New polymorphic microsatellite markers for California sea lions (Zalophus californianus)

Nine microsatellite loci were isolated and characterized from California sea lions (Zalophus californianus). In addition, two of five loci tested from harbour seal (Phoca vitulina) produced a single, clear band in Z. californianus, as did one out of five loci from grey seal (Halichoerus grypus) and one out of two loci from elephant seal (Mirounga sp.). No locus tested from South American fur seal (Arctocephalus australis) amplified in Z. californianus. Locus variability was assessed in California sea lions from Los Islotes rookery, Baja California Sur, Mexico. All loci were variable, with allele numbers ranging from three to 12. © 2005 Blackwell Publishing Ltd.Peer Reviewe

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

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

Stable isotope differences between sea lions (Zalophus) from the Gulf of California and Galapagos Islands

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.Instituto Politécnico Nacional (IPN). Centro Interdisciplinario de Ciencias MarinasCiencias marinasPD

The Making of a Productivity Hotspot in the Coastal Ocean

Highly productive hotspots in the ocean often occur where complex physical forcing mechanisms lead to aggregation of primary and secondary producers. Understanding how hotspots persist, however, requires combining knowledge of the spatio-temporal linkages between geomorphology, physical forcing, and biological responses with the physiological requirements and movement of top predators.) off the Baja California peninsula, Mexico.We have identified the set of conditions that lead to a persistent top predator hotspot, which increases our understanding of how highly migratory species exploit productive regions of the ocean. These results will aid in the development of spatially and environmentally explicit management strategies for marine species of conservation concern

Weak Polygyny in California Sea Lions and the Potential for Alternative Mating Tactics

Female aggregation and male territoriality are considered to be hallmarks of polygynous mating systems. The development of genetic parentage assignment has called into question the accuracy of behavioral traits in predicting true mating systems. In this study we use 14 microsatellite markers to explore the mating system of one of the most behaviorally polygynous species, the California sea lion (Zalophus californianus). We sampled a total of 158 female-pup pairs and 99 territorial males across two breeding rookeries (San Jorge and Los Islotes) in the Gulf of California, Mexico. Fathers could be identified for 30% of pups sampled at San Jorge across three breeding seasons and 15% of sampled pups at Los Islotes across two breeding seasons. Analysis of paternal relatedness between the pups for which no fathers were identified (sampled over four breeding seasons at San Jorge and two at Los Islotes) revealed that few pups were likely to share a father. Thirty-one percent of the sampled males on San Jorge and 15% of the sampled males on Los Islotes were assigned at least one paternity. With one exception, no male was identified as the father of more than two pups. Furthermore, at Los Islotes rookery there were significantly fewer pups assigned paternity than expected given the pool of sampled males (p<0.0001). Overall, we found considerably lower variation in male reproductive success than expected in a species that exhibits behavior associated with strongly polygynous mating. Low variation in male reproductive success may result from heightened mobility among receptive females in the Gulf of California, which reduces the ability of males to monopolize groups of females. Our results raise important questions regarding the adaptive role of territoriality and the potential for alternative mating tactics in this species

Maternal care in the California sea lion at Los Islotes, Gulf of California, Mexico

 Behavioural 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 Niño 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

Ecological factors that determine distribution and abundance of the California sea lion Zalophus Californianus in the Gulf Of California

The population of the California sea lion Zulophus californianus (Lesson, 1828) in the Gulf of California during the breeding seasons of the 1980’s was estimated at 23,256 individuals, and 31,393 if census adjustments are applied. Of this total (23,256), 6.9% were adult males, 5.0% subadult males, 40.7% adult females, 23.9% juveniles, 22.7% pups (less than one year of age) and 0.8% were termed miscellaneous. Eighty-six percent of the 29 sea-lion colonies studied were on islands, while the remaining colonies occupied capes of the mainland. However, around 98.8% of the sea-lion population was counted on islands. The number of islands (available habitat) did not determine the sea-lion distribution in the gulf, but the concentration of its usual preys (sardine, anchovy, mackerel and hake) did. Eighty-two percent of the sea-lion population and its pup production took place in the northern region of the Gulf of California (from Isla San Esteban northward), which seems to be associated with the major abundance of small pelagic fish in the gulf. California sea lions tend to inhabit small- and medium-sized islands (less than 3 km in length), which amount for 80% of the sea-lion population. The probable factors that determine the selection of islands this size are: 1) the absence of terrestrial predators, 2) easier communication of breeding animals and 3) sexual selection advantage for mating individuals. The operational sex ratio varied according to island size in a negative exponential trend. More adult females were available per adult males on smaller islands, since reduced space clumped the females. This clumping effect enhances a higher male-male competition (with an evident advantage for males), but also a higher quality of territorial males for the breeding females

New polymorphic microsatellite markers for California sea lions (Zalophus californianus)

Nine microsatellite loci were isolated and characterized from California sea lions (Zalophus californianus). In addition, two of five loci tested from harbour seal (Phoca vitulina) produced a single, clear band in Z. californianus, as did one out of five loci from grey seal (Halichoerus grypus) and one out of two loci from elephant seal (Mirounga sp.). No locus tested from South American fur seal (Arctocephalus australis) amplified in Z. californianus. Locus variability was assessed in California sea lions from Los Islotes rookery, Baja California Sur, Mexico. All loci were variable, with allele numbers ranging from three to 12. © 2005 Blackwell Publishing Ltd.Peer Reviewe