Subantarctic Fur Seals Arctocephalus Tropicalis Research Articles

Contest competition and injury in adult male sub-Antarctic fur seals

AbstractWe recorded intra-sexual behaviour of adult male sub-Antarctic fur seals Arctocephalus tropicalis at Gough Island, Southern Ocean, during the 1975/76 summer breeding season. Our re-analysed data address male ‘contest competition’, which relates to the costs of intra-sexual disputes, including fights. We considered the risks/benefits of fighting through investigation of injuries (n = 353) sustained by adult males (n = 124) in fights. Injuries were predominantly on the forequarters, especially around the insertion areas of the front flippers (41%) with its sparse pelage, compared to the neck and chest areas combined (29%), an area which is well protected by thick pelage. The infliction of serious, sometimes debilitating, injuries to competitors increases a male’s access to females. Injuries predominate in injured, defeated males that gather at non-breeding sites, suggesting that injuries inflicted by dominant males were successful in excluding competing males from breeding sites.

Long-term changes in petrel populations on Inaccessible Island, Tristan da Cunha, inferred from the diet of Brown Skuas Stercorarius antarcticus

Petrels that breed in burrows and return to their colonies after dark are among the most poorly studied seabirds. Brown Skuas Stercorarius antarcticus (family Stercorariidae) are major predators of burrowing petrels at many seabird breeding islands in the Southern Ocean, so monitoring the diet of skuas can provide insights into petrel population trends. Regurgitated pellets and other prey remains indicate that petrels comprise 94% (monthly range 91–97%) of all prey items in the pellets and other prey remains on Inaccessible Island, Tristan da Cunha. Other seabirds (0.7%), land birds (1.0%), subantarctic fur seals Arctocephalus tropicalis (0.5%) and marine animals (3.5%) make up the remainder of the Brown Skua diet. At least 12 species of petrels are eaten, including two species that are not known to breed on Inaccessible Island, but five taxa comprised over 98% of all petrels eaten: Fregetta storm petrels (44%), White-faced Storm Petrels Pelagodroma marina (23%), Broad-billed Prions Pachyptila vittata (21%), Great Shearwaters Ardenna gravis (6%) and Common Diving Petrels Pelecanoides urinatrix (5%). Pellets containing 2 or 3 avian prey items (15% of pellets) were more likely to contain conspecifics than heterospecifics, indicating either local differences in prey distribution or individual dietary specialisation. The prey composition changed seasonally linked to the phenology of the prey species, with White-faced Storm Petrels more common in the skua diet in spring, and Fregetta storm petrels in summer. Fur seals and Great Shearwaters have become more important in the skua diet, reflecting known or suspected increases in the populations of these species on the island, whereas the populations of Common Diving Petrels and Subantarctic Shearwaters Puffinus elegans may have decreased. Modal tarsal length of Fregetta storm petrels changed from 37 mm in 1987/89 to 39 mm in 2009, suggesting a possible increase of F. tropica relative to F. grallaria in the skua diet. However, overall there has been little change in the diet of Brown Skuas on this island over the last four decades.

Patterns of occurrence of the sub-Antarctic fur seal Arctocephalus tropicalis (Gray 1872) in Southern Brazil: climatic and environmental associations

Patterns of occurrence of the sub-Antarctic fur seal Arctocephalus tropicalis (Gray 1872) in Southern Brazil: climatic and environmental associations

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.

Myeloid and histiocytic sarcomas in subantarctic fur seals Arctocephalus tropicalis, Brazil

Histopathological and immunohistochemical methods were used to diagnose round cell tumors in 2 subantarctic fur seals Arctocephalus tropicalis with marked anemia. Although wild-born, both individuals were placed under human care while juveniles in a Brazilian aquarium. Both pinnipeds were PCR tested for herpesvirus, and 1 was infected with otariid gammaherpesvirus 5 (OtHV-5), previously described in a subantarctic fur seal stranded in Brazil. Although some gammaherpesviruses can cause sarcomas and other neoplasms, it was not possible to definitively associate OtHV-5 with the neoplasm. To our knowledge, these are the first neoplasm records in subantarctic fur seals.

Sub-Antarctic fur seals depredate northern rockhopper penguins at Nightingale Island, Tristan da Cunha

The most plausible hypothesis for declining population trends of some marine top predators at the northern extent of their breeding ranges in the Southern Ocean is that it results from environmental change. Sub-Antarctic fur seals Arctocephalus tropicalis are opportunistic and pelagic foragers that feed on a variety of fish, cephalopods, and crustaceans throughout their range. Penguins are also targeted, but to what extent remains uncertain, with only two records to date: Amsterdam Island, South Indian Ocean, where they kill and feed on northern rockhopper penguins Eudyptes moseleyi; and Gough Island, the southernmost island in the Tristan da Cunha archipelago, South Atlantic Ocean, where they are suspected to be significant predators of northern rockhopper penguins based on an unprecedented number of penguin carcasses (> 100) found floating at sea in 2011. We report the first documented records of such predations from the northern islands in the Tristan archipelago. Over three austral summers (2015–2017), northern rockhopper penguins with severe injuries were frequently observed at Nightingale Island. The cause of the wounds was unknown, but seal or shark attacks seemed probable. In January 2019, the first confirmed sighting of a sub-Antarctic fur seal, predating a healthy northern rockhopper penguin at sea off Nightingale Island was recorded. It remains uncertain whether the large A. tropicalis population at the Tristan da Cunha islands is significant predators of northern rockhopper penguins, but this could partly explain the significant recent decrease in northern rockhopper penguin population numbers.

Preferred, small-scale foraging areas of two Southern Ocean fur seal species are not determined by habitat characteristics

BackgroundTo understand and predict the distribution of foragers, it is crucial to identify the factors that affect individual movement decisions at different scales. Individuals are expected to adjust their foraging movements to the hierarchical spatial distribution of resources. At a small local scale, spatial segregation in foraging habitat happens among individuals of closely situated colonies. If foraging segregation is due to differences in distribution of resources, we would expect segregated foraging areas to have divergent habitat characteristics.ResultsWe investigated how environmental characteristics of preferred foraging areas differ between two closely situated Subantarctic fur seal (Arctocephalus tropicalis) colonies and a single Antarctic fur seal (A. gazella) colony that forage in different pelagic areas even though they are located well within each other’s foraging range. We further investigated the influence of the seasonal cycle on those environmental factors. This study used tracking data from 121 adult female Subantarctic and Antarctic fur seals, collected during summer and winter (2009–2015), from three different colonies. Boosted Regression Tree species distribution models were used to determine key environmental variables associated with areas of fur seal restricted search behaviour. There were no differences in the relative influence of key environmental variables between colonies and seasons. The variables with the most influence for each colony and season were latitude, longitude and magnitude of sea-currents. The influence of latitude and longitude is a by-product of the species’ distinct foraging areas, despite the close proximity (< 25 km) of the colonies. The predicted potential foraging areas for each colony changed from summer to winter, reflecting the seasonal cycle of the Southern Ocean. The model predicted that the potential foraging areas of females from the three colonies should overlap, and the fact they do not in reality indicates that factors other than environmental are influencing the location of each colony’s foraging area.ConclusionsThe results indicated that small scale spatial segregation of foraging habitats is not driven by bottom-up processes. It is therefore important to also consider other potential drivers, e.g. competition, information transfer, and memory, to understand animal foraging decisions and movements.

First record of a leucistic sub-Antarctic fur seal

Anomalous pelage colourations have been reported to occur in several pinniped species and can potentially be used to assess gene flow amongst conspecific populations. Aberrant pelage colour has not been documented in sub-Antarctic fur seals Arctocephalus tropicalis older than pups. Sub-Antarctic fur seals were inspected on two of the beaches at Gough Island, South Atlantic Ocean, in the austral summer of 2018/19. A leucistic adult male was sighted on 09 January 2019, the first recorded leucistic individual for the species. Given the apparent extreme rarity of leucism in this sub-Antarctic pinniped species, it is unlikely to contribute to assessment of gene flow amongst conspecific populations.

Foraging Behavior of Subantarctic Fur Seals Supports Efficiency of a Marine Reserve's Design.

Foraging behaviour of marine top predators is increasingly being used to identify areas of ecological importance. This is largely enabled by the ability of many such species to forage extensively in search of prey that is often concentrated in oceanographically productive areas. To identify important habitat in the Southern Indian Ocean within and around South Africa’s Prince Edward Islands’ Marine Protected Area (MPA), satellite transmitters were deployed on 12 lactating Subantarctic fur seals Arctocephalus tropicalis at Prince Edward Island (PEI) itself. Switching state space models were employed to correct ARGOS tracks and estimate behavioural states for locations along predicted tracks, namely travelling or area restricted search (ARS). A random forest model showed that distance from the study colony, longitude and distance from the Subantarctic Front were the most important predictors of suitable foraging habitat (inferred from ARS). Model-predicted suitable habitat occurred within the MPA in relatively close access to the colony during summer and autumn, but shifted northwards concurrently with frontal movements in winter and spring. The association of ARS with the MPA during summer-autumn was highly significant, highlighting the effectiveness of the recently declared reserve’s design for capturing suitable foraging habitat for this and probably other marine top predator species.

English

The aims of this study were to identify bacteriocinogenic activity in 13 enterococci isolated from fecal samples of wild South American (Arctocephalus australis) and Subantarctic fur seals (Arctocephalus tropicalis); to determine the physicochemical characteristics and antimicrobial spectrum of antimicrobial compounds against Gram-positive and Gram-negative bacteria; and to evaluate the presence of bacteriocin structural genes by PCR. Out of 13 enterococci screened for antimicrobial activity, five enterococci showed activity against Listeria monocytogenes ATCC 35152, an important pathogen linked to food. Of these, only the E. mundtii strain J5 maintained the activity after the pH was adjusted (pH 6.5). The activity of antimicrobial compounds from the E. mundtii strain J5 (ACs-J5) was lost after proteolytic enzyme treatment; however, the activity was maintained after heat, pH (acidic and basic conditions) and chemical treatment. ACs-J5 showed narrow spectrum activity. Only the mundticin KS gene was detected in the J5 strain and no plasmid was present. In conclusion, the properties presented by ACs-J5 make it a valuable biopreservative in food industries in avoiding pathogenic microorganisms such as L. monocytogenes and it should be a good candidate for probiotic application. Key words: Antimicrobial compounds, Enterococcus mundtii, wild fur seal, antilisterial activity.

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.

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.

Vagrant Subantarctic fur seal at Cape Shirreff, Livingston Island, Antarctica

A vagrant adult male Subantarctic fur seal Arctocephalus tropicalis was observed among Antarctic fur seals A. gazella at Cape Shirreff, Livingston Island, Antarctica, which is located to ~4,190 and ~5,939 km from the nearest breeding colonies of Subantarctic fur seals. Although the colony of origin of this animal and the reason for its movement outside its distribution range are unknown, this sighting shows the high dispersal capacity of this species and provides an insight into possible changes in its distribution. Although this vagrant was not observed with females Antarctic fur seal, news sightings in the future could result in viable hybrid, and introgressive hybridization could represent a threat for Cape Shirreff population recovery, if still the population way to go to recover to presailing levels.

Vagrant Subantarctic fur seal in the Mayumba National Park, Gabon

A vagrant adult male Subantarctic fur seal Arctocephalus tropicalis was seen and photographed on the beach in Mayumba National Park in the Gabonese Republic. This is the northern most sighting on record for the species. The likely source of the vagrant is the population at Gough Island, South Atlantic.

Vagrant Subantarctic Fur Seal in the Mayumba National Park, Gabon

A vagrant adult male Subantarctic fur seal Arctocephalus tropicalis was seen and photographed on the beach in Mayumba National Park in the Gabonese Republic. This is the northern most sighting on record for the species. The likely source of the vagrant is the population at Gough Island, South Atlantic.

King-size fast food for Antarctic fur seals

The study of scats of adult male Antarctic fur seals Arctocephalus gazella (AFS) revealed occasional frequent capture of penguins. Although AFS adult males have been occasionally reported to kill king penguins Aptenodytes patagonicus at the shore, here we report the first observations of at-sea predation by AFS on adult king penguins in the Crozet archipelago, southern Indian Ocean. During our 20 days survey, we observed 17 penguins attacked and either severely injured or killed and consumed. Only AFS adult males were seen catching king penguins successfully. Some adult females and sub-adults also attempted to catch penguins, either at sea or in land, and so did subantarctic fur seals Arctocephalus tropicalis individuals. Our results confirm the ability of fur seals to catch and predate large seabirds, even at sea.

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 Cano 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 Iles 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.

Interactions between subantarctic fur seal ( Arctocephalus tropicalis) and cookiecutter shark ( Isistius plutodus) on the coast of Bahia, north-eastern Brazil

The predation of pinnipeds by sharks in tropical or temperate regions is a significant cause of mortality of this group and little is known about these interactions off the Brazilian coast, since the records of these species are occasional, mainly in the north-eastern region. The objective of this study is to report the predator–prey interactions between sub-Antarctic fur seal (Arctocephalus tropicalis) and cookiecutter shark (Isistius brasiliensis) off the coast of Bahia. The present study was based on numbers of pinnipeds stranded, where there had been observed two specimens of sub-Antarctic fur seal, A. tropicalis. The diagnostic identification of shark predators was through the analysis of the morphology and conditions of the wounds compared with specialized literature. The measures are fit in category III, to whose height and width they are similar, suggesting to have been inferred for I. plutodus. This study confirms the necessity for continuing to study the interactions between sharks and pinnipeds in order to better understand the predator–prey relations off the Brazilian coast, as well as to question the extent to which these interactions cause the hindrance of this group.

Analysis of subantarctic fur seal ( Arctocephalus tropicalis) records in Bahia and Sergipe, north-eastern Brazil

The subantarctic fur seal Arctocephalus tropicalis is widely distributed north of the Antarctic convergence. We analysed data concerning vagrant individuals of A. tropicalis encountered on the beaches of Bahia and Sergipe, north-eastern Brazil, using the Instituto Mamiferos Aquaticos database of occurrences reported between 20 July 1990 and 18 August 2005. The information collected for each case included: date, location of the occurrence, condition of the individual, sex, and total length. Twelve occurrences of A. tropicalis were reported in the study area, with 42% corresponding to sub-adult specimens. All individuals were found alive, but only two were in good health. Most occurrences were reported during the months of July, August and September, a period in which south-eastern winds predominate. The importance of developing public educational campaigns as well as population dynamics studies of this species is discussed.

Goose barnacle (Lepas australis) infestation of the Subantarctic fur seal (Arctocephalus tropicalis)

Goose barnacle infestations (Lepas australis) were found on the pelage of two female Subantarctic fur seals (Arctocephalus tropicalis) at Gough Island in the South Atlantic. The infested females were both relatively old at 11 and 15 years of age. We suggest that females might be more prone to infestation than males and that infestation is more common in the older age groups. One of the females was postreproductive and the other had lost its pup of the season, consequently they might have stayed longer at sea after settlement of the goose barnacles and prior to hauling out, than females with pups. Attached to the guard hairs of the seal, the barnacles were clogged with underfur fibres, making it impossible for them to feed, leading to emaciation. A possible explanation for the clogging is that the seals had begun to moult.