Denise J. Greig

Inbreeding: Disease susceptibility in California sea lions

Inbreeding in animals can increase their susceptibility to pathogens, but direct evidence from wild populations is scarce and it is unclear whether all pathogens are affected equally. Here we analyse rescued California sea lions afflicted with a range of different pathogens, and find that sick animals have higher-than-normal parental relatedness, with the extent varying among disease classes. Our findings indicate that mortality in natural populations may not be entirely random and that inbred individuals could act as more effective reservoirs of infectious agents.

Brominated and chlorinated flame retardants in San Francisco Bay sediments and wildlife

Restrictions on the use of polybrominated diphenyl ethers (PBDEs) have resulted in the use of alternative flame retardants in consumer products to comply with flammability standards. In contrast to PBDEs, information on the occurrence and fate of these alternative compounds in the environment is limited, particularly in the United States. In this study, a survey of flame retardants in San Francisco Bay was conducted to evaluate whether PBDE replacement chemicals and other current use flame retardants were accumulating in the Bay food web. In addition to PBDEs, brominated and chlorinated flame retardants (hexabromocyclododecane (HBCD) and Dechlorane Plus (DP)) were detected in Bay sediments and wildlife. Median concentrations of PBDEs, HBCD, and DP, respectively, were 4.3, 0.3, and 0.2 ng g⁻¹ dry weight (dw) in sediments; 1670, <6.0, and 0.5 ng g⁻¹ lipid weight (lw) in white croaker (Genyonemus lineatus); 1860, 6.5, and 1.3 ng g⁻¹ lw in shiner surfperch (Cymatogaster aggregata); 5500, 37.4, and 0.9 ng g⁻¹ lw in eggs of double-crested cormorant (Phalacrocorax auritus); 770, 7.1, and 0.9 ng g⁻¹ lw in harbor seal (Phoca vitulina) adults; and 330, 3.5, and <0.1 ng g⁻¹ lw in harbor seal (P. vitulina) pups. Two additional flame retardants, pentabromoethylbenzene (PBEB) and 1,2-bis(2,4,6 tribromophenoxy)ethane (BTBPE) were detected in sediments but with less frequency and at lower concentrations (median concentrations of 0.01 and 0.02 ng g⁻¹ dw, respectively) compared to the other flame retardants. PBEB was also detected in each of the adult harbor seals and in 83% of the pups (median concentrations 0.2 and 0.07 ng g⁻¹ lw, respectively). The flame retardants hexabromobenzene (HBB), decabromodiphenyl ethane (DBDPE), bis(2-ethylhexyl) tetrabromophthalate (TBPH), and 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB), were not detected in sediments and BTBPE, HBB and TBB were not detected in wildlife samples. Elevated concentrations of some flame retardants were likely associated with urbanization and Bay hydrodynamics. Compared to other locations, concentrations of PBDEs in Bay wildlife were comparable or higher, while concentrations of the alternatives were generally lower. This study is the first to determine concentrations of PBDE replacement products and other flame retardants in San Francisco Bay, providing some of the first data on the food web occurrence of these flame retardants in a North American urbanized estuary.

A Decade of Live California Sea Lion (Zalophus californianus) Strandings Along the Central California Coast: Causes and Trends, 1991-2000

Stranded marine mammals offer a unique sample of relatively inaccessible wild animals that are more likely to represent the diseased segment of the population and are easy to examine thoroughly. Examination of these animals, therefore, offers a method to detect novel diseases in free-living aquatic mammals. Diseases in marine mammals may reflect environmental changes such as ocean pollution, prey shifts, and global warming. To detect spatial and temporal trends in prevalence of such diseases, we reviewed records for 3,707 California sea lions (Zalophus californianus) that stranded live between 1991 and 2000 along the central California coast. Reasons for stranding were determined from a combination of clinical examinations, hematology and serum biochemistry, radiography, gross necropsy, histopathology, microbiology, and biotoxin assays. Over the ten years, 74% of sea lions stranded in Santa Cruz, Monterey and San Luis Obispo Counties, and 83% of these were admitted between May and October each year. Malnutrition was the most common reason for stranding (32%), followed by leptospirosis (27%), trauma (18%), domoic acid intoxication (9%), and cancer (3%). Strandings caused by malnutrition were greatest during the El Nino events of 1992, 1993, and 1998, while strandings caused by leptospirosis accounted for over 60% of strandings in 1991, 1995, and 1999. Although domoic acid was first reported in California sea lions in 1998, there was a small stranding event in 1992 that, based on clinical examinations and histopathology, was probably also caused by domoic acid. The observed prevalence of cancer among stranded animals remained constant over the past ten years at 3%.

Transplacental transfer of organochlorines in california sea lions (Zalophus californianus)

The transplacental transfer of organochlorines (OCs) in California sea lions (Zalophus californianus) was investigated by analyzing blubber samples from 20 female sea lions and their fetuses during the last trimester of pregnancy. A rapid, high-performance liquid chromatographic, photodiode-array method was used to measure blubber concentrations of polychlorinated biphenyls (PCBs), including dioxin-like congeners, as well as DDTs and hexachlorobenzene. Summed values of PCBs (sigmaPCBs), of DDTs (sigmaDDTs), and of PCB toxic equivalents (sigmaPCB TEQs) were calculated from these data. The ratios of mean blubber concentrations of fetal sigmaPCBs to maternal blubber concentrations of sigmaPCBs were 0.45 by wet weight and 0.97 by lipid weight, but these ratios varied widely among mother-fetus pairs. Mean ratios of fetal sigmaDDTs to maternal sigmaDDTs were 0.53 by wet weight and 1.12 by lipid weight. Fetuses were classified into two age groups, based on date of recovery, to examine differences in OC transfer because of gestational age. Fetal to maternal ratios for individual PCB congeners, DDT compounds, and sigmaPCBs, sigmaDDTs, and sigmaPCB TEQs were lower among premature compared with late-term fetuses. These ratios increased for both groups as the logarithmic n-octanol/water partition coefficient (log Kow) for each compound decreased. Linear predictions for sigmaPCB and sigmaDDT concentrations in fetal blubber could be obtained using the sigmaPCB and sigmaDDT concentrations in maternal blubber, maternal and fetal blubber lipid content, maternal mass, and maternal age. Fetal TEQ was explained by maternal TEQ and maternal age. The ability to predict contaminant concentrations in fetal blubber from maternal parameters is important for developing risk assessment models for marine mammals.

Causes of Live Strandings of Northern Elephant Seals ( Mirounga angustirostris ) and Pacific Harbor Seals ( Phoca vitulina ) Along the Central California Coast, 1992-2001

Between January 1992 and December 2001 a total of 1,277 northern elephant seals (Mirounga angustirostris) and 940 Pacific harbor seals (Phoca vitulina) were stranded live along the central California coast. By examining medical records for each of the stranded seals, the primary cause of stranding and the secondary factors contributing to stranding were determined. The majority (88.3%) of animals were young born that year. The most common causes of live strandings for elephant seals included malnutrition (56.6%), Otostrongylus circumlitus infection (12.1%), and northern elephant seal skin disease (9.8%). The most common causes of strandings for harbor seals were malnutrition (51.8%), respiratory disease (9.6%), and trauma (8.0%). Common secondary factors for strandings for both elephant and harbor seals included human interaction, trauma, and ocular disease. For both species of phocid, the highest prevalence of O. circumlitus infection occurred in 1992 and 1993, years of a moderate El Niño-Southern Oscillation event. Phocine herpesvirus-1 infection was a common primary and secondary factor in harbor seal strandings, and the highest prevalence occurred between 1994 and 1998. Human interference in stranding events increased in the past ten years and is most commonly reported on beaches near heavily populated areas.

Metagenomic identification of a novel anellovirus in Pacific harbor seal (Phoca vitulina richardsii) lung samples and its detection in samples from multiple years.

To investigate viral pathogens potentially involved in a mortality event of 21 Pacific harbor seals (Phoca vitulina richardsii) in California in 2000, viral metagenomics was performed directly on lung samples from five individuals. Metagenomics revealed a novel seal anellovirus (SealAV), which clusters phylogenetically with anelloviruses from California sea lions and domestic cats. Using specific PCR, SealAV was identified in lung tissue from two of five animals involved in the 2000 mortality event, as well as one of 20 harbor seal samples examined post-mortem in 2008. The identification of SealAV in multiple years demonstrates that this virus is persistent in the harbor seal population. SealAV is the second anellovirus reported in the lungs of pinnipeds, suggesting that anellovirus infections may be common amongst marine mammals and that more research is needed to understand the roles of these viruses in marine mammal health and disease.

Cyclical changes in seroprevalence of leptospirosis in California sea lions: endemic and epidemic disease in one host species?

BackgroundLeptospirosis is a zoonotic disease infecting a broad range of mammalian hosts, and is re-emerging globally. California sea lions (Zalophus californianus) have experienced recurrent outbreaks of leptospirosis since 1970, but it is unknown whether the pathogen persists in the sea lion population or is introduced repeatedly from external reservoirs.MethodsWe analyzed serum samples collected over an 11-year period from 1344 California sea lions that stranded alive on the California coast, using the microscopic agglutination test (MAT) for antibodies to Leptospira interrogans serovar Pomona. We evaluated seroprevalence among yearlings as a measure of incidence in the population, and characterized antibody persistence times based on temporal changes in the distribution of titer scores. We conducted multinomial logistic regression to determine individual risk factors for seropositivity with high and low titers.ResultsThe serosurvey revealed cyclical patterns in seroprevalence to L. interrogans serovar Pomona, with 4–5 year periodicity and peak seroprevalence above 50%. Seroprevalence in yearling sea lions was an accurate index of exposure among all age classses, and indicated on-going exposure to leptospires in non-outbreak years. Analysis of titer decay rates showed that some individuals probably maintain high titers for more than a year following exposure.ConclusionThis study presents results of an unprecedented long-term serosurveillance program in marine mammals. Our results suggest that leptospirosis is endemic in California sea lions, but also causes periodic epidemics of acute disease. The findings call into question the classical dichotomy between maintenance hosts of leptospirosis, which experience chronic but largely asymptomatic infections, and accidental hosts, which suffer acute illness or death as a result of disease spillover from reservoir species.

Pandemic H1N1 Influenza Isolated from Free-Ranging Northern Elephant Seals in 2010 off the Central California Coast

Interspecies transmission of influenza A is an important factor in the evolution and ecology of influenza viruses. Marine mammals are in contact with a number of influenza reservoirs, including aquatic birds and humans, and this may facilitate transmission among avian and mammalian hosts. Virus isolation, whole genome sequencing, and hemagluttination inhibition assay confirmed that exposure to pandemic H1N1 influenza virus occurred among free-ranging Northern Elephant Seals (Mirounga angustirostris) in 2010. Nasal swabs were collected from 42 adult female seals in April 2010, just after the animals had returned to the central California coast from their short post-breeding migration in the northeast Pacific. Swabs from two seals tested positive by RT-PCR for the matrix gene, and virus was isolated from each by inoculation into embryonic chicken eggs. Whole genome sequencing revealed greater than 99% homology with A/California/04/2009 (H1N1) that emerged in humans from swine in 2009. Analysis of more than 300 serum samples showed that samples collected early in 2010 (n = 100) were negative and by April animals began to test positive for antibodies against the pH1N1 virus (HI titer of ≥1∶40), supporting the molecular findings. In vitro characterizations studies revealed that viral replication was indistinguishable from that of reference strains of pH1N1 in canine kidney cells, but replication was inefficient in human epithelial respiratory cells, indicating these isolates may be elephant seal adapted viruses. Thus findings confirmed that exposure to pandemic H1N1 that was circulating in people in 2009 occurred among free-ranging Northern Elephant Seals in 2010 off the central California coast. This is the first report of pH1N1 (A/Elephant seal/California/1/2010) in any marine mammal and provides evidence for cross species transmission of influenza viruses in free-ranging wildlife and movement of influenza viruses between humans and wildlife.

HEMATOLOGY AND SERUM CHEMISTRY IN STRANDED AND WILD-CAUGHT HARBOR SEALS IN CENTRAL CALIFORNIA: REFERENCE INTERVALS, PREDICTORS OF SURVIVAL, AND PARAMETERS AFFECTING BLOOD VARIABLES

Blood was collected from stranded harbor seal (Phoca vitulina) pups at admission (n=64) and release (n=45) from rehabilitation in 2007 and 2008 and from wild-caught harbor seal pups, subadults, and adults (n=110) in 2004, 2007, and 2008. Blood values measured at the time of admission were not predictive of survival during rehabilitation. Mass was associated with survival until release, and all pups that died weighed less than 10 kg at the time of admission. Do ¨hle bodies were observed in leukocytes from 15% to 22% of the pups in rehabilitation, but not in the wild pups. Thresholds (95% confidence intervals) among wild pups were less than those in the released pups for leukocytes, neutrophils, total cholesterol, alanine aminotransferase (ALT), glucose, phosphorus, sodium, potassium, total protein, albumin, and globulin; thresholds were greater in wild pups than in released pups for hemoglobin (HGB), hematocrit (HCT), and glucose. Thresholds among released pups were less than those in wild pups for HGB, HCT, mean cell volume, chloride, and creatine kinase; thresholds among released pups were greater than those in wild pups for neutrophils, platelets, total cholesterol, triglycerides, ALT, aspartate aminotrans-ferase, sorbitol dehydrogenase, bilirubin, phosphorus, potassium, total protein, and albumin. Age, girth, and geographic location affected the blood variables from wild-caught pups; age class, geographic location, sex, and body condition affected the blood variables of wild-caught, subadult and adult harbor seals.

SEASONAL CHANGES IN CIRCULATING PROGESTERONE AND ESTROGEN CONCENTRATIONS IN THE CALIFORNIA SEA LION (ZALOPHUS CALIFORNIANUS)

Abstract The measurement of circulating reproductive hormone levels provides a relatively noninvasive method for assessing reproductive status. We assessed seasonal changes in concentrations of progesterone and total estrogens from serum samples collected from live stranded (n = 199) and captive (n = 5) California sea lions (Zalophus californianus). Progesterone concentrations increased in the fall (September–November) in both pregnant and nonpregnant animals, with no significant difference associated with pregnancy. Progesterone concentrations were greater in pregnant animals in the spring (February–April) than in nonpregnant animals. Circulating estrogen concentrations in captive, nonpregnant sea lions increased in July and November, correlating with periods of estrus and implantation. These data provide a baseline for studying reproduction in California sea lions.