) across the Canadian Arctic to examine patterns of variability among and within species. FA signatures accurately distinguished phocid seals, walruses, and whales. Belugas and narwhals had the most similar FA signatures of any two species, suggesting substantial overlap in their diets, especially in the narwhal‐wintering area off eastern Baffin Island. Among phocid seals, harp and hooded seals had the most similar FA signatures. Bearded seals were most similar to walruses, which was consistent with the benthic feeding habits of both species. Within species, geographic differences in FA signatures were found over both large (&gt;4,000 km) and small (&lt;100 km) spatial scales. Overall, within‐species differences were smaller than among‐species differences. In general, FA signature patterns were consistent with previous studies of the ecology and diets of arctic marine mammals.

Relationship between milk energy intake and growth rate in suckling mammalian young at peak lactation: an updated meta‐analysis

AbstractThe milk energy intakes and growth rates of suckling young at peak lactation of 62 mammalian species and subspecies, all measured using either the weigh–suckle–weigh, the isotope dilution or the isotope transfer method, were evaluated. The mean daily gross energy intakes (GEI) were as low as 12 kJ in a small rodent (mouse) to as high as 249 MJ in a phocid seal (hooded seal Cystophora cristata), while the daily growth rates at peak lactation ranged from 0.4 to 5.9 kg. Several allometric equations were calculated to explore the relationships between gross energy intake via milk and body weight (BW), growth rate and BW, as well as between gross energy intake via milk and growth rate. The results suggest that both GEI via milk and growth rates are proportional to BW to the power of 0.82. Accordingly, the metabolic weight of suckling mammalian young should be expressed as BW0.82. The predictive values of the calculated equations indicate that suckling young at peak lactation consume c. 883 kJ day−1 kg−1 BW0.82 and have growth rates of 32 g day−1 kg−1 BW0.82. However, large deviations for some species and few outliers were found. These equations could be used to predict values for species that have not been studied, provided that the BW falls within the range of weights used to derive the equations.

Phocid seals, seal lice and heartworms: a terrestrial host–parasite system conveyed to the marine environment

Adaptation of pinnipeds to the marine habitat imposed parallel evolutions in their parasites. Ancestral pinnipeds must have harboured sucking lice, which were ancestors of the seal louse Echinophthirius horridus. The seal louse is one of the few insects that successfully adjusted to the marine environment. Adaptations such as keeping an air reservoir and the ability to hold on to and move on the host were necessary, as well as an adjustment of their life cycle to fit the diving habits of their host. E. horridus are confined to the Northern Hemisphere and have been reported from 9 species of northern phocids belonging to 4 genera, including land-locked seal species. The transmission from seal to seal is only possible when animals are hauled-out on land or ice. Lice are rarely found on healthy adult seals, but frequently on weak and young animals. The seal louse is suggested to play an important role as an intermediate host transmitting the heartworm Acanthocheilonema spirocauda among seals. However, the evidence is restricted to a single study where the first 3 larval stages of the heartworm were shown to develop in the louse. The fourth-stage larvae develop in the blood system of seals and eventually transform into the adult stage that matures in the heart. Since all other studies failed to confirm the presence of heartworm larvae in seal lice, other unknown intermediate hosts could be involved in the transmission of the heartworm. Transplacental transmission of microfilariae in seals has been suggested as an additional possibility, but is not likely to be important since the occurrence of heartworms in adult seals is very rare compared with juveniles. Furthermore, there are no findings of the first 3 larval stages in seals. This review shows that the heartworm infects nearly the same species of seals as the seal louse, except for the grey seal Halichoerus grypus, where the heartworm is absent. Prevalence and intensity of infection differ among regions in the Northern Hemisphere. As for seal lice, heartworms mainly infect immature seals, and after infection the prevalence seems to decrease with increasing age of the host.

Variation and Integration of the Simple Mandibular Postcanine Dentition in Two Species of Phocid Seal

Pinnipeds generally swallow prey whole, and most have simple, homodont, nonoccluding cheek teeth. We investigated whether cheek teeth in seals are more variable and weakly integrated than in terrestrial Carnivora. We measured mandibular length and crown length of mandibular postcanines (PCs) in ringed seals (Pusa hispida; n ¼ 912) from the Canadian Arctic, and harp seals (Pagophilus groenlandicus; n ¼ 636) from Newfoundland and Labrador. PC size was uncorrelated or only weakly correlated with adult mandibular length. PC length and mandibular length were strongly bilaterally symmetrical (r � 0.8 between left and right sides). PC size was moderately variable (coefficients of variation [CVs] ; 7‐10%), and CV varied with position in the toothrow. Adjacent PCs were correlated more strongly in size (to r . 0.8) than PCs more distant from one another. In summary, PC size in ringed and harp seals was slightly more variable than cheek teeth in complex dentitions of fissipeds, and the 2 seals were similar to fissipeds in strong bilateral symmetry in mandibular and PC size, patterned variation along the toothrow, and correlated size between adjacent PCs.

Dimensions of diet segregation in grey seals Halichoerus grypus revealed through stable isotopes of carbon (δ13C) and nitrogen (δ15N)

Although many studies have documented diets for terrestrial mammals, much less is known about prey selection in marine mammals. Variation in body size of terrestrial carnivores is cor- related with mass of prey consumed, and predator size often determines dietary overlap. Grey seals Halichoerus grypus are a size-dimorphic phocid seal inhabiting the Northwest Atlantic, with males 1.5× larger than females. Stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N) provide useful tools for estimating trophic positions and carbon flow to consumers in food webs. δ 13 C and δ 15 N were analyzed for individual adult grey seals from Sable Island, Canada, between 1996 and 2001. Samples of skin were taken in May or September and the same animals were re-sampled when they returned to the breeding colony in January. In addition, samples were taken from juveniles (n = 29) in January 2004. δ 13 C and δ 15 N were also analyzed for 12 fish and 3 invertebrate species from the Scotian Shelf. Adult male (n = 36) and female (n = 36) grey seals exhibited significantly different δ 13 C and δ 15 N values (F1, 70 = 22.40; p < 0.001). On average, males were more enriched in both δ 13 C and δ 15 N than females. While there were no differences between sex in juveniles, signatures were significantly different from adults (F2,101 = 28.05; p < 0.001). Comparison of isotope values from potential prey suggests that adult males feed more heavily on benthic prey, whereas adult females appear to feed more on pelagic prey. Juveniles also appear to feed more on pelagic prey. These results are consistent with known dif- ferences in dive patterns and foraging behaviour in this population. In addition, there was a positive effect of body size on both δ 13 C (t = 2.54, p = 0.014) and δ 15 N (t = 2.48, p = 0.016) and a positive rela- tionship between δ 15 N and the rate of fat accumulation (kg d -1 ). These results suggest an underlying energetic basis to diet variation in grey seals. Finally, examination of the variance in stable isotope ratios suggested that while individual grey seals appear to be relative specialists in their diet, niche breadth was 1.5× greater in males than in females. On average, adult grey seals had a 2 × higher niche breadth than juveniles.

Diving and foraging energetics of the smallest marine mammal, the sea otter (Enhydra lutris)

As the smallest and one of the most recently evolved marine mammals, sea otters face physiological challenges rarely encountered by larger, more derived aquatic species. To examine the effect of these challenges on foraging costs and resultant daily energy budgets, we measured the energetics of resting, grooming, diving and foraging for adult, male sea otters. The energy expended for these different behaviors as determined from open flow respirometry was then standardized across activity budgets measured for wild sea otters to estimate field metabolic rates (FMR). We found that the metabolic rate of captive otters performing single dives ranging in duration from 40 to 192 s was 17.6+/-0.5 ml O(2) kg(-1) min(-1) and only 1.3 times resting rates. This rate increased significantly if the animals foraged during submergence. The cost of a foraging dive for sea otters was nearly twice that predicted for phocid seals, which was attributed in part to elevated locomotor costs associated with buoyancy and swimming style. Our behavioral studies indicate that wild sea otters spend the greatest proportion of the day feeding and resting, with the largest daily energy expenditure (6.1+/-1.1 MJ day(-1)) associated with foraging. The resulting mean FMR for wild sea otters based on the energy expended for all behaviors was 15.7+/-2.7 MJ day(-1) and matched predicted FMR values based upon a regression of known FMR values for other marine mammals across a range of body sizes. This was achieved by counterbalancing elevated foraging costs with prolonged periods of rest on the water surface.

Sex-specific foraging strategies and resource partitioning in the southern elephant seal (Mirounga leonina)

The evolution of resource specializations is poorly understood, especially in marine systems. The southern elephant seal (Mirounga leonina) is the largest of the phocid seals, sexually dimorphic, and thought to prey predominantly on fish and squid. We collected vibrissae from male and female southern elephant seals, and assessed stable C and N isotope ratios along the length of the vibrissae. Given that whiskers grow slowly, this sampling strategy reflects any variation in feeding behaviour over a period of time. We found that isotopic variation among females was relatively small, and that the apparent prey choice and trophic level of females was different from that for males. Further, males showed a very broad range of trophic/prey choice positions, grouped into several clusters, and this included isotopic values too low to match a broad range of potential fish and cephalopod prey tested. One of these clusters overlapped with data for South American sea lions (Otaria flavescens), which were measured for comparison. Both male southern elephant seals and southern sea lions forage over the continental shelf, providing the potential for competition. We discuss the possibility that individual southern elephant seals are pursuing specialist foraging strategies to avoid competition, both with one another, and with the South American sea lions that breed nearby.

Histology of selected tissues of the leopard seal and implications for functional adaptations to an aquatic lifestyle

The microscopic anatomy of the cardio-respiratory system, digestive system, kidney, lymphatic system and integument was investigated in the leopard seal, Hydrurga leptonyx, by examining histological sections of tissues collected from leopard seals in Antarctica and New South Wales, Australia. The majority of the tissues had similar histological features to those described in terrestrial mammals and other pinniped species, particularly phocid seals. Differences noted included readily identifiable Purkinje cells within the endocardium, muscular rather than cartilaginous reinforcement of the smaller airways, a single capillary layer within the alveolar septa, limited and variable keratinization of the oesophageal epithelium, few lymphoid follicles within the lamina propria of the gastrointestinal tract, and an absence of a sporta perimedullaris musculosa described in the kidney of cetaceans and some pinniped species. Adaptations of the lung, spleen and integument, similar to those described in other pinnipeds, including reinforcement of the pulmonary terminal airways, prominent pulmonary interlobular septa, ample smooth muscle in the capsule and trabeculae of the spleen, increased thickness of the epidermis, well-developed dermal sebaceous glands, and a thick blubber layer, appear to confer upon the leopard seal advantages related to its aquatic lifestyle.

Feeding ecology of phocid seals and some walrus in the Alaskan and Canadian Arctic as determined by stomach contents and stable isotope analysis

Feeding habits of ringed (Phoca hispida), bearded (Erignathus barbatus), spotted (Phoca largha) and ribbon (Phoca fasciata) seals and walrus (Odobenus rosmarus) were studied using stomach contents and stable carbon and nitrogen isotopes. Bearded seals fed benthically, primarily crustaceans and mollusks. Both zooplankton and fish were significant prey for ringed seals, while fish was principal spotted seal prey. Few gastric contents were available from ribbon seals. δ15N was positively correlated with age in ribbon seals and δ13C was positively correlated with age in ringed and ribbon seals. δ15N was highest in spotted seals, in agreement with their fish-dominated diet. δ15N was not different between Alaskan-harvested ringed and bearded seals, while δ15N was lowest in ribbon seals and walrus. Carbon-13 was most enriched in bearded seals and walrus reflecting benthic ecosystem use. Canadian ringed seals were depleted in 13C compared to Alaskan pinnipeds, likely because of Beaufort Sea versus Chukchi and Bering seas influence.

Phocine distemper virus in the North and European Seas – Data and models, nature and nurture

Two outbreaks of phocine distemper have severely affected harbour seal ( Phoca vitulina) populations in European and UK waters. The first occurred in 1988 when the causative virus was identified as a new member of the genus morbillivirus. The second outbreak in 2002 was first detected on the same Danish Island of Anholt and involved similar populations and geographical locations. However, despite the obvious similarities between the epidemics, differences in viral transmission and case mortality were found. Harbour seals are highly susceptible to infection while sympatric grey seals ( Halichoerus grypus) are resistant but could be important asymptomatic carriers of the disease. Arctic phocid seals remain the most likely source of the virus and grey seals could be the link between these primary hosts and the harbour seal populations further south. Future epidemiological models should therefore consider including multiple host species. The future conservation and management of harbour seal populations vulnerable to PDV relies on the ability to accurately predict the long-term impact on population abundance and distribution. Although knowledge about the behaviour and pathogenesis of the virus has increased substantially and data on host movements and contact rates are accumulating, studies into the determinants of the host range have lagged behind. The development of more realistic epidemiological models should be combined with studies into the factors controlling species and individual susceptibility. Assessing the risk of infection to endangered but currently unexposed potential host species (such as the Hawaiian monk seal, Monachus schauinslandi) is essential for guiding potential conservation management options, such as vaccination

Intravascular pressure profiles in elephant seals: Hypotheses on the caval sphincter, extradural vein and venous return to the heart

In order to evaluate hemodynamics in the complex vascular system of phocid seals, intravascular pressure profiles were measured during periods of rest-associated apnea in young elephant seals ( Mirounga angustirostris). There were no significant differences between apneic and eupneic mean arterial pressures. During apnea, venous pressure profiles (pulmonary artery, thoracic portion of the vena cava (thoracic vena cava), extradural vein, and hepatic sinus) demonstrated only minor, transient fluctuations. During eupnea, all venous pressure profiles were dominated by respiratory fluctuations. During inspiration, pressures in the thoracic vena cava and extradural vein decreased − 9 to − 21 mm Hg, and − 9 to − 17 mm Hg, respectively. In contrast, hepatic sinus pressure increased 2–6 mm Hg during inspiration. Nearly constant hepatic sinus and intrathoracic vascular pressure profiles during the breath-hold period are consistent with incomplete constriction of the caval sphincter during these rest-associated apneas. During eupnea, negative inspiratory intravascular pressures in the chest (“the respiratory pump”) should augment venous return via both the venae cavae and the extradural vein. It is hypothesized that, in addition to the venae cavae, the prominent para-caval venous system of phocid seals ( i.e., the extradural vein) is necessary to allow adequate venous return for maintenance of high cardiac outputs and blood pressure during eupnea.

Diving behaviour of Mediterranean monk seal pups during lactation and post weaning

Time depth recorders (TDRs) were attached to 3 Mediterranean monk seal pups during a range of periods around weaning, providing a composite picture of activity from the first weeks of life until nutritional independence. The pups entered the water during their first week of life and their diving performance increase progressively with age. All pups spent most of their time at sea (55 to 74%), and their swimming activity was greater at nighttime compared with daytime. Dive per- formance in relation to pup age was poorer compared with other phocid seal species. Dive types were classified using a combination of hierarchical and k-mean clustering. We found 3 dive types: 1 V- shaped and 2 U-shaped. The most common type was U1-dives, mainly used by older pups during 44 to 48% of their total dive time. These dives were relatively deep and long (mean depth = 11.6 ± 9.5 m, mean duration = 149.1 ± 80.6 s). They had long bottom times (100 ± 67 s), suggesting that pups were foraging. Pups appeared to start feeding at the end of lactation.

Individual variation in milk composition over lactation in harbour seals (Phoca vitulina) and the potential consequences of intermittent attendance

We studied milk composition over the course of lactation in 21 harbour seal (Phoca vitulina L., 1758) females on Sable Island, Nova Scotia. Milk fat content increased significantly from 40.8% ± 1.01% at parturition to 50.2% ± 1.39% at day 7 and then remained relatively constant throughout the remainder of lactation. Changes in dry matter mirrored changes in fat content. Protein content averaged about 9% over mid to late lactation. There was considerable between-individual variation in the composition of milk and how it changed over lactation, particularly in milk fat content (CV 9.1%–11.4%). In three females that were separated from their pups for 4–6 days, milk fat content declined by 20%–23% and milk protein content increased by 6%–11%. These changes in milk composition indicate that changes in mammary gland function occur rapidly following the onset of milk stasis in harbour seals. The rapid response of the mammary glands to separation suggests that, in direct contrast to the glands of otariids, the glands of harbour seals rely on regular evacuation to maintain normal function. These results suggest that there may be a significant physiological constraint on the duration that harbour seal females, and presumably other phocid seals, can forage without negatively affecting energy transfer to their pups.