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The Parque Nacional Zona Marina del Archipielago de Espiritu Santo (PNZMAES; Espiritu Santo Archipelago Marine National Park) is unique for its scenic beauty and for housing the only California sea lion (CSL) breeding colony in the Gulf of California with a healthy growing population. The region is economically relevant to artisanal fisheries and tourism service providers, resulting in CSL entanglements and an increase in tourist visitation to the colony. Few years ago, the PNZMAES management plan implemented conservation strategies to protect the different areas essential to the distinct life cycle phases of species of conservation interest like the CSL. In this study, all demographic data and ecological and environmental variables available for this colony were compiled in order to assess its population’s growth trend and evaluate how diet and the entanglement rate have affected CSL abundance and the number of births. The colony continues to grow, and none of the variables analyzed had an effect on population parameters. The rookery is important for the conservation of the species in Mexico as it may become a core population from which historic and current breeding colonies in the Gulf of California at serious risk of disappearing may be recolonized.

Trace element (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd, As, Hg) concentrations were assessed in marine organisms (n = 52) sampled from the Magdalena Bay lagoon complex in Baja California Sur, Mexico, a pristine marine environment. The overall trend of metal concentrations (dry weight) in the organisms was found to be Fe > Zn > Cd > Cu > Mn > Pb > As > Hg > Ni > Cr > Co. Bivalve mollusks (53.83 mg kg−1) contained twofold higher levels of metals than the finfishes (20.77 mg kg−1). Calculated BioConcentration Factor (BCF) values showed that dissolved Mn is readily bioavailable to the organisms, whereas Biota Sediment Accumulation Factor (BSAF) indicated high values for Zn, Cu and Cd. Cd and As levels were observed to be increasing with the trophic levels. Toxic elements, namely Pb, Cd and As in the studied fish species were found to be higher than the values recommended for human seafood consumption. The study provides a comprehensive baseline report on trace element bioaccumulation in several marine organisms that will aid in developing effective conservation strategies of the highly biodiverse lagoon complex.

Bottlenose dolphins (Tursiops truncatus) and pantropical spotted dolphins (Stenella attenuata) co-occur in Golfo Dulce, a fjord-like embayment located in the southern Pacific coast of Costa Rica. We evaluated if spatial overlap by these dolphin species is associated with similar environmental requirements. Presence-only models based on niche theory were constructed by contrasting a set of spatial locations with the responses of the target species to abiotic ecogeographical variables (EGVs: depth, slope, distance to rivers, distance to 200 m isobath, mean sea surface temperature, and variation in sea surface temperature). Models were cross-validated with levels of discrimination that ranged from acceptable to excellent based on the area under the curve assessment (T. truncatus, rainy season: 0.76, dry season: 0.83; S. attenuata, rainy season: 0.84, dry season: 0.89). Both dolphin species occur in Golfo Dulce year-round; the lack of seasonality documented previously was supported by the models. Species distribution models showed no spatial overlap, with differences in EGVs affecting their distribution (T. truncatus: distance to river + distance to 200 m isobath, S. attenuata: depth + sea surface temperature). We argue that the coexistence of both predators in Golfo Dulce is linked to habitat heterogeneity, where critical habitats are spatially differentiated. The lack of fine-scale spatial overlap, along with influential abiotic variables, highlights a process of coexistence for dolphins that are sympatric at the scale of Golfo Dulce, but within the Gulf there is fine-scale allopatry.

The worldwide smallest cetacean, the vaquita (Phocoena sinus), is on the verge of extinction with fewer than 20 individuals left as of summer 2018. The main cause of mortality is bycatch by entanglement in illegal gillnets and environmental changes. Habitat disturbances have negatively impacted prey diversity, and therefore, the vaquita’s feeding success. We investigated the trophic niche of the vaquita and its variability from 1985 to 1993 by quantifying δ13C and δ15N values from bone samples (n = 33). We reconstructed part of vaquita’s refuge food web and identified some prey items. Between 1985 and 1993 the vaquita’s isotopic ellipses shifted moderately, δ13C and δ15N without significant differences, suggesting variations in habitat baseline values and probably prey composition. We observed a high overlap in the ellipses between males and females, suggesting that both sexes were feeding in the same geographic area over several years and with similar prey composition. Together, our results indicate that the vaquita is a generalist high-TL consumer, feeding on benthic and small pelagic prey it maintained similar mean δ15N values for years. Given these results, conservation efforts should intensify to protect the biodiversity of the Upper Gulf of California and the surviving vaquita.

The rate of energy expenditure and acquisition are fundamental components of an animals’ life history. Within mammals, the otariids (sea lions and fur seals) exhibit energetically expensive life styles, which can be challenging in equatorial regions where resources are particularly limited and unpredictable. To better understand how this energetically expensive life history pattern functions in an energetically challenging equatorial system, we concurrently measured the field metabolic rate (FMR) and foraging behavior of lactating Galapagos sea lions (GSL) rearing pups and yearlings. Females with pups tended to forage to the north, diving deeper, epi and mesopelagically compared to females with yearlings, which foraged to the west and performed dives to the sea bed that were shallower. FMR did not differ between females with pups or yearlings but, increased significantly with % time spent at-sea. Females with yearlings had higher water influx, suggesting greater food intake, but had lower body condition. The FMR (4.08±0.6 W/kg) of GSL is the lowest measured for any otariid, but is consistent with Galapagos fur seals which also exhibit low FMR. The observation that these two otariids have reduced energy requirements is consistent with an adaptation to the reduced prey availability of the Galapagos marine environment compared to other more productive marine systems.

The effective size of a population (Ne), which determines its level of neutral variability, is a key evolutionary parameter. Ne can substantially depart from census sizes of present-day breeding populations (NC) as a result of past demographic changes, variation in life-history traits and selection at linked sites. Using genome-wide data we estimated the long-term coalescent Ne for 17 pinniped species represented by 36 population samples (total n = 458 individuals). Ne estimates ranged from 8,936 to 91,178, were highly consistent within (sub)species and showed a strong positive correlation with NC ( $${R}_{\mathrm{adj}}^2$$ = 0.59; P = 0.0002). Ne/NC ratios were low (mean, 0.31; median, 0.13) and co-varied strongly with demographic history and, to a lesser degree, with species’ ecological and life-history variables such as breeding habitat. Residual variation in Ne/NC, after controlling for past demographic fluctuations, contained information about recent population size changes during the Anthropocene. Specifically, species of conservation concern typically had positive residuals indicative of a smaller contemporary NC than would be expected from their long-term Ne. This study highlights the value of comparative population genomic analyses for gauging the evolutionary processes governing genetic variation in natural populations, and provides a framework for identifying populations deserving closer conservation attention. Using comparative population genomics across pinnipeds, this study explores how demographic change and life-history traits are correlated to the effective size of a population and conservation status.

Pinnipeds are effective bioindicators of the abundance of their prey and changes in marine productivity due to natural oceanographic phenomena or fishery exploitation. In Uruguay, two pinniped species breed sympatrically: Arctocephalus australis, with a growing population, and Otaria flavescens, which has a declining population. Given their contrasting population growth trends, we explored how their trophic patterns varied across age-classes over seven decades using dentin collagen δ13C and δ15N values in teeth sampled from stranded organisms. Dentin collagen accumulates isotopic information in annual growth layers, providing sequential information on an animal’s diet throughout its life. Dentin collagen annual growth layers in 50 A. australis teeth and 37 O. flavescens teeth from individuals stranded over ~ 70 years were processed for isotopic analysis. Importantly, δ13C decreased over time in both species (0.024–0.027‰ year–1 in A. australis, and 0.028–0.035‰ in O. flavescens); this pattern reflects the influence of the Suess Effect, a global phenomenon of decreasing δ13C values in marine ecosystems. Isotopic values were relatively constant over time, suggesting that these species maintained a stable trophic niche during the seven decades examined, with O. flavescens exhibiting higher δ13C and δ15N values. Within each species, there was considerable isotopic niche overlap between different age-classes; however, both species occupied different isotopic niches regardless of age-class during all decades. The isotopic niches of the two species converged during the 2000s. Primarily responsible for this convergence were adult A. australis, which overlapped with juvenile and young adult O. flavescens. Moreover, we propose that before the 2000s A. australis fed on prey from different trophic levels while O. flavescens varied its feeding habitat. Our results suggest that these top predators reflect anthropogenic and environmental changes that have occurred over the last seven decades in Uruguayan waters.

Summary The Guadalupe (Arctocephalus townsendi), Juan Fernandez (A. philippii), and Galapagos fur seals (A. galapagoensis) are three closely related species within the Family Otariidae. Their taxonomic status is currently an issue of debate; a new Genus Arctophoca has been suggested, but they are currently all classified as being Arctocephalus. Galapagos fur seal’s taxonomic position is also somewhat open as to whether it is an independent species or a subspecies of the South American fur seal (A. australis).

Summary We summarize the knowledge about the three species of Zalophus sea lions (one believed to be extinct: the Japanese sea lion), explain the latest state of the taxonomy, and briefly describe their behavior, ecology, and life history, pointing out differences among populations within the California sea lion as well as species differences. Important sources of threats to the populations are mentioned. These were hunting in the past, but are now habitat degradation, including pollutants and bycatch through net entanglements.

The aim of this study was to determine the trophic level, trophic breadth, and dietary overlap of two species of otariids (Zalophus californianus and Arctocephalus philippii townsendi) at the San Benito Islands in Baja California, Mexico, using scat analysis, and stable isotope analyses (SIA) of carbon and nitrogen in pup hair and dental collagen. Scat samples were collected during summer and winter. The most important prey for both species during summer was squid, comprising 74% of the A. p. townsendi diet and 45% of that of Z. californianus. In winter, squid was 87% of the A. p. townsendi diet, whereas fish was the predominant food (76%) for Z. californianus. Both species were specialist feeders and reached maximum trophic overlap during the summer (CH = 0.9). SIA of the hair of otariid pups showed significant differences in δ15N (P = 0.001), coinciding with A. p. townsendi's greater consumption of squid. The average δ13C value was significantly lower for A. p. townsendi (−16.3‰ ± 0.2‰), reflecting the species' consumption of squid from pelagic habitats, whereas that of Z. californianus (−15.9‰ ± 0.3‰) was significantly higher, reflecting their consumption of benthic fish. Difference in habitat use was confirmed in δ13C values of dental collagen.

A crucial question in wildlife management concerns the definition of ecologically meaningful population units. For the California sea lion (Zalophus californianus), three population units are recognized in Mexico based on mitochondrial DNA and geographical distances; these units are thought to be genetically isolated. In the present study, we quantitatively compare patterns of shape variation and evaluate different classification approaches to confirm this regional fragmentation among the Mexican colonies and assess sexual dimorphism in skull morphometry. We employed 20 linear measurements of 368 skulls of specimens from the Mexican Pacific (including the Gulf of California), evaluated correlation among the features, and performed multivariate analyses. To provide robustness to the classification by sex and region, we evaluated the use of kernel-based classifiers. According to skull morphometry, the classification of individuals to sex is very reliable, and there is a phenotypic regionalization among colonies that coincides with the proposed regional population structure. We suggest that inside the Gulf, there is gene flow between females but that it is reduced with geographic distance. The phenotypic differences between the Gulf of California and Pacific for both sexes are consistent with the hypothesis of little or no gene flow between these regions.

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.

The Guadalupe fur seal Arctocephalus townsendi (GFS) is known in Latin America as the lobo fino de Guadalupe, oso marino de Guadalupe, or lobo de dos pelos de Guadalupe. Guadalupe Island (GI), off the coast of Baja California, Mexico, is the typical locality where this species occurs; the taxon was first described by Merriam (1897) based on a specimen collected on the island’s west coast. Presently, the GFS distribution is centered onLaboratorio de Ecologia de Pinnipedos “Burney J. Le Boeuf”, Centro Interdisciplinario de Ciencias Marinas, Instituto Politecnico Nacional. Av. IPN s/n, Col. Playa Palo de Santa Rita, C.P. 23096, La Paz, Baja California Sur, Mexico.

Environmental conditions may influence mating behaviour in otariids breeding in areas with elevated temperatures and intense solar radiation. Although they have evolved morphological and physiological adaptations to prevent overheating while breeding on land, under extreme temperature conditions, they must adjust their behaviour in order to thermoregulate. The California sea lion mating system is based on male competition and displays that occur while defending their territories when females are present. We studied the agonistic behaviour of adult males at two breeding colonies in Mexico with contrasting environmental characteristics: Isla Santa Margarita (ISM) (Pacific coast) and Isla San Esteban (ISE) (Gulf of California). The goal of this study was to determine which variables influence where (i.e. on land or in the water) aggressive interactions between adult males occurred using logistic regression analysis. We analysed three scenarios: (1) both islands, (2) only ISM and (3) only ISE. The best model for the first scenario included the air temperature, density of females and type of aggression. The second scenario involved the density of females, and the third scenario included the rate of female interactions. Although the California sea lion mating strategy involves monopolizing critical resources, our results indicate that density of females and rate of female interactions have a significant impact on where male aggressive interactions occur. Our results highlight how changing environmental conditions affect the behavioural plasticity of this species' mating system. Most notably, males inhabiting high-temperature environments use the thermoregulatory strategy of defending territories adjacent to the coast while remaining immersed in the water. This strategy may result in decreased polygyny in the Gulf of California colonies relative to those on the Pacific coast.

Individual specialisation is increasingly recognised to be an ecological and evolutionary process having important consequences for population dynamics of vertebrates. The South American fur seal (SAFS) and the South American sea lion (SASL) are two otariid species with similar ecology that coexist in sympatry in the Uruguayan coast. These two species have contrasting trends and widely different population sizes. The underlying reasons for these population trends, unique in their geographical ranges, remain unknown. We studied the foraging ecology of these otariid species over 2 years at the individual- and population levels using the isotopic ratios (δ13C–δ15N) in whiskers of both sexes. We compared the isotope ratios between species and sexes and used several metrics to characterise the degree of overlap and distinctiveness in the use of isotopic niche space at the individual- and population levels. Interspecific trophic niche overlap was minimal, thus ruling out interspecific competition as the cause for the contrasting population trends of both species. At the intraspecific level, both species had sexual segregation in their foraging areas, but each species had a large overlap in the isotopic niches between sexes. While SAFS had a wider niche and generalist individuals, SASL had the narrower niche with a higher degree of individual specialisation. Behavioural constraints during the breeding season, intraspecific competition and a major dependence on resources of the Uruguayan coastal shelf may explain why SASL had a higher trophic individual specialisation and a larger vulnerability in a heavily exploited habitat by fisheries and, by consequence, a locally declining population trend.

This study focuses on the comparative analysis of variables related to the trophic niche plasticity in the Galapagos sea lion (Zalophus wollebaeki). There is great concern regarding the future of this species, so study of the diet and the way these animals obtain their food is useful to understand and predict their survival possibilities in the long term. The combined use of scat analysis and stable isotopes helps to determine foraging habits of this species in greater detail. The objective of the study was to assess the feeding habits of Z. wollebaeki and its space–time variation. The scat analysis (n = 200) gave as a result space–time changes in the foraging strategies of this species. The isotopic values (n = 80) showed differences in relation to foraging grounds (δ13C: P = 0.001), but also suggested an apparent stability in the trophic level of their diet (δ15N: P = 0.084). These results constitute a relevant finding in the evolutionary behaviour of the species, showing that Z. wollebaeki has developed a high degree of plasticity in its foraging habits that may improve its survival in a highly demanding ecosystem in terms of limited and fluctuating resources.

RATIONALE Tissues with different turnover rates have different isotope compositions and reflect the different periods in an animal's life when the isotopes are incorporated during the growth of tissues. Bone is one of the most used tissues for reconstruction of an animal's diet; however, the time of isotope integration remains unknown for many species. METHODS The δ15N and δ13C values in tooth dentine and bone tissue from the maxilla and mandible of 21 stranded northern elephant seals, Mirounga angustirostris, collected on the San Benito and Magdalena Islands, Mexico, between 2000 and 2008 were compared. Bone and dentine samples from each growth layer within the tooth were analyzed using a PDZ Europa ANCA-GSL elemental analyzer interfaced with a PDZ Europa 20-20 continuous flow gas source mass spectrometer. RESULTS The δ15N and δ13C values were not different between bone structures, indicating similar turnover rates, metabolic activity and amino acid compositions. The differences in the observed δ13C values between tissues are probably indicative of differences in their amino acid compositions, although the similarities in δ15N values indicated less variation from different amino acids. Correlation of the analyses between isotopic values of tissues suggests that the maxilla and/or mandible of M. angustirostris might reflect the δ15N signal incorporated during the last 5 years of life of the individuals. CONCLUSIONS This study demonstrated the usefulness of the applied approach for providing a best approximation of the timing of isotopic integration into the skull of a marine mammal, thereby reducing uncertainty in exploring historic changes in the species' feeding behavior. Copyright © 2013 John Wiley & Sons, Ltd.

We assessed the foraging habits of California sea lions, Zalophus californianus, from Isla Santa Margarita, BCS, Mexico, by analyzing δ13C and δ15N values of dentin collagen. Since dentin is deposited annually in growth layer groups (GLGs), it can be subsampled to construct ontogenetic isotopic profiles at the individual level. We drilled 20 canine teeth and obtained 141 samples for isotopic analysis that were assigned to age-specific categories from GLG-based estimated ages. Pups’ GLGs had the highest mean δ15N values and the lowest mean δ13C values, a pattern likely driven by the consumption of milk. Juveniles had δ15N values between those of pups and adult females, which may reflect continued nursing into the second year or preferential consumption of coastal benthic versus pelagic prey. Significant differences were observed between the sexes of adults; adult females had lower mean δ13C and δ15N values than adult males. Higher isotope values in adult males relative to females may reflect a higher trophic position, but differences in foraging grounds cannot be excluded as a potential explanation because tracking data are not available at this time. Evidence of intra-specific foraging diversification may be related to a strategy to reduce competition within and among age and sex categories.

The feeding behavior of marine predators varies with the level of competition to which they are exposed. Populations living in the same or overlapping geographic regions (sympatric) are generally subject to inter-specific competition, which can lead to the development of differing trophic strategies that maximize both nutritional and reproductive efficiency. The otariids of the islands in the western Galapagos Archipelago represent appropriate subjects for studying the response mechanisms of sympatric species exposed to strong competition, both trophic and spatial. The present study has focused on evaluating the possible differences in the trophic niches of the Galapagos sea lion ( Zalophus wollebaeki ) and the Galapagos fur seal ( Arctocephalus galapagoensis ) over time, based upon the analysis of stable isotope ratios of carbon and nitrogen (δ 13 C and δ 15 N), and observation of both species at sea. A comparative analysis of the isotopic signal of skin samples from pups of both species was performed for rookeries on Fernandina Island between 2003 and 2009. Analyses of the isotopic signal present in prey covering the entire trophic range of these predators were also performed, in order to relate this information to otariid sighting records collected during offshore cruises in 1993–1994 and 2000. The δ 13 C and δ 15 N values defined differences in the feeding zones and in the trophic level of each species; which were related with the interannual variability of the ecosystem, i.e. El Nino and La Nina events. Whereas Z. wollebaeki showed a coastal (inshore) foraging strategy, relying on the consumption of small epipelagic fishes, A. galapagoensis turned out to be a more oceanic (offshore) predator, with a preference for small squid. These results are in good agreement with the distribution of these animals at sea, as indicated by the sighting data. The findings of this study provide new insights to our understanding of how sympatric species exposed to strong inter-specific competition can develop foraging strategies leading to a decreasing level of food competition and facilitate their survival in a stochastic environment that is highly demanding in terms of the availability of resources.

In Uruguay, the South American fur seal population (Arctocephalus australis) is increasing, whereas the South American sea lion (Otaria flavescens) population is declining. Previous research using fecal analysis suggested a high degree of trophic overlap between these species. In this study we used stable isotope analysis to assess whether trophic overlap occurs between female fur seals and sea lions during the breeding season. We measured δ15N and δ13C values in serum and skin from pups of both species (n = 47) to reflect pre- and postpartum maternal feeding habits, respectively. Our results suggested a lack of trophic overlap between lactating females; both serum and skin samples from sea lion pups had significantly greater δ13C and δ15N values than samples from fur seal pups, suggesting that lactating sea lions forage near shore, whereas lactating fur seals forage offshore. The pre- to postpartum diet shift in fur seals would be mainly caused by a reduction in the diversity of the exploited ...

The 2008 IUCN (International Union for Conservation of Nature) review of the status of the world’s mammals identified marine mammals (IUCN 2008) as disproportionally threatened and data poor compared to their terrestrial counterparts, and their status was noted as a particular concern (IUCN 2008, Mace et al. 2008, Schipper et al. 2008). The threats faced by marine mammals were identified as being different, with accidental mortality and pollution being dominant threats that superseded habitat loss, which was identified as the principal concern for land mammals. It was suggested that harvesting remained a major threat for half of the marine mammal species in the world. The distribution of marine mammals was described as being concentrated in tropical and temperate coastal platforms and associated with high levels of primary productivity. Threat levels were highest for marine mammals living in the North Atlantic, North Pacific and Southeast Asia. Range size was described as generally declining toward both poles. Although these generalities are of course correct for all marine mammals, it must be recognized that the larger number of species of cetaceans compared to other marine mammal groups (85 cetaceans, the polar bear Ursus maritimus, 4 extant sirenians and 36 pinniped species) biases the conclusions in the assessment for marine mammals to such a degree that a separate summary for the pinnipeds of the world is warranted. Additionally, a species-level assessment masks some important conservation concerns for pinnipeds with species classified as Least Concern actually containing threatened subspecies ( e.g., ringed seals). Finally, and perhaps most importantly, climate change issues were not specifically addressed in the vast majority of marine mammal assessments done for the 2008 IUCN review (IUCN 2008). We present here a complete assessment of the status and threats facing pinnipeds at the subspecies level, integrating the expected impacts of changing patterns of threat due to global climate change.

California sea lion (Zalophus californianus) rookeries in the Gulf of California are structured genetically in distinct groups. Despite this evidence for regional differentiation, the sea lion population of the Gulf of California is managed as a single unit. To prioritize the allocation of limited resources for conservation and to improve the effectiveness of management actions, ecological differences among rookeries should also be considered. This is important to be able to further define and subsequently manage the rookeries on a regional level. The aim of the present study was to identify patterns of similarity among California sea lion rookeries in the Gulf of California, using nine demographic, biological, ecological, and biogeochemical databases: population censuses, trace metal content in bone, diet diversity, presence of Leptospira serovarieties, stable isotopes, incidence of osteoarthritis, sea surface temperature, and chlorophyll a concentration. A second objective was to characterize each region on the basis of these variables in order to focus management efforts. To examine the overall structure of the sea lion rookeries in the Gulf of California, we analyzed data for different combinations of variables and rookeries using multivariate analysis. The scenario with the highest explanatory power resulted in the separation of the rookeries into four groups: Northern Gulf, Ángel de la Guarda, Central Gulf, and Southern Gulf. Diet and sea surface temperature were the variables that contributed most strongly to the definition of the groups. Groupings showed geographic coherence and were consistent with previously proposed genetic units and oceanographic regions of the Gulf of California. The resulting multivariate pattern should facilitate the management of California sea lion rookeries, provide better tools to protect against environmental contingencies, and help to guide future management plans.

Infections with Brucella ceti and pinnipedialis are prevalent in marine mammals worldwide. A total of 22 California sea lions (Zalophus californianus) were examined to determine their exposure to Brucella spp. at San Esteban Island in the Gulf of California, Mexico, in June and July 2011. Although samples of blood, vaginal mucus and milk cultured negative for these bacteria, the application of rose Bengal, agar gel immunodiffusion, PCR and modified fluorescence polarization assays found that five animals (22.7%) had evidence of exposure to Brucella strains. The data also suggested that in two of these five sea lions the strains involved were of terrestrial origin, a novel finding in marine mammals. Further work will be required to validate and determine the epidemiological significance of this finding.

Pinniped vibrissae provide information on changes in diet at seasonal and annual scales; however, species-specific growth patterns must first be determined in order to interpret these data. In this study, a simple linear model was used to estimate the growth rate of vibrissae from adult female California sea lions (Zalophus californianus) from San Esteban Island in the Gulf of California, Mexico. The δ15N and δ13C values do not display a marked oscillatory pattern that would permit direct determination of the time period contained in each vibrissa; thus, time (age) was calculated in two ways: 1) based on the correlation between the observed number of peaks (Fourier series) in the δ15N profile and the length of each vibrissa, and 2) through direct comparison with the observed number of peaks in the δ15N profile. Cross-correlation confirmed that the two peaks in the δ15N profile reflected the two peaks in the chlorophyll-a concentration recorded annually around the island. The mean growth rate obtained from the correlation was 0.08 ± 0.01 mm d-1, while that calculated based on the observed number of peaks was 0.10 ± 0.05 mm d-1. Both are consistent with the rates reported for adult females of other otariid species (0.07 to 0.11 mm d-1). Vibrissa growth rates vary by individual, age, sex, and species; moreover, small differences in the growth rate can result in significant differences over the time periods represented by the isotopic signal. Thus, it is important to assess this parameter on a species-by-species basis.

Sea lions are generally considered opportunistic feeders. However, studies from different areas suggest their diet consists mostly of four to five types of prey. Previous studies in Galapagos sea lions have identified at least three feeding strategies for this species, suggesting diversification of their diet. Diet diversification is favored in organisms with relatively high trophic position and subject to high intra-specific and low inter-specific competition. Zalophus wollebaeki meet these criteria as the only pinniped on San Cristobal Island, where three sea lion rookeries are located within 11 km: a distance considerably shorter than their 41 km foraging range. To measure the degree of diet diversification, we used scats and stable isotope analyses. A total of 270 scat samples from lactating females and 142 fur samples from sea lion pups were collected during the breeding season 2006. The scat analysis identified distinct diets among rookeries, with minimal trophic overlap (Cλ = 0.19), a trophic level TL = 4.5 (secondary–tertiary carnivore), and trophic breadth of a specialist predator (Bi = 0.37). The mean δ15N and δ13C values were 13.07 ± 0.52 and −16.34 ± 0.37, respectively. No significant difference was found in the δ15N values from the sea lion rookeries, but differences were found inter- and intra-population in δ13C values for pups from different groups (ANOVA P < 0.05). Our results indicate that diet diversification is present in the Galapagos sea lion and may play important role to the survival of the species in a habitat where pinniped populations are limited.

The Guadalupe fur seal population at San Benito Islands is experiencing an exponential increase (r = 18.9%, r2 = 0.96) in this first phase of population growth. A similar pattern (r = 13.3%) was observed for Guadalupe fur seals from Gudalupe Island. The relatively rapid growth of the fur seal population on the San Benito Islands is due mainly to an increase in the number of females during the first 2 yrs and of juveniles during the last 2 yrs. The number of males and pups has been fairly constant over time. Apparently this first phase of population growth has been largely the result of the emigration of animals from GI; the only other breeding colony of the species.

Summary 1. Understanding spatial structure and identifying subpopulations are critical for estimating population growth rates and extinction risk, and as such essential for e!ective conservation planning. However, movement and spatiotemporal environmental data are often unavailable, limiting our abilitytodirectlydefine subpopulations and theirlevel of asynchrony. 2. This study applies a recently developed statistical technique using time-series analysis of abundance data to identify subpopulations. The approach uses multivariate state-space models and Akaike’s Information Criterion-based model selection to quantify the data support for di!erent subpopulation numbers and configurations. This technique is applied to the population of CaliforniasealionsZalophuscalifornianusintheGulfofCalifornia, Mexico, distributedacross13breeding sites. 3. The abundanceof California sea lions in the Gulfof California has declinedover the lastdecade, though not all areas have been equally a!ected. In light of this variation, it is important to understandthepopulation structuretoensureaccurateviabilityassessmentsand e!ectivemanagement. 4. Ourdatasupportthehypothesisthatthe GulfofCaliforniasealion population hasfoursubpopulations, each with 2‐5 breeding sites. The dynamics between several adjacent subpopulations were correlated, suggesting that they experience similar environmental variation. For each subpopulation,weestimatedlong-termgrowthrates,aswell astheenvironmental andobservationvariation. 5. For most of the subpopulations, our estimates of growth rates were considerably lower than those previously reported. In addition, we found considerable variability across subpopulations in theirprojectedriskof severedeclineoverthe next 50 years. 6. Synthesis and applications. We illustrate a new multivariate state-space modelling technique that usestimeseriesofabundancetoquantifythedatasupportfordi!erentsubpopulationconfigurations. OuranalysisoftheCaliforniasealionpopulationintheGulfofCaliforniaindicatesthatthepopulationisspatiallystructuredintofoursubpopulations,eachexhibitingdistinctrisksofextinction.Based on our results, we recommend that conservation and management e!orts in the Gulf of California focus on the two subpopulations with high probabilities of extinction within the next 50 years (NorthernMidri!,SouthernMidri!).Multivariatestate-spacemodelsprovideapracticalapproach to determine the spatial structure of virtually any species; they may be particularly useful for species ofconservationconcernforwhichdataondispersalandenvironmentaldriversarelikelytobescarce.

Spatial or temporal isotopic variation, or both, in primary producers must be controlled for when investigating the foraging and trophic ecology of top consumers using isotopic data. Populations of the sister species Zalophus californianus and Z. wollebaeki are separated by approximately 3,350 km in the eastern tropical Pacific Ocean, which prevents contact and mixing between the 2 populations. To explore differences in trophic ecology between these species, as well as the impact of differences in baseline food-web isotope values between the 2 regions, we compared conventional dietary data derived from analyses of scat contents to isotopic values of hair collected from pups at 13 rookeries in the Gulf of California (Z. californianus) and 11 rookeries on the Galápagos Islands (Z. wollebaeki). Mean ± 1 SD δ13C and δ15N values were −15.9‰ ± 0.5‰ and 21.8 ± 0.7‰ in the Gulf of California, whereas for the Galápagos they were −14.5‰ ± 0.5‰ and 13.1‰ ± 0.5‰. Examination of scat data suggested overlap in 6 of the 10 most common prey consumed by sea lions. Trophic level (TL) derived from scat analysis was positively related with δ15N values for the Gulf of California rookeries, but estimates of TL for each region were similar (4.4 for Galápagos and 4.1 for Gulf of California), suggesting that foraging behavior makes a limited contribution to the large difference in δ15N value between the 2 populations. Particulate organic matter δ15N values near the Galápagos Islands are 5.3‰ lower than values in the Gulf of California, suggesting that the baseline food-web values account for approximately two-thirds of the observed difference in pup hair δ15N values. This study may provide clues to better understand isotopic values of marine top predators migrating across the eastern Pacific Ocean.

We investigate the phylogeography of California (Zalophus californianus) and Galapagos (Z. wollebaeki) sea lions and describe within-population structure for the California sea lion based on mitochondrial DNA. Fifty control-region haplotypes were found, 41 from Z. californianus and 9 from Z. wollebaeki, with three fixed differences between the two species. Ranked population boundaries along the range of Z. californianus were defined based on the Monmonier Maximum Difference Algorithm, resulting in five genetically distinct populations, two in the Pacific Ocean and three inside the Gulf of California. A Minimum Spanning Network showed a strong phylogeographic signal with two well-defined clusters, Z. californianus and Z. wollebaeki, separated by six base-pair differences, supporting the existence of two genetically distinct species with an estimated divergence time of ~0.8 Ma. Results are discussed in the context of the historical geologic and paleoceanographic events of the last 1 Ma in the eastern Pacific.

California sea lions (Zalophus californianus) in the Gulf of California have declined by 20% over the past 2 decades. The lack of data on life-history parameters for this species has limited the development of demographic models to assess the status of this population. We estimated age- and sex-specific annual survival probabilities for California sea lions using resighting data on 5 pup cohorts from 1981 to 2006. We modeled apparent survival and resighting probability using age-class, sex, and time as potential explanatory variables. Apparent survival rates varied for different age- and sex-classes. Only survival of pups varied by year (from 0.556 to 0.998). Survival was the same for immature males and females (0.90), but differed by sex for young (males = 0.90, females = 0.97) and old (males = 0.75, females = 0.91) adults. Resighting probabilities varied by time, age-class, and sex. Resighting probabilities were higher for females than for males, and lowest for juveniles. The survival estimates presented here provide practical insight into understanding age- and sex-specific survival rates for California sea lions.

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 Martir 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.

Three fundamental foraging patterns in air-breathing marine vertebrates have been described: epipelagic, mesopelagic and benthic. Many sea lion species with access to extensive con- tinental shelves have been described as benthic foragers. Coincidently these species are considered threatened. The Galapagos sea lion Zalophus wollebaeki, a top predator in the Galapagos Islands, is also considered threatened in this ecosystem. Sea lions at the central part of the archipelago have access to a vast continental shelf. For this reason we hypothesized that sea lions within this region would dive benthically. In addition, effective protection and conservation of this species requires knowledge of their foraging patterns and habitat utilization. We investigated the diving behaviour and habitat utilization of female Z. wollebaeki of a centrally located colony situated inside the high- est density area of the population using time-depth recorders and satellite telemetry. Three distinct foraging patterns were found and described (shallow, deep and bottom divers), and individuals uti- lizing each pattern foraged in different locations. Epipelagic, mesopelagic and benthic dives were exhibited in the sea lions' diving behaviour, but these dive types were not exclusively associated with a foraging pattern. Between foraging trips females hauled out more frequently on other islands than they did on their breeding colony. The finding of 3 distinct foraging patterns that differ spatially has direct implications for management, particularly with regard to fisheries interactions. Marine pro- tected areas can be implemented in the regions described as Z. wollebaeki foraging areas. Z. wolle- baeki's wide foraging range coupled with their use of multiple haul-out sites should be considered in future studies when determining foraging trip lengths and habitat utilization since presence/absence from the colony does not reflect foraging trip length.