Natural mortality of puffadder shysharks due to Cape fur seals and black‐backed kelp gulls at Seal Island, South Africa

Natural mortality of puffadder shysharks Haploblepharus edwardsii due to two species of marine tetrapod, the Cape fur seal Arctocephalus pusillus pusillus and the black‐backed kelp gull Larus dominicanis vetula , is reported. These data constitute the first multiple observations of natural mortality of any cartilaginous fish due to object play or kleptoparasitism by marine tetrapods. Evidence of range extension of the puffadder shyshark to False Bay, South Africa is presented.     

Biased estimates of fur seal pup mass: origins and implications

The mass of fur seal pups weighed in different years can be used to estimate growth rates or compared with one another to make inferences about the relative condition of a population. However, unless appropriate precautions are taken, many factors can bias estimates of pup mass and lead to incorrect conclusions. Using data collected from tagged and untagged northern fur seal pups ( Callorhinus ursinus ) at the Pribilof Islands, Alaska, I assess how milk consumption, the timing of sampling, and the effects of growth and sample size influence the size of pups captured for weighing. Evidence is presented suggesting that pup mass may increase in a sigmoid fashion, with the most rapid rate of growth occurring when about two months old. This phenomenon can confound efforts to compare the masses of pups weighed on different days in different years, particularly if pups are weighed over the period of rapid growth. Variability in pup mass increases with time because growth rates of individuals vary and because the amount of milk pups consume increases with body size. Thus sample sizes must be increased as the pups grow older in order to detect statistically significant differences in mean body mass. There is also evidence that pups of different ages and sizes are not randomly distributed on the breeding beaches and are not randomly selected for weighing. It appears that the first pups captured for weighing are smaller and younger than subsequent captures, possibly because smaller pups are easier to handle and are segregated to the peripheral rookery regions where sampling begins. These hidden biases, related to sampling error and fur seal biology, must be considered and controlled for when weighing fur seal pups.     

Species-specific cell-matrix interactions are essential for differentiation of alveoli like structures and milk gene expression in primary mammary cells of the Cape fur seal (Arctocephalus pusillus pusillus).

Few models are in place for analysis of extreme lactation patterns such as that of the fur seals which are capable of extended down regulation of milk production in the absence of involution. During a 10-12 month lactation period, female fur seals suckle pups on shore for 2-3 days, and then undertake long foraging trips at sea for up to 28 days, resulting in the longest intersuckling bouts recorded. During this time the mammary gland down regulates milk production. We have induced Cape fur seal (Arctocephalus pusillus pusillus) mammary cells in vitro to form mammospheres up to 900 microm in diameter, larger than any of their mammalian counterparts. Mammosphere lumens were shown to form via apoptosis and cells comprising the cellular boundary stained vimentin positive. The Cape fur seal GAPDH gene was cloned and used in RT-PCR as a normalization tool to examine comparative expression of milk protein genes (alphaS2-casein, beta-lactoglobulin and lysozyme C) which were prolactin responsive. Cape fur seal mammary cells were found to be unique; they did not require Matrigel for rapid mammosphere formation and instead deposited their own matrix within 2 days of culture. When grown on Matrigel, cells exhibited branching/stellate morphogenesis highlighting the species-specific nature of cell-matrix interactions during morphological differentiation. Matrix produced in vitro by cells did not support formation of human breast cancer cell line, PMC42 mammospheres. This novel model system will help define the molecular pathways controlling the regulation of milk protein expression and species specific requirements of the extracellular matrix in the cape fur seal.     

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.     

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.     

EVALUATION OF AN EFFECTIVE METHOD TO ESTIMATE AGE OF CAPE FUR SEALS USING GROUND TOOTH SECTIONS

Teeth of known-age Cape fur seals Arctocephalus pusillus pusillus were used to validate age estimated from ground sections. In the canines, dentine growth layer groups (GLGs) reflected age accurately but no reliable readings could be obtained from GLGs in the cementum. Upper canines were the most suitable for age estimation. By contrast, in the postcanines where the cementum is thicker, only GLGs in the cementum could be used for age determination, but not with the same accuracy as for dentine in the canines. Therefore, it is recommended that GLGs in the dentine be used to determine age in the Cape fur seal. However, pulp cavities in canines closed at about 13 yr and consequently GLGs in the cementum of the postcanines should be used where the pulp cavities of canines are closed. Accurate estimation of age is not possible from the dentine of older animals.     

A new nonlinear model of age-dependent population growth

A new nonlinear age-structured population model is presented. Within its framework the occurence of time-persistent age distributions is possible, even if the population sizes are nonstationary. The age distribution as well as the moments of the generation index can be determined analytically. The proposed model is a nonlinear generalization of Lotka's theory of stable populations.     

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.     

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.     

Mitochondrial DNA structure and colony expansion dynamics of New Zealand fur seals (Arctocephalus forsteri) around Banks Peninsula

New Zealand fur seals are one of many pinniped species that survived the commercial sealing of the eighteenth and nineteenth centuries in dangerously low numbers. After the enforcement of a series of protection measures in the early twentieth century, New Zealand fur seals began to recover from the brink of extinction. We examined the New Zealand fur seal populations of Banks Peninsula, South Island, New Zealand using the mitochondrial DNA control region. We identified a panmictic population structure around Banks Peninsula. The most abundant haplotype in the area showed a slight significant aggregated structure. The Horseshoe Bay colony showed the least number of shared haplotypes with other colonies, suggesting a different origin of re-colonisation of this specific colony. The effective population size of the New Zealand fur seal population at Banks Peninsula was estimated at approximately 2500 individuals. The exponential population growth rate parameter for the area was 35, which corresponds to an expanding population. In general, samples from adjacent colonies shared 4.4 haplotypes while samples collected from colonies separated by between five and eight bays shared 1.9 haplotypes. The genetic data support the spill-over dynamics of colony expansion already suggested for this species. Approximate Bayesian computations analysis suggests re-colonisation of the area from two main clades identified across New Zealand with a most likely admixture coefficient of 0.41 to form the Banks Peninsula population. Approximate Bayesian computations analysis estimated a founder population size of approximately 372 breeding individuals for the area, which then rapidly increased in size with successive waves of external recruitment. The population of fur seals in the area is probably in the late phase of maturity in the colony expansion dynamic.     

Comparison of Helicobacter spp. genetic sequences in wild and captive seals, and gulls

Helicobacter species are widely distributed in the gastrointestinal system of humans and many animal taxa. Investigations of natural infections are essential to elucidating their role within the host. The feces of fur seals Arctocephalus pusillus doriferus and sea lions Neophoca cinerea from 3 separate captive populations, as well as a wild colony from Kangaroo Island, Australia, were examined for the occurrence of Helicobacter spp. The feces from several wild silver gulls Larus novahollandiae were also investigated. As detected by PCR, 18 of 21 samples from captive and 12 of 16 samples from wild seals were positive for Helicobacter spp. Three species were identified in these animals. Whilst one possibly novel type was identified from wild fur seals, the majority of wild and captive individuals had the same species. This species also occurred in more than 1 seal type and in silver gulls, and shared a 98.1 to 100% identity to other Helicobacter spp. from harp seals and sea otters. A similar sequence type to species identified from cetaceans was also detected in several captive seals. This study reports for the first time the presence of Helicobacter spp. in wild and captive seals and demonstrates the diversity and broad-host range of these organisms in the marine host.     

POPULATION ECOLOGY OF SEALS: RETROSPECTIVE and PROSPECTIVE VIEWS

This review focuses on population ecology, with critical accounts of past work and future possibilities in age determination, body growth and condition, estimating abundances, mortality rates and lifespans, reproduction, comparative life histories, population dynamics, population modelling and seals in ecosystems. We suggest ways to reduce errors in age determination and to improve methods of obtaining and presenting growth data. Generalized von Bertalanffy growth equations are promoted as a basis for analysing species differences and intra-population variation in body lengths. Indices other than blubber thickness may be better for following body condition. Catch-effort and survival-index methods of estimating abundances have limited applicability, total counts are only locally useful, and sample counts may only be accurate for scattered, ice-breeding species. Some new techniques for population indices are promising. Pre-adult mortality remains difficult to assess. Although not always recognized, adult mortality rates do increase with age, as well described by Gompertz functions. Existing estimates of lifespans are unreliable, and a new approach is outlined. There are methodological problems in estimating ages of maturity. Corpora albicantia should not be used for back-extrapolation, and more study is needed of use of teeth annuli as indicators of maturity. Age-specific proportions of females parous based on reproductive tracts may disagree with proportions recruited in breeding groups, suggesting that the former may often be in error. Allometric relationships among body sizes and life-history variables need more reliable data, especially since the residuals of such relationships are of greatest interest. Brain size may be a better scalar. Direct evidence of density dependence in population growth of seals is sparse. Early survival has been more widely shown to be density-dependent, but only among polygynous species where crowding on land may be a byproduct of sexual selection; there is as yet no good evidence of trophic restraints. Evidence of density dependence of ages of maturity is generally unconvincing. Predation, especially by sharks, may be critical in some species. Characteristics of equilibrium populations might profitably be sought in mass remains in middens and historic kill sites. More attention should be paid to the search for density-independent influences. Supposed impacts of fisheries and pollutions are not wholly convincing. Natural epidemics may keep some populations below resource or space saturation, and some high-latitude species may show large year-to-year variations in recruitment and abundances. Evidence for such density-independent effects should be sought in residuals of growth curves and in teeth layers. Although surplus yield and production/biomass models have been tried, realistic pinniped models must be completely age-structured and time-dependent. Simple models have questionably assumed stationarity to derive life-history parameters. The best available estimates of density dependence of such parameters give no resolution when extrapolated toward equilibrium, and only limited efforts have been made to introduce stochasticity. Better data, not improved model structures, are needed for better understanding. Recent work has contradicted the assumed voraciousness of seals, but their system impacts and dependencies are not well understood. Extended Lotka-Volterra equations used to model Antarctic food webs, including seals, are merely heuristic. Fixed seal biomasses enter as top-down, driving functions in a Bering Sea model, which accordingly cannot be used to analyse or manage their populations. Some Soviet models are tantalizing but ill-specified. The introduction of harbor seals in well-chosen lakes might give mote insights into system roles than would more elaborate modelling. We wonder if pinniped ecology is well served by too many enthusiasts operating under too many restraints.     

DENSITY DEPENDENCE IN NORTHERN FUR SEALS (CALLORHINUS URSINUS)

This paper summarizes, updates, and interprets information on density-dependent dynamics of populations of the northern fur seal ( Callorhinus ursinus ). Density-dependent changes observed in these populations have involved various aspects of growth (body length, body weight, tooth weight, and size of other skeletal parts, especially the skull), survival, age at maturation, incidence of disease, and time spent foraging. For the population of northern fur seals on St. Paul Island of the Pribilof Islands, which was observed during a major increase and during two significant declines, density-dependent changes that occurred during the growth of the population were reversed during the declines. The Robben Island population in the western Pacific declined after 1965, and the decline was accompanied by changes similar to those observed during the declines on the Pribilof Islands. Although data are not available for all age and sex classes, it appears that most or all components of the populations exhibit similar changes. The overall implication of these changes is that current populations on Robben Island and the Pribilof Islands are reduced to levels below what could be supported by the resources available in their environments. Density dependence for this species is consistent with that of other large mammals, specifically in that vital rates for fur seals ate related to density in a nonlinear fashion.     

A novel approach identified the FOLR1 gene, a putative regulator of milk protein synthesis

This study has utilised comparative functional genomics to exploit animal models with extreme adaptation to lactation to identify candidate genes that specifically regulate protein synthesis in the cow mammary gland. Increasing milk protein production is valuable to the dairy industry. The lactation strategies of both the Cape fur seal (Artocephalus pusillus pusillus) and the tammar wallaby (Macropus eugenii) include periods of high rates of milk protein synthesis during an established lactation and therefore offer unique models to target genes that specifically regulate milk protein synthesis. Global changes in mammary gene expression in the Cape fur seal, tammar wallaby, and the cow (Bos taurus) were assessed using microarray analysis. The folate receptor α (FOLR1) showed the greatest change in gene expression in all three species [cow 12.7-fold (n = 3), fur seal 15.4-fold (n = 1), tammar 2.4-fold (n = 4)] at periods of increased milk protein production. This compliments previous reports that folate is important for milk protein synthesis and suggests FOLR1 may be a key regulatory point of folate metabolism for milk protein synthesis within mammary epithelial cells (lactocytes). These data may have important implications for the dairy industry to develop strategies to increase milk protein production in cows. This study illustrates the potential of comparative genomics to target genes of interest to the scientific community.     

The Use of Surrogate Data in Demographic Population Viability Analysis: A Case Study of California Sea Lions

Reliable data necessary to parameterize population models are seldom available for imperiled species. As an alternative, data from populations of the same species or from ecologically similar species have been used to construct models. In this study, we evaluated the use of demographic data collected at one California sea lion colony (Los Islotes) to predict the population dynamics of the same species from two other colonies (San Jorge and Granito) in the Gulf of California, Mexico, for which demographic data are lacking. To do so, we developed a stochastic demographic age-structured matrix model and conducted a population viability analysis for each colony. For the Los Islotes colony we used site-specific pup, juvenile, and adult survival probabilities, as well as birth rates for older females. For the other colonies, we used site-specific pup and juvenile survival probabilities, but used surrogate data from Los Islotes for adult survival probabilities and birth rates. We assessed these models by comparing simulated retrospective population trajectories to observed population trends based on count data. The projected population trajectories approximated the observed trends when surrogate data were used for one colony but failed to match for a second colony. Our results indicate that species-specific and even region-specific surrogate data may lead to erroneous conservation decisions. These results highlight the importance of using population-specific demographic data in assessing extinction risk. When vital rates are not available and immediate management actions must be taken, in particular for imperiled species, we recommend the use of surrogate data only when the populations appear to have similar population trends.     

Vagrant elephant seal predation on Cape fur seal pups, Plettenberg Bay, South Africa

Vagrant southern elephant seals (Mirounga leonina) are occasionally sighted along the coast of South Africa and are known to feed primarily on fish and squid. Phocid seals are not known to predate on mammals making the events described here exceptional. This note describes the successful and failed attempts of a vagrant male southern elephant seal (M. leonina) to consume Cape fur seal (Arctocephalus pusillus pusillus) pups in Plettenberg Bay, South Africa. Observations were made by crew and passengers aboard a commercial whale-watching vessel during November 2012. This is the first account of elephant seals eating anything other than fish, squid and penguins and suggests considerable plasticity in prey choice dictated by environmental conditions.     

The effect of life-history and mode of inheritance on neutral genetic variability

Formulae for the effective population sizes of autosomal, X-linked, Y-linked and maternally transmitted loci in age-structured populations are developed. The approximations used here predict both asymptotic rates of increase in probabilities of identity, and equilibrium levels of neutral nucleotide site diversity under the infinite-sites model. The applications of the results to the interpretation of data on DNA sequence variation in Drosophila, plant, and human populations are discussed. It is concluded that sex differences in demographic parameters such as adult mortality rates generally have small effects on the relative effective population sizes of loci with different modes of inheritance, whereas differences between the sexes in variance in reproductive success can have major effects, either increasing or reducing the effective population size for X-linked loci relative to autosomal or Y-linked loci. These effects need to be accounted for when trying to understand data on patterns of sequence variation for genes with different transmission modes.     

Key fish species, northern fur seals, Callorhinus ursinus, and fisheries interactions involving walleye pollock, Theragra chalcogramma, in the eastern Bering Sea

The recent decline of the northern fur seal population breeding on the Pribilof Islands has not yet been explained. This study estimates the amounts and sizes of walleye pollock (the fur seal's main prey) removed by predatory fish, fur seals and commercial fisheries in the main fur seal feeding area in the eastern Bering Sea during summer 1985. Fur seals relied primarily on age-1 pollock during 1985, while predatory fish consumed pollock mainly of ages 0-1. The fishery took pollock older than age-3. This indicated no direct effect of fishery removal on fur seal prey abundance, at least during the study period. In the short term, the 1985 pollock fishery may have indirectly affected fur seal prey abundance in a positive manner by removing adult pollock that compete with fur seals for age-1 pollock.     

The intrapopulation structure of the northern fur seal (<Emphasis Type="Italic">Callorhinus ursinus</Emphasis> L.) on Tyuleniy Island during the post-depression years (1993–2009)

The dynamics of the intrapopulation parameters of the northern fur seal on Tyuleniy Island are considered for the period when their population was recovering after a depression. Almost all its characteristics, except for those dependent on density, showed a positive tendency. Dynamic processes in the northern fur seal populations in the post-depression years are found to be based on the demographic transformation of the community, which closely correlates with its qualitative changes, predetermined by the dynamics of its age structure. The process of complete reversal in the state of the fur seal population, which is distinguished by peak values at the depression and in the years of prosperity, is approximately equal to the life span of one generation of these animals.