Cephalopods in the diet of the South African fur seal (Arctocephalus pusillus pusillus)

The stomach contents of 1522 adult seals ( Arctocephalus pusillus pusillus ) and 673 pups, which were collected around the West and South Coasts of Southern Africa, were examined and cephalopod prey identified. About 20 cephalopod species (some identifications were uncertain) were found in the stomachs, of which only six were significant: Loligo vulgaris reynaudii. Sepia spp., Octopus sp., Todaropsis eblanae, Todarodes angolensis and Ocythoe tuberculata. This list suggests that A. pusillus feeds exclusively on the continental shelf, frequently on or near the bottom. Among adults, cephalopod prey varied in importance around the coast. It was most important on the South Coast of South Africa where it comprised 35.0% of the weight of all prey, of which L. v. veynaudii constituted about 88%. On the West Coast cephalopods comprised about 26.6% by weight of all prey, and Octopus sp. predominated, whereas in Namibian waters cephalopods were least important, constituting only 3.4% by weight of all prey, with Todarodes angolensis and Octopus sp. being most significant. Among pups (aged 8–10 months) in the Lüderitz (Namibia) area, cephalopods were about 16.9% of prey by weight, of which Ocythoe tuberculata , small Sepia spp. and Octopoda were most important.     

Behavioral responses of Australian fur seals (Arctocephalus pusillus doriferus) to environmental variations

Observing how pinnipeds respond to variations in climatic and oceanographic conditions informs marine managers on factors that could limit their range, foraging ability and breeding success. Here, we examine how Australian fur seals (Arctocephalus pusillus doriferus) at Seal Rocks, Victoria, Australia, responded to normal climatic conditions from August 2009 to January 2010, which included their Austral spring‐summer breeding period, to investigate their tolerances to a range of environmental stimuli. Seal numbers ashore and a range of climatic variables were collected hourly during daylight periods and compared using Generalized Additive Mixed Models (GAMMs). Air temperature was the most consistent predictor of haul‐out behavior, with seal numbers ashore declining as air temperature increased (effect size ?50%, edf 1.00, P < 0.001). Increased wave height (effect size 74%, edf 1.00, P < 0.001) and wind speed (effect size 79%, edf 1.00, P < 0.001) were associated with increased seal numbers ashore. Potentially, higher air temperatures reduce the seals tolerance to remain out of the water, while high wind/wave action increases at‐sea metabolic costs. These results demonstrate how changes in climate could alter a seal's ability to remain ashore, to rest or breed, and its ability to forage effectively, thus driving changes in population status and range.     

Behavior of Cape fur seals (Arctocephalus pusillus pusillus) in response to spatial variation in white shark (Carcharodon carcharias) predation risk

Foraging and predation risk are often separated at rookeries of marine central place foragers, thus offering an opportunity to gain insight into how predator‐avoidance shapes the behavior of prey. Here we compare the behavior of Cape fur seals (Arctocephalus pusillus pusillus) at two island rookeries with and without white shark (Carcharodon carcharias) predations, and assess seal behavior in relation to marked spatiotemporal variation in risk at the high‐risk site (Seal Island, South Africa). Our results show that seal behavior at the two sites is comparatively similar in summer, when predation risk is low at both sites, but not in winter. Compared to seals at the “low‐risk” site, seals at Seal Island avoided deep‐water habitat around the island at high risk times and restricted their use of this habitat in favor of safe, shallow waters when engaging in social and thermoregulatory behaviors. Seals increased their frequency of jostling, porpoising, and diving when moving through the danger zone and seals in groups were safer than single individuals. Overall, our results suggest that seal behavior around the high‐risk site is strongly affected by predation risk, and show this rookery to be an excellent predator‐prey system at which to evaluate long‐standing ecological hypotheses.     

Increased alertness behavior in Australian fur seals (Arctocephalus pusillus doriferus) at a high vessel traffic haul-out site

Vessel impacts on marine mammals are of growing concern, and marine mammals in urbanized marine environments are at particular risk of exposure. Port Phillip Bay (Victoria, Australia) is one such environment, in which Australian fur seals (AUFS; Arctocephalus pusillus doriferus) haul-out to rest, yet little is known about the impacts of vessels on resting seals. We used remote camera traps to investigate the influence of vessel traffic on AUFS behavior at a nonbreeding haul-out site. Environmental, temporal, and vessel-related variables were all associated with changes in AUFS alertness at this site. All vessel types elicited increased alertness above base-line levels (25%), with recreational and commercial motorized vessels associated with a 5.7%–10.8% increase in alertness. Unidentified vessels, the government vessel, and kayaks were associated with significantly increased alertness of 21.7%, 46.4%, and 60.7%, respectively, though accounted for only 6.2% of vessel observations. Vessels breaching current approach regulations (<5 m) showed a 32% increase in alertness, significantly higher than nonbreach approaches. Partial and complete flushing of the platform was rare, occurring in 1.0% of images analyzed. These results suggest that vessels do elicit a response from AUFS at this haul-out site, and that further monitoring of vessel activity and compliance is required.     

A comparative analysis on cranial ontogeny of South American fur seals (Otariidae: Arctocephalus)

We analysed the cranial ontogeny of male Arctocephalus australis (Zimmermann, 1783) (N = 116), Arctocephalus gazella (Peters, 1875) (N = 69), and Arctocephalus tropicalis (Gray, 1872) (N = 51) to study skull growth and its allometric patterns in the genus. We used 15 metric variables with bivariate and multivariate approaches to detect interspecific similarities and differences between growth trends, which we discussed in the context of phylogeny and life history. We found common trajectories in 20% of variables, detecting that the differences between adults were associated with size. We detected higher growth rates in A. gazella than in A. australis and A. tropicalis, which were associated with shape differences. Amongst the three species, A. tropicalis was morphologically intermediate, showing additional common trends with A. gazella and A. australis, and an intermediate position in the multivariate morphospace. Allometric patterns were also compared with growth trends described for Otaria byronia (Péron, 1816) and Mirounga leonina (Linnaeus, 1758). We detected positive allometry in Arctocephalus for the mastoid width (MW) but negative allometry in O. byronia and M. leonina. This could indicate that males of Arctocephalus exhibited a delayed development of MW. Finally, the presence of common growth trends for the skull length and the postorbital constriction could indicate a conservative pattern within otariids. © 2014 The Linnean Society of London     

Behavior of Cape fur seals (Arctocephalus pusillus pusillus) in relation to temporal variation in predation risk by white sharks (Carcharodon carcharias) around a seal rookery in False Bay,South Africa

The marked differences in predation risk posed by white sharks (Carcarodon carcarias) at island rookeries of Cape fur seals (Arctocephalus pusillus pusillus) offer a quasi‐experimental design within a natural system for exploring how prey adjust their behavior in response to temporal variation in predation risk. Here we compare movement of juvenile and adult Cape fur seals at a high risk (Seal Island) and low risk (Egg Island) rookery. We further compare juveniles and adults at Seal Island in low and high risk seasons and at low and high risk times of day within those seasons. Adult fur seals at Seal Island avoided traversing the zone of high white shark predation risk during the high risk period (0700–0959) in the season of high risk (winter), but not during the low risk season (summer). By contrast, adult fur seals at Egg Island showed no temporal discretion in either season. Unlike juvenile fur seals at Egg Island, juveniles at Seal Island adjusted their temporal movement patterns to more closely mimic adult seal movement patterns. This suggests that exposure to predators is the primary driver of temporal adjustments to movement by prey species commuting from a central place.     

The composition of Australian fur seal (Arctocephalus pusillus doriferus) milk throughout lactation.

The proximate chemical composition of milk was determined throughout lactation in the Australian fur seal (Arctocephalus pusillus doriferus Wood Jones), a temperate species with an 11-mo lactation period typical of most temperate otariids. Average lipid and protein contents were 42% and 10%, respectively, which is similar to that recorded for the polar otariid species but higher than reported in other temperate, long-lactation species. Milk composition, however, varied substantially throughout lactation, with lipid content rising from 30% soon after parturition to 50% at 230 d postpartum before decreasing to 45% toward weaning. The trend in water content was opposite to that of lipid, while protein content increased only slightly during lactation from 10% to 12%. The peak in lipid content occurred at approximately 70% of the way through lactation, similar to that found in the Australian sea lion and several phocid seal species. Significant positive relationships were found between milk lipid content and both the duration of the preceding foraging trip and body mass. A highly significant and close correlation was found between milk water and lipid contents such that gross energy content may be accurately predicted from water content alone. Similar predictive equations have been found for several other otariid and phocid species, but these appear to differ between phylogenetic groups.     

Temporal patterns of milk production in Antarctic fur seals (Arctocephalus gazella)

The timing of milk production in Antarctic fur seals was studied at Bird Island, South Georgia. Like all lactating otariid seals (Pinnipedia: Otariidae), Antarctic fur seal females alternate between short nursing periods ashore and regular foraging trips to sea. Females do not necessarily return to the colony with full mammae, which indicates that mammary volume capacity is unlikely to limit foraging trip duration. Upon arrival at the colony, milk fat (r²= 0.33, P < 0.04) and protein (r²= 0.60, P < 0.002) content were positively correlated to the time spent at sea. A similar trend was observed in the milk produced on land. The rate of milk energy production was much lower at sea (5.02 ± 0.05 MJ day^-1) than on land (23.66 ± 4.4 MJ^-1 day^-1). The rate of milk energy production during the foraging trip was negatively correlated to the time spent at sea (r²= 0.29, P < 0.05), whereas the rate of milk energy production on land was positively correlated (r²= 0.61, P < 0.001) to the duration of the preceding foraging trip. The total amount of milk energy delivered to the pup during each twoday nursing period was positively correlated (r²= 0.60, P < 0.002) to the duration of the previous foraging trip. The overall rate of milk energy delivery, however, was independent of foraging trip duration. This accords with previous observations that the growth rates of Antarctic fur seal pups are unaffected by maternal foraging trip duration patterns.     

Factors affecting weaning weight in Antarctic fur seals Arctocephalus gazella at South Georgia

Summary Relationships between size, body condition, age and feeding-attendance patterns during pup rearing of female Antacrtic fur seals Arctocephalus gazella and their effects on the timing of birth and weaning, pup weight, growth and condition were studied at South Georgia in 1981–1982. Twenty-seven (6 male, 21 female) mother-pup pairs were followed from birth to weaning. The analysis of maternal effects was limited to female pups because of the small sample size of male weaners. High weaning weight was associated with those female pups whose mothers spent more time ashore attending their offspring. Weaning weight showed no relationship with perinatal duration, number of feeding trips to sea, days at sea or date of weaning. A further 63 mother-pup pairs were analysed for the effects of maternal body condition (weight/length), age and timing of birth on offspring body weight and condition. Pup weight and condition were weakly correlated with maternal age in female pups. Male pups born earlier in the season were heavier and in better condition. Maternal and offspring body weight and condition were unrelated. For the Antarctic fur seal population at South Georgia where the food supply was apparently not limiting in summer, maternal condition and foraging time were subordinate to maternal care on land (as expressed by attendance duration) in determining offspring weight at weaning.     

Olfactory discrimination ability of human subjects for ten pairs of enantiomers.

We tested the ability of human subjects to distinguish between enantiomers, i.e. odorants which are identical except for chirality. In a forced-choice triangular test procedure 20 subjects were repeatedly presented with 10 enantiomeric odor pairs and asked to identify the bottle containing the odd stimulus. We found (i) that as a group, the subjects were only able to significantly discriminate the optical isomers of alpha-pinene, carvone and limonene, whereas they failed to distinguish between the (+)- and (-)-forms of menthol, fenchone, rose oxide, camphor, alpha-terpineol, beta-citronellol and 2-butanol; (ii) marked individual differences in discrimination performance, ranging from subjects who were able to significantly discriminate between 6 of the 10 odor pairs to subjects who failed to do so with 9 of the 10 tasks; (iii) that with none of the 10 odor pairs were the antipodes reported to differ significantly in subjective intensity when presented at equal concentrations; and (iv) that error rates were quite stable and did not differ significantly between sessions, and thus, we observed a lack of learning or training effects. Additional tests of the degree of trigeminality and threshold measurements of the optical isomers of alpha-pinene, carvone and limonene suggest that the discriminability of these three enantiomeric odor pairs is indeed due to differences in odor quality. These findings support the assumption that enantioselective molecular odor receptors may only exist for some but not all volatile enantiomers and thus that chiral recognition of odorants may not be a general phenomenon but is restricted to some substances.     

Kin selection may influence fostering behaviour in Antarctic fur seals (Arctocephalus gazella)

Fostering confers obvious advantages to the offspring but is seemingly costly to the caregiver. Such behaviour is particularly paradoxical in seals where the energetic investment in milk is very high and has led to the suggestion that this behaviour may have evolved through either kin selection or reciprocity. We used a combination of genetic and behavioural data to investigate whether kin selection plays a role in the fostering behaviour observed in a well-studied population of Antarctic fur seals (Arctocephalus gazella) from Bird Island, South Georgia. Genotypic data from eight highly polymorphic microsatellite markers were used to estimate relatedness among mother-pup pairs, foster mother-pup pairs and the total population. Mean relatedness was found to be significantly higher for foster mother-pup pairs than that observed for the total population, suggesting that kin selection could have a role in the maintenance of fostering behaviour in this species.     

Tooth growth in male Antarctic fur seals (Arctocephalus gazella) from South Georgia: an indicator of long-term growth history

Growth of upper canine teeth of male Antarctic fur seals ( Arctocephalus gazella ) which died of natural causes at Bird Island, South Georgia, was quantified from measurements of annual layers in longitudinal sections of teeth. Mean age at death was 7.69±0.07 years and this showed a small but significant increase through the period when samples were collected (1972/73–1988/89). There were significant correlations between morphometrics of teeth and those of seals, suggesting that tooth growth provided an indication of body growth. Tooth growth rate was lowest in seals which died early (age 4 years) and increased with age at death. Changes in the growth pattern of teeth suggested that fur seals which became sexually mature early also died early. Tooth growth layers deposited in each calendar year were compared with the expected layer depth based on a linear relationship between layer depth and age at which each layer was deposited. There was significant variation in the depth of tooth growth layers deposited in different years, suggesting that growth was greater in some years than others. No trends in cohort strengths were detected, but particularly poor years for growth were closely related to years in which reproductive performance was also observed to be low. Variations in growth from 1967/68 to 1987/88 were correlated significantly (P < 0.008) with the Southern Oscillation Index of climatic variation.     

Electrophoretic transferrin variation in fur seals (Arctocephalus spp.) at Marion Island

1. Variation in transferrin types were investigated in sympatric populations of two fur seal species which are undergoing limited hybridization at Marion Island. 2. Vertical polyacrylamide gel electrophoresis of serum was performed to demonstrate the transferrin types. 3. The two species appear fixed for alternative alleles: A. tropicalis being homozygous for the fast allele, and A. gazella (with one exception) being homozygous for the slow allele, indicating low gene flow between these two species. The single hybrid tested was homozygous for the slow allele. 4. The use of electrophoretically determined transferrin variation holds promise for the investigation of these and other sympatric fur seal populations.     

Geographic distribution and diversity of mitochondrial DNA haplotypes in South American sea lions (Otaria flavescens) and fur seals (Arctocephalus australis)

Genetic diversity and population structure of two species of South American pinnipeds, Otaria flavescens and Arctocephalus australis, from colonies located along the south-eastern coast of South America, were analysed using mitochondrial DNA haplotypes and compared with two populations of these species from the Pacific coast. A 445 base-pair segment, that included the tRNA-Glu gene (31 bp) and the adjacent cytochrome b gene (414 bp), was amplified using the polymerase chain reaction and sequenced directly. O. flavescens and A. australis showed six and seven haplotypes with 12 and 20 polymorphic sites, respectively. In the Atlantic Ocean there was an individual of A. australis that showed an haplotype that was highly divergent from the others. If this haplotype is excluded, the pattern of haplotype differentiation obtained for both species indicated a possible bottleneck that would have occurred 110,000 years ago, which also affected other pinnipeds. Colonies of the Atlantic and the Pacific did not share haplotypes. This result, based on a limited number of samples for the comparisons between oceans, suggests that populations from both oceans correspond to different evolutionarily significant units. O. flavescens on the Atlantic coast shows two clusters of breeding colonies in Uruguay and Patagonia, separated by a thousand kilometres. Colonies within clusters did not show significant differences in haplotype frequencies, but the difference between the clusters was significant, suggesting that they correspond to different conservation stocks.     

Killing of Cape fur seal (Arctocephalus pusillus pusillus) pups by brown hyenas (Parahyaena brunnea) at mainland breeding colonies along the coastal Namib Desert

Brown hyenas (Parahyaena brunnea) scavenge and kill seal pups at mainland Cape fur seal (Arctocephalus pusillus pusillus) colonies. The prey encounter interval and interval between kills depended on seal density, and increased density resulted in an increase of the capture rate and increase in hunting efficiency from 14% in November to 47% in January. The time brown hyenas spent at the seal colony decreased with increasing seal density and increasing air temperatures. Nevertheless, they were regularly active during the day when less adult seals were present at the colony, which indicates that the attendance of adult seals might play a role in the choice of foraging time. Brown hyenas killed seal pups throughout the study period. The predation rate was independent of the availability of non-violent mortalities, but the absolute number of kills was positively density-dependent. Mass kill events were recorded throughout the study period and are therefore not unusual occurrences. The overabundance of easy and vulnerable prey may lead to an over stimulus situation that triggers killing independent of the consumption of the prey or the hunger state.