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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.

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.

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 natal size influences subsequent reproductive performance in grey seals (Halichoerus grypus) using repeated encounter and reproductive data on a marked sample of 363 females that were measured for length 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 natal 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 natal and adult life stages, however, is weak: longer pups do not grow to be longer than average adults. Thus covariation between natal 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.

This work was funded by the Marine Mammal Commission (MMC19-173). The Office of Naval Research funded the bioenergetic workshop (N000142012392) that provided support for this work. 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. Publisher PDF

Change in breeding phenology is often a response to environmental forcing, but less is known of the mechanism underlying such changes and their fitness consequences. Here, we report on changes in the breeding phenology from a 27‐year longitudinal study (1991–2017) of individually marked, known‐aged grey seals (Halichoerus grypus) on Sable Island, Nova Scotia, Canada. We used generalized linear mixed models and a 3‐step process to develop a model that includes interactions between intrinsic and extrinsic covariates and to test hypotheses about the influence of fixed factors (maternal age, parity, previous reproductive success, pup sex, colony density, Atlantic Multidecal Oscillation (AMO), North Atlantic Oscillation (NAO), and Sea Surface Temperature) and a random factor (female identity) on parturition dates. We also examined the consequences of the shift in birthdates on maternal energy allocation in offspring as measured by pup weaning mass. Birthdates were known for 2,768 pups of 660 known‐age females. For 494 females with ≥2 parturition dates, repeatability as measured by the intraclass correlation was high (mean = 0.66). 87% of the variation in birthdates was explained by a mixed‐effects model that included intrinsic and extrinsic fixed effects. Most of the explained variation was associated with the random effect of female identity. Parity was the most important intrinsic fixed effect, with inexperienced mothers giving birth later in the season than multiparous females. Over almost 3 decades, mean birthdates advanced by 15 days. The mixed model with intrinsic effects and population size, the detrended AMO from the previous year and mean NAO in the previous 3 years explained 80% of the variation with 21% of variation from the fixed effects. Both primiparous and multiparous individuals responded to the climate forcing, and there was strong evidence for heterogeneity in the response. Nevertheless, the shift in birthdates did not impact pup weaning mass., Here, we studied how breeding phenology responds to maternal traits and demographic and environmental conditions over almost three decades and the resulting fitness consequences of those changes in a well‐studied population of grey seals. Mean birthdates advanced by 15 days. Longitudinal data on over 500 individual females showed that maternal birthdates were highly repeatable but despite that repeatability females responded to environmental forcing. Both primiparous and multiparous individuals responded to forcing by AMO, but there was strong evidence for heterogeneity in the response. Despite changing birthdates offspring weaning mass was not affected showing that climate driven changes in breeding phenology may not always have measurable consequences.

Life history variation is thought to be mainly a result of energetic trade-offs among fitness components; however, detecting these trade-offs in natural populations has yielded mixed results. Individual quality and environmental variation may mask expected relationships among fitness components because some higher quality individuals may be able to acquire more resources and invest more in all functions. Thus, life history variation may be more affected by variation in individual quality than varying strategies to resolve energetic trade-offs, e.g. costs of reproduction. Here, we investigated whether variation in female quality or costs of reproduction is a larger factor in shaping differences in life history trajectories by assessing the relationship between survival and individual reproductive performance using a 32-year longitudinal data set of repeated reproductive measurements from 273 individually marked, known-aged female grey seals (Halichoerus grypus) from the Sable Island breeding colony. We defined individual reproductive performance using two traits: reproductive frequency (a female’s probability of breeding) and provisioning performance (provisions given to young measured by offspring mass), computed using mixed effects models separately for (1) all reproductive events, and (2) an age-class specific reproductive investment. Individual differences contributed a large portion of the variance in reproductive traits, with individuals displaying a range in individual reproductive frequencies from 0.45 to 0.94, and a range of average pup weaning masses from 34.9 kg to 61.8 kg across their lifetime. We used a Cormack-Jolly-Seber open-population model to estimate the effect of these reproductive performance traits on adult survival probability. Our approach estimated a positive relationship between reproductive performance and survival, where individuals that consistently invest well in their offspring survive longer. The best supported model estimated survival as a function of age-class specific provisioning performance, where late-life performance was quite 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. These results suggest that in grey seals, individual quality is a stronger driver in life history variation than varying strategies to mitigate trade-offs among fitness components.

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.

Conservation successes of the past several decades provide natural settings to study post-bottleneck evolutionary processes in species undergoing recovery. Here, we study the impact of demographic change on genetic diversity in parallel natural experiments of historical decline and subsequent recovery in two sympatric pinniped species in the Northwest Atlantic, the gray seal (Halichoerus grypus atlantica) and harbor seal (Phoca vitulina concolor). We compare genetic diversity at the mitochondrial control region today to diversity in archaeological specimens, which represent the populations prior to the regional bounties of the late 1800s to mid-1900s that drastically reduced population sizes and led to local extirpations. We further assess genetic diversity throughout recovery, using biological collections from ongoing long-term studies of both species. Overall, the genetic data are consistent with the historical presence of large, genetically diverse populations of pinnipeds prior to human exploitation, and suggest that gray seals were more dramatically impacted by historical bottlenecks than harbor seals in the Northwest Atlantic. Current mitochondrial diversity in both species is relatively high, and we observe little change over the past several decades during a period of roughly parallel rapid population increases. However, there remain large differences in haplotype composition between pinniped populations of pre-exploitation and today, a lasting genetic signature of historical exploitation that is likely to persist into the future.

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.

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.

Atlantic halibut (Hippoglossus hippoglossus) have a long history of exploitation in the Northwest Atlantic and have gone through several periods of high biomass followed by a population crash. An assessment model using data collected on the Scotian Shelf and southern Grand Banks shows that the population peaked in 1984, then decreased sharply to a low in 1993. Several management measures were taken during the decline, including reductions in total allowable catch and a minimum size limit. Concurrently, removals by the otter trawl fishery were drastically reduced following the collapse of the cod (Gadus morhua) fishery. In 2003, recruitment increased and continued to be high for 6 years. Fishing mortality rates were moderate in the late 1990s and 2000s and the population increased. By 2009, the Atlantic halibut population was highly productive with both high biomass and high levels of recruitment. The coincidence in the timing of population recovery and management actions indicates that effective management contributed to the recovery of Atlantic halibut.

Population increases over the past several decades provide natural settings in which to study the evolutionary processes that occur during bottleneck, growth, and spatial expansion. We used parallel natural experiments of historical decline and subsequent recovery in two sympatric pinniped species in the Northwest Atlantic, the gray seal (Halichoerus grypus atlantica) and harbor seal (Phoca vitulina vitulina), to study the impact of recent demographic change in genomic diversity. Using restriction site‐associated DNA sequencing, we assessed genomic diversity at over 8,700 polymorphic gray seal loci and 3,700 polymorphic harbor seal loci in samples from multiple cohorts collected throughout recovery over the past half‐century. Despite significant differences in the degree of genetic diversity assessed in the two species, we found signatures of historical bottlenecks in the contemporary genomes of both gray and harbor seals. We evaluated temporal trends in diversity across cohorts, as well as compared samples from sites at both the center and edge of a recent gray seal range expansion, but found no significant change in genomewide diversity following recovery. We did, however, find that the variance and degree of allele frequency change measured over the past several decades were significantly different from neutral expectations of drift under population growth. These two cases of well‐described demographic history provide opportunities for critical evaluation of current approaches to simulating and understanding the genetic effects of historical demographic change in natural populations.

In populations of colony-breeding marine animals, foraging around colonies can lead to intraspecific competition. This competition affects individual foraging behavior and can cause density-dependent population growth. Where behavioral data are available, it may be possible to infer the mechanism of intraspecific competition. If these mechanics are understood, they can be used to predict the population-level functional response resulting from the competition. Using satellite relocation and dive data, we studied the use of space and foraging behavior of juvenile and adult gray seals (Halichoerus grypus) from a large (over 200,000) and growing population breeding at Sable Island, Nova Scotia (44.0 (o)N 60.0 (o)W). These data were first analyzed using a behaviorally switching state-space model to infer foraging areas followed by randomization analysis of foraging region overlap of competing age classes. Patterns of habitat use and behavioral time budgets indicate that young-of-year juveniles (YOY) were likely displaced from foraging areas near (10 km) the breeding colony by adult females. This displacement was most pronounced in the summer. Additionally, our data suggest that YOY are less capable divers than adults and this limits the habitat available to them. However, other segregating mechanisms cannot be ruled out, and we discuss several alternate hypotheses. Mark-resight data indicate juveniles born between 1998 and 2002 have much reduced survivorship compared with cohorts born in the late 1980s, while adult survivorship has remained steady. Combined with behavioral observations, our data suggest YOY are losing an intraspecific competition between adults and juveniles, resulting in the currently observed decelerating logistic population growth. Competition theory predicts that intraspecific competition resulting in a clear losing competitor should cause compensatory population regulation. This functional response produces a smooth logistic growth curve as carrying capacity is approached, and is consistent with census data collected from this population over the past 50 years. The competitive mechanism causing compensatory regulation likely stems from the capital-breeding life-history strategy employed by gray seals. This strategy decouples reproductive success from resources available around breeding colonies and prevents females from competing with each other while young are dependent.

Tracking of marine animals has increased exponentially in the past decade, and the resulting data could lead to an in-depth understanding of the causes and consequences of movement in the ocean. However, most common marine tracking systems are associated with large measurement errors. Accounting for these errors requires the use of hierarchical models, which are often difficult to fit to data. Using 3 case studies, we demonstrate that Template Model Builder(TMB), a new R package, is an accurate, efficient and flexible framework for modelling movement data. First, to demonstrate that TMB is as accurate but 30 times faster than bsam, a popular R package used to apply state-space models to Argos data, we modelled polar bear Ursus maritimus Argos data and compared the locations estimated by the models to GPS locations of these samebears. Second, to demonstrate how TMB’s gain in efficiency and frequentist framework facilitate model comparison, we developed models with different error structures and compared them to find the most effective model for light-based geolocations of rhinoceros auklets Cerorhinca monocerata.Finally, to maximize efficiency through TMB’s use of the Laplace approximation of the marginal likelihood, we modelled behavioural changes with continuous rather than discrete states. This new model directly accounts for the irregular sampling intervals characteristic of Fastloc-GPS data of grey seals Halichoerus grypus. Using real and simulated data, we show that TMB is a fast and powerful tool for modelling marine movement data. We discuss how TMB’s potentialreaches beyond marine movement studies

Influenza A virus (IAV) has been associated with multiple unusual mortality events (UMEs) in North Atlantic pinnipeds, frequently attributed to spillover of virus from wild-bird reservoirs. To determine if endemic infection persists outside of UMEs, we undertook a multiyear investigation of IAV in healthy, live-captured Northwest Atlantic gray seals (Halichoerus grypus). From 2013 to 2015, we sampled 345 pups and 57 adults from Cape Cod, MA, USA and Nova Scotia, Canada consistently detecting IAV infection across all groups. There was an overall viral prevalence of 9.0% (95% confidence interval (CI): 6.4%–12.5%) in weaned pups and 5.3% (CI: 1.2%–14.6%) in adults, with seroprevalences of 19.3% (CI: 15.0%–24.5%) and 50% (CI: 33.7%–66.4%), respectively. Positive sera showed a broad reactivity to diverse influenza subtypes. IAV status did not correlate with measures of animal health nor impact animal movement or foraging. This study demonstrated that Northwest Atlantic gray seals are both permissive to and tolerant of diverse IAV, possibly representing an endemically infected wild reservoir population., National Institute of Allergy and Infectious Diseases (U.S.), Massachusetts Institute of Technology. Sea Grant College Program (Project 2013-DOH- 45-LEV), Natural Sciences and Engineering Research Council of Canada, United States. National Marine Fisheries Service (Grants NMFS #17670-01, NMFS #10080-95 and FWS #53514-13003), National Institute of Allergy and Infectious Diseases (U.S). Centers of Excellence for Influenza Research and Surveillance Program (Grant HHSN272201400008C)

Despite 2 decades of very low fishing levels, numerous NW Atlantic demersal fish stocks have failed to recover from collapsed states or are presently collapsing. In the southern Gulf of St. Lawrence, adult natural mortality (M) appears to be the demographic rate that most limits population productivity in at least 3 species: Atlantic cod Gadus morhua, white hake Urophycis tenuis and winter skate Leucoraja ocellata. The causes of elevated M are not well understood, though there is indirect evidence consistent with an effect of predation by grey seals Halichoerus grypus. However, direct evidence is lacking due to uncertainty in the seal diet. Consequently, Monte Carlo simulations were undertaken using data on the spatial overlap between the seals and the fishes and a seal food-consumption model, to estimate the plausibility that different seal-diet compositions could explain observed M levels. Under the simulation assumptions, we find that predation could explain up to 20 to 50% of M in adult white hake and cod even if these species comprise a small percentage of grey seal diets (

The development of foraging strategies as animals mature depends upon experience, stage-specific physiology, the onset of reproductive maturity and the reproductive costs incurred by each sex. To understand the ontogeny of foraging behaviour, we compared movement behaviour of 24 young-of-year (YOY) juveniles (12 male, 12 female) with 6 subadult (4 male, 2 female) and 81 adult (43 male, 38 female) grey seals Halichoerus grypus. We used a behaviour discriminating state-space model followed by a series of mixed-effects models to examine trip structure and habitat use in these age classes. In foraging trips, tortuosity and speed of outbound travel were not different in YOY, subadults and adults, suggesting that YOY navigate as well as older animals. On average, however, YOY trips lasted 1.2 to 3.5 d longer and required up to twice as much transit time to reach foraging areas that were 1.5 to 3 times farther from haul-out sites than those of subadults and adults. This sug- gests an overall apparent higher foraging effort for YOY. Differences, however, were highly season- ally dependent. In all groups, apparent foraging effort decreased in the summer and increased in the winter, which is consistent with seasonal changes in prey distribution and energy content. Adult for- aging patterns showed complex seasonal patterns influenced by both reproductive cycles and sea- sonal environmental variation, whereas annual foraging patterns of YOY and subadults, neither of which invest in reproduction, were simpler and appeared more closely tied to seasonal changes in prey availability and condition. Although foraging in the same habitats, male and female YOY showed small but significant differences in movement behaviour and trip structure. These differences are unlikely to be due to size difference, which is minimal at this age, and suggest that sex-related differences in foraging develop early before sexual size dimorphism is significantly expressed.

Inter-specific competition for prey is thought to influence the structure of ecological communities and species niche breadth. Harp seals Pagophilus groenlandicus and hooded seals Cystophora cristata are geographically overlapping and highly migratory predators in the North Atlantic ocean. Hooded seals are known to dive deeper and longer than harp seals and are more closely associated with the continental shelf edge and deep ocean. Quantitative fatty acid (FA) signa- ture analysis (QFASA) was recently developed to estimate the species composition of diets by statis- tically comparing FA signatures of predator adipose tissue with that of potential prey. Using QFASA, we estimated diets for harp (adults, n = 294; juveniles, n = 232) and hooded (adults, n = 115; juveniles, n = 38) seals from the pre- and post-breeding periods between 1994 and 2004. We found evidence of inter- and intra-specific variation in diets, diet quality and breadth, reflecting different foraging tac- tics. Harp seal diets were comprised predominantly of amphipods, Arctic cod, capelin, herring, sand lance and redfish. Hooded seal diets were composed primarily of amphipods, Atlantic argentine, capelin, euphausiids and redfish. Relative to the other species, harp seals consumed twice the propor- tion of amphipods, while hooded seals consumed 3 times the proportion of redfish; percentages of capelin were similar. QFASA provided new evidence of the importance of amphipods in the diets of both species and of the pronounced differences in the proportions of pelagic forage fish between demographic groups.

Individuals of different age, sex, and morphology are expected to exhibit differences in dietary niches largely owing to sexual dimorphism, ontogenetic niche shifts, and resource polymorphism. Harp ( Pagophilus groenlandicus (Erxleben, 1777)) and hooded ( Cystophora cristata (Erxleben, 1777)) seals are geographically overlapping and highly migratory predators in the North Atlantic Ocean. These species differ in their diving behaviour, with hooded seals diving deeper, longer, and more associated with the continental shelf edge and deep ocean than harp seals. We examined blubber fatty acid (FA) composition (N = 37; 93% of total FA by mass) of harp (adults N = 294; juveniles N = 232) and hooded (adults N = 118; juveniles N = 38) seals to test hypotheses about sources of intrinsic (age and sex) and extrinsic (geographic location, season, year) variations in diets. A significant difference in FA profiles suggested dietary segregation between species. We found significant effects of sex and age class on FA profiles, with these being more pronounced in the highly size-dimorphic hooded seals than in harp seals. FA profiles of both species also varied between inshore and offshore sampling locations and between prebreeding and postbreeding periods. Finally, FA profiles of harp seals differed among years, which was coincident with large changes in prey distribution and availability in the mid-1990s.

What animals consume is perhaps one of the most fundamental questions in ecology. Limitations of stomach content and faecal analyses have led to the development of alternative bio- chemical methods, namely fatty acid (FA) signature analysis and stable isotope (SI) analysis. Propor- tional estimates of diet composition can be made at the level of the individual by statistically match- ing a consumer's FA signature to an inclusive prey database, after accounting for predator metabolism effects in a mixing model. Both of these approaches provide inferences about or quanti- tative estimates of diet that are time-integrated and readily applied to most taxa of interest, thereby alleviating many problems associated with conventional analysis. Moreover, analysis is done at the level of individual predators, thereby increasing our ability to detect differences amongst various demographic groups. However, it is difficult to validate diet estimates from either of these methods in the field, particularly for wide-ranging aquatic predators such as seals or seabirds consuming complex diets. Concurrent sampling of individual predators for both stable isotopes and fatty acids provide 1 such independent test. To that effect, we analyzed SI and FA for grey seals Halichoerus grypus (n = 75) and potential fish and invertebrate prey (n = 45). We show 2 lines of evidence for the convergence of stable isotope and fatty acid estimates of diet. First, in fish, invertebrates and grey seals, principal components derived from fatty acid signatures are correlated to the stable-carbon iso- tope (δ 13 C) signature of the same species. Second, both the estimated portion of pelagic prey and the trophic level of the diet derived from the quantitative analysis of fatty acid signatures of individual seals are positively correlated with the stable-carbon (δ 13 C) and stable-nitrogen (δ 15 N) signatures in those same individuals. The corroboration of independent measures of diet provides further validation of these biochemical methods to understand the foraging ecology of consumers.

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.

Hays, Graeme C. et al., 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., Workshop funding was granted to M.T., A.M.M.S., and C.M.D. by the UWA Oceans Institute, the Australian Institute of Marine Science, and the Office of Sponsored Research at King Abdullah University of Science and Technology (KAUST).

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.

1. Intraspecific variation in diet can be an important component of a species niche breadth. We tested the hypothesis that sex differences in seasonal foraging behaviour and energy storage of sexually size dimorphic grey seals Halichoerus grypus (Fabrisius 1971) are reflected in differences in the diet and niche breadth. Diet composition was estimated for 496 adult (226 males, 270 females) and 91 juvenile (46 males/45 females; all 6 months old) grey seals sampled between 1993 and 2000 using quantitative fatty acid signature analysis. Niche breadth and overlap were estimated using the Shannon-Weaver diversity index (H') and the Morisita-Horn index (C(H)), respectively. 2. Sand lance Ammodytes dubius (Reinhardt 1837) and redfish Sebastes sp. (Cuvier 1829) accounted for a high proportion of the diet in both sexes and age groups. However, the diets of adult males were significantly more diverse across all seasons (H': males 0.36 +/- 0.007 vs. females 0.28 +/- 0.007) and less energy dense in spring (male 5.3 +/- 0.07 kJ g(-1) vs. females 5.6 +/- 0.09 kJ g(-1)) than those of adult females. 3. Season and sex explained most of the observed variation in adult diets, but there were significant sex-season interactions. These differences were most evident during the post-breeding (spring) foraging period when energy acquisition is important to female recovery of nutrient stores needed to support pregnancy. Females selected fewer and higher quality prey species in spring than males. 4. There were no sex differences in the diets of juvenile grey seals. Although many of the species overlapped with those eaten by adults, juvenile niche breadth (H': 0.41 +/- 0.014, n = 91) was significantly broader than that of adults (H': 0.30 +/- 0.011, n = 115). Juvenile diets were also of lower energy density (5.3 +/- 0.04 kJ g(-1)) than those of adults (5.6 +/- 0.09 kJ g(-1)), suggesting less selectivity in these young and relatively naïve predators. 5. Sex-specific seasonal changes in diet correspond to seasonal changes in diving behaviour and rate of body energy accumulation of adult males and females. Sex-specific reproductive requirements appear to be a primary factor generating the intraspecific variation in the seasonal foraging ecology of this large marine carnivore. However, sex differences in the breadth and energy content of diets also suggest the influence of body-size dimorphism as a factor shaping the diet of this species.

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.

Our best understanding of marine mammal mating systems comes from land-mating pinnipeds. Logistical problems of observing behavior at sea have limited our ability to make inferences about species with aquatic-mating systems, which comprise over half the pinnipeds. The mating systems of these species likely involve different mating tactics than land-mating species. We used several methods in combination (e.g., animal-borne cameras, radio telemetry, time-depth recorders, and DNA paternity assessment) to provide a comprehensive study of the aquatic-mating tactics of harbor seal males. Males decreased time offshore (26.0 vs 14.8%) and increased time near shore (33.8 vs 43.7%) between premating and mating periods, respectively. Concomitantly, males reduced foraging effort and increased activities associated with competition for females (e.g., visual/vocal displays and threats). As females come into estrus near the end of lactation and spend more time at sea, males reduced their near-shore ranges (4.2 vs 1.0 km2), which were clustered within 1–1.5 km of the beach where females attended their pups. Body mass of males was not a major factor affecting their reproductive behavior. From a small number of paternity assignments to study males, it appears that females select males. These combined results are more consistent with a lek-type mating system than with the territorial or female defense systems characteristic of land-mating pinnipeds.

Pinnipeds are a diverse group of aquatic carnivores that exhibit wide variation in body size, milk composition, lactation strategies, and the length of maternal care. We used 12 pinniped life-history and ecological traits to test hypotheses concerning the influence of phylogeny, maternal body size, breeding substrate, and other factors on the evolution of lactation strategies. We used independent contrasts to account for phylogenetic effects on correlations between traits. Our findings indicate that the negative relationships between maternal mass and lactation length and between maternal mass and the percentage of time spent at sea by females during lactation are not recent adaptations, but likely a result of phylogenetic history and an evolutionary grade shift in lactation length, which occurred when the phocids diverged from the otariids. Differences in body size between the ancestral phocid and otariid impacted their foraging strategies and metabolic rates, which subsequently influenced lactation strategies. The fat-storage abilities of large phocids may have allowed them to exploit remote and patchy prey resources and thereby reduce time spent feeding during lactation. We also suggest that an early divergence in the mammary gland structure of phocids and otariids is a fundamental influence on pinniped lactation strategies. Although estimates are lacking for several key species, body size appears to have little adaptive influence on the lactation length of extant species. Instead, an abbreviated lactation period seems to be adaptive in minimizing the relative milk energy expended over lactation, although it may have initially evolved to reduce maternal overhead, especially in ancestral fasting phocids. Subsequently, a brief lactation in phocids was also selected through the effects of terrestrial predation, the instability of breeding on pack-ice, and the energy benefits of increasing milk energy output.

Sex differences in foraging behaviour have been attributed to size dimorphism, niche divergence, and sex-specific fitness-maximizing strategies. Although sex differences in diving behaviour of marine carnivores are thought to result in sex differences in diet, this is not known for any species over temporal scales relevant to life-history characteristics. We examined blubber fatty acid (FA) profiles of gray seals, Halichoerus grypus (Fabricius, 1791), a sexually size-dimorphic species in which sex differences in foraging behaviour have been observed. FA profiles reflect prey consumed over a period of weeks or months. FA profiles of adult males and females varied significantly by season but there was a season by sex interaction, indicating that seasonal changes in diet differed by sex. FA profiles of adults also varied interannually, with a significant sex by year interaction. Interannual variability may have been a response to changes in ocean-bottom temperatures affecting prey availability or changes in prey abundance. Adult FA profiles differed from those of 6-month-old juveniles; however, there was no evidence of sex differences in the diet of younger animals. Our results indicate that sex differences in the foraging behaviour of adults are reflected in differences in diet at multiple temporal scales.

The purpose of this study was to examine the importance of body size and body composition as determinants of conditional mating tactics exhibited in male grey seals. We combined behavioral observations with measures of energy expenditure and success on 42 known-age individuals during the breeding seasons of 1997–2001 at Sable Island, Canada. Males with a large body mass arrived at the breeding grounds with more body fat and body energy and catabolized less body protein than smaller males. Males consumed 1.9 6 0.2 MJ day � 1 , and those with a smaller percentage of body fat had higher rates of food energy intake. The amount of body energy on arrival was positively correlated with the duration of the breeding period. Males that exhibited the primary mating tactic of consortship were heavier, had absolutely more body fat and body energy, and sustained breeding longer than those males that did not exhibit the primary tactic. Amongst all males, body mass showed a quadratic relationship with the number of female consorts mated and the estimated number of pups sired. Thus, intermediate-sized males mated with the most consorts and achieved the highest success. Intermediate body size may be optimal during breeding due to greater agility in male combat. Body size was an important determinant of mating tactics used by male grey seals. A large body size provided an energetic advantage of greater endurance while an intermediate body size may provide greater competitive ability in acquiring consortships. Key words: body size, conditional mating tactics, endurance rivalry, energetics, Halichoerus grypus, pinnipeds, reproductive behavior. [Behav Ecol]

Accurate estimates of the diets of predators are required in many areas of ecology, but for many species current methods are imprecise, limited to the last meal, and often biased. The diversity of fatty acids and their patterns in organisms, coupled with the narrow limitations on their biosynthesis, properties of digestion in monogastric animals, and the prevalence of large storage reservoirs of lipid in many predators, led us to propose the use of quantitative fatty acid signature analysis (QFASA) to study predator diets. We present a statistical model that provides quantitative estimates of the proportions of prey species in the diets of individual predators using fatty acid signatures. We conducted simulation studies using a database of 28 prey species (n = 954 individuals) from the Scotian Shelf off eastern Canada to investigate properties of the model and to evaluate the reliability with which prey could be distinguished in the model. We then conducted experiments on grey seals (Halichoerus grypus, n = 25) and harp seals (Phoca groenlandica, n = 5) to assess quantitative characteristics of fatty acid deposition and to develop calibration coefficients for individual fatty acids to account for predator lipid metabolism. We then tested the model and calibration coefficients by estimating the diets of experimentally fed captive grey seals (n = 6, switched from herring to a mackerel/capelin diet) and mink kits (Mustela vison, n = 46, switched from milk to one of three oil-supplemented diets). The diets of all experimentally fed animals were generally well estimated using QFASA and were consistent with qualitative and quantitative expectations, provided that appropriate calibration coefficients were used. In a final case, we compared video data of foraging by individual free- ranging harbor seals (Phoca vitulina, n = 23) fitted with Crittercams and QFASA estimates of the diet of those same seals using a complex ecosystem-wide prey database. Among the 28 prey species in the database, QFASA estimated sandlance to be the dominant prey species in the diet of all seals (averaging 62% of diet), followed primarily by flounders, but also capelin and minor amounts of other species, although there was also considerable individual variability among seals. These estimates were consistent with video data showing sandlance to be the predominant prey, followed by flatfish. We conclude that QFASA provides estimates of diets for individuals at time scales that are relevant to the ecological processes affecting survival, and can be used to study diet variability within individuals over time, which will provide important opportunities rarely possible with other indirect methods. We propose that the QFASA model we have set forth will be applicable to a wide range of predators and ecosystems.

Interspecific correlations are commonly used to explore the adaptive functions of life history traits in pinnipeds. Although adaptive conclusions are improved by the use of comparative methods that account for underlying phylogenetic relationships among species, they are still dependent on the quality of life history data. We collected pinniped species estimates for 12 maternal and offspring life history traits and evaluated these estimates based on sample size, duration of study, and methods used to obtain the data. Although excellent data exist for some species, high-quality estimates in all 33 species are not available for any of the traits studied. High-quality estimates of maternal postpartum mass are known for 12 species, neonate birth mass for 21, pup rate of mass gain for 12, lactation length for 10, and weaning mass for 10. High-quality estimates of milk composition, milk energy output, and maternal foraging behavior during lactation are limited to ≤ 50% of species, with a taxonomic bias favoring the larger phocid species. Obtaining data on small-bodied phocid species will be critical to gaining a better understanding of the relative roles of body size and phylogeny in the evolution of pinniped lactation strategies.

Summary 1. Air-breathing marine predators can modify their diving behaviour to accommodate different patterns of prey abundance and distribution and may do so at multiple temporal scales (individual dives, bouts of dives and foraging trips). 2. The grey seal, Halichoerus grypus , is a size-dimorphic, capital breeding species in which sex differences in foraging ecology have previously been found at the scale of individual dives. In this study, diving behaviour of male and female adult grey seals was examined at the temporal scales of dive bouts (41 males/46 females) and foraging trips (7 males/9 females) during the 8-month prebreeding foraging period between 1992 and 1999 to investigate whether sex differences were evident at longer temporal scales. 3. Foraging trip duration did not differ between males and females. However, females (the smaller sex) spent significantly more time diving and less time hauled-out on land between trips than males. This suggests that females are more selective than males when searching for prey. These differences are consistent with the effects of body-size dimorphism on diving behaviour. 4. Virtually all dives occurred in bouts. At this scale, males and females showed significantly different seasonal patterns of most bout characteristics, including bout duration, percentage of bout spent at depth and effort (hours spent in bouts day − 1 ). 5. Grey seals used four different types of bouts, differing in duration, depth, percentage bout spent at depth and the shape of individual dives within the bout. Males and females differed in the proportion of each bout type used and in the seasonal and day‐ night distribution of bout types. 6. Few bout characteristics varied significantly among years, despite interannual variation in prey abundance. Where interannual differences did occur, both sexes behaved in a similar way. 7. Different seasonal patterns in bouts of diving by males and females could not be accounted for by body-size dimorphism or niche divergence, but were consistent with the hypothesis that females must recover condition earlier in the year than males to support the energetic costs of reproduction.

Annual censuses of the number of harbour seal Phoca vitulina pups born on Sable Island Canada showed an increasing trend during the 1980s, but a rapid decline through the 1990s from 625 pups in 1989 to only 32 by 1997. Weekly surveys of the North Beach of the island during the 1991–98 breeding seasons showed that the number of adults and juveniles also declined during the 1990s. Despite the dramatic demographic changes, maternal postpartum mass, pup birth mass, relative birth mass, lactation duration, pup weaning mass and relative weaning mass showed no significant trends during 1987–96. However, two traits did change. The age structure of parturient females increased significantly, indicating reduced recruitment to the breeding population. Mean birth date increased by 7 days during the early 1990s, suggesting nutritional stress of females and later implantation dates. This nutritional stress may in turn have been caused by increased competition from the rapidly increasing grey seal population on Sable Island. Although minimum estimates of shark-inflicted mortality can account for much of the decline, evidence suggests that food shortage arising from interspecific competition may have also played a role in causing the decline of the population through effects on fecundity and juvenile survival.

Both body size dimorphism and sex differences in the relative costs and benefits associated with acquiring energy for reproduction have been advanced to explain the evolution of sex differences in foraging behaviour. We examined the extent to which these factors influenced sex differences in the diving behaviour of a size-dimorphic, capital breeder, the grey seal, Halichoerus grypus. Using time-depth data loggers, we examined the diving behaviour of 46 male and 49 female grey seals for 7 months before parturition and mating. Males and females showed significantly different seasonal patterns in the characteristics of individual dives and dive effort. Compared with males, females showed significantly higher levels of dive effort immediately following moult and in the 3 months before parturition. Females also had longer dives (5.5 versus 4.9 min) and spent more time at depth (3.4 versus 2.7 min), whereas males dived deeper (57 versus 49 m). Males dived consistently throughout the day, whereas females showed strong diurnal patterns in dive depth, duration and frequency. The diving behaviour and rates of mass gain by females suggested a pattern of foraging consistent with early accumulation of body energy to support pregnancy and the subsequent lactation period during which females fast. Males, on the other hand, showed diving behaviour and rates of mass gain consistent with a more gradual accumulation of energy stores. Our results suggest that sex differences in the seasonal patterns of diving behaviour reflect sex differences in the costs and benefits of stored energy for reproduction rather than the influence of body size dimorphism alone.

We examined the diving behaviour of breeding male grey seals (Halichoerus grypus) at Sable Island, Nova Scotia, from 1997 to 2001. The proportion of time spent at sea varied between 0 and 78% (N = 30). Males engaged in deep (43.4 ± 3.3 m (mean ± SE), N = 27) diving, and these dives were clustered into bouts, which mostly occurred during long trips (62.2 ± 14.7 h). We suggest that males spent time foraging during deep dives. Shallow diving (5.9 ± 0.1 m, N = 27) accounted for 40.8% of dives, which were also clustered into bouts that mostly occurred during short trips (2.1 ± 0.37 h). We suggest that shallow diving comprised a suite of behaviours, but included little foraging behaviour. Phenotypic traits had little influence on diving behaviour. Further work is required to understand the extent to which foraging behaviour enhances reproductive success, and whether shallow diving is a component of the mating tactics of male grey seals at Sable Island.