Individual Quality Drives Life History Variation in a Long-Lived Marine Predator.

AbstractIndividual quality and environmental conditions may mask or interact with energetic trade-offs in life history evolution. Deconstructing these sources of variation is especially difficult in long-lived species that are rarely observed on timescales long enough to disentangle these effects. Here, we investigated relative support for variation in female quality and costs of reproduction as factors shaping differences in life history trajectories using a 32-year dataset of repeated reproductive measurements from 273 marked, known-age female gray seals (Halichoerus grypus). We defined individual reproductive investment using two traits, reproductive frequency (a female's probability of breeding) and provisioning performance (offspring weaning mass). Fitted hierarchical Bayesian models identified individual investment relative to conspecifics (over a female's entire life and in three age classes) and subsequently estimated how these investment metrics and the Atlantic Multidecadal Oscillation are associated with longevity. Individual differences (i.e., quality) contributed a large portion of the variance in reproductive traits. Females that consistently invest well in their offspring relative to other females survive longer. The best-supported model estimated survival as a function of age class-specific provisioning performance, where late-life performance was particularly variable and had the greatest impact on survival, possibly indicating individual variation in senescence. There was no evidence to support a trade-off in reproductive performance and survival at the individual level. Overall, these results suggest that in gray seals, individual quality is a stronger driver in life history variation than individual strategies resulting from energetic trade-offs.

Sequence Diversity and Differences at the Highly Duplicated MHC-I Gene Reflect Viral Susceptibility in Sympatric Pinniped Species.

Differences in disease susceptibility among species can result from rapid host-pathogen coevolution and differences in host species ecology that affect the strength and direction of natural selection. Among 2 sympatric pinniped species that differ in sociality and putative disease exposure, we investigate observed differences in susceptibility through an analysis of a highly variable, duplicated gene family involved in the vertebrate immune response. Using high-throughput amplicon sequencing, we characterize diversity at the 2 exons that encode the peptide binding region of the major histocompatibility complex class I (MHC-I) gene in harbor (N = 60) and gray (N = 90) seal populations from the Northwest Atlantic. Across species, we identified 106 full-length exon 2 and 103 exon 3 sequence variants and a minimum of 11 duplicated MHC-I loci. The sequence variants clustered in 15 supertypes defined by the physiochemical properties of the peptide binding region, including a putatively novel Northwest Atlantic MHC-I diversity sublineage. Trans-species polymorphisms, dN/dS ratios, and evidence of gene conversion among supertypes are consistent with balancing selection acting on this gene. High functional redundancy suggests particularly strong selection among gray seals at the novel Northwest Atlantic MHC-I diversity sublineage. At exon 2, harbor seals had a significantly greater number of variants per individual than gray seals, but fewer supertypes. Supertype richness and private supertypes are hypothesized to contribute to observed differences in disease resistance between species, as consistently, across the North Atlantic and many disease outbreaks, gray seals appear to be more resistant to respiratory viruses than harbor seals.

Genetic association with boldness and maternal performance in a free-ranging population of grey seals (Halichoerus grypus).

Individual variation in quantitative traits clearly influence many ecological and evolutionary processes. Moderate to high heritability estimates of personality and life-history traits suggest some level of genetic control over these traits. Yet, we know very little of the underlying genetic architecture of phenotypic variation in the wild. In this study, we used a candidate gene approach to investigate the association of genetic variants with repeated measures of boldness and maternal performance traits (weaning mass and lactation duration) collected over an 11- and 28-year period, respectively, in a free-ranging population of grey seals on Sable Island National Park Reserve, Canada. We isolated and re-sequenced five genes: dopamine receptor D4 (DRD4), serotonin transporter (SERT), oxytocin receptor (OXTR), and melanocortin receptors 1 (MC1R) and 5 (MC5R). We discovered single nucleotide polymorphisms (SNPs) in each gene; and, after accounting for loci in linkage disequilibrium and filtering due to missing data, we were able to test for genotype-phenotype relationships at seven loci in three genes (DRD4, SERT, and MC1R). We tested for association between these loci and traits of 180 females having extreme shy-bold phenotypes using mixed-effects models. One locus within SERT was significantly associated with boldness (effect size = 0.189) and a second locus within DRD4 with weaning mass (effect size = 0.232). Altogether, genotypes explained 6.52-13.66% of total trait variation. Our study substantiates SERT and DRD4 as important determinants of behaviour, and provides unique insight into the molecular mechanisms underlying maternal performance variation in a marine predator.

Large offspring have enhanced lifetime reproductive success: Long-term carry-over effects of weaning size in gray seals (Halichoerus grypus).

An individual's size in early stages of life may be an important source of individual variation in lifetime reproductive performance, as size effects on ontogenetic development can have cascading physiological and behavioral consequences throughout life. Here, we explored how size-at-young influences subsequent reproductive performance in gray seals (Halichoerus grypus) using repeated encounter and reproductive data on a marked sample of 363 females that were measured for length after weaning, at ~4 weeks of age, and eventually recruited to the Sable Island breeding colony. Two reproductive traits were considered: provisioning performance (mass of weaned offspring), modeled using linear mixed effects models; and reproductive frequency (rate at which a female returns to breed), modeled using mixed effects multistate mark-recapture models. Mothers with the longest weaning lengths produced pups 8 kg heavier and were 20% more likely to breed in a given year than mothers with the shortest lengths. Correlation in body lengths between weaning and adult life stages, however, is weak: Longer pups do not grow to be longer than average adults. Thus, covariation between weaning length and future reproductive performance appears to be a carry-over effect, where the size advantages afforded in early juvenile stages may allow enhanced long-term performance in adulthood.

Ontogeny of movement patterns in naïve grey seal pups inhabiting a complex continental shelf ecosystem.

Most vertebrate offspring must transition from the relative security of parental care (nutrition and protection) to independent foraging. Offspring face many challenges during this critical period, particularly in species where parental care ends at weaning, such as the grey seal (Halichoerus grypus). We studied the development of movement behaviour in naïve grey seal pups from their first trips to sea to about five months of age. Twenty-five (12 males and 13 females) newly-weaned pups were fitted with satellite-linked GPS tags on Sable Island, Nova Scotia, Canada in January 2016. The influence of fixed effects (pup size, sex, week) and the random effect of pup identity on trip characteristics were examined. Movement behaviour was analyzed using a move persistence mixed-effects model. Habitat use was highly variable among individuals and covered much of the geographic distribution of the population. Unlike older juveniles, subadults, and adults in this population, most naïve pups used multiple haulout sites to begin and end trips. There was little evidence of area-restricted search behaviour during trips, suggesting that naïve pups were using an opportunistic foraging tactic that may result in more variable foraging success than that of older, experienced animals. Naïve pups made longer trips with longer haulout durations between them than observed for older greys seals. Males and females differed in some trip characteristics, but sex effects were small over the first few months of life. Offspring size at weaning was not a useful predictor of trip characteristics. Move persistence of grey seal pups was initially high and then decreased over time as individuals gained experience. Both intrinsic and extrinsic factors were influential on the movements of grey seal pups. Greater body length at weaning, longer duration spent on shore after weaning, shallower water column depth, and farther distance from shore were all associated with lower move persistence. Female grey seal pups had lower move persistence than males. Overall, the movements of naïve grey seal pups during the first few months of life were characterized by extensive exploration, but move persistence decreased over time suggesting they may be using an exploration-refinement foraging tactic.

Primiparous and multiparous females differ in mammary gland alveolar development: implications for milk production.

Mammary gland capacity is influenced by the number of secretory cells in the gland, the activity of those cells and the size and arrangement of the alveoli that they form. Although reproductive experience has been shown to affect the total number of secretory cells in the gland, its potential effect on the structural development of lobulo-alveolar tissues has not been directly investigated. To examine whether reproductive experience affects lobulo-alveolar development, we took mammary gland biopsies at early and peak lactation from primiparous and multiparous grey seal (Halichoerus grypus) females and used histological techniques to compare cell density, alveolar density and alveolar size within secretory lobules. Primiparous females had a significantly higher cell density compared with multiparous females throughout lactation, suggesting that primiparous females have smaller, less-developed secretory cells. Primiparous females had a significantly smaller average alveolar size compared with multiparous females throughout lactation. Although alveolar density was higher in primiparous females compared with multiparous females at early lactation, there was no significant difference between the groups at peak lactation. These results suggest that the mammary gland of primiparous females may have both a lower secretory capacity and a lower storage capacity on a relative basis than those of multiparous females and demonstrate, for the first time, that reproductive experience has a significant effect on both the rate and pattern of mammary gland alveolar development and, potentially, on a female's capacity for milk production.

Measuring repeatability of compositional diet estimates: An example using quantitative fatty acid signature analysis.

By measuring the temporal consistency, or repeatability, in the diets of predators, we can gain a better understanding of the degree of individual specialization in resource utilization and implications for predator-prey interactions, population dynamics, and food web structure. To measure repeatability, we require repeated diet estimates of individuals over time, such as those derived from quantitative fatty acid signature analysis (QFASA), a popular diet estimation technique. However, diet estimates are often lengthy compositional vectors with many zeros, as some prey will not be consumed by all individuals, precluding the use of previously proposed measures of repeatability. In this paper, we propose a novel approach for inferring repeatability for multivariate data and, in particular, compositional diet estimates. We extend the commonly used measure of repeatability for univariate data to the multivariate compositional setting by utilizing the mean squares obtained from a nonparametric multivariate analysis of variance, and an appropriate choice of statistical distance. Our measure and its extension are compatible with both balanced and unbalanced data sets. Associated confidence intervals via nonparametric bootstrapping are also developed for the case of QFASA diet estimates that incorporate both sampling error and measurement error, where the latter error arises because the diets of predators are estimated. Simulation study results suggest that for practical levels of repeatability, our methods yield confidence intervals with the desired coverage probability even when the sample size relative to the dimension of the data (i.e., number of prey species eaten) is small. We tested our methods using QFASA diet estimates for free-ranging Northwest Atlantic grey seals. Given the importance of understanding how predator diets vary over time and space, our method may find broad application to other compositional diet estimates, including those derived from the stomach or fecal contents, and stable isotope analyses.

Key questions in marine mammal bioenergetics.

Bioenergetic approaches are increasingly used to understand how marine mammal populations could be affected by a changing and disturbed aquatic environment. There remain considerable gaps in our knowledge of marine mammal bioenergetics, which hinder the application of bioenergetic studies to inform policy decisions. We conducted a priority-setting exercise to identify high-priority unanswered questions in marine mammal bioenergetics, with an emphasis on questions relevant to conservation and management. Electronic communication and a virtual workshop were used to solicit and collate potential research questions from the marine mammal bioenergetic community. From a final list of 39 questions, 11 were identified as 'key' questions because they received votes from at least 50% of survey participants. Key questions included those related to energy intake (prey landscapes, exposure to human activities) and expenditure (field metabolic rate, exposure to human activities, lactation, time-activity budgets), energy allocation priorities, metrics of body condition and relationships with survival and reproductive success and extrapolation of data from one species to another. Existing tools to address key questions include labelled water, animal-borne sensors, mark-resight data from long-term research programs, environmental DNA and unmanned vehicles. Further validation of existing approaches and development of new methodologies are needed to comprehensively address some key questions, particularly for cetaceans. The identification of these key questions can provide a guiding framework to set research priorities, which ultimately may yield more accurate information to inform policies and better conserve marine mammal populations.

Variation in individual reproductive performance amplified with population size in a long-lived carnivore.

Individual variation in reproductive ability is a key component of natural selection within populations, driving the evolution of life histories and population responses to changing environmental conditions. Evidence that population density affects individual-level fitness in wild populations is limited, particularly for long-lived animals, which are difficult to observe on a biologically relevant scale. We tested for individual heterogeneity in reproductive performance in female grey seals (Halichoerus grypus) using 35 yr of mark-resighting data at Sable Island, Canada (43.93° N 59.91° W). We used Bayesian generalized linear mixed-effect models and multistate open robust design mark-resight models to investigate whether population size negatively influences individual reproductive performance. We measured reproductive performance in two ways: reproductive frequency (the probability of returning to the island to breed) and annual provisioning performance (the probability of successfully weaning a pup given a female bred). Sighting histories of 1,655 known-aged females with a total of 22,961 pupping events were used for analysis. After accounting for effects of female age, parity, and random year effects, we found that both provisioning performance and reproductive frequency demonstrated a strong, positive correlation with population size. Among-individual variance in reproductive traits and responses to population size indicated considerable heterogeneity in overall reproductive performance. As population size grew, "robust" females increased their reproductive performance more than their more "frail" conspecifics in both reproductive traits, resulting in an amplification of differences among individuals. Consequently, simulations from posterior distributions revealed a large fitness consequence of heterogeneity in this population, with "frail" individuals having 47.1% fewer successful pups than more "robust" females (mean reproductive output ± SD: 9.12 ± 3.77 pups for frail individuals, 16.97 ± 2.94 for robust individuals). Repeatability of overall reproductive performance across environments indicates individual quality may be more influential to lifetime reproductive success than costs associated with reproductive investment. This quantification of relative fitness and its dynamics is crucial to understanding broad evolutionary processes in natural populations.

Sex-specific, seasonal foraging tactics of adult grey seals (Halichoerus grypus) revealed by state-space analysis.

In many large pelagic animals, observing behavior is limited to observation by radio or satellite telemetry. In many cases, discriminating different behaviors from telemetry data has been a key, but often elusive, goal. Here we use state-space models (SSMs) to fit a correlated random walk (CRW) model that switches between two unobserved behavioral states (nominally foraging and traveling) to 41 male and 43 female adult grey seal (Halichoerus grypus) satellite telemetry tracks. The SSM results reveal markedly different spatial behavior between the sexes, fitting well with sexual size dimorphism and known dietary differences, suggesting that the sexes deal with seasonal prey availability and reproductive costs differently. From these results we were also able to produce behaviorally informed habitat use maps, showing a complex and dynamic network of small, intensely used foraging areas. Our flexible SSM approach clearly demonstrates sex-related behavioral differences, fine scale spatial and temporal foraging patterns, and a clearer picture of grey seal ecology and role in the Scotian Shelf ecosystem.

Translating Marine Animal Tracking Data into Conservation Policy and Management.

There have been efforts around the globe to track individuals of many marine species and assess their movements and distribution, with the putative goal of supporting their conservation and management. Determining whether, and how, tracking data have been successfully applied to address real-world conservation issues is, however, difficult. Here, we compile a broad range of case studies from diverse marine taxa to show how tracking data have helped inform conservation policy and management, including reductions in fisheries bycatch and vessel strikes, and the design and administration of marine protected areas and important habitats. Using these examples, we highlight pathways through which the past and future investment in collecting animal tracking data might be better used to achieve tangible conservation benefits.

Linking movement, diving, and habitat to foraging success in a large marine predator.

Establishing where and when predators forage is essential to understanding trophic interactions, yet foraging behavior remains poorly understood in large marine carnivores. We investigated the factors leading to foraging success in gray seals (Halichoerus grypus) in the Northwest Atlantic in the first study to use simultaneous deployments of satellite transmitters, time depth recorders, and stomach-temperature loggers on a free-ranging marine mammal. Thirty-two seals were each fitted with the three types of instrumentation; however, complete records from all three instruments were obtained from only 13 individuals, underscoring the difficulty of such a multi-instrument approach. Our goal was to determine the characteristics of diving, habitat, and movement that predict feeding. We linked diving behavior to foraging success at two temporal scales: trips (days) and bouts (hours) to test models of optimal diving, which indicate that feeding can be predicted by time spent at the bottom of a dive. Using an information-theoretic approach, a Generalized Linear Mixed Model with trip duration and accumulated bottom time per day best explained the number of feeding events per trip, whereas the best predictor of the number of feeding events per bout was accumulated bottom time. We then tested whether characteristics of movement were predictive of feeding. Significant predictors of the number of feeding events per trip were angular variance (i.e., path tortuosity) and distance traveled per day. Finally, we integrated measures of diving, movement, and habitat at four temporal scales to determine overall predictors of feeding. At the 3-h scale, mean bottom time and distance traveled were the most important predictors of feeding frequency, whereas at the 6-h and 24-h time scales, distance traveled alone was most important. Bathymetry was the most significant predictor of feeding at the 12-h interval, with feeding more likely to occur at deeper depths. Our findings indicate that several factors predict feeding in gray seals, but predictor variables differ across temporal scales such that environmental variation becomes important at some scales and not others. Overall, our results illustrate the value of simultaneously recording and integrating multiple types of information to better understand the circumstances leading to foraging success.

Continued decline of an Atlantic cod population: how important is gray seal predation?

The continental shelf ecosystem on the Eastern Scotian Shelf (ESS) has experienced drastic changes. Once common top predators are a small fraction of their historical abundance, and much of the current community structure is now dominated by pelagic fishes and invertebrates. Embedded within this food web, Atlantic cod and gray seal populations have recently exhibited nearly opposite trends. Since 1984, cod populations have decreased exponentially at a rate averaging 17% per year, whereas gray seals have continued to increase exponentially at a rate of 12%. We reexamined the impact of gray seals on Atlantic cod dynamics using more than 30 years of data on the population trends of cod and gray seals while incorporating new information on seal diet and seasonal distribution. The closure of the cod fishery over 10 years ago allowed for a better estimation of natural mortality rates. We quantified the impact of seals on ESS cod by (1) estimating trends in seal and cod abundance, (2) estimating the total energy needed for seal growth and maintenance from an energetics model, (3) using estimates of the percentage of cod in the total diet derived from quantitative fatty acid signature analysis (QFASA) and of the size-specific selectivity of cod consumed (derived from otoliths collected from fecal samples), and (4) assuming a gray seal functional response. Uncertainties of the model estimates were calculated using the Hessian approximation of the variance-covariance matrix. Between 1993 and 2000, cod comprised, on average, < 5% of a gray seal's diet. Our model shows that, since the closure of the fishery, gray seals have imposed a significant level of instantaneous mortality (0.21), and along with other unknown sources of natural mortality (0.62), are contributing to the failure of this cod stock to recover.

Key Questions in Marine Megafauna Movement Ecology.

It is a golden age for animal movement studies and so an opportune time to assess priorities for future work. We assembled 40 experts to identify key questions in this field, focussing on marine megafauna, which include a broad range of birds, mammals, reptiles, and fish. Research on these taxa has both underpinned many of the recent technical developments and led to fundamental discoveries in the field. We show that the questions have broad applicability to other taxa, including terrestrial animals, flying insects, and swimming invertebrates, and, as such, this exercise provides a useful roadmap for targeted deployments and data syntheses that should advance the field of movement ecology.

A novel approach to quantifying the spatiotemporal behavior of instrumented grey seals used to sample the environment.

BACKGROUND: Paired with satellite location telemetry, animal-borne instruments can collect spatiotemporal data describing the animal's movement and environment at a scale relevant to its behavior. Ecologists have developed methods for identifying the area(s) used by an animal (e.g., home range) and those used most intensely (utilization distribution) based on location data. However, few have extended these models beyond their traditional roles as descriptive 2D summaries of point data. Here we demonstrate how the home range method, T-LoCoH, can be expanded to quantify collective sampling coverage by multiple instrumented animals using grey seals (Halichoerus grypus) equipped with GPS tags and acoustic transceivers on the Scotian Shelf (Atlantic Canada) as a case study. At the individual level, we illustrate how time and space-use metrics quantifying individual sampling coverage may be used to determine the rate of acoustic transmissions received. RESULTS: Grey seals collectively sampled an area of 11,308 km (2) and intensely sampled an area of 31 km (2) from June-December. The largest area sampled was in July (2094.56 km (2)) and the smallest area sampled occurred in August (1259.80 km (2)), with changes in sampling coverage observed through time. CONCLUSIONS: T-LoCoH provides an effective means to quantify changes in collective sampling effort by multiple instrumented animals and to compare these changes across time. We also illustrate how time and space-use metrics of individual instrumented seal movement calculated using T-LoCoH can be used to account for differences in the amount of time a bioprobe (biological sampling platform) spends in an area.

Animal-borne acoustic transceivers reveal patterns of at-sea associations in an upper-trophic level predator.

Satellite telemetry data have substantially increased our understanding of habitat use and foraging behaviour of upper-trophic marine predators, but fall short of providing an understanding of their social behaviour. We sought to determine whether novel acoustic and archival GPS data could be used to examine at-sea associations among grey seals (Halichoerus grypus) during the fall foraging period. Fifteen grey seals from Sable Island, Canada were deployed with Vemco Mobile Transceivers and Satellite-GPS transmitters in October 2009, 13 of which were recaptured and units retrieved 79 ± 2.3 days later during the following breeding season, December 2009-January 2010. An association between two individuals was defined as a cluster of acoustic detections where the time between detections was <30 min. Bathymetry, travel rate, and behavioural state (slow and fast movement) were determined for each GPS archival point (3.7 ± 0.1 locations recorded per hour). Behavioural state was estimated using a hidden Markov model. All seals had been involved in associations with other instrumented seals while at sea, with a total of 1,872 acoustic detections recorded in 201 associations. The median number of detections per association was 3 (range: 1-151) and the median duration of an association was 0.17 h (range: <0.1-11.3 h). Linear mixed-effects models showed that associations occurred when seals were exhibiting slow movement (0.24 ± 0.01 ms(-1)) on shallow (53.4 ± 3.7 m) offshore banks where dominant prey is known to occur. These results suggest the occurrence of short-term associations among multiple individuals at foraging grounds and provide new insights into the foraging ecology of this upper-trophic marine predator.

Jellyfish support high energy intake of leatherback sea turtles (Dermochelys coriacea): video evidence from animal-borne cameras.

The endangered leatherback turtle is a large, highly migratory marine predator that inexplicably relies upon a diet of low-energy gelatinous zooplankton. The location of these prey may be predictable at large oceanographic scales, given that leatherback turtles perform long distance migrations (1000s of km) from nesting beaches to high latitude foraging grounds. However, little is known about the profitability of this migration and foraging strategy. We used GPS location data and video from animal-borne cameras to examine how prey characteristics (i.e., prey size, prey type, prey encounter rate) correlate with the daytime foraging behavior of leatherbacks (n = 19) in shelf waters off Cape Breton Island, NS, Canada, during August and September. Video was recorded continuously, averaged 1:53 h per turtle (range 0:08-3:38 h), and documented a total of 601 prey captures. Lion's mane jellyfish (Cyanea capillata) was the dominant prey (83-100%), but moon jellyfish (Aurelia aurita) were also consumed. Turtles approached and attacked most jellyfish within the camera's field of view and appeared to consume prey completely. There was no significant relationship between encounter rate and dive duration (p = 0.74, linear mixed-effects models). Handling time increased with prey size regardless of prey species (p = 0.0001). Estimates of energy intake averaged 66,018 kJ • d(-1) but were as high as 167,797 kJ • d(-1) corresponding to turtles consuming an average of 330 kg wet mass • d(-1) (up to 840 kg • d(-1)) or approximately 261 (up to 664) jellyfish • d(-1). Assuming our turtles averaged 455 kg body mass, they consumed an average of 73% of their body mass • d(-1) equating to an average energy intake of 3-7 times their daily metabolic requirements, depending on estimates used. This study provides evidence that feeding tactics used by leatherbacks in Atlantic Canadian waters are highly profitable and our results are consistent with estimates of mass gain prior to southward migration.

The influence of reproductive experience on milk energy output and lactation performance in the grey seal (Halichoerus grypus).

Although evidence from domestic and laboratory species suggests that reproductive experience plays a critical role in the development of aspects of lactation performance, whether reproductive experience may have a significant influence on milk energy transfer to neonates in wild populations has not been directly investigated. We compared maternal energy expenditures and pup growth and energy deposition over the course of lactation between primiparous and fully-grown, multiparous grey seal (Halichoerus grypus) females to test whether reproductive experience has a significant influence on lactation performance. Although there was no difference between primiparous females in milk composition and, thus, milk energy content at either early or peak lactation primiparous females had a significantly lower daily milk energy output than multiparous females indicating a reduced physiological capacity for milk secretion. Primiparous females appeared to effectively compensate for lower rates of milk production through an increased nursing effort and, thus, achieved the same relative rate of milk energy transfer to pups as multiparous females. There was no difference between primiparous and multiparous females in the proportion of initial body energy stores mobilised to support the costs of lactation. Although primiparous females allocated a greater proportion of energy stores to maternal maintenance versus milk production than multiparous females, the difference was not sufficient to result in significant differences in the efficiency of energy transfer to pups. Thus, despite a lower physiological capacity for milk production, primiparous females weaned pups of the same relative size and condition as multiparous females without expending proportionally more energy. Although reproductive experience does not significantly affect the overall lactation performance of grey seals, our results suggest that increases in mammary gland capacity with reproductive experience may play a significant role in the age-related increases in neonatal growth rates and weaning masses observed in other free-ranging mammals.

The implications of stress on male mating behavior and success in a sexually dimorphic polygynous mammal, the grey seal.

Studies on primates and other taxa have shown that the physiological response of an individual to stress reflects their social status. We combined behavioral observations with measures of stress to test the hypothesis that stress is an important physiological determinant of mating behavior and success in the male grey seal. Known-age males (N=19) were studied during the breeding seasons of 2004 and 2005 at Sable Island, Canada. The stressor was a capture and restraint period of 35 min and serial samples of cortisol and testosterone were taken as measures of stress. The mean baseline concentrations of cortisol and testosterone were 9.7+/-0.5 ug/dl and 6.2+/-0.6 ng/mL, respectively. The baseline cortisol concentration was negatively correlated with the duration of time a male spent at a site (r=-0.507, P=0.027), which was a strong correlate of mating success (r=0.659, P=0.002). All males experienced an increase in the concentration of cortisol during the restraint period (79.1+/-8.4%; CV=46.1%). The percentage rise in cortisol during restraint was correlated with the mean duration of time spent at a site (r=0.544, P=0.016) and thus success. The concentration of testosterone also increased during the restraint period (32.8+/-9.7%). This might be an adaptive response to maintaining the ability to reproduce while under stress. Our study indicates that stress is an important determinant of success in male grey seals. More successful males might exhibit an adaptive response to stress by maintaining low concentrations of cortisol during breeding.

Body condition at weaning affects the duration of the postweaning fast in gray seal pups (Halichoerus grypus).

Gray seals (Halichoerus grypus) undergo a terrestrial postweaning fast (PWF) that depletes energy reserves acquired during the suckling interval. Plasticity in PWF duration may ensure that pups of variable body condition depart for sea with adequate energy reserves. To test this hypothesis, we examined body condition of 30 gray seal pups at weaning and monitored their PWF duration. On average, fat accounted for 47.3% +/- 0.7% of their 53.2 +/- 1.3-kg weaning mass. Although fasting duration averaged 21 +/- 1.1 d (n = p28), there was considerable variation in fasting duration (9 to > 31 d) and the resulting age when pups departed to sea (26 to > 49 d). Percent fat at weaning(38.6%-54.6%) was positively correlated with fasting duration(n = 28, r = 0.376, P = 0.0489). In contrast, total body gross energy (735.3-1,447.4 MJ) and body mass (39.0-66.0 kg) were not correlated with fasting duration. Thus, body composition,not overall body reserves, predicted fasting duration, but the effect was weak, indicating that other factors also account for the observed variation in fasting duration. We speculate that pups with greater percent fat more effectively utilized lipid and conserved protein while meeting metabolic costs throughout the PWF. As a result, fatter pups extended the PWF duration,which may be critical for development of diving physiology and may have facilitated their survivorship to age 1.