Violetta R Beklemisheva
Full Text Available Karyotype evolution in Carnivora is thoroughly studied by classical and molecular cytogenetics and supplemented by reconstructions of Ancestral Carnivora Karyotype (ACK. However chromosome painting information from two pinniped families (Odobenidae and Otariidae is noticeably missing. We report on the construction of the comparative chromosome map for species from each of the three pinniped families: the walrus (Odobenus rosmarus, Odobenidae-monotypic family, near threatened Steller sea lion (Eumetopias jubatus, Otariidae and the endemic Baikal seal (Pusa sibirica, Phocidae using combination of human, domestic dog and stone marten whole-chromosome painting probes. The earliest karyological studies of Pinnipedia showed that pinnipeds were characterized by a pronounced karyological conservatism that is confirmed here with species from Phocidae, Otariidae and Odobenidae sharing same low number of conserved human autosomal segments (32. Chromosome painting in Pinnipedia and comparison with non-pinniped carnivore karyotypes provide strong support for refined structure of ACK with 2n = 38. Constructed comparative chromosome maps show that pinniped karyotype evolution was characterized by few tandem fusions, seemingly absent inversions and slow rate of genome rearrangements (less then one rearrangement per 10 million years. Integrative comparative analyses with published chromosome painting of Phoca vitulina revealed common cytogenetic signature for Phoca/Pusa branch and supports Phocidae and Otaroidea (Otariidae/Odobenidae as sister groups. We revealed rearrangements specific for walrus karyotype and found the chromosomal signature linking together families Otariidae and Odobenidae. The Steller sea lion karyotype is the most conserved among three studied species and differs from the ACK by single fusion. The study underlined the strikingly slow karyotype evolution of the Pinnipedia in general and the Otariidae in particular.
Cullen, Thomas M; Fraser, Danielle; Rybczynski, Natalia; Schröder-Adams, Claudia
Sexual selection is one of the earliest areas of interest in evolutionary biology. And yet, the evolutionary history of sexually dimorphic traits remains poorly characterized for most vertebrate lineages. Here, we report on evidence for the early evolution of dimorphism within a model mammal group, the pinnipeds. Pinnipeds show a range of sexual dimorphism and mating systems that span the extremes of modern mammals, from monomorphic taxa with isolated and dispersed mating to extreme size dimorphism with highly ordered polygynous harem systems. In addition, the degree of dimorphism in pinnipeds is closely tied to mating system, with strongly dimorphic taxa always exhibiting a polygynous system, and more monomorphic taxa possessing weakly polygynous systems. We perform a comparative morphological description, and provide evidence of extreme sexual dimorphism (similar to sea lions), in the Miocene-aged basal pinniped taxon Enaliarctos emlongi. Using a geometric morphometric approach and combining both modern and fossil taxa we show a close correlation between mating system and sex-related cranial dimorphism, and also reconstruct the ancestral mating system of extant pinnipeds as highly polygynous. The results suggest that sexual dimorphism and extreme polygyny in pinnipeds arose by 27 Ma, in association with changing climatic conditions. © 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.
Kienle, Sarah S; Berta, Annalisa
One adaptation crucial to the survival of mammalian lineages that secondarily transitioned from land to water environments was the ability to capture and consume prey underwater. Phocid seals have evolved diverse feeding strategies to feed in the marine environment, and the objectives of this study were to document the specialized feeding morphologies and identify feeding strategies used by extant phocids. This study used principal component analysis (PCA) to determine the major axes of diversification in the skull for all extant phocid taxa and the recently extinct Caribbean monk seal (n = 19). Prey data gathered from the literature and musculoskeletal data from dissections were included to provide a comprehensive description of each feeding strategy. Random Forest analysis was used to determine the morphological, ecological and phylogenetic variables that best described each feeding strategy. There is morphological evidence for four feeding strategies in phocids: filter; grip and tear; suction; and pierce feeding. These feeding strategies are supported by quantitative cranial and mandibular characters, dietary information, musculoskeletal data and, for some species, behavioral observations. Most phocid species are pierce feeders, using a combination of biting and suction to opportunistically catch prey. Grip and tear and filter feeding are specialized strategies with specific morphological adaptations. These unique adaptations have allowed leopard seals (Hydrurga leptonyx) and crabeater seals (Lobodon carcinophaga) to exploit novel ecological niches and prey types. This study provides the first cranial and mandibular morphological evidence for the use of specialized suction feeding in hooded seals (Cystophora cristata), northern elephant seals (Mirounga angustirostris) and southern elephant seals (Mirounga leonina). The most important variables in determining the feeding strategy of a given phocid species were cranial and mandibular shape, diet, and phylogeny. These results provide a framework for understanding the evolution and adaptability of feeding strategies employed by extant phocid species, and these findings can be applied to other pinniped lineages and extinct taxa.
Full Text Available http://dx.doi.org/10.5007/2175-7925.2013v26n2p185 The hypothesis that pinnipeds have a common origin gained support during the 1980s in discussions focused on the systematics of the group. However, the limited knowledge of the anatomy of several species and the frequent variation in several character states make it difficult to clarify the phylogenetic relationships of pinnipeds. Our purpose was to review the anatomical characters of the syncranium and dentition used in phylogenetic analyses by studying the otariids Otaria byronia (n=25 and Arctocephalus australis (n=48. Some interpretations of characters presented in the literature were found to be questionable, notably: (1 shape and position of the premaxillary tuberosity; (2 orientation of the maxillary postcanine alveoli; (3 naso-labialis fossa; (4 shape of the jugal contact with the zygomatic process of temporal; (5 relief and length of the tympanic bone; (6 relationship between the height of the condylar process in relation to the lower postcanine teeth alveoli; (7 individualization of the canal of the cochlear aqueduct and round window; (8 separation of the openings for the cranial nerves VII and VIII in the internal auditory meatus; (9 lingual cingulum on the third upper incisor; (10 development of the metaconid of the fifth upper postcanine tooth, and (11 number of roots in the second to fourth upper postcanine teeth and fifth lower postcanine tooth. These observations indicate the relevance and the need for detailed anatomical descriptions of pinnipeds for understanding their phylogenetic relationships and, consequently, their evolutionary relationships.
Rybczynski, Natalia; Dawson, Mary R; Tedford, Richard H
Modern pinnipeds (seals, sea lions and the walrus) are semi-aquatic, generally marine carnivores the limbs of which have been modified into flippers. Recent phylogenetic studies using morphological and molecular evidence support pinniped monophyly, and suggest a sister relationship with ursoids (for example bears) or musteloids (the clade that includes skunks, badgers, weasels and otters). Although the position of pinnipeds within modern carnivores appears moderately well resolved, fossil evidence of the morphological steps leading from a terrestrial ancestor to the modern marine forms has been weak or contentious. The earliest well-represented fossil pinniped is Enaliarctos, a marine form with flippers, which had appeared on the northwestern shores of North America by the early Miocene epoch. Here we report the discovery of a nearly complete skeleton of a new semi-aquatic carnivore from an early Miocene lake deposit in Nunavut, Canada, that represents a morphological link in early pinniped evolution. The new taxon retains a long tail and the proportions of its fore- and hindlimbs are more similar to those of modern terrestrial carnivores than to modern pinnipeds. Morphological traits indicative of semi-aquatic adaptation include a forelimb with a prominent deltopectoral ridge on the humerus, a posterodorsally expanded scapula, a pelvis with relatively short ilium, a shortened femur and flattened phalanges, suggestive of webbing. The new fossil shows evidence of pinniped affinities and similarities to the early Oligocene Amphicticeps from Asia and the late Oligocene and Miocene Potamotherium from Europe. The discovery suggests that the evolution of pinnipeds included a freshwater transitional phase, and may support the hypothesis that the Arctic was an early centre of pinniped evolution.
Full Text Available Cases of dental agenesis, supernumerary teeth and dental losses are presented in three species of South American Otariids: Arctocephalus australis (Zimmermann, 1783, A. tropicalis (Gray, 1872 and Otaria flavescens (Shaw, 1800. For the first time, congenital and acquired dental anomalies were comparatively diagnosed in skull samples from southern Brazil and nearby areas. The skulls and mandibles were accessed in the scientific collection of mammals of the Federal University of Santa Catarina, southern Brazil. Agenesis was found only among maxillary post-canine teeth, especially the distal ones (PC/6, due to an evolutionary trend towards reduction of the number of post-canine teeth in this family. Maxillary and mandibular supernumerary teeth were found in A. australis and A. tropicalis, but their positioning is unrelated to cases regarding phylogenetic and evolutionary implications. Dental losses were found in all species and different stages of alveolar obliteration suggest that this process is common in Otariids and does not affect their survival. The investigation of congenital and acquired dental anomalies in pinnipeds can provide information on dental formula evolution in Pinnipeds and in the phylogenetic relationships among Carnivora.
Ocorrência de Mirounga leonina Linnaeus (Pinnipedia, Phocidae no extremo-sul do Brasil: agressão e patologias Occurrence of Mirüunga leonina Linnaeus (Pinnipedia, Phocidae from Southernmost Brazil: injury and pathologies
César Jaeger Drehmer
Full Text Available A male specimen of Mirounga leonina Linnaeus, 1758 age estimated betvveen 7-8 years old, collected at Santa Vitória do Palmar, Rio Grande do Sul State, soutiiernmost Brazil (32º44'S and 53º22'W is presented. Ali the skeleton was recovered except the rostral region. It shows an advanced osteomyelitis in the lefl dentary, extending from the synfisis until the middle portion of the body; as well as Scheuermann disease at lumbar vertebrae. Such diseases could explain its presence at that locality, where rt was shot. The bullct was recovered from the rostrum, and might be responsible for death. This is the first vhlually complete skeleton of M. leonina recovered from Brazilian coast.
Osteopatologias e alterações dentárias em Otaria byronia (Pinnipedia, Otariidae da costa do Rio Grande do Sul, Brasil Osteopathologies and tooth alterations in Otaria byronia (Pinnipedia, Otariidae from Rio Grande do Sul coast, Brazil
Patrícia Rodrigues Braunn
Full Text Available Bone diseases and tooth alterations in 47 specimens of Otaria byronia (Blainville, 1820, from southern Brazilian coast, were analized. Tooth wear and the associated bone pathologies were determined, as well as their percentuals. The main infection was osteomyelitis associated with tooth alterations, such as fractures and attrition, both of them exposing the pulp chamber. Tooth attrition increases with age, favoring fractures and their complications, including osteomyelitis, causing a high frequency of them in specimens presenting more pronounced tooth wear. In one specimen tuberculosis was found in the maxilla, perhaps primarily pulmonary. The high frequency of enamel hypoplasia might reflect cyclic food deficit. Infections and tooth fractures might be related to behaviour, such as fishermen interaction, territorial fighting, and accidents during food capture.
King, Judith E.
In 1972 and 1973 a total of three young fur seals was stranded in New Caledonia, much further north than any fur seal normally occurs. Comparison of the skulls of these young animals with similar sized skulls of young fur seals from Australia (Arctocephalus pusillus doriferus) and New Zealand (Arcto
Silveira, Tony Leandro Rezende da; Robaldo, Ricardo Berteaux; Pinto Colares, Elton; Bianchini,Adalto; Muelbert, Mônica Mathias Costa; Martínez, Pablo Elias; Pereira, Eliane Machado; Valente, Ana Luisa Schifino
Corynosoma bullosum is a parasite of pinnipeds while Corynosoma cetaceum is considered a parasite of cetaceans. Until now, there were no records of parasitism by C. cetaceum in phocids. This study reports C. bullosum and the first record of C. cetaceum in Mirounga leonina from Antarctica Corynosoma bullosum é um parasito de pinípedes enquanto Corynosoma cetaceum se destaca pelo parasitismo em cetáceos. Até o momento, não haviam registros de C. cetaceum em focídeos. Este estudo relata a oco...
STEWARDSON, CAROLYN L.; HEMSLEY, SUSAN; MEYER, MIKE A.; CANFIELD, PAUL J.; MAINDONALD, JOHN H.
The gross and microscopic anatomy of the Cape fur seal heart, lung, liver, spleen, stomach, intestine and kidneys (n = 31 seals) is described. Absolute and relative size of organs from 30 male seals are presented, with histological examination conducted on 7 animals. The relationship between log body weight, log organ weight and age was investigated using linear regression. Twenty five animals were of known age, while 6 were aged from counts of incremental lines observed in the dentine of tooth sections. For the range of ages represented in this study, body weight changes were accurately described by the exponential growth equation, weight = wort, with body weight increasing by 23% per annum until at least 9–10 y of age. Organ weight increased at a rate of between 25% and 33% per annum until at least 9–10 y of age, with the exception of the intestines, where exponential increase appeared to have ceased by about 7 y. The relationship between body weight and organ weight was investigated using logarithmic transformations of the allometric equation, y = axb, where the exponent b is 1 if organ weight is proportional to body weight. Most organs increased in proportion to the body. However, the heart, liver and spleen had exponents b > 1, suggesting that these organs increased at a faster rate than the body. The basic anatomical features of the viscera were similar to those of other pinnipeds, with some exceptions, including the arrangement of the multilobed lung and liver. Apart from the large liver and kidneys, relative size of the organs did not differ greatly from similar sized terrestrial carnivores. The histological features of the organs were generally consistent with those previously described for this species and other otariids. The heart, as in other pinnipeds, was unlike that of cetacea in not having unusually thick endocardium or prominent Purkinje cells. Notable histological features of the lungs included prominent fibrous septa, prominent smooth muscle bundles, cartilage extending to the level of the alveolar sacs and ample lymphoid tissue. The spleen had a thick capsule, well developed trabeculae and plentiful plasma cells. Abundant parietal cells were present in the fundic glands and lymphoid follicles were present in the gastric lamina propria, particularly in the pyloric region. Small intestinal villi were very long but this could have resulted from underlying chronic inflammation. Lymphoid follicles were prominent in the colon. The kidney reniculi each had a complete cortex, medulla and calyx, but a sportaperi medullaris musculosa was not identified. PMID:10529060
Samuel Gomes de Farias Júnior
Full Text Available On May 12, 2003, a crabeater seal (Lobodon carcinophagus was seen 3km upstream of the mouth of the Cação River (22º54’S; 43º50’W, southern Rio de Janeiro State. It was a female of 212cm in length, weighing approximately 180kg. A week prior (May 5, the same specimen (identified by a parallel scar pattern had been observed at Costão Beach (24º19’S; 47º00’W, Peruíbe, São Paulo State. Two days later, the animal reappeared at Barra do Sahy Beach (23º47’S; 45º33’W, São Sebastião, São Paulo. Subsequently, the seal’s further northerly displacement to Cação River made a total distance covered of 229km. The occurrence of two cold fronts and the prevalence of southern currents in the first fortnight of May may have favored the displacement of this Ocorrência de Lobodon carcinophagus no Rio de Janeiro animal to areas of low latitude in southeastern Brazil. On June 16, 2003, a male of approximately 200cm in length was seen in Tombo Beach (24º00’S ; 46º18’W, Guarujá (São Paulo. It was the second appearance of L. carcinophagus in São Paulo in 41 days. This note confirms the occasional occurrence of this species along the Brazilian coast, and provides insights into the dispersion of the species in the southwestern Atlantic.
Anomalias e patologias dentárias em Arctocephalus G. Saint-Hilaire & Cuvier (Pinnipedia, Otariidae da costa do Rio Grande do Sul, Brasil Tooth anomalies and pathologies in Arctocephalus G. Saint-Hilaire & Cuvier (Pinnipedia, Otariidae of Rio Grande do Sul coast, Brazil
César Jaeger Drehmer
Full Text Available The studied species were Arctocephalus australis (Zimmermann, 1783 and Arctocephalus tropicalis (Gray, 1872, (five specimens of each one. Anomalies were discussed under the light of theories which relate the ancestry of pinnipeds with the Ursidae; as well as concerning the evolutionary trends supposed for the Otariidae. Pathologies were related to alimentary and reproductive habits.
Case 3058. Arctocephalus F. Cuvier, 1826 and Callorhinus Gray, 1859 (Mammalia, Pinnipedia): proposed conservation by the designation of Phoca pusilla Schreber,  as the type species of Arctocephalus; and Otaria Peron, 1816 and Eumetopias Gill, 1866: proposed conservation by the designation of Phoca leonina Molina, 1782 as the type species of Otaria
Gardner, A.L.; Robbins, C.B.
The purpose of this application is to conserve the accustomed understanding and usage of the fur seal name Arctocephalus F. Cuvier, 1826 by the designation of Phoca pusilia Schreber,  as the type species, thus conserving also the name Callorhinus Gray, 1859. At present Phoca ursina Linnaeus, 1758 is the valid type species of both Arctocephalus and Callorhinus. The name Arctocephalus relates to a genus of some seven fur seals from the southern hemisphere, while Callorhinus is used for the single species C. ursinus (Linnaeus) from the northern hemisphere. It is also proposed that the universal understanding of the names Otaria Peron, 1816 and Eumetopias Gill, 1866 should be conserved for the southern and northern sea lions respectively by designating Phoca leonina Molina, 1782 (for which the valid specific name is P. byronia de Blainville, 1820) as the type species of Otaria. At present Phoca jubata Schreber,  is the type species of Otaria and the name Otaria is a senior subjective synonym of Eumetopias. The four genera Arctocephalus, Callorhinus, Otaria and Eumetopias are all placed in the family OTARIIDAE Gray, 1825.
As is usual in university museums, the Zoological Museum of the University of Amsterdam (now Institute of Taxonomic Zoology) had in its collection some representative material of marine Carnivora (Pinnipedia, at the time it was believed that the animals belonged to a monophyletic taxon). Some
Schröder, Christiane; Bleidorn, Christoph; Hartmann, Stefanie; Tiedemann, Ralph
Investigating the dog genome we found 178965 introns with a moderate length of 200-1000 bp. A screening of these sequences against 23 different repeat libraries to find insertions of short interspersed elements (SINEs) detected 45276 SINEs. Virtually all of these SINEs (98%) belong to the tRNA-derived Can-SINE family. Can-SINEs arose about 55 million years ago before Carnivora split into two basal groups, the Caniformia (dog-like carnivores) and the Feliformia (cat-like carnivores). Genome comparisons of dog and cat recovered 506 putatively informative SINE loci for caniformian phylogeny. In this study we show how to use such genome information of model organisms to research the phylogeny of related non-model species of interest. Investigating a dataset including representatives of all major caniformian lineages, we analysed 24 randomly chosen loci for 22 taxa. All loci were amplifiable and revealed 17 parsimony-informative SINE insertions. The screening for informative SINE insertions yields a large amount of sequence information, in particular of introns, which contain reliable phylogenetic information as well. A phylogenetic analysis of intron- and SINE sequence data provided a statistically robust phylogeny which is congruent with the absence/presence pattern of our SINE markers. This phylogeny strongly supports a sistergroup relationship of Musteloidea and Pinnipedia. Within Pinnipedia, we see strong support from bootstrapping and the presence of a SINE insertion for a sistergroup relationship of the walrus with the Otariidae.
@@ 鳍脚目(Pinnipedia)字源来自拉丁文:Pina或Penna是翼或羽毛的意思. 它们主要吃鱼,也吃软体动物或甲壳动物,皆为荤食.某些以渔业为主要国民经济收入的国家,认为它们是发展渔业的大敌,被当地渔民视为所谓的"害兽",而滥加捕杀,以致近年来鳍脚目的兽类数量锐减.国际上已将它们列为保护对象,而加以重点保护.
Arnason, Ulfur; Adegoke, Joseph A; Bodin, Kristina; Born, Erik W; Esa, Yuzine B; Gullberg, Anette; Nilsson, Maria; Short, Roger V; Xu, Xiufeng; Janke, Axel
The strict orthology of mitochondrial (mt) coding sequences has promoted their use in phylogenetic analyses at different levels. Here we present the results of a mitogenomic study (i.e., analysis based on the set of protein-coding genes from complete mt genomes) of 60 mammalian species. This number includes 11 new mt genomes. The sampling comprises all but one of the traditional eutherian orders. The previously unrepresented order Dermoptera (flying lemurs) fell within Primates as the sister group of Anthropoidea, making Primates paraphyletic. This relationship was strongly supported. Lipotyphla ("insectivores") split into three distinct lineages: Erinaceomorpha, Tenrecomorpha, and Soricomorpha. Erinaceomorpha was the basal eutherian lineage. Sirenia (dugong) and Macroscelidea (elephant shrew) fell within the African clade. Pholidota (pangolin) joined the Cetferungulata as the sister group of Carnivora. The analyses identified monophyletic Pinnipedia with Otariidae (sea lions, fur seals) and Odobenidae (walruses) as sister groups to the exclusion of Phocidae (true seals).
Flynn, John J; Finarelli, John A; Zehr, Sarah; Hsu, Johnny; Nedbal, Michael A
This study analyzed 76 species of Carnivora using a concatenated sequence of 6243 bp from six genes (nuclear TR-i-I, TBG, and IRBP; mitochondrial ND2, CYTB, and 12S rRNA), representing the most comprehensive sampling yet undertaken for reconstructing the phylogeny of this clade. Maximum parsimony and Bayesian methods were remarkably congruent in topologies observed and in nodal support measures. We recovered all of the higher level carnivoran clades that had been robustly supported in previous analyses (by analyses of morphological and molecular data), including the monophyly of Caniformia, Feliformia, Arctoidea, Pinnipedia, Musteloidea, Procyonidae + Mustelidae sensu stricto, and a clade of (Hyaenidae + (Herpestidae + Malagasy carnivorans)). All of the traditional "families," with the exception of Viverridae and Mustelidae, were robustly supported as monophyletic groups. We further have determined the relative positions of the major lineages within the Caniformia, which previous studies could not resolve, including the first robust support for the phylogenetic position of marine carnivorans (Pinnipedia) within the Arctoidea (as the sister-group to musteloids [sensu lato], with ursids as their sister group). Within the pinnipeds, Odobenidae (walrus) was more closely allied with otariids (sea lions/fur seals) than with phocids ("true" seals). In addition, we recovered a monophyletic clade of skunks and stink badgers (Mephitidae) and resolved the topology of musteloid interrelationships as: Ailurus (Mephitidae (Procyonidae, Mustelidae [sensu stricto])). This pattern of interrelationships of living caniforms suggests a novel inference that large body size may have been the primitive condition for Arctoidea, with secondary size reduction evolving later in some musteloids. Within Mustelidae, Bayesian analyses are unambiguous in supporting otter monophyly (Lutrinae), and in both MP and Bayesian analyses Martes is paraphyletic with respect to Gulo and Eira, as has been
钟志军; 杜昕颖; 彭广能; 黄克和; 陈泽良; 于爽; 徐杰; 王玉飞; 白耀霞; 陈燕芬; 付思美; 王同坤; 汪舟佳
Brucellae are Gram-negative,facultative intracellular bacteria that can infect many species of animals and man.Six species are currently recognized within the genus Brucella：B.melitensis,B.abortus,B.suis,B.neotomae,B.ovis,and B.canis.This classification is mainly based on differences in pathogenicity and in host preferences.Although the six species can be differentiated by conventional phenotypic tests,these species display a high degree of DNA homology in DNA-DNA hybridization assays（90% identity）.Therefore it has been proposed that the Brucella genus should comprise only one species i.e.B.melitensis and that the other species should be considered as biovars.However,several molecular genotyping methods have shown of significant DNA polymorphism Brucella species allowing the species to be correctly differentiated.This is also true for the recent marine mammal Brucella isolates,which two new species names have been proposed,i.e.B.pinnipediae and B.cetaceae,according to the classical criteria of host preferentialism（pinnipeds and cetaceans respectively） and specific molecular markers.This article reviews the evolution and taxonomy of Brucella.%布鲁菌属革兰氏阴性兼性胞内寄生菌,能感染多种宿主动物和人。该属可分为6个典型种,包括羊种、牛种、猪种、沙林鼠种、绵羊附睾种以及犬种布鲁菌等。此分类是基于其致病性以及宿主偏好性的差异划分。尽管6个种通过传统表型试验能区分,但布鲁菌种内采用DNA-DNA杂交证明DNA同源性高度一致（相似性大于90%）。因此有人提议布鲁菌由单一种组成,即布鲁菌属中只有羊种布鲁菌,其他种都是羊种菌的生物亚型之一。然而基于其他分子技术的基因分型表明其DNA多态性表现明显,说明目前对这个种的分型还是比较准确。而最近分离的海洋种布鲁氏
M. Octavio Maravilla-Chávez
Full Text Available This paper describes for the first time the relative abundance, population structure and numeric variation of California sea lions in the Gulf of California, Mexico, during four different seasons. The relative abundance estimates varied from the highest 17,162 sea lions in July of 1990 (summer to a minimum 7,470 in February of 1992 (winter, representing a reduction of 10,000 sea lions. Hypotheses about the migration of part of the population to the Pacific Ocean were compared and discussed against their residency inside the Gulf, and seasonal dispersion of individuals along this inner sea.O leão marinho da Califórnia (Zalophus californianus californianus é a única espécie de Otariidae (PINNIPEDIA que vive em permanência no Golfo da Califórnia, México. Vive em grupos, principalmente em rochas, ilhas ou porções de praias de algumas ilhas. Este artigo descreve pela primeira vez as variações da abundância e estrutura populacional dos leões marinhos desta região, nas quatro estações do ano. Realizamos seis censos, entre Outubro de 1989 e Janeiro de 1992 (3 censos correspondendo ao outono e um a cada uma das outras estações. Os censos foram feitos de barco, em terra ou combinados, com contagem direta e separando os indivíduos em 5 classes de idade e sexo. As estimativas de abundância variaram de 17,162 indivíduos, em Julho de 1990 (na Primavera, ao mínimo de 7,470, no Inverno de 1992, o que representa uma redução de 10,000 leões marinhos. A hipótese da migração de parte da população para o Oceano Pacífico é discutida e comparada com a de residência da população, bem como a nossa proposta de uma dispersão dos indivíduos pelo Golfo do Califórnia.