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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.

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.

As a top predator, California sea lions (Zalophus californianus) can be used as sentinels to record ecosystem conditions because of the trace metals that bioaccumulate in their tissues and are biomagnified in the trophic webs. The concentration of 11 trace elements (Al, As, Cd, Co, Cu, Fe, Hg, Ni, Pb, Se, and Zn) was measured in California sea lion skulls from four regions of the Gulf of California (Mexico): Northern Gulf, Ángel de la Guarda, Central Gulf, and Southern Gulf. The aims of this study were (1) to determine and compare the mean concentration of trace elements among the four regions, and (2) to estimate the pollution situation of each region using the more toxic trace elements. The elements found in higher concentration in sea lion bone were Al (overall mean of 73.70 µg g–1) and Zn (60.78 µg g–1). Only the concentration of As and Hg showed significant differences among regions: As was higher in the Central Gulf than in Ángel de la Guarda and the Northern Gulf, while Hg was higher in the Northern Gulf and Ángel de la Guarda than in the Central and Southern Gulf. The comparative analysis of the pollution situation indicated that the Central Gulf was the most affected by As and Cd, and the Northern Gulf and Ángel de la Guarda by Hg. Regions with different trace element concentrations may reflect different feeding habits and oceanographic conditions, and are congruent with other regional patterns suggested for the Gulf of California.

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.

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.

Stable isotope and scat analyses were used in concert to determine trophic level and dietary overlap among California sea lions from different rookeries in the Gulf of California. Isotopic analysis of the fur of sea lion pups revealed differences in δ 15 N and δ 13 C values among rookeries during the breeding season. Mean δ 15 N and δ 13 C values varied from 20.2‰ to 22.4‰ and from -15.4%o to -14.0‰, respectively. The pattern of differences among rookeries was similar between years in most cases. Isotopic variations among rookeries were associated with differences in prey consumption. There was a significant correlation between δ 15 N value and trophic level, as determined by scat analysis. Joint application of isotopic and scat analyses allowed us to identify how the feeding habits of sea lions vary with location. Our results suggest the presence of spatial structure in available prey as well as the localized use of prey by sea lions across the Gulf of California.

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 (lambda1), 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.

Estimates of demographic parameters are essential for assessing the status of populations and assigning conservation priority. In light of the difficulties associated with obtaining such estimates, vital rates are rarely available even for well-studied species.We present the first estimates of age-specific birth rates for female California sea lions (Zalophus californianus) >10 yr of age. These rates were estimated from the reproductive histories of five cohorts of animals branded as pups between 1980 and 1984 at Los Islotes colony in the Gulf of California, Mexico. Age-specific birth rates varied among age classes and ranged between 0.06 and 0.80. The highest birth rates were observed for females between 10 and 15 yr of age, with decreased birth rates among older females. The effect of age, year, and resighting effort were explored using logistic regression analysis. Based on Akaike Information Criteria, birth rates were best explained by female age, while year and resighting effort did not have a significant effect. The odds ratio of producing a pup decreased with age but did not change significantly for middle-aged females. Our estimates of age-specific birth rates are consistent with general patterns observed for other large vertebrates

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.

espanolSe analizaron algunos componentes conductuales del cuidado materno en el lobo marino de California en una colonia pequena del sur del Golfo de California, comparandolos entre un ano de condiciones ambientales normales (1996) y uno con condiciones afectadas por El Nino (1998). Los componentes que se consideraron fueron frecuencia, duracion, intensidad y tasa del amamantamiento, y frecuencia y duracion de los viajes de alimentacion. Los parametros de la intensidad de la inversion materna que se emplearon fueron peso, densidad y tasa de crecimiento de las crias. En ningun ano se encontraron diferencias significativas entre el peso de las crias machos y hembras, en la tasa de crecimiento ni en la densidad corporal; al comparar estos parametros entre anos tampoco hubo diferencias. La tasa diaria de amamantamiento y la intensidad disminuyeron en 1996 conforme las crias crecian, pero en 1998 la tasa de amamantamiento se mantuvo constante y la intensidad se incremento. Los resultados indican que la diferencia en 1998 posiblemente sea una estrategia alternativa de crianza cuando las condiciones ambientales se encuentran empobrecidas. La duracion de los viajes de alimentacion fue significativamente mayor en 1998 que en 1996 (2.05 ± 0.87 d y 1.3 ± 0.60 d, respectivamente); para 1996 se estimo la duracion del ciclo (tiempo en viaje de alimentacion + periodo de atencion en tierra) en 2.07 ± 1.5 d. Dos variables se relacionaron con la tasa de crecimiento de las crias: la intensidad del amamantamiento y la frecuencia de los viajes de alimentacion. EnglishBehavioural components of maternal assistance in the California sea lion at a small colony in the southern part of the Gulf of California were analyzed and compared between one year with normal environmental conditions (1996) and one influenced by El Nino (1998). The components considered were the frequency, duration, intensity and rate of lactation, and the frequency and duration of the feeding trips. The parameters employed to measure the intensity of the maternal investment were the weight, density and growth rate of the pups. No significant differences were found in both years between the weight of female and male pups, growth rate and body density; when comparing these parameters between the years, no significant differences were found either. In 1996, the daily lactation rate and the intensity decreased while the pups grew, but in 1998 the lactation rate remained constant and the intensity increased. The results indicate that the difference found in 1998 is probably due to the use of an alternative breeding strategy when the environmental conditions are poor. The duration of the feeding trips was significantly greater in 1998 than in 1996 (2.05 ± 0.87 d and 1.3 ± 0.60 d, respectively). For 1996, the estimation of the cycle duration (time of feeding trip + time of assistance in rookery) was 2.07 ± 1.5 d. Two variables were associated with the growth rate of the pups: intensity of lactation and frequency of the feeding trips.

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 < 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.

Several years of census at two colonies in the Gulf of California (Los Cantiles, situated in the northern portion and Los Islotes in the south) were used to define the reproductive period of the California sea lion (Zalophus californianus californianus) in this area. The pattern of births (the length of the breeding period and the mean date of birth) is described using two models: a direct model, based on cumulative counts, and an indirect model, which related the photoperiod and the implanting of the blastocyte. The results of both models show that births begin earlier at Los Cantiles and that synchronization among females was less pronounced at Los Islotes. The mean arrival time of females was similar at both colonies, but differences were observed among the males. This suggests the existence of distinct competitive tactics that may be related to geographic position and the size of the colony. When results are compared with those from San Nicolas (California), it is clear that at Los Cantiles, the reproductive period is more prolonged, begins earlier, and that the time between giving birth and copulation for Gulf sea lions (intervals >30 days) is greater than that estimated for California (21 days).

A primary hepatic carcinoma with a neuroendocrine pattern was detected in an adult female California sea lion (Zalophus californianus) found dead on Granito Island in the Gulf of California (Mexico) in January 1996. At necropsy, several light yellow nodules of different sizes were observed on the entire surface of the liver and spleen. Microscopic examination of these nodules using routine haematoxylin-eosin stain, revealed cubic, polyhedral and pleomorphic cells with three to four bizarre mitotic figures per field (40×). An immunohisto-chemistry test revealed a positive reaction of indirect immunoperoxide to cytokeratin (CK2). This is the first known case of a primary hepatic carcinoma in free-ranging California sea lions from Mexican waters.

Human exploitation can lead to genetic bottlenecks associated with reduced genetic variability and lower fitness. The population of California sea lions (Zalophus californianus) in the Gulf of California, Mexico, was hunted during the 19th and 20th centuries, potentially leading to a genetic bottleneck; however, even exploitation that leads to low population sizes does not always cause genetic bottlenecks. Understanding the genetic consequences of past sea lion hunts is critical to the conservation of the Gulf of California sea lion population, which is currently declining and is genetically distinct from other populations. We used available data from 10 amplified polymorphic microsatellite loci in 355 individuals from six Mexican colonies. Microsatellite data were analyzed using diverse approaches (BOTTLENECK and M-ratio) to determine if a genetic bottleneck had occurred. Our results indicate that human exploitation did not cause a genetic bottleneck in the sea lion population of the Gulf of California. Simulation analyses revealed that a reduction in genetic variability would have been detected if fewer than 100 individuals had remained after exploitation. We conclude that past exploitation was not as severe as previously thought and did not cause a genetic bottleneck in the Gulf of California sea lion population. Nevertheless, historical hunts specifically targeted adult males and this sexbiased exploitation may have influenced the population dynamics and overall fitness. Key words: genetic variability, male-biased exploitation, Pinnipedia, Gulf of California. La explotacion humana puede causar cuellos de botella geneticos asociados con una variabilidad genetica reducida y menor aptitud. La poblacion del lobo marino de California (Zalophus californianus) en el Golfo de California, Mexico, fue objeto de una explotacion prolongada durante los siglos XIX y XX que pudo haber causado un cuello de botella genetico. Sin embargo, la explotacion que deriva tamanos poblacionales bajos no siempre causa cuellos de botella geneticos. El conocimiento de las consecuencias geneticas de la caza del lobo marino de California es critico para la conservacion de la poblacion del Golfo de California, que esta en declive y es geneticamente distinta de otras poblaciones. En este estudio usamos una base de datos de 10 marcadores polimorficos de microsatelite amplificados en 355 individuos pertenecientes a seis colonias mexicanas. Estos datos fueron analizados con diversos metodos (BOTTLENECK y razon M) para determinar si ocurrio un cuello de botella genetico. Nuestros resultados indican que la explotacion historica del lobo marino no causo un cuello de botella genetico en la poblacion del Golfo de California; sin embargo, las simulaciones sugieren que si la poblacion hubiese sido reducida a menos de 100 individuos si hubiesemos detectado una reduccion de la variabilidad genetica. Con base en estos resultados concluimos que la explotacion historica de esta poblacion no fue tan intensa como se pensaba previamente y, por tanto, no causo un cuello de botella genetico. No obstante, la explotacion se concentro en machos adultos y este sesgo podria haber afectado la dinamica poblacional de estas colonias y su aptitud general.

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 (SPCB) in the pups averaged 104 mg/kg lipid (range, 49-384 mg/kg). No statistically significant differences in SPCB 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 SPCB 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. Keywords—Polybrominated diphenyl ethers Polychlorinated biphenyls Galapagos sea lions Galapagos Islands Atmospheric transport

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 (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 (r 2=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.

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 titersor = 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.