Lack of functional alpha-lactalbumin prevents involution in Cape fur seals and identifies the protein as an apoptotic milk factor in mammary gland involution

The mammary gland undergoes a sophisticated programme of developmental changes during pregnancy/lactation. However, little is known about processes involving initiation of apoptosis at involution following weaning. We used fur seals as models to study the molecular process of involution as these animals display a unique mammary gland phenotype. Fur seals have long lactation periods whereby mothers cycle between secreting copious quantities of milk for 2 to 3 days suckling pups on land, with trips to sea alone to forage for up to 23 days during which time mammary glands remain active without initiating apoptosis/involution.

Bathymetry and frontal system interactions influence seasonal foraging movements of lactating subantarctic fur seals from Marion Island

Sixteen lactating subantarctic fur seals Arctocephalus tropicalis were satellite-tracked during the winter of 2006 (n = 6), summer of 2006/07 (n = 6) and autumn/winter (n = 4) of 2007, from Marion Island, Southern Ocean. Despite varied individual movement patterns, a favoured foraging area lay to the northeast of the island. In contrast to findings for populations at similar latitudes, seals from Marion Island did not undertake short overnight foraging trips, but trips consistently went beyond 300 km from the island. This aligns with the at-sea duration of lactating seals’ foraging trips from temperate Amsterdam Island, but differs from subantarctic Crozet and Macquarie islands. Time spent at sea, maximum distances travelled and movement variation of tracks from the island varied seasonally. Faecal analysis suggests the diet comprised primarily myctophid fish with limited seasonal variation. Well-defined areas of restricted movement coincided with significant bathymetric features to the west/northwest of the Crozet Plateau, with the Del Caño Rise clearly being important. Positive and negative sea-surface height anomalies (compared to the mean) appeared to be preferred by most seals across seasons. Higher summer sea-surface temperatures correlated with the movements of some seals. Higher chlorophyll a concentrations dictated transit and foraging areas during summer. Bathymetrically influenced oceanographic variables likely explain these preferred long-distance eastward movements. The Îles Crozet and Marion island subantarctic fur seals differ in their foraging ecology despite being neighbours. Conversely, the subantarctic fur seal populations from the distant Amsterdam and Marion islands appear to be similarly influenced by such environmental factors.

Interannual variation in pup production and the timing of breeding in benthic foraging Australian fur seals

¯Large interannual variations in reproductive success caused by fluctuations in oceanography and prey availability are common to many species of air breathing epipelagic predators. In contrast, little is known about variation in benthic foragers such as Australian fur seals (Arctocephalus pusillus doriferus). Between 1997 and 2007, pup production was assessed in 9 yr, while the timing of breeding and adult female condition was assessed in 5 yr at Kanowna Island in Bass Strait, southeastern Australia. Pup production was variable ( ¯x = 1,726 ± 42, range = 1,386–2,301), but without temporal trend, as was median birth date ( ¯x = 23 November±1, range = 21–25 November) and pupping synchrony (period of 90% births: ¯x = 28 ± 2 d, range = 23–31 d). Pup production was negatively correlated with median birth date and positively correlatedwith female condition,winter sea-surface temperature (SST) and zonal wind strength within Bass Strait. Pup production was also negatively correlated with SST in the previous summer within Bass Strait and in the eastern Great Australian Bight upwelling region. The results suggest that the reproductive success of Australian fur seals is influenced by oceanography but less so than in otariids foraging epipelagically in major upwellings. Despite spanning several El Niño events, no correlation between pup production and the Southern Oscillation Index was observed.

Continued population recovery by Australian fur seals

Australian fur seals (Arctocephalus pusillus doriferus) are conspicuous, top-level predators in coastal waters of south-eastern Australia that were over-harvested during the 1800s and have had a delayed recovery. A previous species-wide estimate of live pups in 2002 recorded a near-doubling of annual pup production and a 5% annual growth rate since the 1980s. To determine if pup production increased after 2002, we estimated live pup numbers in 2007. Pups were recorded at 20 locations: 10 previously known colonies, three newly recognised colonies and seven haul-out sites where pups are occasionally born. Two colonies adjacent to the Victorian coast accounted for 51% of live pups estimated: Seal Rocks (5660 pups, 25.9%) and Lady Julia Percy Island (5574 pups, 25.5%). Although some colonies were up and some were down in pup numbers, the 2007 total of 21 882±187 (s.e.) live pups did not differ significantly from a recalculated estimate of 21 545±184 in 2002, suggesting little change to overall population size. However, the colonisation of three new sites between 2002 and 2007 indicates population recovery has continued.

Influences on fecundity in Australian fur seals (Arctocephalus pusillus doriferus)

Recovery of the Australian fur seal (Arctocephalus pusillus doriferus) population has been slower than that of other fur seals, perhaps due to nutritional constraints on fecundity. However, the population doubled in recent decades, suggesting that reproductive rates may have changed. Pregnancy rates and birthrates were estimated and the influences of maternal age, size, condition, and lactation status were investigated over 3 consecutive breeding seasons (2003–2005). Mid-gestation pregnancy rate, estimated from plasma progesterone concentrations, was 84% ± 3% (mean ± SE) and was negatively influenced only by age (P< 0.001). Birthrate, estimated from observations of females with newborn offspring during the breeding season, was 53% 6 3% (mean ± SE) and was influenced negatively by lactation status (P = 0.035). The difference between pregnancy rates and birthrates suggests that a high degree of late-gestation abortion occurs, especially in younger females. Lactation status was not influenced by any variables, and the high rate (86% ± 2%; mean ± SE) suggests that many offspring are suckled beyond the typical weaning period. Although relationships between reproductive rates and body condition were not found, the results are consistent with a nutritional stress hypothesis. The recent increase in population growth is not due to increased fecundity, which remains low compared to other otariids. Paradoxically, high pregnancy rates were observed in young females (3 years), suggesting that rapid maturity is adaptive for benthic foragers.

Behavioural responses of Australian fur seals to boat-based ecotourism

This study examined Australian fur seal behavioural responses to boat approaches at breeding colonies in Bass Straight. Results indicated that responses varied based on previous exposure to boats, approach distance, and time of day, and provided valuable information to management agencies regarding the effective management of ecotourism.

Factors influencing the winter haulout behaviour of Weddell seals : consequences for satellite telemetry

An understanding of pinniped haulout behaviour can provide information on how animals interact with their environment, their foraging strategies and the behaviour of their prey. For Weddell seals Leptonychotes weddelli, knowledge of haulout patterns and the environmental drivers of haulout is comprehensive for the austral spring and summer, but is poorly described outside this period. Pinniped behaviour is commonly examined using satellite telemetry; however, it is unclear whether the behavioural state of the seal can itself influence data acquisition. We examined haulout behaviour of female Weddell seals in eastern Antarctica over 3 winters (March to August, 2006–2008) using satellite-linked data loggers. Haulout behaviour followed a diel cycle with predominantly nocturnal haulouts. The environmental variables wind speed and temperature were influential on haulout, with seals tending to haul out more in lower winds and at higher temperatures. Haulout duration decreased across the winter, as did the number of satellite uplinks, suggesting that haulout duration played a role in data acquisition. There was no evidence of a decline in tag condition over this period, indicating that the decrease in uplinks was primarily the result of the winter behaviour of the seals. Overall, the number of haulout locations in the data set was over-represented, with more uplinks per hour occurring when the seals were hauled out than when they were at sea. For Weddell seals and other ice seals, tracking data that include haulout locations can bias spatial representations of foraging behaviour (e.g. haulout sites may be mistaken for regions of area-restricted search).

Differential mobilization of blubber fatty acids in lactating Weddell seals : evidence for selective use

A major source of energy during lactation in mammals is provided through the mobilization of blubber fatty acids (FAs). We investigated the extent to which FAs were mobilized to support both maternal metabolic requirements and milk production in the Weddell seal and how this was reflected in the FA composition of the pup’s blubber at the end of lactation (EL). FA composition of postpartum female blubber was similar in the 2 yr of study (2002 and 2003) but differed markedly by EL. Pup blubber FAs (at EL) were also different between years and did not match that of the mother’s milk or blubber. Milk FA composition changed during lactation, which may have been a reflection of an increase in pup energy demands at different stages of development. In addition, there was evidence of feeding by some females during lactation, with higher levels of some FAs in the milk than in the blubber. Our results indicate that differential mobilization of FAs occurred in lactating Weddell seals and that this was related to total body lipid stores at postpartum. Furthermore, growing pups did not store FAs unmodified, providing evidence that selective use does occur and also that using FA composition to elucidate dietary sources may be problematic in growing individuals.

Feast or famine : evidence for mixed capital–income breeding strategies in Weddell seals

Evolved patterns of resource expenditure for reproduction have resulted in a life history continuum across species. A strictly capital-breeding strategy relies extensively on stored energy for reproduction, whereas income breeding uses energy acquired throughout the reproductive period. However, facultative income breeding has been shown in some classically capital-breeding animals, and was originally thought to provide a nutritional refuge for smaller females incapable of securing sufficient reserves during pre-partum foraging. We examined milk composition and milk output for the Weddell seal to determine to what degree lactation was aided by food intake, and what factors contributed to its manifestation. Milk composition was independent of maternal post-partum mass and condition, but did change over lactation. Changes were most likely in response to energetic and nutritional demands of the pup at different stages of development. During early lactation, females fasted and devoted 54.9% of total energy loss to milk production. Later in lactation 30.5% more energy was devoted to milk production and evidence suggested that larger females fed more during lactation than smaller females. It appears that Weddell seals may exhibit a flexible strategy to adjust reproductive investment to local resource levels by taking advantage of periods when prey are occasionally abundant, although it is restricted to larger females possessing the physiological capacity to dive for longer and exploit different resources during lactation. This supports the assumption that although body mass and phylogenetic history explain most of the variation in lactation patterns (20–69%), the remaining variation has likely resulted from physiological adaptations to local environmental conditions. Our study confirms that Weddell seals use a mixed capital–income breeding strategy, and that considerable intraspecific variation exists. Questions remain as to the amount of energy gain derived from the income strategy, and the consequences for pup condition and survival.

Influence of maternal mass and condition on energy transfer in Weddell seals

* 1
Environmental variation influences food abundance and availability, which is reflected in the reproductive success of top predators. We examined maternal expenditure, offspring mass and condition for Weddell seals in 2 years when individuals exhibited marked differences in these traits.
* 2
For females weighing 355 kg there was a positive relationship between maternal post-partum mass (MPPM) and lactation length, but below this there was no relationship, suggesting that heavier females were able to increase lactation length but lighter females were restricted to a minimum lactation period of 33 days.
* 3
Overall, females were heavier in 2002, but in 2003 shorter females were lighter than similar-sized females in 2002 suggesting that the effects of environmental variability on foraging success and condition are more pronounced in smaller individuals.
* 4
There was no relationship between MPPM and pup birth mass, indicating pre-partum investment did not differ between years. However, there was a positive relationship between MPPM and pup mass gain. Mass and energy transfer efficiency were 10·2 and 5·4% higher in 2002 than 2003, which suggests costs associated with a putatively poor-resource year were delayed until lactation.
* 5
Heavier females lost a higher proportion of mass during lactation in both years, so smaller females may not have been able to provide more to their offspring to wean a pup of similar size to larger females.
* 6
MPPM had only a small influence on total body lipid; therefore, regardless of mass, females had the same relative body composition. Females with male pups lost a higher percentage of lipid than those with female pups, but by the end of lactation female pups had 4·5% higher lipid content than males.
* 7
It appears that for Weddell seals the consequences of environmentally induced variation in food availability are manifested in differences in maternal mass and expenditure during lactation. These differences translate to changes in pup mass and condition at weaning with potential consequences for future survival and recruitment.

Chemical immobilization of adult female Weddell seals with tiletamine and zolazepam: effects of age, condition and stage of lactation

Background

Chemical immobilization of Weddell seals (Leptonychotes weddellii) has previously been, for the most part, problematic and this has been mainly attributed to the type of immobilizing agent used. In addition to individual sensitivity, physiological status may play an important role. We investigated the use of the intravenous administration of a 1:1 mixture of tiletamine and zolazepam (Telazol®) to immobilize adult females at different points during a physiologically demanding 5–6 week lactation period. We also compared performance between IV and IM injection of the same mixture.
Results

The tiletamine:zolazepam mixture administered intravenously was an effective method for immobilization with no fatalities or pronounced apnoeas in 106 procedures; however, there was a 25 % (one animal in four) mortality rate with intramuscular administration. Induction time was slightly longer for females at the end of lactation (54.9 ± 2.3 seconds) than at post-parturition (48.2 ± 2.9 seconds). In addition, the number of previous captures had a positive effect on induction time. There was no evidence for effects due to age, condition (total body lipid), stage of lactation or number of captures on recovery time.
Conclusion

We suggest that intravenous administration of tiletamine and zolazepam is an effective and safe immobilizing agent for female Weddell seals. Although individual traits could not explain variation in recovery time, we suggest careful monitoring of recovery times during longitudinal studies (> 2 captures). We show that physiological pressures do not substantially affect response to chemical immobilization with this mixture; however, consideration must be taken for differences that may exist for immobilization of adult males and juveniles. Nevertheless, we recommend a mass-specific dose of 0.50 – 0.65 mg/kg for future procedures with adult female Weddell seals and a starting dose of 0.50 mg/kg for other age classes and other phocid seals.

Individual variation of in-air female ‘pup contact’ calls in Weddell seals, Leptonychotes weddellii

Vocal recognition may function as a critical factor in maintaining the phocid mother-pup bond during lactation. For vocal recognition to function, the caller must produce individually distinct calls that are recognised by their intended recipient. Mother-pup vocal recognition has been studied extensively in colonial otariids and appears to be characteristic of this family. Although less numerous, empirical studies of phocid species have revealed a range of recognition abilities. This study investigated whether Weddell seal (Leptonychotes weddellii) females produce individually distinct 'pup contact' calls that function during natural pair reunions. Fifteen calls from each of nine females recorded in the Vestfold Hills, Antarctica were analysed. One temporal, nine fundamental frequency and five spectral characteristics were measured. Results of the cross-validated Discriminant Function Analysis revealed that mothers produce individually distinct calls with 56% of calls assigned to the correct individual. The probability of achieving this level of discrimination on novel data by chance alone is highly improbable. Analysis of eight mother-pup reunions recorded near McMurdo Sound, Antarctica further demonstrated that these 'pup contact' calls function during natural pair reunions. Behavioural analysis also revealed that pups were chiefly responsible for establishing and maintaining close contact throughout the reunion process. Our study therefore demonstrates that Weddell seal females produce calls with sufficient stereotypy to allow pups to identify them during pair reunions, providing evidence of a functioning mother-pup vocal recognition system.