Fur Seal Population Research Articles

Prevalence and source of entanglements in Cape fur seals (Arctocephalus pusillus pusillus) in South Africa

Global pollution is increasing, and marine mammals are commonly affected by marine debris. This study combined data from multiple sources to help understand the prevalence, characteristics and demographic profile of Cape fur seals (Arctocephalus pusillus pusillus) entangled in anthropogenic items. Overall, 383 cases of entanglement in seals were identified with a regional prevalence for South Africa of 0.12 %, i.e., just over one in every thousand animals. Fishing materials were the primary cause of entanglements (70 %), with most entanglements observed on adults (n = 249, 65 %), particularly adult females (n = 95, 66 % of all sex-determined entangled seals). This study highlights the need for correct disposal of waste, particularly that derived from the fishing industry to mitigate the impact of marine pollution on the welfare and conservation of marine fauna in South Africa.

Little evidence of inbreeding depression for birth mass, survival and growth in Antarctic fur seal pups

Inbreeding depression, the loss of offspring fitness due to consanguineous mating, is generally detrimental for individual performance and population viability. We investigated inbreeding effects in a declining population of Antarctic fur seals (Arctocephalus gazella) at Bird Island, South Georgia. Here, localised warming has reduced the availability of the seal’s staple diet, Antarctic krill, leading to a temporal increase in the strength of selection against inbred offspring, which are increasingly failing to recruit into the adult breeding population. However, it remains unclear whether selection operates before or after nutritional independence at weaning. We therefore used microsatellite data from 885 pups and their mothers, and SNP array data from 98 mother–offspring pairs, to quantify the effects of individual and maternal inbreeding on three important neonatal fitness traits: birth mass, survival and growth. We did not find any clear or consistent effects of offspring or maternal inbreeding on any of these traits. This suggests that selection filters inbred individuals out of the population as juveniles during the time window between weaning and recruitment. Our study brings into focus a poorly understood life-history stage and emphasises the importance of understanding the ecology and threats facing juvenile pinnipeds.

Quantifying wildlife conflicts with metabarcoding and traditional dietary analyses: applied to seabird predation by long-nosed fur seals

Wildlife conflicts require robust quantitative data on incidence and impacts, particularly among species of conservation and cultural concern. We apply a multi-assay framework to quantify predation in a southeastern Australian scenario where complex management implications and calls for predator culling have grown despite a paucity of data on seabird predation by recovering populations of long-nosed fur seals (Arctocephalus forsteri). We apply two ecological surveillance techniques to analyze this predator’s diet – traditional morphometric (prey hard-part) and environmental DNA metabarcoding (genetic) analyses using an avian specific primer for the 12S ribosomal RNA (rRNA) gene – to provide managers with estimated predation incidence, number of seabird species impacted and inter-prey species relative importance to the predator. DNA metabarcoding identified additional seabird taxa and provided relative quantitative information where multiple prey species occur within a sample; while parallel use of both genetic and hard-part analyses revealed a greater diversity of taxa than either method alone. Using data from both assays, the estimated frequency of occurrence of predation on seabirds by long-nosed fur seals ranged from 9.1–29.3% of samples and included up to 6 detected prey species. The most common seabird prey was the culturally valued little penguin (Eudyptula minor) that occurred in 6.1–25.3% of samples, higher than previously reported from traditional morphological assays alone. We then explored DNA haplotype diversity for little penguin genetic data, as a species of conservation concern, to provide a preliminary estimate of the number of individuals consumed. Polymorphism analysis of consumed little penguin DNA identified five distinct mitochondrial haplotypes – representing a minimum of 16 individual penguins consumed across 10 fur seal scat samples (equivalent to 10.1% of samples). We recommend rapid uptake and development of cost-effective genetic techniques and broader spatiotemporal sampling of fur seal diets to further quantify predation and hotspots of concern for wildlife conflict management.

Vulnerability to fluctuations in prey and predation landscape in a central place foraging marine predator

IntroductionHuman-induced environmental change is driving a global redistribution of biodiversity, resulting in shifting prey and predation landscapes. These shifting landscapes can lead to changes in behavior, health, and vital rates, with potential implications for population dynamics.MethodsIn the present study, a state-dependent life-history theory model was developed to investigate the individual- and population-level responses of Australian fur seals (Arctocephalus pusillus doriferus) to changes in prey availability and at-sea mortality risk.ResultsRates of pregnancy, pup nursing, and abortion were unaffected by prey availability in the simulated population. Likewise, on-land and at-sea durations were largely unaffected by prey availability, with more pronounced affects for nonreproductive and pregnant females than for lactating females. There was a strong influence of prey availability on the proportion of females that were concurrently pregnant and lactating, largely due to an increase in pup abandonments under low prey availability scenarios. This effect on pup abandonments also had flow on effects for pup recruitment. Increasing at-sea mortality risk resulted in greater offspring losses due to maternal death. The combined impact of prey availability and at-sea mortality risk on the number of simulated female offspring reaching sexual maturity was substantial.DiscussionConsequently, our results suggest high vulnerability of the Australian fur seal population to shifting prey and predation landscapes. These results indicate a need for continued monitoring of Australian fur seal pup production and population dynamics in the face of rapid environmental change.

АНАЛИЗ ДИНАМИКИ СЕВЕРНОГО МОРСКОГО КОТИКА (CALLORHINUS URSINUS) ОСТРОВА ТЮЛЕНИЙ НА ОСНОВЕ ПРОСТЕЙШЕЙ МАТЕМАТИЧЕСКОЙ МОДЕЛИ ЛОКАЛЬНОЙ ПОПУЛЯЦИИ

The northern fur seal (Callorhin usursinus), inhabiting North Pacific, has long been a valuable commercial target. This work continues a series of studies aimed at analyzing the dynamics and reproductive characteristics of the northern fur seal population on the Tyuleniy Island. The paper provides analyzes of intrapopulation parameters influence on the population sex ratio and pups production.

АНАЛИЗ СТРУКТУРЫ ПРОМЫСЛА И ДИНАМИКИ РОСТА СТАДА СЕВЕРНОГО МОРСКОГО КОТИКА (CALLORHINUS URSINUS) ОСТРОВА ТЮЛЕНИЙ В ПЕРИОД ЭКСПЛУАТАЦИИ И ПОСЛЕ ЕЁ ЗАВЕРШЕНИЯ

Based on a long time series providing biological monitoring data of the Northern fur seal population on Tyuleny Island and detailed information on the harvesting characteristics of this population, we have analyzed trends in its growth. The research results of changes in the average reproductive success of bulls and the age structure of Northern fur seal males on Tyuleny Island are presented as indicators of harvesting impact on the reproductive potential of the population. Evidence has shown that selective harvesting was practiced, where most productive bulls were removed from the population. This led to a significant change in the age structure of the population and a significant reduction in the population growth. Despite a slight increase in the natural survival of almost all age groups, the population growth slowed down sharply. The proximity of the growth potential indicator to the critical unitary value revealed in recent years leads to a bleak forecast. Further growth in the Northern fur seal population, if any, will not be rapid. To accelerate it, it is necessary to provide a new natural restructuring of the population structure, improving its qualitative composition and increasing the proportion of males with high reproductive success.

Long-term decline in body condition of female Australian fur seals: potential causes and implications

The Australian fur seal (Arctocephalus pusillus doriferus, AUFS) population is still recovering from the over-exploitation of the commercial-sealing era (18th and 19th centuries). While the population is considered to be only < 47% of its pre-harvest size, it now represents the greatest resident marine predator biomass in the south-eastern Australian marine ecosystem. The region is experiencing rapid environmental change and, as a keystone predator species, the AUFS is an indicator of ecosystem health. In the present study, the body mass, standard length and body condition index (BCI) were analysed between 1997-2021 in adult female AUFS provisioning pups on Kanowna Island (northern Bass Strait), the third largest colony for the species. While substantial inter-annual fluctuations were observed, there was no temporal trend in standard length during the 23-year study period. In contrast, body mass and, consequently, BCI decreased significantly, suggesting the population is experiencing changing nutritional conditions. While these changes do not appear to be due to competition with commercial fisheries or population expansion, weak but significant negative relationships were observed between BCI and 1-year lagged sea surface temperature and summer zonal winds in the Bonney Upwelling region, and both current- and 2-year lagged Indian Ocean Dipole (IOD). These findings suggest the BCI of AUFS may continue to decline under predicted climate change conditions. While a lack of a concurrent decline in pup production could indicate a degree of nutritional tolerance or flexibility in energy allocation, further monitoring is required to assess decreases in reproductive parameters (e.g., birth mass, pre-weaning growth rates) or vital rates, which would be expected with continued nutritional stress.

The Alaskan Fur-Seal Crisis: Science, Capital, and Multilateralism in the Settlement of International Biodiversity Disputes

Abstract The history of the Alaskan fur-seal crisis shows that the development of international environmental law and the peaceful settlement of biodiversity-related disputes can occur over the very long term, through a dynamic, iterative, and cyclical process that involves four key steps: the sorting of competing interests; the sifting of evidence and expert opinion; convergence on shared values; and the articulation of new regulatory regimes that reflect those values. The fur-seal dispute followed this pattern; it occurred over a period of more than 25 years during which the parties initiated several resets of the cycle until finally reaching a durable multilateral agreement grounded in a commitment to the rule of law and the rational use of natural resources. The main obstacles that prevented a more timely and efficient resolution were scientific uncertainty and risk to investment capital. The parties found they could not reach agreement on the causes of the decline of fur-seal populations, but they could agree on a regulatory model that incented the reallocation of private capital away from unsustainable activities, and that provided for an equitable sharing of public revenues in the long term, including through compensatory payments in exchange for restraint in the exercise of legal rights. This manuscript traces the origins of the dispute and the steps taken to reach a solution, including the several joint scientific inquiries commissioned by the parties, and invites discussion about how the lessons of the fur-seal crisis could be applied to avoid and resolve future biodiversity-related disputes.

Seasonal and interannual variability in the diet of young and subadult male Antarctic fur seals as revealed by stable C and N isotope ratios

Detailed knowledge of marine mammal diet is critical to understand their ecological roles and for the adequate management of marine resources. Antarctic fur seals ( Arctocephalus gazella) in the Southern Atlantic Ocean rely largely on Antarctic krill ( Euphausia superba) during the summer months, but their winter diet remains largely unknown. Here, stable carbon and nitrogen isotope ratios in whiskers and blood of young (2–3 years old) and subadult (4–7 years old) Antarctic fur seal males from the South Shetland Islands were used to assess the seasonal and interannual changes in the krill contribution to their diet. The stable isotope ratios revealed that krill dominated the diet of young and subadult male Antarctic fur seals year-round, with penguins, and not fish, as the second major prey, regardless of year and season. The year-round reliance of young and subadult male Antarctic fur seals on krill should be considered for ecosystem-based fisheries management, as they represent the bulk of the fur seal population remaining off Antarctica during the winter months.

The Harvest Effect on Dynamics of Northern Fur Seal Population: Mathematical Modeling and Data Analysis Results

We examine population trends in light of male harvest data considering the long-time series of population data on northern fur seals at Tyuleniy Island. To answer the question has the way males were harvested influenced the population trajectory, we analyzed the visual harem size and birth rate dynamics of the population, as well as the strategy and intensity of the harvest. We analyzed the dynamics of the sex ratio in the early (1958–1988) period to estimate parameters in the late period (1989–2013) based on the observed number of bulls and pups, while utilizing the distribution of reproductive rates obtained from pelagic sealing. Using a matrix population model for the observed part of the population (i.e., the male population), we analyzed the population growth rate associated with changes in both birth and survival rates considering the stochastic effects. Observations allow us to reject the hypothesis of nonselective harvest. Among the variety of natural and anthropogenic factors that could contribute to the decrease in the birth rate in the population, the effect of selective harvesting seems to be the most realistic.

EVALUATION OF TRACE ELEMENT CONCENTRATIONS IN THE SERUM AND VIBRISSAE OF PERUVIAN PINNIPEDS (ARCTOCEPHALUS AUSTRALIS AND OTARIA BYRONIA).

Concentrations of 15 trace elements (aluminum, arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, nickel, selenium, tin, vanadium, and zinc) were determined in vibrissae (whiskers) and serum of two sympatric pinniped species, the Peruvian fur seal population (PFS; Arctocephalus australis Peruvian subpopulation) and South American sea lion (SASL; Otaria byronia) at Punta San Juan, Peru during 2011-19 sampling events. Element concentrations were 2-20 times higher in vibrissae than in serum. Vibrissae and serum concentrations of several elements, including aluminum, arsenic, and lead, suggest that environmental contaminants may affect the health of pinnipeds at Punta San Juan. Although toxicity thresholds are unknown in pinnipeds, high concentrations of some elements (especially aluminum, arsenic, and lead) may have adverse impacts on their health such as immunosuppression and impaired reproduction. Arsenic was the only element that increased in mean vibrissae concentration throughout the study period. Female SASL vibrissae contained a mean arsenic concentration three times higher than the male SASL vibrissae mean arsenic concentration, and twice as high as the arsenic mean for all PFS vibrissae. The mean male SASL vibrissae cadmium concentration was five times higher than the vibrissae cadmium mean for both PFS males and females and nearly three times higher than the vibrissae cadmium mean for SASL females. Serum concentrations of aluminum, arsenic, copper, and manganese were significantly higher during moderate to extreme El Niño years compared to La Niña years. With stronger and more frequent El Niño-Southern Oscillation events predicted in the future, it is vital to understand how these trace elements may affect pinniped population health.

Sustained reduction in numbers of Australian fur seal pups: Implications for future population monitoring.

Fur seal populations in the Southern Hemisphere were plundered in the late 1700s and early 1800s to provide fur for a clothing industry. Millions of seals were killed resulting in potentially major ecosystem changes across the Southern Hemisphere, the consequences of which are unknown today. Following more than a century of population suppression, partly through on-going harvesting, many of the fur seal populations started to recover in the late 1900s. Australian fur seals (Arctocephalus pusillus doriferus), one of the most geographically constrained fur seal species, followed this trend. From the 1940s to 1986, pup production remained at approximately 10,000 per year, then significant growth commenced. By 2007, live pup abundance had recovered to approximately 21,400 per year and recovery was expected to continue However, a species-wide survey in 2013 recorded a 20% decline, to approximately 16,500 live pups. It was not known if this decline was due to 2013 being a poor breeding year or a true population reduction. Here we report the results of a population-wide survey conducted in 2017 and annual monitoring at the most productive colony, Seal Rocks, Victoria that recorded a large decline in live pup abundance (-28%). Sustained lower pup numbers at Seal Rocks from annual counts between 2012–2017 (mean = 2908 ± 372 SD), as well as the population-wide estimate of 16,903 live pups in 2017, suggest that the pup numbers for the total population have remained at the lower level observed in 2013 and that the 5-yearly census results are not anomalies or representative of poor breeding seasons. Potential reasons for the decline, which did not occur range-wide but predominantly in the most populated and long-standing breeding sites, are discussed. To enhance adaptive management of this species, methods for future monitoring of the population are also presented. Australian fur seals occupy several distinct regions influenced by different currents and upwellings: range-wide pup abundance monitoring enables comparisons of ecosystem status across these regions. Forces driving change in Australian fur seal pup numbers are likely to play across other marine ecosystems, particularly in the Southern Hemisphere where most fur seals live.

An Old Pathogen in a New Environment–Implications of Coxiella burnetii in Australian Fur Seals (Arctocephalus pusillus doriferus)

The Australian fur seal (Arctocephalus pusillus doriferus) has experienced a slower than expected population recovery since the end of the commercial sealing era, with a high third trimester abortion rate. There is currently no known proximate cause. Coxiella burnetii (Cb) is a well-known cause of abortion in domestic and wildlife species and an important zoonotic pathogen. It has been recorded from a small number of northern hemisphere marine mammals and may be a potential contributory factor to decreasing populations of northern fur seals (Callorhinus ursinus) and Steller sealions (Eumetopias jubatus). It has not been recorded from marine mammals in the southern hemisphere but is well documented in ruminants and wildlife in Australia as a cause of reproductive failure. Third trimester aborted fetuses (n = 46) and full-term placentas (n = 66) from Australian fur seals, were collected on Kanowna Island and Seal Rocks in Bass Strait, south-eastern Australia. Utilizing routine hematoxylin and eosin histopathology, Cb immunohistochemistry and two different qPCR targets–htpAB and com1, Cb was identified. Routine histopathology and immunohistochemistry were insensitive for the detection of Cb. The detected Cb prevalence ranged from 10.6% for com1 up to 40.9% with htpAB. Coxiella burnetti was readily detected in full-term placentas but in aborted fetal material only in a single placenta associated with a still birth. The exact significance is currently unclear, but this highlights that Cb is present in Australian fur seals, breeding in Bass Strait. Bass Strait is in one of the world’s fastest warming oceanic regions and marine mammals breeding in the area are likely to be key indicators of marine ecosystem stressors. This first description of Cb in a marine mammal from the southern hemisphere, highlights the need to further investigate the potential risks this pathogen poses to Australian fur seals and sympatric marine mammals. Additionally, it is important to determine the zoonotic risk of this pathogen to persons working with, and in proximity of, Australian fur seal breeding colonies.

Establishing a reference interval for acute phase proteins, cytokines, antioxidants and commonly measured biochemical and hematologic parameters in the northern fur seal (Callorhinus ursinus)

Over the past several decades there has been a precipitous decline of northern fur seals (Callorhinus ursinus; NFS) at their breeding grounds on the Pribilof Islands in the Bering Sea. The cause of this decline is likely multifactorial and could include changes in environmental parameters, prey abundance and distribution as well as exposure to pathogens and pollutants. Evaluation of inflammatory markers and antioxidant levels of the current population of fur seals in addition to hematologic and biochemical profiles could provide important information regarding health and subclinical or clinical disease in this population. Serum and plasma samples were obtained from clinically healthy adult female NFS and references intervals were determined for multiple parameters that can be altered in response to the presence of disease and environmental stressors. We established a reference interval for cytokines involved in acute inflammation and infection (TNFa, IL1, IL6, IL8, KC, IL10, C-reactive Protein) by utilizing commercially available canine cross-reactive antibodies. Reference intervals were also established for reactive oxygen species (hydrogen peroxide and malondialdehyde), as well as antioxidant levels (vitamin E and selenium) and acute phase proteins evaluated by serum electrophoresis. To improve the ability to compare and interpret indicators of health and disease in this species, we developed reference intervals for commonly utilized hematologic and biochemical tests in addition to the aforementioned markers of oxidative stress and inflammatory biomarkers. There were several animals identified as outliers indicating that they may have had subclinical illness or inflammation. Further investigation utilizing these tests in clinically ill animals and comparison to animals that exhibit normal behavior and no overt signs of illness could increase our understanding of the utility of measuring these parameters in this species.

First-Year Survival of Northern Fur Seals (Callorhinus ursinus) Can Be Explained by Pollock (Gadus chalcogrammus) Catches in the Eastern Bering Sea

The Pribilof northern fur seal (Callorhinus ursinus) herd in the eastern Bering Sea has declined by ~70% since the 1970s, for elusive reasons. Competition for pollock (Gadus chalcogramma) with the commercial fishery has been suspected as a contributing factor, but no correlative relationship between fishing activity and fur seal population declines has heretofore been demonstrated. Here, we present evidence for a moderately strong inverse relationship between fishery catches of pollock and first-year survival of fur seals, based on three different approaches to evaluation. We suspect this relationship results from the dependence of lactating female fur seals on locating dense and extensive schools of pollock near the Pribilof Islands to efficiently provide nutrition for their pups, because the pollock fishery also targets these same schools, and when fished, the remnants of these schools are fragmented and dispersed, making them more difficult for fur seals to locate and exploit. Inadequately fed pups are less likely to survive their initial independent residence at sea as they migrate south from the Pribilof Islands in the fall. Our results imply that pollock catches above ~1,000,000 t within ~300 km of the Pribilof Islands may continue to suppress first-year survival of Pribilof fur seals below the estimated equilibrium survival value of 0.50, leading to continued decline of the population.

The status of the fur seal population (Arctocephalus gazelle) on the southern border of the distribution area (the Argentine Islands archipelago)

The study of the population status of Arctocephalus gazella (Peters, 1875) in waters of the Argentine Islands was carried out in the period from April 2015 to March 2016 in accordance with the objectives of the State Target Scientific and Technical Research Program of Ukraine in Antarctica for 2011–2020. The aim of the article is to study the population dynamics and distribution of the southern fur seal in waters of the Argentine Islands. Due to the lack of data on the specifics of the seal’s dispersal in different periods of the year and the dynamics of the species population at the southern border of the distribution range, the results of the research are relevant and of great importance. In the second half of the 20th century, some publications presented the results of monitoring of pinnipeds at the Argentine Islands and adjacent territories, but the objects of these studies usually were other seal species: Hydrurga leptonyx, Lobodon carcinophagus, Leptonychotes weddelli, and Mirounga leonina. In the early 21st century, monitoring of the fauna of the Argentine Islands was carried out by Ukrainian biologists. However, they focused on Leptonychotes weddelli and less on other species of pinnipeds. The field material was collected in waters of the Argentine Islands, which is located in the Pacific sector of Antarctica. The fur seal population census and distribution studies were conducted according to the generally accepted methods. After breeding season on the subantarctic islands, during the migration southwards, fur seals reach the Argentine Islands, usually in the third decade of January. In the summer of 2016, the first fur seal was recorded within the archipelago on 31 January. During the study period, the largest number of animals within the archipelago was recorded in March–April and it ranged from 300 to 400 individuals. On the islands of the archipelago, the main resting places of seals were identified. The movement of animals northwards starts in May, consequently a decrease in the number of animals in this region is observed at that time. The last individuals are recorded in the first half of August. In 2015, migration began in May and ended in early August. There are several periods that were characterized by intensive migration of the animals: late June, 5–8 July, and 29 July to 6 August. In winter, one individual was last found within the archipelago on 12 August. The migration is launched by the worsening of weather conditions, formation of a continuous ice cover, reduced availability of food, and other factors.

Developing UAV Monitoring of South Georgia and the South Sandwich Islands’ Iconic Land-Based Marine Predators

Many remote islands present barriers to effective wildlife monitoring in terms of challenging terrain and frequency of visits. The sub-Antarctic islands of South Georgia and the South Sandwich Islands are home to globally significant populations of seabirds and marine mammals. South Georgia hosts the largest breeding populations of Antarctic fur seals, southern elephant seals and king penguins as well as significant populations of wandering, black-browed and grey-headed albatross. The island also holds important populations of macaroni and gentoo penguins. The South Sandwich Islands host the world’s largest colony of chinstrap penguins in addition to major populations of Adélie and macaroni penguins. A marine protected area was created around these islands in 2012 but monitoring populations of marine predators remains a challenge, particularly as these species breed over large areas in remote and often inaccessible locations. During the 2019/20 austral summer, we trialled the use of an unoccupied aerial vehicle (UAV; drone) to monitor populations of seals, penguins and albatross and here we report our initial findings, including considerations about the advantages and limitations of the methodology. Three extensive southern elephant seal breeding sites were surveyed with complete counts made around the peak pupping date, two of these sites were last surveyed 24 years ago. A total of nine islands, historically recorded as breeding sites for wandering albatross, were surveyed with 144 fledglings and 48 adults identified from the aerial imagery. The UAV was effective at surveying populations of penguins that nest on flat, open terrain, such as Adélie and chinstrap penguin colonies at the South Sandwich Islands, and an extensive king penguin colony on South Georgia, but proved ineffective for monitoring macaroni penguins nesting in tussock habitat on South Georgia as individuals were obscured or hidden by vegetation. Overall, we show that UAV surveys can allow regular and accurate monitoring of these important wildlife populations.

Genetic diversity and kinship relationships in one of the largest South American fur seal (Arctocephalus australis) populations of the Pacific Ocean

AbstractThe genetic diversity of populations is the basis for individual fitness and potential adaptability to environmental changes. The South American fur seal (Arctocephalus australis) is a pinniped species that is widely distributed along the southern cone of South America. However, two distinct populations have evolved: the Northern Pacific/Peruvian population and the Southern Pacific/Atlantic population. One of the main breeding colonies of the Southern Pacific/Atlantic population is located on Guafo Island, in southern Chilean Patagonia. This breeding colony represents the closest reproductive population to the remote Peruvian group. Therefore, our study aimed to determine whether the Guafo colony may potentially facilitate gene flow, contribute new alleles, and increase genetic variability of the Peruvian populations, thereby linking the Northern and Southern Pacific populations for the species. In this study, species‐specific microsatellite markers were developed to genetically characterize Guafo Island's South American fur seal population. Our results confirm that the Guafo colony is a panmictic population with evidence of lack of genetic structure. Further, our results indicate that most individuals are unrelated and that half‐siblings are rare, suggesting that polygyny in this species is less frequent than previously thought. Finally, based on the identification of multiple pairs of full siblings, we also present the first genetic evidence of twins in South American fur seals. These attributes suggest that the Guafo colony is a large, panmictic population, which could act as a potential genetic reservoir, and ultimately assist in linking two genetically distinct populations.

Trends in sympatric otariid populations suggest resource limitations in the Peruvian Humboldt Current System

Sympatric species evolve mechanisms to avoid competition and coexist. In the Humboldt Current System (HCS), populations of South American sea lions (SASL, Otaria byronia) and South American fur seals (SAFS, Arctocephalus australis) fluctuate mostly due to ENSO events and prey availability. We evaluate population trajectories of Peruvian sympatric otariids and discuss mechanisms for competition and/or resource limitation. For this purpose, we analyzed population trajectories of SASL and SAFS in a sympatric breeding site in Punta San Juan, Peru between 2001 and 2019. Wavelet analysis was used to extract trends and derivatives to estimate rates and turning points. Age-class proportions and biomass times series were constructed from weekly counts and evaluated. Both populations show a growth phase and subsequent decline. SAFS started to decline ~2.25 years before and at a rate 1.5 times faster than SASL. Decrease in juvenile age-class suggests that resource limitation is the main contributing factor for current population decline.

Fish prey of sub-Antarctic fur seals Arctocephalus tropicalis at the Tristan da Cunha Islands, South Atlantic Ocean

Some top predator populations in the South Atlantic and South Indian oceans are in decline, presumably contingent upon reduced food availability, precipitated by climate change. This phenomenon impacts on the positions of major ocean frontal zones which are hypothesised to act as natural dispersal borders for fish in the Southern Ocean. We investigate this hypothesis by establishing the fish diet of sub-Antarctic fur seals, Arctocephalus tropicalis, at Tristan da Cunha Island (37°15′S, 12°25′W) and Gough Island (40°19′S, 9°57′W), South Atlantic Ocean. The diets of these island populations, located on either side of the Subtropical Convergence, are compared with published dietary information from populations further south on islands located within the Polar Frontal Zone. To this end, fur seal scats were collected and analysed for remains of hard parts from prey in 2012–2013. The myctophid fish Gymnoscopelus piabilis, Protomyctophum tenisoni and Symbolophorus barnardi predominated in the diet. Lampichthys gemellarii, Myctophum aurolaternatum, S. barnardi and the Diaphus genus are recorded for the first time in the diet of A. tropicalis. Sub-Antarctic fur seal populations clustered around the Subtropical Convergence (~ 41°40′S), compared with those in the Polar Frontal Zone (~ 47°25′S to ~ 50°47′S), showed a considerable difference in the myctophid fish prey taken. The latitudinal differences in the fish diet of sub-Antarctic fur seals support suggestions that major frontal zones act as natural dispersal borders for fish in the Southern Ocean.