Risk factors for an outbreak of leptospirosis in California sea lions (Zalophus californianus) in California, 2004

Leptospirosis has been reported in California sea lions (Zalophus californianus) since 1970; however, the source of infection and mode of transmission remain unknown. To elucidate these features, demographic and environmental risk factors for leptospirosis were evaluated. California sea lion stranding records from northern California for 2004 were used to identify cases of leptospirosis (n = 316) and controls (n = 143). Demographic characteristics (age class, sex) and environmental factors, representing surrogates for exposure to dogs, cattle, rainfall, and freshwater sources, were compared between cases and controls with the use of a geographic information system (GIS) and logistic regression. Multivariate analyses revealed that summer and autumn seasons, juvenile age class, male sex, high dog-park density, and close proximity to dog parks were significantly associated with leptospirosis in sea lions, whereas county farmland cattle density, rainfall levels 30 days prior to stranding, human density, and proximity to freshwater sources were not associated. Thus, dogs and dog parks, or factors associated with them, might be further investigated to assess their relationship to leptospirosis in sea lions.     

Lifetime coastal and oceanic foraging patterns of male Guadalupe fur seals and California sea lions

Carcasses of adult and subadult male Guadalupe fur seals (GFSs) are beached on Isla Magdalena, representing about 73% of all GFSs beachings since 2003. Analysis of carbon and nitrogen stable isotopes in dentin collagen from male GFSs was used in an attempt to distinguish animals from two possible locations of origin: the oceanic Guadalupe Island (GI) and the coastal San Benito Islands (SBI). Samples of conterminous and contemporary California sea lions (CSLs) were included as representative of coastal predators. Two distinct groups of GFSs were evident based on δ¹³C values: coastal GFSs with higher δ¹³C values than CSLs, and oceanic GFSs with lower δ¹³C values than CSLs. Significant temporal trends were observed in the δ¹⁵N values; values for oceanic GFSs and CSLs increased annually (0.082‰ and 0.089‰, respectively), while those for coastal GFS decreased annually by 0.183‰. The isotopic segregation of oceanic and coastal GFS males, presumably from GI and SBI respectively, has been present at least since the mid-1990s. This segregation may be due to dissimilar ingestion of prey from oceanic vs. coastal origin prior to their seasonal co-occurrence in the Gulf of Ulloa.     

Epizootic vesicular disease in captive California sea lions

An epizootic of vesicular disease occurred in a group of semi-domesticated California sea lions (Zalophus californianus) during the months of April and May 1997. Ten castrated mature male sea lions, ages 12 to 19 yr, were housed in three adjacent open-ocean net enclosures in San Diego Bay (California, USA). Four animals (40%) developed oral and extremity vesicles, anorexia, and were reluctant to perform learned behaviors. One animal developed vesicles but maintained a normal appetite and behavior. The remaining animals showed no clinical signs of infection. Virus (designated FADDL 7005) was isolated from four of the five animals that developed vesicles. Serum antibody titers to FADDL 7005, a previously untyped calicivirus, were demonstrated in animals that showed any combination of clinical signs and in two animals that did not show any clinical signs. No virus was isolated from five fecal samples collected from four of the group animals. Clinical signs lasted 4 to 20 days in affected animals. All affected animals recovered from infection. An experimental swine was inoculated with FADDL 7005 and developed vesicular disease, which was transmitted to another experimental swine upon contact. It is proposed that FADDL 7005 is a new San Miguel sea lion virus.     

First evidence for adoption in California sea lions

Demographic parameters such as birth and death rates determine the persistence of populations. Understanding the mechanisms that influence these rates is essential to developing effective management strategies. Alloparental behavior, or the care of non-filial young, has been documented in many species and has been shown to influence offspring survival. However, the role of alloparental behavior in maintaining population viability has not been previously studied. Here, we provide the first evidence for adoption in California sea lions and show that adoption potentially works to maintain a high survival rate of young and may ultimately contribute to population persistence. Alloparental behavior should have a positive effect on the population growth rate when the sum of the effects on fitness for the alloparent and beneficiary is positive.     

Isolation of a novel adenovirus from California sea lions Zalophus californianus

Viral hepatitis associated with adenoviral infection has been reported in California sea lions Zalophus californianus admitted to rehabilitation centers along the California coast since the 1970s. Canine adenovirus 1 (CAdV-1) causes viral hepatitis in dogs and infects a number of wildlife species. Attempts to isolate the virus from previous sea lion hepatitis cases were unsuccessful, but as the hepatitis had morphologic features resembling canine infectious hepatitis, and since the virus has a wide host range, it was thought that perhaps the etiologic agent was CAdV-1. Here, we identify a novel adenovirus in 2 stranded California sea lions and associate the infection with viral hepatitis and endothelial cell infection. Phylogenetic analysis confirmed the classification of the sea lion adenovirus in the Mastadenovirus genus with the most similarity to tree shrew adenovirus 1 (TSAdV-1, 77%). However, as the sea lion adenovirus appeared to be equally distant from the other Mastadenovirus species based on phylogenetic analysis, results indicate that it represents an independent lineage and species. Although sequences from this novel virus, otarine adenovirus 1 (OtAdV-1), show some similarity to CAdV-1 and 2, it is clearly distinct and likely the cause of the viral hepatitis in the stranded California sea lions.     

The fecal viral flora of California sea lions

California sea lions are one of the major marine mammal species along the Pacific coast of North America. Sea lions are susceptible to a wide variety of viruses, some of which can be transmitted to or from terrestrial mammals. Using an unbiased viral metagenomic approach, we surveyed the fecal virome in California sea lions of different ages and health statuses. Averages of 1.6 and 2.5 distinct mammalian viral species were shed by pups and juvenile sea lions, respectively. Previously undescribed mammalian viruses from four RNA virus families (Astroviridae, Picornaviridae, Caliciviridae, and Reoviridae) and one DNA virus family (Parvoviridae) were characterized. The first complete or partial genomes of sapeloviruses, sapoviruses, noroviruses, and bocavirus in marine mammals are reported. Astroviruses and bocaviruses showed the highest prevalence and abundance in California sea lion feces. The diversity of bacteriophages was higher in unweaned sea lion pups than in juveniles and animals in rehabilitation, where the phage community consisted largely of phages related to the family Microviridae. This study increases our understanding of the viral diversity in marine mammals, highlights the high rate of enteric viral infections in these highly social carnivores, and may be used as a baseline viral survey for comparison with samples from California sea lions during unexplained disease outbreaks.     

Diet estimation in California sea lions,Zalophus californianus

We performed a captive feeding experiment using California sea lions to assess biases associated with estimating pinniped diet using scats and spews. Sea lions were fed nine of their natural prey species: anchovy, sardine, Pacific mackerel, jack mackerel, hake, steelhead smolts, shortbelly rockfish, pink salmon, and market squid. Recovery percentages varied among prey species using otoliths and were improved for adult salmon and sardine using the all‐structure method. Numerical and graded length correction factors provided better estimates of number and size of prey consumed. Four models used to determine the proportions of prey species consumed by a sea lion population were tested. The all‐structure method and variable biomass reconstruction model, in conjunction with numerical and graded length correction factors, provided more accurate estimates than without. We provide numerical correction factors for all prey species, including correction factors for specific salmon bones: vertebrae, branchials, radials, teeth, gill rakers, and hypurals.     

Control of pulmonary surfactant secretion in adult California sea lions

Marine mammals have a spectacular suite of respiratory adaptations to deal with the extreme pressures associated with deep diving. In particular, maintaining a functional pulmonary surfactant system at depth is critical for marine mammals to ensure that inspiration is possible upon re-emergence. Pulmonary surfactant is secreted from alveolar type II (ATII) cells and is crucial for normal lung function. It is not known whether ATII cells have the ability to continue to secrete pulmonary surfactant under pressure, or how secretion is maintained and controlled. We show here that surfactant secretion in California sea lions (Zalophus californianus) was increased after high pressures (25 and 50 atm) of short duration (30 min), but was unaffected by high pressures of long duration (2 h). This is in contrast to a similar sized terrestrial mammal (sheep), where surfactant secretion was increased after high pressures of both long and short duration. Z. californianus and terrestrial mammals also show similar responses to stimulatory hormones and autonomic neurotransmitters. It therefore seems that an increase in the quantity of surfactant in seal lungs after diving is most likely caused by mechanostimulation induced by pressure and volume changes, and that seals are adapted to maintain constant levels of surfactant under long periods of high pressure.     

The development of the pulmonary surfactant system in California sea lions

Pulmonary surfactant has previously been shown to change during development, both in composition and function. Adult pinnipeds, unlike adult terrestrial mammals, have an altered lung physiology to cope with the high pressures associated with deep diving. Here, we investigated how surfactant composition and function develop in California sea lions (Zalophus californianus). Phosphatidylinositol was the major anionic phospholipid in the newborn, whereas phosphatidylglycerol was increased in the adult. This increase in phosphatidylglycerol occurred at the expense of phosphatidylinositol and phosphatidylserine. There was a shift from long chain and polyunsaturated phospholipid molecular species in the newborn to shorter chain and mono- and disaturated molecular species in the adult. Cholesterol and SP-B concentrations were also higher in the adult. Adult surfactant could reach a lower equilibrium surface tension, but newborn surfactant could reach a lower minimum surface tension. The composition and function of surfactant from newborn California sea lions suggest that this age group is similar to terrestrial newborn mammals, whereas the adult has a "diving mammal" surfactant that can aid the lung during deep dives. The onset of diving is probably a trigger for surfactant development in these animals.     

Rapid behavioural diagnosis of domoic acid toxicosis in California sea lions

Domoic acid is a neurotoxic metabolite of widely occurring algal blooms that has caused multiple marine animal stranding events. Exposure to high doses of domoic acid, a glutamate agonist, may lead to persistent medial temporal seizures and damage to the hippocampus. California sea lions (Zalophus californianus) are among the most visible and frequent mammalian victims of domoic acid poisoning, but rapid, reliable diagnosis in a clinical setting has proved difficult owing to the fast clearance of the toxin from the blood stream. Here, we show that the behavioural orienting responses of stranded sea lions diagnosed with domoic acid toxicosis habituate more slowly to a series of non-aversive auditory stimuli than do those of sea lions with no apparent neurological deficits. A signal detection analysis based on these habituation measures was able to correctly identify 50 per cent of subjects with domoic acid toxicosis while correctly rejecting approximately 93 per cent of controls, suggesting potential diagnostic merit.     

Effects of inhalational anesthesia on blood gases and pH in California sea lions

Despite the widespread use of inhalational anesthesia with spontaneous ventilation in many studies of otariid pinnipeds, the effects and risks of anesthetic‐induced respiratory depression on blood gas and pH regulation are unknown in these animals. During such anesthesia in California sea lions (Zalophus californianus), blood gas and pH analyses of opportunistic blood samples revealed routine hypercarbia (highest P_CO2 = 128 mm Hg [17.1 kPa]), but adequate arterial oxygenation (P_O2 > 100 mm Hg [13.3 kPa] on 100% inspiratory oxygen). Respiratory acidosis (lowest pH = 7.05) was limited by the increased buffering capacity of sea lion blood. A markedly widened alveolar‐to‐arterial P_O2 difference was indicative of atelectasis and ventilation‐perfusion mismatch in the lung secondary to hypoventilation during anesthesia. Despite the generally safe track record of this anesthetic regimen in the past, these findings demonstrate the value of high inspiratory O₂ concentrations and the necessity of constant vigilance and caution. In order to avoid hypoxemia, we emphasize the importance of late extubation or at least maintenance of mask ventilation on O₂ until anesthetic‐induced respiratory depression is resolved. In this regard, whether for planned or emergency application, we also describe a simple, easily employed intubation technique with the Casper “zalophoscope” for sea lions.     

Seroepidemiology of parapoxvirus infections in captive and free-ranging California sea lions Zalophus californianus

Cutaneous nodular lesions caused by parapoxvirus infections are commonly observed in stranded pinnipeds following their arrival at rehabilitation facilities. An indirect enzyme-linked immunosorbent assay (ELISA) was developed and validated to determine exposure to parapoxviruses in California sea lions Zalophus californianus in captivity and in the wild. The diagnostic performance of this assay was evaluated using receiver-operating characteristic analysis. At a selected cut-off value, the calculated sensitivity was 100% (95% CI = 86 to 100%) and the specificity was 100% (95% CI = 87 to 100%). Analysis of sera collected from 26 affected sea lions during various stages of the disease revealed anti-parapoxvirus antibodies in all affected sea lions prior to the development of cutaneous pox lesions. This indicated that previous exposure to a parapoxvirus does not confer protection against clinical disease. In at least 7 cases, exposure to the virus occurred during hospitalization. Analysis of paired sera from 74 unaffected sea lions indicated subclinical infections in at least 3 animals. Finally, the prevalence of anti-parapoxviral antibodies in 761 free-ranging California sea lions captured and tested was 91% (95% CI = 89 to 93%). This indicated that infection with a parapoxvirus is a common occurrence in the wild and that the release of captive sea lions infected with parapoxvirus into the wild should not increase the risk of a parapoxvirus outbreak in free-ranging sea lions.     

Specialized foraging habits of adult female California sea lions Zalophus californianus

Individual foraging specialization occurs when organisms use a small subset of the resources available to a population. This plays an important role in population dynamics since individuals may have different ecological functions within an ecosystem related to habitat use and prey preferences. The foraging habitat fidelity and degree of specialization of California sea lions (Zalophus californianus) were evaluated by analyzing the stable isotopes values of carbon and nitrogen in vibrissae collected from 16 adult females from the reproductive colony on Santa Margarita Island, Magdalena Bay, Mexico, in 2012 and 2013. Based on the degree of individual specialization in δ¹⁵N, 62.5% of the females assessed can be considered specialist consumers focusing on the same prey or different prey from the same trophic level. The degree of individual specialization in δ¹³C indicated that 100% of the individuals showed fidelity to their foraging habitat as some fed in the lagoon, others foraged along the coast, and a third group preferred prey from the pelagic environment during both the breeding and nonbreeding seasons, suggesting diversification of foraging areas. Foraging area fidelity persisted despite the 2°C increase in the sea surface temperature over the course of the study period.     

Weak polygyny in California sea lions and the potential for alternative mating tactics

Female aggregation and male territoriality are considered to be hallmarks of polygynous mating systems. The development of genetic parentage assignment has called into question the accuracy of behavioral traits in predicting true mating systems. In this study we use 14 microsatellite markers to explore the mating system of one of the most behaviorally polygynous species, the California sea lion (Zalophus californianus). We sampled a total of 158 female-pup pairs and 99 territorial males across two breeding rookeries (San Jorge and Los Islotes) in the Gulf of California, Mexico. Fathers could be identified for 30% of pups sampled at San Jorge across three breeding seasons and 15% of sampled pups at Los Islotes across two breeding seasons. Analysis of paternal relatedness between the pups for which no fathers were identified (sampled over four breeding seasons at San Jorge and two at Los Islotes) revealed that few pups were likely to share a father. Thirty-one percent of the sampled males on San Jorge and 15% of the sampled males on Los Islotes were assigned at least one paternity. With one exception, no male was identified as the father of more than two pups. Furthermore, at Los Islotes rookery there were significantly fewer pups assigned paternity than expected given the pool of sampled males (p<0.0001). Overall, we found considerably lower variation in male reproductive success than expected in a species that exhibits behavior associated with strongly polygynous mating. Low variation in male reproductive success may result from heightened mobility among receptive females in the Gulf of California, which reduces the ability of males to monopolize groups of females. Our results raise important questions regarding the adaptive role of territoriality and the potential for alternative mating tactics in this species.     

First findings of Cryptosporidium and Giardia in California sea lions (Zalophus californianus)

We report the detection and identification of Cryptosporidium and Giardia from 1 of 3 species of pinnipeds. Fecal samples were collected from Pacific harbor seal (Phoca vitulina richardsi), northern elephant seal (Mirounga angustirostris), and California sea lion (Zalophus californianus) in the northern California coastal area. By means of fluorescently labeled monoclonal antibodies, Cryptosporidium oocysts were detected in 3 samples from California sea lions, 1 of which also contained Giardia cysts. Oocysts of Cryptosporidium and cysts of Giardia were morphologically indistinguishable from oocysts of C. parvum and cysts of G. duodenalis from other animal origins. Oocysts and cysts were then purified using immunomagnetic separation techniques and identified by polymerase chain reaction (PCR), from which species-specific products were obtained. Sequence analysis revealed that the 452-bp and 358-bp PCR products of Cryptosporidium isolated from California sea lion had identities of 98% with sequences of their template fragments of C. parvum obtained from infected calves. Based on morphological, immunological, and genetic characterization, the isolates were identified as C. parvum and G. duodenalis, respectively. The findings suggested that California sea lions could serve as reservoirs in the environmental transmission of Cryptosporidium and Giardia.     

Monitoring glucocorticoid response to rehabilitation and research procedures in California and Steller sea lions

We used serum and fecal corticosteroid analysis to study the physiological response to a range of invasive and non-invasive procedures in sea lions. Four experimental groups of California sea lions (Zalophus californianus; Group A: restraint only [n=9], Group B: gas anesthesia without surgery [n=10], Group C: minimally invasive surgery [n=10], and Group D: invasive surgery [n=5]) were monitored for adrenal response. Feces were collected opportunistically from 72 hr before 72 hr post procedure for corticosterone analysis. All experimental groups showed substantial individual variation and no significant change in corticosterone levels after the procedures. Additional fecal and serum corticoid samples were collected from six free-ranging Steller sea lions (Eumetopias jubatus) in temporary captivity undergoing abdominal implantation of long-term telemetry devices. Only one sea lion exhibited a significant fecal corticosterone increase in response to the surgery. Capture and restraint appear to elicit a greater glucocorticoid response than invasive or non-invasive procedures. J. Exp. Zool. 309A:73-82, 2008. (c) 2008 Wiley-Liss, Inc.