Epizootiology of Brucella infection in Australian fur seals

Novel members of the bacterial genus Brucella have recently emerged as pathogens of various marine mammal species and as potential zoonotic agents. We investigated the epizootiology of Brucella infection in Australian fur seals (Arctocephalus pusillus doriferus) by establishing demographic and temporal variations in antibody prevalence, attempting isolation of the causative agent, and determining whether this potential pathogen is involved in frequent abortions observed in this pinniped species. Two competitive enzyme-linked immunosorbent assays (cELISAs), an indirect ELISA, and a fluorescence polarization assay (FPA) were used to test sera for Brucella antibodies. The FPA and cELISA proved suitable for use in this species. Significant differences in antibody prevalence were found between age classes of seals sampled between 2007 and 2009 at one colony. Pups sampled at this site (n=134) were negative for Brucella antibodies by all serologic tests but 17 of 45 (38%) of juveniles were antibody-positive. Antibody prevalence in adult females was significantly higher than in juveniles (P=0.044). Antibody prevalence for adult females between 2003 and 2009 varied significantly over time (P=0.011), and for individuals sampled between 2003 and 2005, the likelihood of pregnancy was greater in individuals positive for Brucella antibodies (P=0.034). Inflammatory lesions suggestive of infectious agents were found in 14 of 39 aborted Australian fur seal pups, but pathologic changes were not uniformly consistent for Brucella infection. Culture and PCR investigations on fetal tissues were negative for Brucella. Culture and PCR on selected fresh or frozen tissues from 36 juvenile and adult animals were also negative. We suspect that the prevalence of active infection with Brucella in Australian fur seals is low relative to antibody prevalence.     

Serologic survey for potential pathogens and assessment of disease risk in Australian fur seals

The introduction of pathogens into populations of animals with no previous exposure to them and, therefore, no immunologic protection, can result in epizootics. Predicting the susceptibility of populations to infectious diseases is crucial for their conservation and management. Australian fur seals (Arctocephalus pusillus doriferus) have a relatively small population size, a restricted range, and form dense aggregations. These factors make this species vulnerable to epizootics of infectious diseases that spread by direct animal-to-animal contact. Blood samples were collected from 125 adult female Australian fur seals between 2007 and 2009 and tested for exposure to selected pathogens. The testing protocol was based on pathogens important to marine mammal health or those significant to public and livestock health. No antibodies were detected to morbilliviruses, influenza A viruses, six Leptospira serovars, Mycobacterium tuberculosis-complex species, or Toxoplasma gondii. Overall antibody prevalence to an unidentified Brucella sp. was 57% but varied significantly (P<0.02) between 2007 (74%) and 2008 (53%). The findings indicate Brucella infection may be enzootic in the Australian fur seal population. Further investigations are required to isolate the bacteria and establish if infection results in morbidity and mortality. Australian fur seals remain vulnerable to the threat of introduced disease and should be managed and monitored accordingly.     

Prey capture and processing behaviors vary with prey size and shape in Australian and subantarctic fur seals

When hunting at sea, pinnipeds should adapt their foraging behaviors to suit the prey they are targeting. We performed captive feeding trials with two species of otariid seal, Australian fur seals (Arctocephalus pusillus doriferus) and subantarctic fur seals (Arctocephalus tropicalis). This allowed us to record detailed observations of how their foraging behaviors vary when presented with prey items that cover the full range of body shapes and sizes encountered in the wild. Small prey were captured using suction alone, while larger prey items were caught in the teeth using raptorial biting. Small fish and long skinny prey items could then be swallowed whole or processed by shaking, while all prey items with body depths greater than 7.5 cm were processed by shaking at the water's surface. This matched opportunistic observations of feeding in wild Australian fur seals. Use of “shake feeding” as the main prey processing tactic also matches predictions that this method would be one of the only tactics available to aquatic tetrapods that are unable to secure prey using their forelimbs.     

Tuberculosis in a wild subantarctic fur seal from Argentina

The first case of tuberculosis is described in a wild subantarctic fur seal (Arctocephalus tropicalis) found on the Argentine coast. There was hydrothorax and white firm granulomatous lesions of 40-50 mm in diameter in the lungs. Lesions consisted of a central area of caseous necrosis, an intermediate zone of epithelioid and lymphocytic mononuclear cells, and a peripheral zone of connective tissue. Biochemical and drug sensitivity tests and inoculation of Guinea pigs confirmed the identification as Mycobacterium tuberculosis complex. Arctocephalus tropicalis is the fifth pinniped species in which the M. tuberculosis complex has been detected. Since subantarctic fur seals are widely distributed in the Southern Hemisphere, it is possible that the tuberculosis cases may have a common origin and could spread to other austral regions and species.     

AGING LIVE ANTARCTIC FUR SEALS AND SOUTHERN ELEPHANT SEALS

This study describes a method for extracting post-canine or incisor teeth from live antarctic fur seals ( Arctocephalus gazella ) and southern elephant seals ( Mirounga leonina ) respectively and their use to determine age in a field situation. Dental elevators were used to loosen the teeth from the alveolus and periodental ligament. Most teeth were removed within l-2 min and a total of 214 and 81 teeth were collected by this method from antarctic fur seals and southern elephant seals respectively. No seal recaptured at intervals up to a year after a tooth was extracted showed signs of infection or distress related to removal of the tooth. Teeth were thin-sectioned for the purpose of aging. In both species cementum growth layer groups were a more satisfactory indicator of age than dentinal growth layer groups. Estimates of age from cementum growth layers were confirmed for Antarctic fur seals using seals which had been tagged as pups up to 16 yr before sampling.     

Vagrant Antarctic fur seals at Gough Island in 2009

The Antarctic fur seal Arctocephalus gazella at Gough Island (40°20′S, 09°54′W) in the South Atlantic Ocean, first seen in October/November 2005, was recorded again in September–October 2009. Up to three different individual Antarctic fur seals were sighted on a single day, on a particular beach. A total of seven different individuals were recorded over a 3-week period, well before the onset of the breeding (pupping) season of the resident population of Subantarctic fur seals A. tropicalis. Positively identified individuals were all male, mostly subadult and lean. Only a fraction (~20%) of the available beaches was searched, and it is unknown if the Antarctic fur seals were still present at Gough Island during the austral summer breeding season of southern fur seals.     

Vagrant Antarctic pinnipeds at Gough Island

Opportunistic sightings of Antarctic fur seals Arctocephalus gazella and a leopard seal Hydrurga leptonyx at Gough Island (40°20′S, 09°54′W) in the South Atlantic Ocean represent the northernmost island records for vagrant Antarctic fur seals, and only the second for a vagrant leopard seal at Gough Island. Some ten different individual Antarctic fur seals were sighted on a single day, up to seven on a single beach. An overall total of 18 individuals were recorded over a 7-week period in October/November 2005, before the onset of the breeding (pupping) season of the resident population of Subantarctic fur seals Arctocephalus tropicalis. Most were immature, male and mostly in good condition (n = 11, 61%); one mature male and six putative females were also present. All had departed after 23 November, although only a fraction of the available beaches was searched.     

Effects of seismic surveys on New Zealand fur seals during daylight hours: Do fur seals respond to obstacles rather than airgun noise?

The responses of New Zealand fur seals (Arctocephalus forsteri) during a three‐dimensional marine seismic survey were recorded in the first quantified investigation of the effects of seismic exploration operations on otariid seals. The survey was over the continental slope off southern New Zealand, where fur seals dive to forage at night and rest on the surface during daylight hours. Data were restricted to daylight sightings from the source vessel while towed seismic gear was fully deployed, with comparisons made between fur seal responses when airguns were off and when airguns were operating at full power. Results were inconclusive. Comparisons were confounded because both sighting rate and distance first seen decreased with deteriorating sea state. The key finding of this study was that the source vessel and towed gear created physical obstacles that often generated responses from fur seals. A more thorough investigation is recommended in order to differentiate between responses to airgun noise and responses to physical obstacles, and improvements are suggested to rectify shortfalls in data collection that should generate conclusive outcomes.     

Metagenomic Survey of Viral Diversity Obtained from Feces of Subantarctic and South American Fur Seals

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.     

PERMANENT GENETIC RESOURCES: Ten novel polymorphic dinucleotide microsatellite loci cloned from the Antarctic fur seal Arctocephalus gazella

Ten new dinucleotide microsatellite loci were isolated from the Antarctic fur seal Arctocephalus gazella. These markers should prove useful for studying the reproductive ecology of Antarctic fur seals and other related pinniped species.     

A panel of new microsatellite loci for genetic studies of antarctic fur seals and other otariids

Nine dinucelotide microsatellite loci were developed in the Antarctic fur seal Arctocephalus gazella. Each locus possessed between 4 and 9 alleles in a sample of twenty individuals sampled from Bird Island, South Georgia, and expected heterozygosity ranged from 0.52 to 0.84. All but one of the loci conformed to Hardy–Weinberg equilibrium and no evidence was found for genotypic disequilibrium. Additionally, all of the loci successfully cross-amplified in the South American fur seal Arctocephalus australis, the New Zealand fur seal Arctocephalus forsteri and the Steller’s sea lion Eumetopias jubatus, and six also yielded products in the more distantly related harbour seal Phoca vitulina and walrus Odobenus rosmarus. These loci should prove useful for studies of the population genetics of Antarctic fur seals and other important otariid species.     

Internal physiology of live krill revealed using new aquaria techniques and mixed optical microscopy and optical coherence tomography (OCT) imaging techniques

The Guadalupe fur seal (Arctocephalus townsendi) is a specialist predator feeding on prey present in one trophic level. Data related to the diet of the Guadalupe fur seal are few. It is still unknown where most of the individuals forage or the composition of their diet. On Isla Guadalupe, the San Benito Archipelago and the Farallon Islands, fur seals primarily feed on pelagic and coastal squids. However, differences between colonies were found probably caused by differences in diversity and abundance of prey species over the continental shelf and the pelagic environment, and maybe due to the plasticity of the species in their foraging behavior. Diet composition of the Guadalupe fur seal might reflect adaptations to local and temporal environmental conditions. The aim of this work was to consider historical information, add new information, identify main prey species, and determine where in the marine regions the Guadalupe fur seals feed.     

Laminae in the teeth of the Cape fur seal used for age determination

A sample of 40 known age Cape fur seal, $\text{Arctocephalus pusillus}$ canine teeth were histologically and manually sectioned and examined for laminae to determine if these growth layers could be used for age determination in this species of seal. Results of this investigation indicate that two laminae (one opaque and one translucent) are deposited per annum and that these structures provide an accurate method for aging seals 2 years old or less; agreement between age and laminae was also obtained for seals up to 8 years of age, but the small number (N = 3) of known-aged canines older than two years does not permit a definite conclusion as to the applicability of the method throughout the life span of the Cape fur seal.     

Ménage à trois on Macquarie Island: hybridization among three species of fur seal (Arctocephalus spp.) following historical population extinction

Human-induced changes to natural systems can cause major disturbances to fundamental ecological and population processes and result in local extinctions and secondary contacts between formerly isolated species. Extensive fur seal harvesting during the nineteenth century on Macquarie Island (subantarctic) resulted in extinction of the original population. Recolonization by three species has been slow and complex, characterized by the establishment of breeding groups of Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalus tropicalis) and presumed nonbreeding (itinerant) male New Zealand fur seals (Arctocephalus forsteri). One thousand and seven pups from eight annual cohorts (1992-2003) were analysed using mitochondrial control region data (RFLP) and 10 microsatellite loci to estimate species composition and hybridization. Antarctic fur seals predominated, but hybridization occurred between all three species (17-30% of all pups). Involvement of New Zealand fur seals was unexpected as females are absent and males are not observed to hold territories during the breeding season. The proportion of hybrids in the population has fallen over time, apparently owing to substantial influxes of pure Antarctic and subantarctic individuals and non-random mating. Over 50% of New Zealand hybrids and 43% of Antarctic-subantarctic hybrids were not F(1), which indicates some degree of hybrid reproductive success, and this may be underestimated: simulations showed that hybrids become virtually undetectable by the third generation of backcrossing. While human impacts seem to have driven novel hybridization in this population, the present 'time slices' analysis suggests some biological resistance to complete homogenization.     

SUCCESSFUL USE OF A TRANSLOCATION PROGRAM TO INVESTIGATE DIVING BEHAVIOR IN A MALE AUSTRALIAN FUR SEAL, ARCTOCEPHALUS PUSILLUS DORIFERUS

This study reports some of the first foraging behavior data collected for male fur seals. A nonbreeding male Australian fur seal, Arctocephalus pusillus doriferus , captured at a commercial salmon farm in southern Tasmania, Australia, was relocated 450 km from the site of capture. The animal was equipped with a geolocating time-depth recorder that recorded diving behavior and approximate location for the 14.4 d that it took the seal to travel down the east coast of Tasmania and be recaptured at the salmon farm. During its time at sea, the seal spent most of its time over the relatively shallow shelf waters. It spent 30% of its time ashore on a number of different haul-out sites. The deepest dive was 102 m and the maximum duration was 6.8 min. "Foraging" type dives made up 31.2% of the time at sea and had a median duration of 2.5 min and a median depth of 14 m. The seal performed these dives more commonly during the latter part of its time at sea, while it was on the east coast. Unlike other fur seal species studied to date, there was no evidence of a diurnal foraging pattern; it made dives at all times of the day and night.     

NEWS

ABSTRACT

Australian fur seals Arctocephalus pusillus doriferus are colonial breeding animals forming dense social groups during the breeding season. During this time, males establish and defend territories through physical conflicts, stereotyped posturing and vocalisations. While vocalisations are suggested to play an important role in male recognition systems, it has received little attention. Recordings of nine adult male Australian fur seals were made during the 2000 and 2001 breeding seasons at Kanowna Island (39° 10′S, 146° 18′ E), Bass Strait, Australia. The in-air bark vocalisations of territory-holding males were used to characterise the Bark Call and to determine whether males produce individually distinct calls, which could be used as a basis for vocal recognition. Seventeen frequency and temporal variables were measured from a total of 162 barks from nine individual males. The Bark Series was more reliably classified (83%) to the correct caller compared to the Bark Unit. This was assigned with less certainty (68%), although the classification was still relatively high. Findings from this study indicate that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition in male Australian fur seals.     

Serum chemistry and antibodies against pathogens in antarctic fur seals, Weddell seals, crabeater seals, and Ross seals

Information on health parameters, such as antibody prevalences and serum chemistry that can reveal exposure to pathogens, disease, and abnormal physiologic conditions, is scarce for Antarctic seal species. Serum samples from Antarctic fur seals (Arctocephalus gazella, n=88) from Bouvet?ya (2000-2001 and 2001-2002), and from Weddell seals (Leptonychotes weddellii, n=20), Ross seals (Ommatophoca rossii, n=20), and crabeater seals (Lobodon carcinophagus, n=9) from the pack-ice off Queen Maud Land, Antarctica (2001) were analyzed for enzyme activity, and concentrations of protein, metabolites, minerals, and cortisol. Adult Antarctic fur seal males had elevated levels of total protein (range 64-99 g/l) compared to adult females and pups (range 52-79 g/l). Antarctic fur seals had higher enzyme activities of creatine kinase, lactate dehydrogenase, and amylase, compared to Weddell, Ross, and crabeater seals. Antibodies against Brucella spp. were detected in Weddell seals (37%), Ross seals (5%), and crabeater seals (11%), but not in Antarctic fur seals. Antibodies against phocine herpesvirus 1 were detected in all species examined (Antarctic fur seals, 58%; Weddell seals, 100%; Ross seals, 15%; and crabeater seals, 44%). No antibodies against Trichinella spp., Toxoplasma, or phocine distemper virus (PDV) were detected (Antarctic fur seals were not tested for PDV antibodies). Antarctic seals are challenged by reduced sea ice and increasing temperatures due to climate change, and increased anthropogenic activity can introduce new pathogens to these vulnerable ecosystems and represent a threat for these animals. Our data provide a baseline for future monitoring of health parameters of these Antarctic seal species, for tracking the impact of environmental, climatic, and anthropogenic changes in Antarctica over time.     

Fur seals at Macquarie Island: post-sealing colonisation,trends in abundance and hybridisation of three species

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The first breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954–2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is significant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been affected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.     

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.