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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.

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.

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.

Tooth wear in marine mammals has been attributed to age, feedinghabits, behavior, and contaminants. Advanced tooth wear in some Californiasea lions, including some of very young age (<5 yr), in the Gulf of California,suggests that there are variations in chemical composition of toothparts, wherein the concentrations of certain trace minerals might be anomalous,making them more susceptible to erosion. The concentrations of theessential minerals Ca, P, K, Na, Fe, Mg, and Zn in the dentition of Zalophusc. californianus are documented for the first time and are compared for sealion teeth with different degrees of wear. Canine teeth and molars from 45skulls collected at 15 localities since 1978 were digested in perchloric acidand analyzed using atomic adsorption spectrometry, the results beingexpressed 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 wasone between ages (p = 0.02). A higher degree of wear was observed up to 7yr of age than from this age onward. Mineral concentrations did notexplain 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 particularlysignificant for the females (r2 = 0.112, r = -0.335, p = 0.039). Females couldbe more prone to decalcification because of their annual bone investmentin their offspring. Animals of both sexes were susceptible to tooth wear astheir age increased, but the higher frequency of animals between 4 and 7yr suggests an impact on survival at early stages probably linked to deficientfeeding and chronic malnutrition. [ABSTRACT FROM AUTHOR]