Metal-specific biomagnification and trophic dilution in the coastal foodweb of the California sea lion (Zalophus californianus) off Bahía Magdalena, Mexico: The role of the benthic-pelagic foodweb in the trophic transfer of trace and toxic metals.

Trace metals concentrations along with stable isotopes ratios were measured in marine algae, sea grass, sponges, echinoderms, mollusks, crustaceans, fishes, and the California sea lion, to assess the bioaccumulation potential and detect potential risks for top predators off Bahia Magdalena, Mexico. We assessed the trophic magnification factor (TMF) to determine the potential for biomagnification of 11 trace metals. The concentrations of Fe and Zn were one order of magnitude higher than all other metals. Concentrations of As, Cu, Cd, Co, Cr, Fe, Mn and Ni correlated negatively with trophic level, supporting trophic dilution (TMF < 1, p > 0.05), while Zn and Hg had significant trophic magnification (TMF > 1, p < 0.05) when assessing only the benthic-pelagic foodweb. This research provides a baseline concentration of metals in multiple species, metal-specific foodweb bioaccumulation and biomagnification of mercury, underscoring the key role of the macrobenthic community as biovectors for trophic transfer of Hg through the foodweb to the California sea lion.

Determinants of genetic variation across eco-evolutionary scales in pinnipeds.

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 ([Formula: see text] = 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.

Trace elements in marine organisms of Magdalena Bay, Pacific Coast of Mexico: Bioaccumulation in a pristine environment.

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.

Vibrissa growth rate in California sea lions based on environmental and isotopic oscillations.

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.

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

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

Metal concentrations in demersal fish species from Santa Maria Bay, Baja California Sur, Mexico (Pacific coast).

Concentrations of 11 trace metals (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd, As, Hg) in 40 fish species from Santa Maria Bay, Baja California Sur, Mexico, the strategically important area for marine mammals and organisms were analyzed. Based on their concentrations the ranking of metals Fe>Zn>Ni>Cr>Mn>Pb>Cu>Co>As>Cd>Hg suggests that organism size, metabolism and feeding habits are correlated with metal concentrations. Local geological formations affect the concentrations of different metals in the aquatic environment and are subsequently transferred to fishes. The correlation analysis suggests that metabolism and nurturing habits impact the concentration of metals. Concentrations of Fe and Mn appear to be influenced by scavenging and absorption processes, which vary by species. The considerable variability in the metal concentrations obtained in different species underscores the importance of regular monitoring.

Infection of California sea lions (Zalophus californianus) with terrestrial Brucella spp.

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.

Timing of isotopic integration in marine mammal skull: comparative study between calcified tissues.

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 δ(15)N and δ(13)C 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 δ(15)N and δ(13)C values were not different between bone structures, indicating similar turnover rates, metabolic activity and amino acid compositions. The differences in the observed δ(13)C values between tissues are probably indicative of differences in their amino acid compositions, although the similarities in δ(15)N 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 δ(15) N 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.

Polychlorinated biphenyls and polybrominated diphenyl ethers in Galapagos sea lions (Zalophus wollebaeki).

Concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) were measured in muscle-blubber biopsy samples from 21 Galapagos sea lion (Zalophus wollebaeki) pups that were live captured in the Galapagos Islands (Ecuador) using gas chromatography/high-resolution mass spectrometry. Only traces of PBDEs were detected in one male pup, whereas PCDDs and PCDFs were not detected in any sample. The total concentration of PCBs (ΣPCB) in the pups averaged 104 µg/kg lipid (range, 49-384 µg/kg). No statistically significant differences in ΣPCB were observed among the four study sites in the Galapagos Islands. Concentrations of PCB congeners in Galapagos sea lion pups were dominated by low-molecular-weight congeners. These results suggest that global transport is the main source for PCBs in Galapagos sea lions. The ΣPCB levels were below immunotoxic and endocrine-disruption thresholds in pinnipeds, suggesting a limited risk of adverse health effects. The present study indicates that Galapagos sea lions can serve as a useful sentinel of pollutants with a long-range transport capacity and that Galapagos Islands are not exempt from the threats of global pollutants despite its remote locale.

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.

A noninvasive demographic assessment of sea lions based on stage-specific abundances.

A pressing need exists to develop new approaches for obtaining information on demographic rates without causing further threats to imperiled animal populations. In this paper, we illustrate and apply a data-fitting technique based on quadratic programming that uses stage-specific abundance data to estimate demographic rates and asymptotic population growth rates (lambda). We used data from seven breeding colonies of California sea lions (Zalophus californianus) in the Gulf of California, Mexico. Estimates of lambda were similar to those from previous studies relying on a diffusion approximation using trends in total abundance. On average, predicted abundances were within 24% of the observed value for the inverse estimation method and within 29% of the observed value for the diffusion approximation. Our results suggest that three of the seven populations are declining (lambda < 1), but as many as six may be at risk. Elasticity and sensitivity analyses suggest that population management in most sites should focus on the protection of adults, whose survival generally contributes the most to lambda. The quadratic programming approach is a promising noninvasive technique for estimating demographic rates and assessing the viability of populations of imperiled species.

Estimating sustainable bycatch rates for California sea lion populations in the Gulf of California.

Commercial and subsistence fisheries pressure is increasing in the Gulf of California, Mexico. One consequence often associated with high levels of fishing pressure is an increase in bycatch of marine mammals and birds. Fisheries bycatch has contributed to declines in several pinniped species and may be affecting the California sea lion (Zalophus californianus) population in the Gulf of California. We used data on fisheries and sea lion entanglement in gill nets to estimate current fishing pressure and fishing rates under which viable sea lion populations could be sustained at 11 breeding sites in the Gulf of California. We used 3 models to estimate sustainable bycatch rates: a simple population-growth model, a demographic model, and an estimate of the potential biological removal. All models were based on life history and census data collected for sea lions in the Gulf of California. We estimated the current level of fishing pressure and the acceptable level of fishing required to maintain viable sea lion populations as the number of fishing days (1 fisher/boat setting and retrieving 1 day's worth of nets) per year. Estimates of current fishing pressure ranged from 101 (0-405) fishing days around the Los Machos breeding site to 1887 (842-3140) around the Los Islotes rookery. To maintain viable sea lion populations at each site, the current level of fishing permissible could be augmented at some sites and should be reduced at other sites. For example, the area around San Esteban could support up to 1428 (935-2337) additional fishing days, whereas fishing around Lobos should be reduced by at least 165 days (107-268). Our results provide conservation practitioners with site-specific guidelines for maintaining sustainable sea lion populations and provide a method to estimate fishing pressure and sustainable bycatch rates that could be used for other marine mammals and birds.

Extinciones en el mar: mitos y realidades / Extinctions in the sea: myths and realities

No hay duda de que el hombre ha provocado cantidad de extinciones, sobre todo en el medio terrestre. En el mar, en cambio, comprobar más allá de la duda razonable que el último representante de una especie ha desaparecido de la faz de la tierra es una tarea más difícil. En el presente trabajo se muestran los resultados más importantes de una rigurosa revisión de las extinciones marinas documentadas durante los últimos 200 años. Se encontró que ~50 por ciento de las extinciones y extirpaciones de especies marinas resultan dudosas porque no se considera información crítica acerca de su distribución espacio-temporal, o bien la evidencia que se utiliza para evaluarlas es insuficiente o inadecuada. Se concluye que 1) el hombre es capaz de eliminar especies marinas, en particular aquellas que naturalmente son más propensas a la extinción; 2) las extinciones registradas en el mar son menos frecuentes que las del medio terrestre, y a pesar de que existe una tendencia positiva en el número promedio de extinciones documentadas durante los siglos XIX y XX, la tendencia de las extinciones registradas es negativa en los últimos 100 años; 3) antes de declarar una especie como extinta, la evidencia que apoya tal declaración debe ser evaluada con todo el rigor científico; y 4) declarar de manera prematura la extinción de especies, pudiera afectar negativamente los propios esfuerzos que se inviertan para la conservación.

Relation of dental wear to the concentrations of essential minerals in teeth of the California sea lion Zalophus californianus californianus.

Tooth wear in marine mammals has been attributed to age, feeding habits, behavior, and contaminants. Advanced tooth wear in some California sea lions, including some of very young age (<5 yr), in the Gulf of California, suggests that there are variations in chemical composition of tooth parts, wherein the concentrations of certain trace minerals might be anomalous, making them more susceptible to erosion. The concentrations of the essential minerals Ca, P, K, Na, Fe, Mg, and Zn in the dentition of Zalophus c. californianus are documented for the first time and are compared for sea lion teeth with different degrees of wear. Canine teeth and molars from 45 skulls collected at 15 localities since 1978 were digested in perchloric acid and analyzed using atomic adsorption spectrometry, the results being expressed in milligrams per 100 g. An index of tooth wear (Id) was established, involving the average wear on the teeth and the age of the organism. No significant difference was detected in the variables, but there was one between ages (p = 0.02). A higher degree of wear was observed up to 7 yr of age than from this age onward. Mineral concentrations did not explain the excessive wear observed (correlation, p > 0.09; ANOVA, p > 0.15); however, the Ca concentration of the teeth was inversely proportional to the age of the animal (sexes combined, p = 0.026) and particularly significant for the females (r2 = 0.112, r = -0.335, p = 0.039). Females could be more prone to decalcification because of their annual bone investment in their offspring. Animals of both sexes were susceptible to tooth wear as their age increased, but the higher frequency of animals between 4 and 7 yr suggests an impact on survival at early stages probably linked to deficient feeding and chronic malnutrition.

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.