Topographic spatial characterisation of grey seal Halichoerus grypus breeding habitat at a sub-seal size spatial grain

Expansion within breeding colonies may critically depend upon the availability of suitable breeding habitat. Here we use topographic modelling in a GIS to characterise suitable pupping habitat and accurately predict the pattern of colonisation in an expanding grey seal breeding colony – the Isle of May (Scotland). We use high resolution images from large format aerial photographs of the colony to generate sub‐metre accurate Digital Terrain Models (DTMs). GIS modelling with these DTMs provides topographic measures of elevation, slope and ease of access to sea and freshwater pools at a 2 m grid cell size. Seal locations during the 1994 breeding season, with sex‐age class, were also digitised from the same images. We examine how the physical attributes of cells (locations) with and without pups differ and identify areas suitable for pupping but remaining unoccupied during 1994. We predict patterns of future colonisation by characterising areas differentiated by the densities of pups within 5 m grid cells and identifying areas, both occupied or unoccupied, with a potential for increased future pupping densities. Our predictions were tested by examining pup distributions observed in the 1998 breeding season. Occupied sites were significantly closer to freshwater pools and access to the sea (p<0.001) than unoccupied sites suggesting that proximity to water may restrict colony expansion before all areas of suitably flat terrain are occupied. All pup density classes occurred in sites with similar slope values and distance to pools. However, higher pupping densities occurred closer to access points (p=0.014). Pup densities observed in 1998 revealed that our 1994 predictions were accurate (p<0.0001). Only 12% of 466 grid cells had higher densities in 1998 than predicted, of which 88% differed by only 1 pup. These incorrectly classified cells occurred at the expanding edge of the colony (in a more topographically homogenous area) and at the main access points from the sea (major traffic zones). These results demonstrate the value of the accurate quantification of topographic parameters at the appropriate spatial grain (in this case below the size of the individual) for use in habitat classification and predictions of habitat utilisation.     

Philopatry, Site Fidelity and Local Kin Associations within Grey Seal Breeding Colonies

Abstract Colonially breeding animals such as grey seals typically have a discrete number of breeding sites. The extent to which offspring are philopatric (return to breed at their natal site) and the prevalence of philopatry by sex of pup has fundamental consequences for the social and genetic structure within and between each colony.
Grey seals born and marked by tagging and cohort brands at colonies on North Rona, Outer Hebrides since 1960 and at the Isle of May, Firth of Forth since 1981 have shown philopatry. Overall re-sight rates of 1620 pups tagged at North Rona and 1667 pups at the Isle of May ranged from 0 to 17%. Although most evidence of philopatry relates to females, males at each colony displayed philopatry. In addition, females born at N. Rona pupped closer to their natal sites than would be expected by chance (p = 0.005), providing evidence of fine scale natal site fidelity. Females born at the Isle of May did not show the same degree of fine scale natal site fidelity, but there was considerable individual variation. The spatial scale of philopatry shown by seals differed according to the local area within each island. Fidelity of known adult females to pupping sites at both colonies was high. In addition, we found an instance of mother and daughter pupping together away from the daughter's natal site.
These data: (i) provide evidence of philopatry in both sexes at each site; (ii) describe occurrences of fine scale philopatry at both sites; (iii) show that mothers and offspring occupied the same areas on the colony, suggesting the possibility of highly related groups within colonies, which would provide conditions for kin-specific altruistic behaviours; (iv) suggest the possibility of individual or kin recognition, even though contact between mothers and offspring has been thought to cease after the 18 d lactation period.     

Dispersion and site fidelity of breeding female grey seals (Halichoerus grypus) on North Rona, Scotland

Female grey seals ( Halichoerus grypus ) formed breeding aggregations on the island of North Rona, Scotland. Aggregations of females were associated particularly with gullies leading from the sea, leaving large areas of available space unoccupied. Changes in the degree of aggregation of females during the breeding season were similar in 1987, 1988 and 1989. Pronounced aggregations occurred in the early and late parts of each breeding season.
Of 67 breeding females marked in 1985, 62 (93%)) returned to N. Rona to breed in at least one season up to 1989, but 18 (27%) were present in all five years. Females came ashore up to 14 days before giving birth and 82% were observed first in the vicinity of their subsequent pupping site. Between 1985 and 1989, marked females which returned were faithful to their previous pupping sites, even when the previous pup had died. There was no evidence of a gradual change in the location of individual pupping sites over time. This pupping site fidelity may generate aggregations whose location, timing and composition is predictable.     

Effects of maternal age and condition on parturition and the perinatal period of Antarctic fur seals

The effect of maternal age and condition on the date of parturition and the duration of the perinatal period of Antarctic fur seals at Bird Island, South Georgia, were investigated over three consecutive breeding seasons. Females rear young during a four-month lactation period in a highly seasonal but predictable environment. Although females may first pup at three years of age, they did not attain full adult size until six years of age; older females (≥ 6 years) tended to be heavier, longer, and in better condition than younger females (3–5 years). Older females returned to breeding beaches earlier and could occupy the most suitable pupping sites, and gave birth when densities of animals on the beaches were low (i.e. more favourable for pup survival). Females that arrived earlier were able to remain ashore longer with their pups prior to departing on their first foraging trips but this was unrelated to either maternal age or condition. Younger females returned later in the pupping season, possibly as a result of late implantation due to smaller energy reserves than older and larger females. In 1990 all females arrived late, were in poorer condition, gave birth to lighter pups, and had shorter perinatal periods. This suggests that not only was implantation late but that females returned to an area of low food availability prior to parturition.     

Influence of the physical environment and conspecific aggression on the spatial arrangement of breeding grey seals

Understanding the habitat requirements of a species for breeding is essential for its conservation, particularly if the availability of suitable habitat is a limiting factor for population growth. This is postulated to be the case for grey seals, one of the more abundant marine apex predators in northern European waters. In common with similar studies that have investigated the habitat preferences of breeding grey seals, we use abiotic (topographical, climatological) attributes but, unlike previous work, we also incorporate behavioural variables, particularly the occurrence of aggressive interactions between females and the presence of neighbouring seals. We used two Generalized Additive Models (GAM) in a sequential and iterative fashion. The first model links the occurrence of aggression at particular points in the colony to local topography derived from a Geographical Information System (GIS), presence of neighbouring seal pups and the day of the breeding season. The output of this GAM is used as one of the explanatory variables in a GAM of daily variation in the spatial distribution of births. Although proximity of a birth site to a water source and the presence of neighbouring seal pups both had significant influences on the distribution of newborn pups over time and space, at the scale of the study site it was found that simple rules could predict pup distribution more efficiently than a complex individual-based simulation model.     

Sighting patterns reveal unobserved pupping events to revise reproductive rate estimates for Hawaiian monk seals in the main Hawaiian Islands

We used sighting reports, including decades of citizen-reported Hawaiian monk seal (Neomonachus schauinslandi) sightings, to describe female breeding biology and reproductive success in the main Hawaiian Islands. We first used this data set to describe the timing of events in the female reproductive cycle. We then conducted an expert review of patterns in sighting histories to detect unobserved pupping events. Finally, we estimated the age-specific reproductive curve for female monk seals in the main Hawaiian Islands. Charting reproductive cycles showed indications of the robust condition of female monk seals in the main Hawaiian Islands; they nursed pups 12% longer than their counterparts in the Northwestern Hawaiian Islands and regained condition to molt more quickly after weaning a pup. By examining sighting histories, we were able to infer 25 unobserved pupping events that had previously gone uncounted. We accounted for additional uncertainty with a randomization procedure. After accounting for unobserved pupping events, the age-specific reproductive rate of main Hawaiian Islands monk seals exceeded 0.70 for prime aged females (8–18 years). This is the highest reproductive rate reported for any of the Hawaiian monk seal breeding sites, illustrating the important role of the main Hawaiian Islands population in Hawaiian monk seal recovery.     

Distribution, pup production and mortality of New Zealand sea lion

Surveys were undertaken at Campbell Island / Motu Ihupuku during January and February 2008, to determine the distribution and pup production of New Zealand sea lions (NZ sea lion; Phocarctos hookeri). In addition, necropsies were performed at the main breeding site of Davis Point to determine the principal causes of early mortality for NZ sea lion pups. In total, 397 pups were tagged and 186 untagged pups were found dead, giving a minimum pup production of 583 pups and a one month of age mortality estimate of 40%. This represents a higher pup production than previous estimates from Campbell Island (although survey techniques are not comparable), and equates to 21% of the total pup production for NZ sea lions in the 2007/08 season. Early pup mortality was high (40%) at Campbell Island, with trauma, starvation, and drowning in rock pools and peat mires the major causes of death. Pups were concentrated in two colonial breeding sites: Davis Point on the north shore of Perseverance Harbour (76%) and a newly recorded breeding site (Paradise Point) on the southern shore of Perseverance Harbour (21%). Non-colonial breeding or single pups occurred around the southern parts of the island from sea level to 400 m; however, these only contributed 3% of the known pup production.     

How mothers find their pups in a colony of Antarctic fur seals

In Antarctic fur seals, Arctocephalus gazella, mothers must identify their own young among hundreds or even thousands of pups, if they are to invest in their own offspring and avoid misdirecting their parental care. When returning to their breeding colony from a foraging trip of several days at sea, mothers have to find and identify their young before suckling can occur. There appears to be little confusion about which pup belongs to a mother, and adoption is absent or rare. Using behavioral observations, we investigated the means by which female Antarctic fur seals identified their pups in a breeding colony of about 750 mother-pup pairs on Kerguelen Island. We evaluated the importance of vision, scent communication, vocalizations, and rendezvous locations as possible explanations of how mothers find their pups. Every pup that a mother examined, whether her own or not, exchanged naso-nasal inspection with her, suggesting a strong role for olfactory communication in individual recognition. Both mothers and pups called to each other, and mothers that searched for pups over a longer period gave more calls and encountered more pups. Thus, vocalizations may have been used to attract pups that might be offspring. Nursing usually occurred in the same place from the end of one maternal visit to the colony and the arrival at the beginning of the next visit, suggesting that nursing locations may serve as a meeting place, or rendezvous, for mothers and pups. These results suggest that finding pups is a two-stage process for females, in which pups for sampling are attracted by calls or examined at the previous nursing location, and then individual identification is made by olfactory cues.     

Variation in Female Grey Seal (Halichoerus grypus) Reproductive Performance Correlates to Proactive-Reactive Behavioural Types

Consistent individual differences (CIDs) in behaviour, indicative of behavioural types or personalities, have been shown in taxa ranging from Cnidaria to Mammalia. However, despite numerous theoretical explanations there remains limited empirical evidence for selective mechanisms that maintain such variation within natural populations. We examined behavioural types and fitness proxies in wild female grey seals at the North Rona breeding colony. Experiments in 2009 and 2010 employed a remotely-controlled vehicle to deliver a novel auditory stimulus to females to elicit changes in pup-checking behaviour. Mothers tested twice during lactation exhibited highly repeatable individual pup-checking rates within and across breeding seasons. Observations of undisturbed mothers (i.e. experiencing no disturbance from conspecifics or experimental test) also revealed CIDs in pup-checking behaviour. However, there was no correlation between an individuals’ pup-checking rate during undisturbed observations with the rate in response to the auditory test, indicating plasticity across situations. The extent to which individuals changed rates of pup-checking from undisturbed to disturbed conditions revealed a continuum of behavioural types from proactive females, who maintained a similar rate throughout, to reactive females, who increased pup-checking markedly in response to the test. Variation in maternal expenditure (daily mass loss rate) was greater among more reactive mothers than proactive mothers. Consequently pups of more reactive mothers had more varied growth rates centred around the long-term population mean. These patterns could not be accounted for by other measured covariates as behavioural type was unrelated to a mother’s prior experience, degree of inter-annual site fidelity, physical characteristics of their pupping habitat, pup sex or pup activity. These findings are consistent with the hypothesis that variation in behavioural types is maintained by spatial and temporal environmental variation combined with limits to phenotype-environment matching.     

Behaviour of female and pup grey seals Halichoerus grypus during the breeding period at Froan, Norway

We studied the behaviour of grey seals, Halichoerus grypus , during the breeding period at Froan, Norway, and compared our findings with existing studies on grey seals at breeding sites in Britain and Canada. The pups at Froan spent more time in water than pups at other breeding sites. While on-shore, the pups at Froan spent most of their time resting, behaviour similar to pups at other breeding sites. Lactating females at Froan spent most of their time in the sea, thus differing from females at most other breeding sites which spend most of their time on-shore. While in the sea, the females at Froan spent most time diving, typically interrupted by regular periods of surface swimming.     

Grey seal, Halichoerus grypus, energetics: females invest more in male offspring

Grey seal females transfer large amounts of energy to their pups during the brief lactation period. The costs of lactation have been measured using weight changes of mother and pup pairs. Large females come ashore to give birth earlier in the season and lose weight more rapidly than smaller females. The sex ratio of Grey seal pups born is skewed towards males in the early part of the breeding season. Male pups are larger at birth and gain weight more rapidly than female pups, and their mothers show a correspondingly faster rate of weight loss than mothers of female pups. The energy costs of gestation and lactation to a Grey seal mother are 31 GJ for male pups and2–8 GJ for female pups. Males are therefore 10% more costly in energy terms to raise to weaning. Because, on average, large females arrive at breeding sites before smaller animals, biased results on weight changes would be obtained from methods which do not use repeated weighings. We suggest that the high efficiencies of lactation estimated for Harp seals compared with other phocid seals could be accounted for by such a bias.     

Female distribution, genetic relatedness, and fostering behaviour in harbour seals, Phoca vitulina

Although harbour seals may not recognize their relatives, relatives could be chosen preferentially for fostering (i.e. kin selection) if harbour seals display natal philopatry coupled with breeding site fidelity, and thus kin are clustered within the colony. We used behavioural and genetic data to investigate population structure within the Sable Island breeding colony and to test whether harbour seals tend to foster related pups. Adult females on Sable Island showed a high level of breeding-colony site fidelity but low levels of within-colony site fidelity both within and between years. Similarly, although lactating females showed a clumped distribution, group composition was highly variable, suggesting that this study colony was not composed of groups of related animals. DNA fingerprint data supported the hypothesis that female distribution within the colony was not correlated with genetic relatedness. Furthermore, the mean DNA band sharing among foster dyads did not differ significantly from that for unrelated animals. These results indicate that among harbour seals, related pups are not usually chosen preferentially for fostering and hence, kin selection is not likely to be influencing the occurrence of this behaviour. Copyright 1999 The Association for the Study of Animal Behaviour.     

Foraging locations of female New Zealand sea lions (

Figure of Eight Island is located in the southern end of the Auckland Islands and hosts the smallest breeding colony of New Zealand (NZ) sea lions (Phocarctos hookeri). Between 1995/96 and 2005/06, pup production in this colony decreased by 57% (from 144 to 62 pups). In contrast, there was a 30% decrease in pup production in the largest colony in the north-east of the Auckland Islands over the same period. NZ sea lions in the Auckland Islands area are subject to by-catch deaths and resource competition from subantarctic trawl fisheries. The present study investigated where four lactating females from Figure of Eight Island foraged during the austral summer of 2007/08 and compared their foraging areas with female NZ sea lions from the northern Auckland Islands breeding locations (Enderby and Dundas islands) and with fisheries activities. Females foraged south of Adams Island (the southernmost Auckland Island), predominantly at the edge of the Auckland Islands shelf, but those from Figure of Eight Island made shorter foraging trips within more concentrated areas than females from Enderby or Dundas islands. The 59 female NZ sea lions satellite-tracked to date from Figure of Eight, Enderby and Dundas islands foraged over the entire area of the Auckland Islands shelf and many (including three of the four females from Figure of Eight Island) had extensive overlap with subantarctic trawl fisheries. Further research is needed to determine whether the foraging behaviour of females from Figure of Eight Island is linked to their greater decline in pup production.     

PUP PRODUCTION AND POPULATION TRENDS OF THE AUSTRALIAN FUR SEAL (ARCTOCEPHALUS PUSILLUS DORIFERUS)

We estimated the number of live Australian fur seal pups using capture-markresights, direct ground counts, or aerial photography at all breeding sites following the pupping season of November-December 2002. Pups were recorded at 17 locations; nine previously known colony sites, one newly recognized colony and seven haul-out sites where pups are occasionally born. In order of size, the colonies were Lady Julia Percy Island (5,899 pups), Seal Rocks (4,882), The Skerries (2,486), Judgment Rocks (2,427), Kanowna Island (2,301), Moriarty Rocks (1,007), Reid Rocks (384), West Moncoeur Island (257), and Tenth Island (124). The newly recognized site was Rag Island, in the Cliffy Group, where we recorded 30 pups. We also recorded pups at the following haul-out sites: Cape Bridge-water (7 pups), Bull Rock (7), Wright Rock (5), Twin Islet (1), The Friars (1), He des Phoques (1), and Montague Island (1). In total, we estimate there were 19,819 (SE = 163) live pups at the time of the counts. We discuss trends in pup numbers and derive current population estimates for the Australian fur seal.     

Harbor seal use of glacier ice and terrestrial haul‐outs in the Kenai Fjords,Alaska

Harbor seals, Phoca vitulina, use diverse haul‐out substrates including ice calved by tidewater glaciers. Numbers of seals at glacial and terrestrial haul‐outs on the southeastern Kenai Peninsula, Alaska, were assessed using aerial, vessel, and video surveys. Mean annual abundance at glacial and terrestrial haul‐outs differed temporally. From 2004 to 2011, numbers of seals counted during the molt increased 5.4%/yr at glacial haul‐outs and 9%/yr at terrestrial haul‐outs while numbers of pups increased 5.0%/yr at glacial sites and 1.5%/yr at terrestrial sites. Numbers of seals without pups counted during pupping increased 7.96%/yr at glacial sites and 5.1%/yr at terrestrial sites. Results indicate that pupping and molting locations are not equivalent and population monitoring during the molt does not necessarily reflect habitat association of pupping seals. Ratios of pups to total seals counted during pupping and the subsequent molt were used to contrast habitat use. Low proportions of pups at terrestrial haul‐outs, relative to most glacial haul‐outs, indicate an overall preference for pupping in glacial haul‐outs. High proportions of pups at most glacial sites (during pupping and molting) suggest reduced use of tidewater glacier habitats by nonbreeders and molting seals. Results suggest more seals associate with glacial haul‐outs than currently estimated.     

Seasonal changes in the distribution and composition of common seal (Phoca vitulina) haul-out groups

Seasonal changes in the distribution and composition of common seal haul–out groups were followed in a study area in Orkney, Scotland. A marking programme was also undertaken, using both conventional and radio–tags, to study individual movements between sites and seasonal changes in site–use. Certain haul–out sites were used only in the breeding season, while others were used during the winter. Seals were seen at one site all year round and at another during only the pre–pupping and moult period. On one island where two sites were used during the summer, there were significant differences in the sex ratio of groups at the two sites: at one site males predominated and few pups were seen; on another, nearby, mothers and pups were regularly seen, although the site was also used by males. There was also evidence for segregation of the sexes outside the breeding season. Repeated observations of marked seals showed that seals used several different haul–out sites throughout the year, and that the seasonal changes in abundance at different sites resulted from individual changes in site–use. These changes in site–use are discussed in relation to feeding movements, breeding requirements and the physical characteristics of different sites.     

Grey seal (Halichoerus grypus) pup production at North Rona: A study of birth and survival statistics collected in 1972

The Grey seal breeding assembly on North Rona was studied throughout autumn 1972. Weekly censuses provided data on birth rate and mortality. It is estimated that 1736 pups were born in 1972. This is about 500 less than the mean production estimate for this assembly during the period 1959–71, possibly a result of disturbance of the breeding site by the expedition. About 600 of the pups died before putting to sea. The mean date of birth and the duration of the pupping season agree closely with earlier work on North Rona, although the mean daily birth rate curve is somewhat irregular, perhaps because there was an unusually dry spell of weather at a critical time in the pupping season. An improved estimate of mortality at this assembly showed a relationship with pup density similar to that observed at the Fame Islands. Techniques for estimating pup production (and consequently total population), though not reliable for determining absolute values, are useful for indicating trends and they suggest a stable population of 8000–9000 animals at North Rona. Such estimates might be improved by the use of better methods of aerial photography.     

Photo-ID-based estimates of reproductive patterns in female harbor seals

Variations in reproductive patterns offer important insights into the dynamics of pinniped populations, but collecting data on reproduction for species that spend much of the breeding season in the water is problematic. We used land‐based photo‐identification techniques to collect individual‐based data on the timing of pupping, total pup production, and lactation duration in a population of harbor seals in NE Scotland. Capture–Mark–Recapture (CMR) techniques were used to overcome potential biases due to changes in probability of capture, and provide estimates of lactation duration based upon changes in the “survival” of mother–pup bonds. A mean birth date of 20 June is the first direct estimate of parturition date for UK harbor seals. Information on cumulative births indicated that the peak daily haul‐out count accounted for 77% of total pup production. CMR‐based estimates of lactation duration suggest that 50% of mothers had weaned their pups, when pups were 21‐d old. These results highlight the potential for using photo‐ID techniques to study harbor seal reproductive patterns at sites where intensive capture and marking is not possible for logistic, legislative, or ethical reasons.     

Lactating Females Do Not Discriminate Between Their Own Young and Unrelated Pups in the Communally Breeding Rodent, Octodon degus

Females in numerous rodent species engage in communal nesting and breeding, in which they share one or more nests to rear their young. A potential cost of communal nesting and breeding is that mothers divert resources to unrelated offspring. One way mothers could avoid this cost is to recognize and favour their own young over unrelated offspring when allocating maternal effort. We assessed whether female degus (Octodon degus), a communally nesting and breeding caviomorph rodent, discriminate between their own and unrelated offspring during lactation. Female degus previously have been shown to distinguish between their own and unrelated pups when exposed to odours from both. We measured pup discrimination based on differences in the retrieval behaviour of females that were in early or intermediate lactation directed towards their own and unrelated offspring; offspring presented were of similar or different age. Before any event of pup retrieval, lactating females spent similar amounts of time and interacted to a similar extent with their own and unrelated pups. During pup retrieval, all lactating females transported both pups to the nest. Neither relatedness to pups, nor pup‐age differences, influenced the order in which pups were retrieved to the nest. Dams waited similar amounts of time before retrieving the first pup when the first transported young was their own or unrelated. Likewise, females waited similar amounts of time before retrieving the second pup when the pup transported first was their own or unrelated. The time between first and second pup transport events was longer when dams were in early when compared with intermediate lactation, but only when pups were of similar age. All experimental subjects nursed unrelated pups after they were retrieved. Collectively, our results do not support the hypothesis that communally breeding female degus use their recognition ability to discriminate against unrelated offspring in favour of their own young.     

BEHAVIORAL EVIDENCE OF THERMAL STRESS FROM OVERHEATING IN UK BREEDING GRAY SEALS

Gray seals ( Halichoerus grypus ) in the UK exhibit clear preferences for pupping close to pools of water on inland breeding sites. The reasons for this are unclear as seals are thought to derive all their water requirements from the metabolism of fat. Likewise, the prospect of seals overheating during the UK's cool, damp, autumnal breeding seasons, has seemed unlikely, but has not been previously explored. Here, we provide preliminary behavioral evidence of thermal stress in female gray seals breeding on the island of North Rona, Scotland. Video footage provided measures of proximity to, and the proportion of animals bathing in, pools in relation to meteorological data (temperature, mean sea-level pressure, rainfall, wind speed and direction) on four dates spread through a single breeding season. The proportion of females close to pools increased with pressure (warmer, drier conditions) and decreased on wetter days. In addition, analyses of colony-wide patterns of seal dispersion showed that females tended to be closer to pools of water at higher pressures and temperatures and at lower wind-speeds. These results provide the first evidence of thermal stress and behavioral thermoregulation through access to pools of water in a phocid breeding in temperate autumnal conditions.