Vagrant sub-Antarctic fur seal at tropical Ascension Island, South Atlantic Ocean

Knowledge of extra-limital movements of seals improves our understanding of species’ dispersal and dispersion abilities and patterns, and perhaps environmental changes. Canvassing and internet literature searches revealed the sighting of a vagrant adult male sub-Antarctic fur seal Arctocephalus tropicalis on the coast adjacent to George Town (7° 56′ S, 14° 25′ W), Ascension Island, in 2010. Although finer details of the sighting are sketchy, this is the first sighting of any seal at Ascension Island, and the northernmost sighting on record for the species on the mid-Atlantic Ridge islands. The likely source of the vagrant is the population at Gough Island (40° 20′ S, 9° 54′ W) some 3624 km further south in the Atlantic. The vagrant likely moved westward from Gough Island to the Brazilian coast, then northwards in coastal waters, eventually reaching Ascension Island.http://link.springer.com/journal/300hj2022Mammal Research InstituteZoology and Entomolog

Cephalopod diet of juvenile male southern elephant seals Mirounga leonina at Marion Island, South Indian Ocean

DATA AVAILABILITY : The stomach content data, together with appropriate species identification, has been entered into an Excel file. This data base is available upon request.Southern elephant seals Mirounga leonina have a circumpolar distribution and migrate across broad geographic regions. Therefore, they can provide important insights into the responses of top predators to changes in the environment, especially those effected by climate change. For this, determining trophic interactions is key, and thus it is important to investigate the diet of all populations of M. leonina in the Southern Ocean. Limited literature exists on the diet of southern elephant seals at the Prince Edward Islands in the sub-Antarctic. During August and September 1976, the stomach contents of two juvenile male southern elephant seals were opportunistically collected at Marion Island (46o54’S, 37o51’E), and later analysed. Accumulated cephalopod beaks (n = 137) representing 18 taxa in nine decapod families were found. Onychoteuthidae was numerically the most abundant (28.7%), followed by Brachioteuthidae (21.8%), Neoteuthidae (12.6%), and Histioteuthidae (9.2%). Slosarczykovia circumantarctica (Brachioteuthidae) was the most abundant species (19.5%) followed by Batoteuthis skolops (Batoteuthidae) at 12.6%. Allometric equations using lower rostral lengths showed that the southern elephant seals ingested cephalopods with mantle length between 5.2 and 39.9 cm and weighing between 0.003 and 2.62 kg. There was only one very digested crustacean, and no recognizable fish remains in the stomach contents. The continuation of the investigation relies on examination of natural mortalities and dietary items obtained by stomach lavage of individuals, complemented by, for example, stable isotope compositions captured along the length of vibrissae and within dentinal growth layer groups of teeth as proxies for the elephant seals’ trophic ecology.https://link.springer.com/journal/3002023-07-17hj2023Mammal Research InstituteZoology and Entomolog

Aspects of the skin morphology in the sub-Antarctic fur seal Arctocephalus tropicalis

DATA AVAILABILITY : The original database no longer exists. The photomicrographs on which the histological descriptions and parameter definitions are based will be available upon request.SUPPLEMENTARY FILE 1—ESM 1a. Photomicrograph (no scale available) of a cross section through the furred skin of a sub-Antarctic fur seal showing the two principal layers: (a) the outer epidermis, (b) the underlying dermis, (c) a common pilary canal, (d) a guard hair, and (e) associated under hairs. The glandular nature of the dermis is evident, although the poor resolution and low magnification complicates the clear separation of (f) sebaceous glands (usually adjacent to pilosebaceous units) and (g) sweat glands (usually around base of pilosebaceous units). ESM 1b Photomicrograph (no scale available) of a cross section through the naked skin of a sub-Antarctic fur seal showing the coiled, tubular nature of the secretory portion of a sweat gland. ESM 1c Photomicrograph (no scale available) of a cross section through the dermis of the furred skin of a sub-Antarctic fur seal, parallel to the surface of the skin, showing (a) guard hairs and (b) associated under hairs. In the one instance (c) both the guard hair and the associated under hairs are situated in the common pilary canal close to opening up at the surface of the skin. (DOCX 5680 KB)SUPPLEMENTARY FILE 2—ESM 2 Table 1. Common pilary canal density of sweat glands in the furred and naked skin of adult male sub-Antarctic fur seals. ESM 2 Table 2 Volume of the secretory section of sweat glands in the furred and naked skin of adult male sub-Antarctic fur seals (DOCX 30 KB)The present study examined whether sweat glands are present in the skin of sub-Antarctic fur seals, Arctocephalus tropicalis, using standard histological procedures and light microscopy. Aspects of the microanatomy and histology of skin were described to elucidate structure and function. Sweat glands were present both in the furred areas of the body trunk, as well as in naked skin areas of the flippers. The density of the apocrine sweat glands appeared higher in fur-covered areas than in naked areas, while the size of sweat glands was similar amongst naked and fur-covered skin. The superficial position of sweat glands in the dermis of naked skin areas and the large, coiled, tubular nature of the secretory portion seem to indicate sweat gland activity in contrast to the deep lying, narrow sweat glands in fur-covered areas.Open access funding provided by University of Pretoria.https://link.springer.com/journal/435hj2023Mammal Research InstituteZoology and Entomolog

Vagrant Antarctic fur seals at the Tristan da Cunha Islands

Antarctic fur seals Arctocephalus gazella mainly breed at islands south of the Antarctic Polar Front, but stragglers occasionally occur farther north, with records from Gough Island (40 S, 10 W) in the central South Atlantic Ocean in October/November 2005 and September/ October 2009. We report the first record from Tristan da Cunha (37 S, 12 W) in September 2013, and another individual that was observed at Gough Island. Both individuals were lean, lethargic subadult males that were present before the onset of the breeding (pupping) season of the resident populations of subantarctic fur seals Arctocephalus tropicalis.http://link.springer.com/journal/3002015-11-30hb201

The diet of the subantarctic fur seal Arctocephalus tropicalis at Marion Island

Scats of subantarctic fur seals Arctocephalus tropicalis at Marion Island were collected from 1996 to 2,000, to examine temporal variability in the diet, factors affecting the variability and how the diet differed from that of the Antarctic fur seal A. gazella in the same period. For A. tropicalis, 19 prey species, of which 18 were fish and one a cephalopod, were identified in 213 scats. Fish were the main prey, occurring in 98.1 % of scats, whereas the cephalopod was present in only 1.4 % of scats. Amongst fish species, Myctophidae were most abundant, with Gymnoscopelus piabilis, G. fraseri and Electrona carlsbergi being the commonest prey items. Other fish families present in the diet in small numbers were Channichthyidae, Paralepididae, Nototheniidae, Microstomatidae and Notosudidae. Fish eaten ranged in size from Protomyctophum bolini and Krefftichthys anderssoni of standard length (SL) 25 mm to a single Dissostichus eleginoides of SL 249 mm. Differences in the diet existed between summer and winter. However, prey type accounted for most variability in the diet. In previous studies based on scats, a dominance of fish in the diet of A. tropicalis was also found at Possession Island (Iles Crozet), Amsterdam Island and Macquarie Island, but the dominant prey species differed between the various localities, also suggesting that prey availability is a major determinant of diet. At Marion Island, from 1996 to 2000 the diet of A. gazella comprised similar prey to that of A. tropicalis, but the proportional contribution of prey types differed in instances.National Research Foundation (NRF) and the University of Pretoria (UP), Department of Environmental Affairs.http://link.springer.com/journal/300hb201

Age-related reproductive variation in a wild marine mammal population

Life history theory predicts a change in reproduction success with age as energy resources are limited and must be allocated effectively to maximise reproduction and survival. In this study we use three reproductive performance measures; maternal expenditure, offspring weaning mass and first year survival to investigate the role maternal age plays in successful reproduction. Long-term uninterrupted life history data available for Marion Island’s southern elephant seals and mass change estimates from photogrammetry data allow for assessment of age related reproduction performance and trade-offs. Known-aged adult females were photographed for photogrammetric mass estimation (n=29) and their pups weighed at weaning during the 2009 breeding season. Maternal age and proportional mass loss positively influenced pup weaning mass. In turn first year pup return rates (as a proxy for survival) were assessed through the intensive mark-recapture program. Pup survival increased with female age and weaning mass. Pups of young females aged 3 to 6 years have a lower 1st year survival probability compared to pups of older and larger females.http://link.springer.com/journal/300hb201

Spatial variation in female southern elephant seal mass change assessed by an accurate non-invasive photogrammetry method

Physically weighing large marine mammals sequentially over time has presented researchers with a logistical challenge and has severely limited sample sizes. Using a well-established photogrammetry method we developed a simple mathematical method to calculate accurate mass measurements at specific stages in the life cycle of a top marine predator. Female southern elephant seals (n523) at Marion Island were sampled sequentially using photogrammetry and three-dimensional models (based on each photogrammetry project) were built for estimation of body mass. Simple equations were applied to obtain mass at critical instances in their life cycle. Marion Island elephant seal mass data was compared to data obtained from physically weighed elephant seals from King George, South Georgia and Macquarie islands. Females from Marion Island are smaller, but their percentage lactation mass loss is similar to females from these other populations. The similarity of percentage mass loss during lactation between different female populations illustrates the accuracy and practicality of the photogrammetric method over a temporal scale. Photogrammetric mass estimation can be used alongside datasets of physically weighed animals and can greatly benefit ecology and life history studies.http://journals.cambridge.orgam201

Regional differences in plastic ingestion among Southern Ocean fur seals and albatrosses

Weprovide data on regional differences in plastic ingestion for two Southern Ocean top predators: Arctocephalus fur seals and albatrosses (Diomedeidae). Fur seals breeding on Macquarie Island in the 1990s excreted small (mainly 2–5 mm) plastic fragments, probably derived secondarily from myctophid fish. No plastic was found in the scats of these seals breeding on three islands in the southwest Indian and central South Atlantic Oceans, despite myctophids dominating their diets at these locations. Compared to recent reports of plastic ingestion by albatrosses off the east coast of South America, we confirm that plastic is seldom found in the stomachs of Thalassarche albatrosses off South Africa, but found no Diomedea albatrosses to contain plastic, compared to 26% off South America. The reasons for such regional differences are unclear, but emphasize the importance of reporting negative as well as positive records of plastic ingestion by marine biota.National Research Foundation and the Universities of Cape Town and Pretoria.http://www.elsevier.com/locate/marpolbul2017-03-30hb2016Mammal Research InstituteZoology and Entomolog

Accuracy of using visual identification of white sharks to estimate residency patterns

Determining the residency of an aquatic species is important but challenging and it remains unclear what is the best sampling methodology. Photo-identification has been used extensively to estimate patterns of animals’ residency and is arguably the most common approach, but it may not be the most effective approach in marine environments. To examine this, in 2005, we deployed acoustic transmitters on 22 white sharks (Carcharodon carcharias) in Mossel Bay, South Africa to quantify the probability of detecting these tagged sharks by photo-identification and different deployment strategies of acoustic telemetry equipment. Using the data collected by the different sampling approaches (detections from an acoustic listening station deployed under a chumming vessel versus those from visual sightings and photo-identification), we quantified the methodologies’ probability of detection and determined if the sampling approaches, also including an acoustic telemetry array, produce comparable results for patterns of residency. Photo-identification had the lowest probability of detection and underestimated residency. The underestimation is driven by various factors primarily that acoustic telemetry monitors a large area and this reduces the occurrence of false negatives. Therefore, we propose that researchers need to use acoustic telemetry and also continue to develop new sampling approaches as photo-identification techniques are inadequate to determine residency. Using the methods presented in this paper will allow researchers to further refine sampling approaches that enable them to collect more accurate data that will result in better research and more informed management efforts and policy decisions.Conceived and designed the experiments: RLJ DGD EG MNB. Performed the experiments: RLJ. Analyzed the data: EG RLJ DGD. Wrote the paper: DGD EG RLJ MNB.World Wildlife Fund – South Africa, the South African Department of Environmental Affairs (and Tourism), and the International Fund for Animal Welfare.http://www.plosone.or

Unmarked individuals in mark-recapture studies : comparisons of marked and unmarked southern elephant seals at Marion Island

The presence of unmarked individuals is common in mark–recapture study populations; however, their origin and significance in terms of population dynamics remain poorly understood. At Marion Island, southern Indian Ocean, where virtually all southern elephant seal Mirounga leonina pups born annually (1983–2008) were marked in a long-term mark–resight study, large numbers of unmarked seals occur. Unmarked seals originate either from marker (tag) loss or from immigration. We aimed to identify patterns in the occurrence of marked and unmarked individuals that will allude to the possible origin and significance of the untagged component of the population, predicting that tag loss will add untagged seals to mainly adult age categories whereas migrating untagged individuals will be mostly juveniles.We fitted a generalized linear model using the factors month, year and age-class to explain the relative abundance of untagged seals (tag ratio) from 1997 to 2009. Site usage of untagged seals relative to tagged seals was assessed using a binomial test. Untagged seals, predominantly juveniles, were present in the highest proportions relative to tagged seals during the winter haulout (tagged seals/total seals less than 0.3) and the lowest proportion (approximately 0.5) during the female breeding haulout, increasing in relative abundance from 1997 to 2009. Untagged seals were distributed evenly across suitable haulout sites while tagged seals displayed high local site fidelity and occurred in greater numbers at or near large breeding beaches. Untagged seals are considered to be mostly migrant seals that disperse from other islands within the southern Indian Ocean and haul out at Marion Island during non-breeding haulouts in particular. Some of these seals immigrate to the breeding population, which can be a key component of the local population dynamics.We emphasize the need for mark–recapture studies to evaluate the role of the unmarked component of a population, thereby inducing a more confident estimation of demographic parameters from the marked sample.The Department of Science and Technology, through the National Research Foundation (NRF).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1442-9993ab201