Browsing by Author "GEORGENASCIMENTO, M"

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    A CASE OF PARASITE-MEDIATED COMPETITION - PHENOTYPIC DIFFERENTIATION AMONG HOOKWORMS UNCINARIA SP (NEMATODA, ANCYLOSTOMATIDAE) IN SYMPATRIC AND ALLOPATRIC POPULATIONS OF SOUTH-AMERICAN SEA LIONS OTARIA-BYRONIA, AND FUR SEALS ARCTOCEPHALUS-AUSTRALIS (CARNIVORA, OTARIIDAE)
    (1992) GEORGENASCIMENTO, M; LIMA, M; ORTIZ, E
    Hookworms in otariids are considered to meet the conditions and to fulfill the predictions set forth in the theoretical literature to define a likely case of host coexistence mediation by a shared pathogen. The intensity of infections, the prevalence of skin lesions and the morphometry of hookworms Uncinaria spp. were examined in South American sea lions and fur seals sampled along the Chilean and the Uruguayan coasts in spring and summer 1981 to 1991. In sympatric host populations from Uruguay, there were clear differences in intensity of infections, prevalence of skin lesions, and body size of the hookworms from the two host species. Sea lions from Chile, allopatric to fur seal populations, are less intensively infected and hookworms found in these sea lions have the smallest body size reported in otariids, while those from South American fur seals are the largest. Hookworms found in sea lion pups from populations sympatric to fur seals revealed intermediate values in intensity and in body size, and the sea lion pups had the highest prevalence of skin lesions. Other reports of hookworms in otariids show intermediate morphometry, following a general linear trend of differentiation in size. Consequently, they are considered to belong to the same, widely distributed species Uncinaria lucasi Stiles, 1901.
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    FEEDING ECOLOGY OF THE SOUTH-AMERICAN SEA LION OTARIA-FLAVESCENS - FOOD CONTENTS AND FOOD SELECTIVITY
    (1985) GEORGENASCIMENTO, M; BUSTAMANTE, R; OYARZUN, C
    While predation by pinnipeds is likely to be important in shaping the structure of marine communities, there are few reports from the southeastern Pacific Ocean where pinniped populations are abundant and a massive fishing industry has developed in recent years. The food contents of 29 South American sea lions Otaria flavescens Shaw, 1800 and quantitative information on the occurrence of prey taxa are reported by frequency and mass. Estimates of the relative abundance of prey taxa in the environment, daily and annual food consumption rates, and sea lions'' food selectivity are given. Sea lions tend to consume slow swimming, bentho-demersal fish species, rather than the more abundant pelagic fish species in the study area. The jack mackerel Trachurus murphyi (Nichols) was the most frequent prey item found in the alimentary tracts and in the environment, but it was not preferred nor was it an important contributor of biomass to the diet. The non-commericial hake Macruronus magellanicus (Lonnberg) was the most preferred and the most important by mass in the diet. Estimated annual consumption of cusk eels (Genypterus spp.) revealed that sea lions took .apprx. 7 times more fish in mass than those annually landed in the study area. Unfortunately, estimates of standing stocks of standing stocks for the different prey taxa consumed by the sea lions are not yet available, and so the magnitude of their impact on fisheries is difficult to evaluate.
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    OGMOGASTER-HEPTALINEATUS N-SP (TREMATODA, NOTOCOTYLIDAE) FROM THE CHILEAN SEA LION OTARIA-FLAVESCENS
    (1983) CARVAJAL, J; DURAN, LE; GEORGENASCIMENTO, M
    O. heptalineatus nov. is described from the Chilean sea lion Otaria flavescens. Distinct characteristics of the species are: presence of 7 longitudinal ridges on the ventral surface, cirrus armed with scales, testes and ovary deeply lobed and eggs circular with short polar filaments. This is the 1st report of Ogmogaster from South America and the 1st report of Otaria flavescens as a host for this genus.
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    TRYPANSOMA-HUMBOLDTI N-SP FROM THE CHILEAN CATSHARK, SCHROEDERICHTHYS-CHILENSIS (GUICHENOT, 1848)
    (1987) MORILLAS, J; GEORGENASCIMENTO, M; VALERIA, H; KHAN, RA
    The morphology of Trypanosoma humboldti n. sp. is described from living and stained specimens obtained from the blood of a catshark, Schroederichthys chilensis. This represents the first report of a trypanosome in fish from the eastern Pacific ocean. It is distinguished by its size and apparent lack of pleomorphism. The presence of a leech, Branchellion ravenellii, attached to the catshark, raises the possibility that it can act as a vector. Additionally, this leech is recorded for the first time from the Pacific Ocean.