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Understanding temporal patterns of marine mammal occurrence is useful for establishing conservation strategies. We used a 38 yr-long dataset spanning 1976 to 2013 to describe temporal patterns and trends in marine mammal strandings along a subtropical stretch of the east coast of South America. This region is influenced by a transitional zone between tropical and temperate waters and is considered an important fishing ground off Brazil. Generalized Additive Models were used to evaluate the temporal stranding patterns of the most frequently stranded species. Forty species were documented in 12,540 stranding events. Franciscana (n = 4,574), South American fur seal, (n = 3,419), South American sea lion (n = 2,049), bottlenose dolphins (n = 293) and subantarctic fur seal (n = 219) were the most frequently stranded marine mammals. The seasonality of strandings of franciscana and bottlenose dolphin coincided with periods of higher fishing effort and strandings of South American and subantarctic fur seals with post-reproductive dispersal. For South American sea lion the seasonality of strandings is associated with both fishing effort and post-reproductive dispersal. Some clear seasonal patterns were associated with occurrence of cold- (e.g. subantarctic fur seal) and warm-water (e.g. rough-toothed dolphin) species in winter and summer, respectively. Inter-annual increases in stranding rate were observed for franciscana and South American fur seal and these are likely related to increased fishing effort and population growth, respectively. For subantarctic fur seal the stranding rate showed a slight decline while for bottlenose dolphin it remained steady. No significant year to year variation in stranding rate was observed for South American sea lion. The slight decrease in frequency of temperate/polar marine mammals and the increased occurrence of subtropical/tropical species since the late 1990s might be associated with environmental changes linked to climate change. This long-term study indicates that temporal stranding patterns of marine mammals might be explained by either fishing-related or environmental factors.

1. The degree of individual specialization in resource use differs widely among wild populationswhere individuals range from fully generalized to highly specialized. This interindividualvariation has profound implications in many ecological and evolutionary processes. A recentreview proposed four main ecological causes of individual specialization: interspecific andintraspecific competition, ecological opportunity and predation.2. Using the isotopic signature of subsampled whiskers, we investigated to what degree threeof these factors (interspecific and intraspecific competition and ecological opportunity) affectthe population niche width and the level of individual foraging specialization in two fur sealspecies, the Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalustropicalis), over several years.3. Population niche width was greater when the two seal species bred in allopatry (low interspecificcompetition) than in sympatry or when seals bred in high-density stabilized colonies (highintraspecific competition). In agreement with the niche variation hypothesis (NVH), higherpopulation niche width was associated with higher interindividual niche variation. However, incontrast to the NVH, all Antarctic females increased their niche width during the interbreedingperiod when they had potential access to a wider diversity of foraging grounds and associatedprey (high ecological opportunities), suggesting they all dispersed to a similar productive area.4. The degree of individual specialization varied among populations and within the annualcycle. Highest levels of interindividual variation were found in a context of lower interspecificor higher intraspecific competition. Contrasted results were found concerning the effect ofecological opportunity. Depending on seal species, females exhibited either a greater or lowerdegree of individual specialization during the interbreeding period, reflecting species-specificbiological constraints during that period.5. These results suggest a significant impact of ecological interactions on the population nichewidth and degree of individual specialization. Such variation at the individual level may bean important factor in the species plasticity with significant consequences on how it mayrespond to environmental variability.

Antarctic and Sub-Antarctic pinnipeds are well-known seasonal visitors of the Southwest Atlantic Ocean. According to the literature, at their breeding grounds, they feed mainly on a variety of fish, cephalopods, and crustaceans. During the non-breeding period and far away from its breeding colonies, little is known about their feeding habits. Here, we present records of predation on aquatic birds by Antarctic and Sub-Antarctic pinnipeds off northern Argentinian coast (37°27′ S, 57°06′ W to 41°50' S 65°02' W). We examined the gastrointestinal contents of 22 specimens of three pinnipeds species (Arctocephalus gazella [n = 10], A. tropicalis [n = 11] and Hydrurga leptonyx [n = 1]) collected from 1996 to 2023. Aquatic birds remains were found in the gastrointestinal tracts of three individuals (13.64%): two A. gazella and one H. leptonyx. We identified feathers, and other bird parts by comparing them to specimens from scientific collections and descriptions/illustrations from the literature. Two of the three aquatic birds found in the gastrointestinal tracts were most probably Magellanic Penguins (Spheniscus magellanicus), whereas the other one was a Great grebe (Podiceps major). To our knowledge, this is the first study reporting predation on aquatic birds by Antarctic pinnipeds far from their breeding colonies.

This study presents the pattern of occurrence of sub-Antarctic fur seals (SAFS), Arctocephalus tropicalis, in the southern Brazilian coast and evaluate its association with climatic variability and anomalies in the concentration of chlorophytes and sea surface temperature in the reproductive colonies of Gough and Tristan da Cunha Islands. Date, sex, and age class of 254 stranded SAFS recorded between 1992 and 2013 were analyzed. Representative indexes of the patterns of climatic variability and environmental variables were obtained between four and five months before the records, the assumed interval of displacement for species between their closest breeding colonies and the southern Brazilian coast. The species was observed in southern Brazil between May and November each year, and most individuals were adult males. The records of SAFS on the southern Brazilian coast were associated with low concentration of chlorophytes interacting with negative sea surface temperature anomalies, and positive events of South Annular Mode, South Atlantic Ocean Dipole and Indian Ocean Dipole. Climatic variability is influencing the ecology SAFS, because it affects the environmental factors, that act as a driver of dispersion of the species. These variables had been interacting together in the region of the breeding colonies, and possibly during the fur seals’ journey towards the Brazilian coast. Considering the current scenario of global climate change, we expect that SAFS will continue to disperse to areas beyond their regular distribution, not only in the direction of the coasts of southern continents, but also further south, towards higher latitudes.

The Brazilian South coast seasonally hosts numerous marine species, observed particularly during winter months. Some animals, including fur seals, are found dead or debilitated along the shore and may harbor potential pathogens within their microbiota. In the present study, a metagenomic approach was performed to evaluate the viral diversity in feces of fur seals found deceased along the coast of the state of Rio Grande do Sul. The fecal virome of two fur seal species was characterized: the South American fur seal (Arctocephalus australis) and the Subantarctic fur seal (Arctocephalus tropicalis). Fecal samples from 10 specimens (A. australis, n = 5; A. tropicalis, n = 5) were collected and viral particles were purified, extracted and amplified with a random PCR. The products were sequenced through Ion Torrent and Illumina platforms and assembled reads were submitted to BLASTx searches. Both viromes were dominated by bacteriophages and included a number of potentially novel virus genomes. Sequences of picobirnaviruses, picornaviruses and a hepevirus-like were identified in A. australis. A rotavirus related to group C, a novel member of the Sakobuvirus and a sapovirus very similar to California sea lion sapovirus 1 were found in A. tropicalis. Additionally, sequences of members of the Anelloviridae and Parvoviridae families were detected in both fur seal species. This is the first metagenomic study to screen the fecal virome of fur seals, contributing to a better understanding of the complexity of the viral community present in the intestinal microbiota of these animals.

Acoustic structure, behavioral context, and caregiver responses to infant distress vocalizations (cries) are similar across mammals, including humans. Are these similarities enough for animals to respond to distress vocalizations of taxonomically and ecologically distant species? We show that mule deer (Odocoileus hemionus) and white-tailed deer (Odocoileus virginianus) mothers approach a speaker playing distress vocalizations of infant marmots (Marmota flaviventris), seals (Neophoca cinereaandArctocephalus tropicalis), domestic cats (Felis catus), bats (Lasionycteris noctivagans), humans (Homo sapiens), and other mammals if the fundamental frequency (F0) falls or is manipulated to fall within the frequency range in which deer respond to young of their own species. They did not approach to predator sounds or to control sounds having the same F0 but a different structure. Our results suggest that acoustic traits of infant distress vocalizations that are essential for a response by caregivers, and a caregiver’s sensitivity to these acoustic traits, may be shared across diverse mammals.

We 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.

The prevalence of cryptorchidism, a condition when one or more testes failed to move to their proper position(s), was evaluated for sub-Antarctic fur seals from Gough Island, South Atlantic. The reproductive tracts of male fur seals (n = 123) were examined and reproductive organs measured in a previous study. Only one fur seal, a 5-year-old sexually mature male, had one inguinal testis on the right side, and a small abdominal one situated below the kidney on the same side. A matching contralateral testis could not be located, neither in the scrotum or inguinal canal nor within the abdominal cavity. Amongst pinnipeds, cryptorchids rarely occurred in northern fur seals (0.01% to 0.02% prevalence), harbour seals (undetermined prevalence) and in sub-Antarctic fur seals (0.8% prevalence). Inconsequential on a population level, the rare instances of cryptorchidism in seals are interesting curiosities.

We report on an occurrence of ocular albinism in sub-Antarctic fur seal (Arctocephalus tropicalis) pups born on Marion Island, Prince Edward Archipelago. While previous observations have documented pups with atypical lanugo pelage colorations, this is the first case involving hypopigmentation of both fur and other tissues, including the eyes and nails. During the austral summer of 2021/22, we encountered four sub-Antarctic fur seal pups displaying this anomalous pigmentation. These anomalous individuals were found along two beaches on the island’s western side and one beach on the eastern side during an island-wide fur seal census. Although the characteristics observed strongly suggest ocular albinism, confirmation would be necessary through genetic analyses. The absence of melanin in mammalian eyes is known to compromise visual acuity, which may likely result in reduced survival beyond the weaning period, explaining the paucity of such adults in this well-observed population.

Marine top predators show fidelity to foraging areas with predictable high-quality food patches. Areas of predictable prey yield are of conservation importance, and telemetry data aid in identifying such areas. This study examined colony-specific and intra-individual foraging site fidelity of lactating subantarctic fur seals Arctocephalus tropicalis from Marion Island, Southern Ocean (46° 54’ S, 37° 45’ E), during summer and winter, comparing commitment to foraging areas across seasons. Thirty females were tracked in 2009–2013, resulting in 109 foraging trips for analyses. Inter-annually, preferred foraging areas in summer were consistently ~200 km due east of Marion Island towards the Gallieni Rise. Summer individuals’ core utilization areas overlapped by an estimated 32.84% (CI: 24.53–41.94%). Seals responded to a decrease in regional productivity in winter by foraging in more distant, alternative areas. In winter, individuals changed their travelling direction to northeast of Marion Island and foraged further afield, around the Del Caño Rise and along the Southwest Indian Ridge. Despite preferring some foraging areas in winter, there was a low amount of overlap 6.03% (CI 4.02–9.16%) of individual core utilization areas. The foraging grounds identified in this study have not been included in prior conservation assessments and are important for conserving this globally significant, and currently declining, population of subantarctic fur seals and perhaps other top predators breeding at Marion Island as well. Differences between foraging areas preferred in winter and summer highlight the importance of sampling during different seasons when using telemetry data for the identification of potential pelagic conservation areas.