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

The behaviours used by mammalian predators to capture and process their prey play a pivotal role in determining hunting success when targeting different species, or prey in different foraging environments. This is especially true in aquatic environments, where marine mammals like pinnipeds encounter a wide range of prey species while hunting both in open water and near the sea floor. However, due to difficulties faced when observing behaviour in diving mammals, little is known about the mechanics of prey handling in most pinnipeds species. The aim of this thesis was to remedy this by performing captive feeding trials that explored how foraging behaviours varied under different conditions for otariid species that have not been studied before now. When capturing small fish in open water, Australian fur seals (Arctocephalus pusillus doriferus) used raptorial biting. Rather than simply snapping at prey with the jaws, this involved combined use of biting and suction, where they used suction to draw prey within range of the teeth before the jaws snapped shut. In contrast, when capturing prey concealed within a feeding device, fur seals used strong suction alone to draw prey into the mouth. Australian and subantarctic fur seals (Arctocephalus tropicalis) swallowed small prey whole after the initial capture, while large prey was first brought to the surface and processed into smaller pieces by shaking. By chewing on prey between shakes, the fur seals created weak points that made it more likely to break when shaken further. Australian sea lions (Neophoca cinerea) were also able to chew and shake food; however, unlike fur seals, they also tore food held between their forelimbs and teeth. By directly observing how prey capture and processing occurs in otariid pinnipeds, we are able to begin to draw broader comparisons between these species and the other main clades of pinnipeds. Phocine phocids (the northern seals) also use biting and suction when capturing large vs. small prey, but unlike fur seals they are able to grip prey in clawed forelimbs while processing it with their teeth. Monachine phocids (the “southern” seals) have forelimbs intermediate in morphology between the clawed phocines and highly derived otariids. Those that have been studied or observed seem to display similar behaviours to the fur seals from our studies. Australian sea lions are unusual in being similar to phocine seals that hold prey in their forelimb flippers, but rather than using claws to secure prey, they squeezed prey between flat palms. These patterns highlight key differences in behaviour that may relate to differences in forelimb morphology that stem from the degrees to which each clade has adapted its anatomy for aquatic locomotion. By making direct observations of behaviour for a wide range of pinniped species we can therefore identify patterns that provide a better understanding of the role that foraging behaviour played throughout pinniped evolution. These results also provide insights into how prey capture and processing behaviours influence the foraging choices made by seals hunting at sea, providing insights into what makes pinnipeds such successful marine predators.

Skull morphometrics of two populations of Subantarctic fur seal (Arctocephalus tropicalis) were compared in order to identify possible geographic variation as an indicator of gene flow between the populations, as well as a potential tool to identify the source of vagrant seals. Nineteen metric variables were recorded from skulls of adult male seals from Marion Island (n=31) and Gough Island (n=41). Comparative univariate and multivariate statistical analyses conducted on the two population samples included standard statistics (mean, standard deviation, coefficient of variation, range), multivariate analysis of variance, stepwise discriminant function analysis, cluster analysis and principal component analysis. No significant separation between the two island groups, based on cranial characteristics of adult males, was found. These findings suggest that gene flow is occurring between these populations.We conclude that skull morphometrics cannot be used to identify the origins of vagrant Subantarctic fur seals.

Samples of pups from the expanding populations of Subantarctic fur seals (Arctocephalus tropicalis) atMarion and Gough islands were weighed at specific ages between birth and weaning in the period 1993-2000. Growth was estimated and compared between years, sexes, sites of different density, and populations. Pups of comparable age were consistently heavier at Marion Island than at Gough Island, probably reflecting relative prey resource abundance. No changes in pupgrowth rates were apparent over the study period, nor was there any evidence that growth was affected by ENSO events. Measures of pup growth at Marion Island were complemented by measures of maternal attendance behaviour during three summer andwinter seasons. More years of data are required to determine patterns between attendance, growth, resource conditions and population abundance trends.

Subantarctic fur seals (Arctocephalus tropicalis) appear as stragglers on New Zealand coasts. Four records are noted, the most recent at Antipodes Island in December 1989.

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.

Time spent in the water and diving behaviour of subantarctic fur seals (Arctocephalus tropicalis (Gray, 1872)) at Amsterdam Island in the southern Indian Ocean were investigated using time–depth recorders throughout the pup-rearing period. The main finding of this study, contrary to the findings of previous studies conducted on other fur seal species, was the decrease in the mean daily amount of time spent in the water throughout the pup-rearing period. The decrease in the amount of time spent in the water by older individuals compared with younger ones is likely to be related to the reduction of the pups' energy expenditure with a decreasing provisioning rate by their mothers. No change in the number of dives or the amount of time dedicated to diving relative to the time spent in the water could be detected throughout the pup-rearing period. The mean maximum dive depth increased with pup age and decreased with pup mass, and maximum dive duration was also found to increase with pup age. The positive effect of pup size on dive rates was the only relationship suggesting that pups' growth performance may act positively on the ontogeny of their diving capabilities. The large interindividual variation in the amount of time spent in the water and in dive rates, and the absence of any clear relationship with pup mass and pup growth performance, suggest the existence of alternative strategies: either pups invest more energy in developing their swimming and diving abilities, to the detriment of the body fat stores, or reduce their activity level to enhance body fat stores to increase their postweaning survival rate.

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 post-reproductive 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.

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.

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.

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.

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.

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.

The prostate glands of male Subantarctic fur seals Arctocephalus tropicalis , taken at Gough Island (40°20'S, 09°54'W) between November 1977 and October 1978, were examined. Significant changes in the mass of the prostate, the diameter of the alveoli and height of the secretory epithelium precede the breeding season and support the fact that A. tropicalis is a seasonal breeder. Peak activity of the prostate is reached during November-January. We propose that seasonal changes in the prostate gland, and in male reproductive activity in general, may be cued by changing photoperiod. Micro-anatomical features of the prostate of the male Subantarctic fur seal differ between different age groups. Peak prostate mass, alveoli diameter and secretory cell height indicate that Subantarctic fur seal males reach full adulthood at 10–11 years of age.

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.