California Sea Lion Pups Research Articles

Trace metal concentrations in California sea lions from rookeries exposed to different levels of coastal urbanization in Baja California, Mexico.

Concentrations of total mercury, total selenium, and cadmium ([THg], [TSe], [Cd]) were determined in hair of California sea lion (Zalophus californianus) pups from four islands of the Gulf of California and the Baja California Pacific coast (NG, CG, NP, and CP) to identify geographical differences and the effect of Se against Hg toxicity (TSe:THg molar ratio). THg displayed a strong north-south trend for both ecoregions, while TSe presented a significantly high concentration only for CG. TSe:THg molar ratios decreased when [THg] increased, with the lowest ratios presenting in NG pups, in which [THg] exceeded toxicological thresholds of concern. [Cd] presented similar values at all study sites except CG, which presented the lowest level. The present study shows that proximity to urbanized coastal areas has a strong influence on [THg] in pups, while [TSe] and [Cd] are probably more related to the physiological requirements of the species, and environmental conditions.

ISOLATION, CHARACTERIZATION, AND ANTIMICROBIAL SUSCEPTIBILITY OF BACTERIA ISOLATED FROM SEA LION (ZALOPHUS CALIFORNIANUS) PUPS IN NORTHWESTERN MEXICO.

Bacterial infections have been documented in marine mammals for decades, and some are considered emerging pathogens with zoonotic potential. The aerobic oral (n=16) and rectal (n=17) bacterial microbiota and their antimicrobial resistance were characterized for 17 apparently healthy California sea lion pups (Zalophus californianus) captured with a hoop net in Farallon Island, Sinaloa, Mexico, in 2016. Bacteriologic cultures, Analytical Profile Index, and PCR were used to identify bacterial species. The Escherichia coli phylogenetic groups were identified by PCR, Salmonella serotypes were identified, and resistance to antibiotics was evaluated. Overall, 39 bacterial species were isolated, including E. coli and Salmonella spp. (35.9% each) and Pseudomonas aeruginosa (28.2%). For E. coli, UNKNOWN phylogroup was the most prevalent (57.7%), followed by the A phylogroup (37.1%). Most Salmonella serotypes were identified as Newport (92.8%); serotype Saintpaul was also identified (7.2%). Sea lions with bacterial co-colonization included 24.2%, from which two bacterial species were isolated, and 3% with three species. Overall, 59% of bacteria were resistant to at least one antibiotic tested, and 25.6% were extensively drug resistant. Bacteria were highly resistant to ampicillin and cefotaxime. This study demonstrates the importance of characterizing the microbiome of sea lions, and the potential effect of pathogens with antimicrobial resistance on wildlife conservation and public health.

Stress-related and reproductive hormones in hair from three north Pacific otariid species: Steller sea lions, California sea lions and northern fur seals.

Assessing the physiological impact of stressors in pinnipeds is logistically challenging, and many hormones are altered by capture and handling, limiting the utility of metabolically active tissues. Hair is increasingly being used to investigate stress-related and reproductive hormones in wildlife populations due to less-invasive collection methods, being metabolically inert once grown and containing multiple biomarkers of ecological interest. We validated enzyme immunoassays for measuring aldosterone, cortisol, corticosterone, and testosterone in lanugo (natal hair grown in utero) samples collected from Steller sea lions (Eumetopias jubatus), California sea lions (Zalophus californianus), and northern fur seals (Callorhinus ursinus). We applied laboratory validation methods including recovery of added mass, parallelism and dilution linearity. We found no effects due to differences in alcohol- versus detergent-based cleaning methods. Further, there were no significant differences in hormone concentrations in hair samples collected immediately after the molt and the subsequent samples collected over 1 year, indicating steroid hormones are stable once deposited into pinniped hair. We found no sex differences in any hormone concentrations, likely due to the lanugo being grown in utero and influenced by maternal hormone concentrations. For Steller sea lion and California sea lion pups, we found hormone concentrations significantly differed between rookeries, which warrants future research. Hair provides a novel tissue to explore the intrinsic or extrinsic drivers behind hormone measurements in otariids, which can be paired with multiple health-related metrics to further investigate possible drivers of physiological stress.

Atypical Red Blood Cells Are Prevalent in California Sea Lion Pups Born during Anomalous Sea Surface Temperature Events.

To date, there is limited knowledge of the effects that abnormal sea surface temperature (SST) can have on the physiology of neonate pinnipeds. However, maternal nutritional deficiencies driven by alimentary restrictions would expectedly impact pinniped development and fitness, as an adequate supply of nutrients is essential for growth and proper functioning of all body systems, including red blood cell synthesis and clearance. Here, we investigated red blood cell morphology of California sea lion (CSL) pups from the San Benito Archipelago born during the 2014 and 2015 anomalously high SST events recorded in the northeastern Pacific Ocean. We examined whether atypical erythrocyte morphologies were more common in 2015, when the high SST event was more pronounced, and whether the stable isotope signature of pup fur, as an indicator of maternal feeding strategies, accounted for the number of atypical cells. Various atypical erythrocyte morphologies were more prevalent and more abundant than reference values. Evidence of iron deficiency was found in both years, and only pups born in 2014 showed evidence of active erythropoiesis. Microcytes and reticulocytes were more common in pups with higher isotopic δ13C and lower δ15N values, suggesting a probable relationship between maternal feeding strategies and the effect of climatic anomalies on red blood cell physiology of their pups. As developing pinnipeds require increased oxygen storage capacity for diving and foraging, the presence of atypical erythrocytes could be relevant to CSL pup fitness if the underlying cause is not reverted. This study is a first step to explore the effects that climatic alterations in the marine environment can have on the blood physiology of developing individuals.

Changes in mucosal and serum immunoglobulin levels of California sea lions during early development

To date, most studies on pinniped immunoglobulins have focused on circulating antibodies. However, systemic and local immune activities differ in terms of maturation, intensity, and types of effectors that participate. Here, we examined levels of three immunoglobulin isotypes, IgG, IgM and IgA, in the blood and mucosal membranes of free-living California sea lion pups. We investigated whether age, body condition and sex influenced their concentration. Isotype levels varied among tissues, with age-related patterns that could be indicative of differential regulation along development. Serum IgG and IgA increased linearly with age, reaching adult levels at five months of age, while IgM remained unchanged. Mucosal isotypes tended to be low in newborns and remained so until five months of age. Regardless of age, pups with better condition tended to have higher anal IgG levels and higher genital IgA levels, suggesting that their synthesis and transport to the mucosal membranes is costly. Intersex differences were only observed in the genital mucosa, where all isotypes differed between male and female pups, regardless of age, presumably due to histological and anatomical differences.

Possible relation between enrichment of δ15N in the top predator Zalophus californianus and the expansion of the oxygen minimum zone

Stable isotopes of nitrogen were analyzed from the fur of nursing California sea lion (CSL) pups (that depend nutritionally on their mother’s milk for nourishment) collected in the thirteen rookeries from the Gulf of California from 1999 to 2014. Additionally, analyses were obtained from vibrissae of adult females at Los Islotes, a sea lion rookery in Bahia de La Paz with the longest record of CSL pup isotope information. The data show that consistent 15N enrichment occurred at all sea lion rookeries from the Gulf of California. Scat samples covering this time period showed no trend that might explain the δ15N enrichment as a result of shifts in feeding behavior. The enrichment pattern is paralleled by similar shifts in the enrichment of settling particulate organic matter (POM) recovered from sediment traps in the Bahia de La Paz, as well as published changes in POM δ15N in sediment cores from a number of coastal basins along the Pacific coast since 1990. The data are best explained by progressive transfer to surface waters of fractionated 15N nitrogen associated with the expansion of the Oxygen Minimum Zone in the Eastern Tropical Pacific, which is most intense along the coast of Mexico. In the Gulf of California, all levels of the food web are enriched in δ15N values with respect to similar counterparts outside of the region. We propose the nitrogen isotope composition in sea lions as an effective and easy method to monitor the regional expansion of the OMZ in the Eastern Tropical Pacific.

Climatic anomaly affects the immune competence of California sea lions.

The past decades have been characterized by a growing number of climatic anomalies. As these anomalies tend to occur suddenly and unexpectedly, it is often difficult to procure empirical evidence of their effects on natural populations. We analysed how the recent sea surface temperature (SST) anomaly in the northeastern Pacific Ocean affects body condition, nutritional status, and immune competence of California sea lion pups. We found that pup body condition and blood glucose levels of the pups were lower during high SST events, although other biomarkers of malnutrition remained unchanged, suggesting that pups were experiencing early stages of starvation. Glucose-dependent immune responses were affected by the SST anomaly; specifically, pups born during high SST events had lower serum concentrations of IgG and IgA, and were unable to respond to an immune challenge. This means that not only were pups that were born during the SST anomaly less able to synthesize protective antibodies; they were also limited in their ability to respond rapidly to nonspecific immune challenges. Our study provides empirical evidence that atypical climatic conditions can limit energetic reserves and compromise physiological responses that are essential for the survival of a marine top predator.

Protein and RNA extraction from mucosal swabs: a minimally invasive source of ecological data for studies of natural populations

Summary Mucosal swabs have long been used to study various physiological processes in humans. In contrast, systematic sampling of mucosae is rare for wild animals, and except for its use as a source of DNA for population genetics, its potential as a tool to study physiologically relevant processes of natural populations has not been explored fully. We collected swabs from the rectal, genital, nasal and oral mucosae of California sea lion pups and investigated differences in RNA and protein yield, quality and integrity between storage times and mucosal types. Downstream applications were tested on the extracted products to determine the potential value of mucosal sampling in free‐ranging mammals. For most samples, RNA yield was stable regardless of storage time, and RNA quality and integrity were equal for all mucosal types. Ribosomal fragments of sizes expected for mammals, yeast and bacteria were observable in genital and rectal samples, but in nasal and oral samples only bacterial ribosomal fragments were observable. Amplification of selected transcripts was successful for all samples. The protein profile was distinct between mucosae, and samples with high protein yields were useful for antibody detection. Our study demonstrates that mucosal swabbing is a minimally invasive tool that yields useful physiological data for free‐ranging wildlife. Minimum experience is needed to collect samples, processing is inexpensive, and downstream applications for ecological studies are realistic.

Investigations of peritoneal and intestinal infections of adult hookworms (Uncinaria spp.) in northern fur seal (Callorhinus ursinus) and California sea lion (Zalophus californianus) pups on San Miguel Island, California (2003)

The peritoneal cavity (PNC) and intestine of northern fur seal (Callorhinus ursinus) pups and California sea lion (Zalophus californianus) pups that died in late July and early August, 2003, on San Miguel Island, California, were examined for hookworms. Prevalence and morphometric studies were done with the hookworms in addition to molecular characterization. Based on this and previous molecular studies, hookworms from fur seals are designated as Uncinaria lucasi and the species from sea lions as Uncinaria species A. Adult hookworms were found in the PNC of 35 of 57 (61.4%) fur seal pups and of 13 of 104 (12.5%) sea lion pups. The number of hookworms located in the PNC ranged from 1 to 33 (median = 3) for the infected fur seal pups and 1 to 16 (median = 2) for the infected sea lion pups. In addition to the PNC, intestines of 43 fur seal and 32 sea lion pups were examined. All of these pups were positive for adult hookworms. The worms were counted from all but one of the sea lion pups. Numbers of these parasites in the intestine varied from 3 to 2,344 (median = 931) for the fur seal pups and 39 to 2,766 (median = 643) for the sea lion pups. Sea lion pups with peritoneal infections had higher intensity infections in the intestines than did pups without peritoneal infections, lending some support for the hypothesis that peritoneal infections result from high-intensity infections of adult worms. There was no difference in intestinal infection intensities between fur seal pups with and without peritoneal infections. Female adult hookworms in the intestines of both host species were significantly larger than males, and sea lion hookworms were larger than those in fur seals. Worms in the intestine also were larger than worms found in the PNC. Gene sequencing and (RFLP) analysis of (PCR) amplified (ITS) ribosomal DNA were used to diagnose the species of 172 hookworms recovered from the PNC and intestine of 18 C. ursinus and seven Z. californianus hosts. These molecular data revealed that U. lucasi (hookworm of C. ursinus) and Uncinaria species A (of Z. californianus) infrequently mature in the intestine of the opposite host species in California rookeries. However, there is no support from molecular data for the hypothesis that cross-infection with "the wrong" Uncinaria species is a contributing factor in these cases of host peritonitis. The major significance of this research is the unusual finding of adult hookworms in the PNC of so many dead pups. No obvious explanation for this occurrence could be determined. Further research, like in the present study, should help understand and monitor the apparent ever changing role of hookworm disease in the health of northern fur seal and California sea lion pups on SMI.

Serum cortisol in California sea lion pups (Zalophus californianus californianus)

AbstractMarine ecosystems are exposed to a wide variety of factors that may produce disturbances in their structure and functioning. The Gulf of California supports fisheries, tourism, intensive agriculture, mining, and more recently, shrimp aquaculture. Under such conditions, animals are forced to cope with several changes in their environment that can contribute to animal welfare problems. Serum cortisol level analysis may be a particularly useful means of assessing the physiological status of mammals potentially affected by increasing human activity in the Gulf of California, such as the California sea lion (Zalophus californianus californianus). In this study, we report for the first time the serum cortisol concentration of free-living, wild California sea lion pups. The analysis was performed in eleven rookeries along the Gulf of California. Two consecutive blood samples (S1 and S2) were obtained from 56 sea lion pups following a capture, handling and anaesthesia regime, and cortisol was measured by radioimmunoassay. Female pups showed higher serum cortisol than males in the first sample. In males, the second sample was significantly higher than the first. Cortisol levels in the two samples of both sexes combined differed between the Southern and Midriff-region rookeries. This information could be useful to assess welfare in wild populations of sea lions and to determine anthropogenic factors in the Gulf of California that may contribute to stress and reduced welfare.

Prevalence and characterization of Salmonella spp. among marine animals in the Channel Islands, California

Salmonella enterica is a zoonotic pathogen that has been isolated from free-ranging marine mammals throughout the world, with animals in the Channel Islands of California (USA) showing the highest prevalence. The goal of this study was to determine prevalence, antimicrobial sensitivity and genetic similarity using pulsed-field gel electrophoresis (PFGE) of Salmonella in several non-domestic animal species on San Miguel and San Nicolas Islands. Fecal samples were collected from 90 California sea lion Zalophus californianus pups, 30 northern elephant seal Mirounga angustirostris pups and 87 western gulls Larus occidentalis in the Channel Islands and 59 adult male sea lions in Puget Sound, WA (USA). Salmonella were isolated, identified and serotyped, followed by antimicrobial susceptibility testing and PFGE. Of the California sea lion pups that were sampled on the islands, 21% (n = 19) were positive for Salmonella, whereas no adults males in Puget Sound were positive. Of the northern elephant seal pups sampled, 87% (n = 26) were harboring Salmonella. Only 9% (n = 8) of western gulls were shedding Salmonella, with one of these gulls harboring the only antimicrobial resistant isolate. The serotypes found in these animals were Enteritidis, Montevideo, Newport, Reading, and Saint Paul. The only serotype that showed variation on PFGE was Newport. The pinnipeds of the Channel Islands harbor Salmonella at a higher prevalence than pinnipeds from other geographic areas observed in previous studies. Researchers and veterinarians should exercise increased caution when working with these animals due to the zoonotic potential of Salmonella.

Trace Metal Concentrations in the Hair of Zalophus californianus Pups and their Relation to Feeding Habits

The levels of six trace metals (Hg, Se, Pb, Cu, Fe, and Zn) were measured in the hair of California sea lion pups from eight rookeries in the Gulf of California, with the aim of relating these levels with the animals feeding habits, trophic level, and delta(15)N signatures at each locality. Trace metal levels were seen to vary significantly between sample sites as were tendencies associated with feeding habits. Mercury concentrations showed a clear positive correlation with trophic level (r = 0.73, p = 0.06) as well as the delta(15)N values of the rookeries (r = 0.79, p = 0.033). This was explainable via the process of biomagnification, although other elements did not follow the same tendency. High Cu concentrations in the hair (18 and 47 microg g(-1); ANOVA, p < 0.05) were observed at San Pedro Mártir and San Esteban, where the consumption of squid is higher than at other localities (approximately 17% and approximately 27% of the diet, respectively). Se and Hg concentrations correlated positively (r = 0.73, p = 0.038), probably the result of detoxification processes, a phenomenon previously reported in marine mammals. In light of the high degree of philopatry among sea lions in the Gulf and their pups' dependence exclusively upon their mother's milk during the first months of life, the analysis of trace metals in the easily sampled hair of the pups, offers an indirect way of monitoring the toxicology of the sea lion populations.

Contrasting effects of heterozygosity on survival and hookworm resistance in California sea lion pups

Low genetic heterozygosity is associated with loss of fitness in many natural populations. However, it remains unclear whether the mechanism is related to general (i.e. inbreeding) or local effects, in particular from a subset of loci lying close to genes under balancing selection. Here we analyse involving heterozygosity-fitness correlations on neonatal survival of California sea lions and on susceptibility to hookworm (Uncinaria spp.) infection, the single most important cause of pup mortality. We show that regardless of differences in hookworm burden, homozygosity is a key predictor of hookworm-related lesions, with no single locus contributing disproportionately. Conversely, the subsequent occurrence of anaemia due to blood loss in infected pups is overwhelmingly associated with homozygosity at one particular locus, all other loci showing no pattern. Our results suggest contrasting genetic mechanisms underlying two pathologies related to the same pathogen. First, relatively inbred pups are less able to expel hookworms and prevent their attachment to the intestinal mucosa, possibly due to a weakened immune response. In contrast, infected pups that are homozygous for a gene near to microsatellite Hg4.2 are strongly predisposed to anaemia. As yet, this gene is unknown, but could plausibly be involved in the blood-coagulation cascade. Taken together, these results suggest that pathogenic burden alone may not be the main factor regulating pathogen-related mortality in natural populations. Our study could have important implications for the conservation of small, isolated or threatened populations, particularly when they are at a risk of facing pathogenic challenges.

Seasonal prevalence and intensity of hookworms (Uncinaria spp.) in California sea lion (Zalophus californianus) pups born in 2002 on San Miguel Island, California

Intestines of California sea lion (Zalophus californianus) pups (n= 204), born in 2002 on San Miguel Island, California, were examined for hookworms (Uncinaria spp.) as part of a seasonal mortality study from June through December 2002 and January 2003. The investigation was planned to coincide with most of the previously established hookworm infection period of the pups. Prevalence of hookworms in dead pups was 100% for each month of the study. The geometric mean intensity of infections per month was: 94.03 (n=30) for June, 629.09 (n=50) for July, 319.90 (n=31) for August, 159.90 (n=30) for October, 109.03 (n=30) for November, 37.84 (n=24) for December 2002 and 11.05 (n=9) for January 2003. In addition to the temporal pattern, the infection intensity was higher for pups in good condition and for male pups. An inter-year comparison of hookworm counts from dead pups collected in July of 1996, 2000, and 2002 also demonstrated higher intensity in pups in better condition but sex-differences in intensity were inconsistent across years. The inter-year comparison also demonstrated higher intensities in dead pups collected from portions of the rookery with sandy substrate versus rocky substrate. No annual differences in intensity were found after adjusting for substrate and condition.

Photomicrographic images of some features of Uncinaria spp (Nematoda: Ancylostomatidae) from otariid pinnipeds

Photomicrographs of several morphologic features of hookworms (Uncinaria spp) from northern fur seal (Callorhinus ursinus) and California sea lion (Zalophus californianus) pups are presented. The main purpose is to show and describe some physical characteristics of hookworms from the two hosts; it is not to decide from these attributes whether the Uncinaria spp are the same species. The number of species of Uncinaria in pinnipeds is uncertain and specimens need to be examined from the various infected seals and sea lions before the taxonomy of these parasites can be clarified. Information in the present paper should aid in this determination.

Penetration of the small intestine of a California sea lion (Zalophus californianus) pup by adult hookworms (Uncinaria spp).

During a study on the mortality of California sea lion (Zalophus californianus) pups born on San Miguel Island, California in 2002, two adult female hookworms (Uncinaria spp) were found penetrating the serosal surface of the intestinal wall and protruding into the peritoneal cavity of one pup. Documentation and a description of this unexpected finding and associated lesions are presented here. Also, adult hookworms were found in the peritoneal fluid of two other dead Z. californianus pups.

Fatty acids in plasma of California sea lion pups (Zalophus c. californianus) from Los Islotes, Baja California Sur, Mexico

Nutritious fats include all the lipids ingested as food and are composed mainly of triglycerides mixed with smaller quantities of other lipids. Fatty acids (FA) constitute the part of most nutritious interest in triglycerides. The fatty acid composition was assesed in the blood plasma of California sea lion pups (Zalophus c. californianus) from Los Islotes, Baja California Sur, in the Gulf of California, during 1999. Blood samples were obtained from 35 anesthetized sea lion pups, 21 males (M) and 14 females (F). The plasma was separated by centrifugation and stored with different antioxidants. The FA profile was determined by gas chromatography with flame ionization detection (FID). There was a great variation both in presence and quantity of fatty acids (FA) among animals. The sea lion with the least number of FA had 12 and the one with the most had 29 FA. Twelve saturated FA (SFA) were identified, 9 monounsaturated (MUFA) and 10 poly unsaturated (PUFA). The most frequent SFA in both groups were C14:0, C16:0 and C18:0, and the most abundant ones were: C15:0 (10.4 and 13.7 mg/100mL, in M and F respectively) and C18:0 (4.3 and 6.1, respectively). C16:1, C17:1 and C18:1n-9t were the most frequent MUFA, ant the most abundant ones were C17:1 and C24:1 (3.2 and 3.5, and 3.3 and 2.9 mg/100mL in M and F, respectively). C15:1 was very abundant in females (5.4 mg/ 100mL) when compared with males (0.91), and was the only one of all the FA identified showing a statistical difference P &lt; 0.05. The most abundant MUFA was C18:1n-9t (10.6 and 7.8 mg/100 mL, in M and F respectively). In both groups the most frequent PUFA detected were C18:2n-6t, C22:2, C:22:6n-3 and C20:3n-6, showing the latter the highest concentration (20.3 and 26.5 mg/ 100mL, in M and F respectively). The 20:3 n-3 was identified only in two males. The SFA with the lowest concentration was C12:0 (0.030 and 0.45 mg/100 mL), and C11:0 was detected only in five animals. Four n-6FA (C18:2, C18:3, C20:3 and C20:4) and three n-3FA (C20:3, C20:5 and C22:6) were identified. Two trans-FA were also identified, C18:1t and C18:2t. The FA values were very heterogeneous so in females as in males, probably influenced by different fasting periods of the pups. Given that during the sampling period the body condition of pups was within the normal values estimated for the Gulf of California, the plasmatic FA values of the pups can be used as reference values regarding other populations.

EVIDENCE OF LEPTOSPIRA INTERROGANS INFECTION IN CALIFORNIA SEA LION PUPS FROM THE GULF OF CALIFORNIA

Forty-two urine and 96 blood and serum samples were obtained from California sea lion (Zalophus californianus) pups from the Gulf of California during the 2000 reproductive season. Antibody prevalence to 13 serovars of Leptospira interrogans was determined by microagglutination tests (MAT); presence of pathogenic leptospires was detected by polymerase chain reaction (PCR). Samples with antibody titers > or = 1:25 or 115 bp fragments on ethidium bromidestained 1.5% agarose gels were considered positive. Antibody prevalence was 54% overall with highest prevalence against serovar cynopteri (50% of all positive reactions). Highest antibody titers (1:50) were detected against serovars cynopteri and pomona. Polymerase chain reaction products were observed in two of 42 urine samples, six of 96 blood samples, and one of 96 serum samples. Presence of PCR products in blood and serum was demonstrated in pups that were seronegative. Kruskall-Wallis tests and corresponding post hoc Tukey tests (alpha = 0.05) showed that prevalence of leptospirosis was significantly different among all rookeries. The high seroprevalence (54%), low antibody titers (maximum 1:50), absence of pups showing clinical signs indicative of the disease, and lack of recent reports of increased mortality of sea lions in the Gulf of California are suggestive of the presence of enzootic host-adapted serovars. Crowding in rookeries as well as the presence of bats and rodents on some of the islands may explain infection by L. interrogans (sensu lato) and some of the differences in seroprevalence among reproductive rookeries.

Estimation of body volume and body density in California sea lion pups

Body volume was measured directly by the water displacement method and using three different geometric models, consisting of a series of cones and truncated cones, in California sea lion (Zalophus californianus) pups from the Gulf of California. Volume is required for the estimation of density, an indicator of the ratio of fat to lean mass. A model consisting of two cones and four truncated cones predicted body volume with greatest accuracy (volume=1·11+1·06&amp;;estimated volume, r2=0·90, P&lt;0·001, SEE=0·673, N=274). This model, however, was not adequate to estimate absolute pup body density (mass to volume ratio), as it yielded values poorly correlated with observed body density (r=0·14, P=0·02). However, the regression line of mass on volume indicated that density decreased with volume, so the mass to volume ratio is a biased estimate of density and is not appropriate for comparing whole body density among sea lion pups. The direct analysis of the relationship between body mass and body volume (observed or estimated) through analysis of covariance provided a better tool to compare the relative density among pups of different sex, populations, or born in different years. The results from such analyses are consistent with previous evidence of sex and age effects on body composition.

Current prevalence of adult Uncinaria spp. in northern fur seal ( Callorhinus ursinus) and California sea lion ( Zalophus californianus) pups on San Miguel Island, California, with notes on the biology of these hookworms

A prevalence survey for hookworms ( Uncinaria spp.) was done in northern fur seal ( Callorhinus ursinus) and California sea lion ( Zalophus californianus) pups on San Miguel Island, CA, in 2000. Intestines of dead pups were examined for adult hookworms in July. These parasites were found in 95% of 20 fur seal pups and 100% of 31 sea lion pups. The number of hookworms varied from 4 to 2142 ( x ̄ =760 ) in fur seal pups and from 20 to 2634 ( x ̄ =612 ) in sea lion pups. A direct relationship was evident between body condition and number of hookworms in the pups; that is, pups in poor condition had fewer hookworms than those in good condition. There was a decline in the number of hookworms in sea lion pups in 2000 compared to collections in 1996. Eggs of Uncinaria spp. were found in rectal feces (collected in late September and early October) of none of 35 (0%) live fur seal pups and 41 of 48 (85%) live sea lion pups. Packed cell volume values, determined for most of the same live pups, were essentially normal for C. ursinus but were much lower than normal for most Z. californianus. Hookworm larvae were not found in blubber of fur seal and sea lion pups or in rookery sand in July. Rookery sand, positive for live hookworm larvae when put in a refrigerator, was negative at removal 2.5 years later. The average number of eggs in utero of female hookworms was 285 for three specimens from a fur seal pup and 281 from three specimens from a sea lion pup. One hookworm larva was recovered from milk stripped from the teats of a stranded Z. californianus female at The Marine Mammal Center, Sausalito, CA.