Seals and fisheries in South Africa — competition and conflict

Wickens, P. A.; Japp, D. W.; Shelton, Peter A.; Kriel, F; Goosen, P. C.; Rose, B; Augustyn, C. J.; Bross, C. A. R.; Penney, Andrew J.; Krohn, Rachel

doi:10.2989/02577619209504741

Cited by 67 publications

(64 citation statements)

References 8 publications

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“…De forma simple, se pensaba que disminuyendo las poblaciones de mamíferos marinos, las capturas pesqueras se incrementarían en una proporción directa a lo consumido por los mamíferos, ahora disponible para la pesca (Yodzis, 1998). Esta interpretación fue utilizada para promover la reducción en el tamaño de algunas poblaciones de mamíferos marinos (Wickens et al, 1992).…”

Section: Introductionunclassified

Solapamiento trofico entre el lobo marino de un pelo Otaria flavescens y la pesqueria de arrastre demersal del golfo San Matias, Patagonia, Argentina

Romero

Dans²,

González

et al. 2011

lajar

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RESUMEN.A nivel internacional, paralelo a la declinación y al colapso de pesquerías de gran escala, surgió un interés creciente por el estudio de las interacciones entre mamíferos marinos y pesquerías. El golfo San Matías (Patagonia, Argentina) es considerado un ecosistema pesquero independiente de las aguas de la Plataforma Continental Argentina, con condiciones oceanográficas y biológicas particulares. La condición de sistema semi-cerrado podría generar escenarios particulares para la interacción entre la flota pesquera de arrastre de fondo y la población de lobos marinos de un pelo Otaria flavescens. En el presente trabajo se caracterizó la dieta del predador y la composición de las capturas pesqueras a fin de evaluar el solapamiento trófico entre ambos componentes. A partir de este análisis y la comparación de las tallas de las presas consumidas, se encontró que la posibilidad de una interacción competitiva entre la flota pesquera y los lobos marinos, a partir de la utilización de recursos similares, sería baja en el ecosistema del golfo San Matías. Palabras clave: Otaria flavescens, lobo marino, golfo San Matías, pesquería de arrastre, solapamiento trófico, Patagonia argentina.Trophic overlap between the South American sea lion Otaria flavescens and the demersal trawl fishery in San Matías Gulf, Patagonia, Argentina ABSTRACT. As world fisheries began to decline and massive collapses were observed, the competition between marine mammals and fisheries became an issue of growing concern. San Matías Gulf (Patagonia, Argentina) is considered to be a fishery ecosystem independent of the Argentine Continental Shelf waters, with particular oceanographic and biological properties. As a semi-enclosed ecosystem, this gulf may generate particular scenarios for interactions between the demersal trawl fishery fleet and the population of South American sea lions Otaria flavescens. In this paper, the diet of the top predator and the composition of fishery catches were characterized in order to assess the trophic overlap between these two components. This analysis and a comparison of the sizes of prey consumed revealed a low probability of competition for similar resources between the fishing fleet and the marine mammals in the San Matías Gulf ecosystem.

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Section: Introductionunclassified

Solapamiento trofico entre el lobo marino de un pelo Otaria flavescens y la pesqueria de arrastre demersal del golfo San Matias, Patagonia, Argentina

Romero

Dans²,

González

et al. 2011

lajar

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“…This assumption is known as stationarity. However, many pinniped species, including the Cape fur seal, have been subject to periodic harvest (Wickens et al 1991) and compete with a growing fishing industry (Wickens et al 1992). When the effects of anthropogenic activity on pinniped populations are taken into consideration, the above assumption must be questioned.…”

Section: Body Weight and Agementioning

confidence: 99%

Gross and microscopic visceral anatomy of the male Cape fur seal, Arctocephalus pusillus pusillus (Pinnipedia: Otariidae), with reference to organ size and growth

Stewardson

Hemsley

Meyer³

et al. 1999

Journal of Anatomy

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The gross and microscopic anatomy of the Cape fur seal heart, lung, liver, spleen, stomach, intestine and kidneys (n l 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 l w o r t , 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 l ax b , 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.

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“…El krill, Nyctiphanes australis (Sars, 1883), cuando forma densas agregaciones en Nueva Zelanda, es consumido por cardúmenes de Thyrsites atun (Euphrasen, 1791) con mayor frecuencia que los peces solitarios (O'Driscoll 1998 (Gilchrist, 1913) y Sardinops sagax (Jenyns, 1842) (Wickens et al 1992), y se han reportado diferencias en la dieta en relación con su estado ontogénico y sexo (Griffiths 2002).…”

Section: Introductionunclassified

Cambios en la morfometría bucal y su relación con la dieta de Thyrsites atun (Euphrasen, 1791) en el centro-sur de Chile

Duarte

Ibáñez

Chong

2007

Rev. chil. hist. nat.

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Seals and fisheries in South Africa — competition and conflict

Cited by 67 publications

References 8 publications

Solapamiento trofico entre el lobo marino de un pelo Otaria flavescens y la pesqueria de arrastre demersal del golfo San Matias, Patagonia, Argentina

Solapamiento trofico entre el lobo marino de un pelo Otaria flavescens y la pesqueria de arrastre demersal del golfo San Matias, Patagonia, Argentina

Gross and microscopic visceral anatomy of the male Cape fur seal, Arctocephalus pusillus pusillus (Pinnipedia: Otariidae), with reference to organ size and growth

Cambios en la morfometría bucal y su relación con la dieta de Thyrsites atun (Euphrasen, 1791) en el centro-sur de Chile

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