http://hdl.handle.net/1834/1339 Wed, 16 May 2012 22:11:47 GMT 2012-05-16T22:11:47Z http://www.oceandocs.org:80/retrieve/4173/Argentine-ss.jpg http://hdl.handle.net/1834/1339 http://hdl.handle.net/1834/4187 Title: Historia de vida temprana de la corvina rubia (Micropogonias furnieri, Sciaenidae) en el Estuario del Río de La Plata Authors: Braverman, M. Abstract: This study encompasses the bio-physical interactions of whitemouth croaker (Micropogonias furnieri) early life stages living in La Plata estuary (Argentina-Uruguay, South America) to understand how they take advantage of the estuarine dynamics while traveling from spawning to nursery areas and undergoing ontogenetic and associated ecological changes. The analyses used include studies of spatio-temporal distribution length-dependent patterns; growth patterns looking for settlement marks in otoliths; and development related to metamorphosis and ontogenetic variations of the diet and trophic level. Samples and data come from vertically stratified samplings from 3 cruises (2005, 2006 and 2009). Distributional data also comes from an historic database. Results demonstrate that retention mechanisms maintain croaker early-life stages (3-45 mm SL) alternatively moving horizontally along the bottom salinity front, mixing the length classes. Planktonic larvae (16 mm SL) have a life span of 30-50 days. Metamorphosis and settlement occurs simultaneously from 9 to 18 mm SL. The diet changes significantly from copepod to mysids 20 days after settlement (20-22 mm SL). In the context of saltatory ontogeny, these events represent a threshold in the species early-life history. Regarding spatial processes, retention in the front would allow larvae and early juveniles to benefit from food accumulation in the region; the high turbidity as shelter against predators, and the closeness to the main nursery ground. Thus, the dynamics of this estuarine system and the species reproductive strategy may be the reason of the high population abundance. Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/1834/4187 2011-01-01T00:00:00Z http://hdl.handle.net/1834/4190 Title: Dinámica y manejo de la captura incidental de peces en la pesquería del langostino patagónico (Pleoticus muelleri) Authors: Góngora, M.E. Abstract: This work characterizes the composition and dynamics of the incidental catch in the patagonian shrimp (Pleoticus muelleri) fishery, with special emphasis on the bycatch of common hake (Merlucius hubbsi). The Observer Program coordinated by the Chubut Province (Argentina) and used to monitor the fishery is evaluated. The factors that explain the variability of hake bycatch rates are analyzed, different statistical estimators are evaluated and possible strategies for controlling bycatch are discussed. The study is centered on the double-otter-trawl freezers, responsible for 75 percent of the Argentine shrimp landings. This fleet operates in San Jorge Gulf, in waters under the jurisdiction of the provinces of Chubut and Santa Cruz, and in waters of the platform near the gulf, in the area that is currently closed to protect hake juveniles. The incidental catch was composed of 81 species of fish: two species of mixins, 25 species of cartilaginous fishes and 54 of bone fishes, belonging to 50 families. Of these 81 species, 21 taxa had not been previously reported for central Patagonia (SW Atlantic). Two different fish assemblages were identified based on the analysis of qualitative abundance and frequency of occurrence: one in the region of Santa Cruz and the other in the northem coastal zone of San Jorge Gulf. Life-history characteristics, species abundance and status of conservation according to IUCN categories were used to identify nine species for which the bycatch in the shrimp fishery may not be sustainable, three of which are threatened and three vulnerable; the impact on two species could be sustainable but monitoring would be needed, 32 species appear in low frequency so the impact would be insignificant, and the level of impact is unknown for 39 species. Hake was the dominant species in the bycatch, in terms of both abundance and frequency. Analysis conducted using generalized mixed-effects models suggest that hake catch per set (CPUE) reported by the observers is markedly affected by the fishing area, the observer, the vessel, and the interaction between area and two-month period, area-year and vessel-year. Although substantial differences were encountered between areas, with some zones characterized by generally higher bycatch rates than others, there was no single area that could be identified as especially problematic in a consistent manner over the years. The observer effect is attributed to the methodology used to estimate the catch, whose precision depends on the observer expertise. The vessel was one of the main factors that explained the variability in hake CPUE, an effect that was apparently associated with the captain rather than with structural features of the vessel. The performance of different estimators of hake bycatch was compared by applying them to real and simulated data. Bycatch estimates were very sensible to the estimator employed. Estimators based on CPUE sample mean and based on mixed-effects models had better properties than those based on the hake-to-shrimp catch ratio. Finally, different strategies for the control of bycatch in the shrimp fishery are discussed in the light of the results, including selectivity devices, closures in space and time and bycatch quotas. Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/1834/4190 2011-01-01T00:00:00Z http://hdl.handle.net/1834/4204 Title: Variación interanual del mesozooplancton en la plataforma bonaerense en primavera: introducción de nuevas metodologías para su análisis Authors: Di Mauro, R. Abstract: The distribution and abundance of mesozooplankton (specially copepod, cladoceran and appendicularian species) of the Buenos Aires shelf obtained in spring, during the years 2002, 2003 and 2004, were analysed. A small bongo net provided with 67 and 220 µm meshes, was employed in order to obtain a complete representation of the size spectrum of the mesozooplankton. The analysis included both the traditional optical method and the a new automatic image analysis (ZooImage). The results were related with the oceanographic conditions, which were, in general similar to the mean conditions for the study area. The finer mesh (67 µm) allowed a more accurate estimation of the abundance and biomass of small copepod species ( 1mm total length), producing the tick mesh (220 µm) more than 90 of underestimation for adults and/or development stages of dominant species like the copepods Oithona nana, Paracalanus parvus, Euterpina acutifrons and Parvocalanus in individuals with trunk length smaller than 600 µm. Small species dominated the area with non significant interannual differences of their abundance, in most of cases. Three faunistic areas were defined, which were characterized by key species. Acartia tonsa, P. crassirostris, P. parvus y Podon polyphemoides caracterized the Estuarine Area. O. nana, Microsetella norvegica, Evadne nordmanni y Oikopleura dioica, defined the Coastal Area, and the large copepods ( 1 mm of total length) such as Calanoides carinatus, Drepanopus forcipatus, Centropages brachiatus, Clausocalanus brevipes, Ctenocalanus vanus, and the cyclopoid O. helgolandica defined the Shelf Area. High abundance of potential zooplanktonic prey in sectors where highest densities of Engraulis anchoita larvae were recorded, allow to suppose that food is not limitant for larval growth and survival. ZooImage method, employed for the first time in the Argentine Sea, presented an accuracy similar to the traditional optical method for the abundance and biomass estimation of copepods and appendicularians. Due to the quicky obtention of results, this kind of analysis represent a very useful tool, adequate to the fisheries programs requirements.crassirostris. The underestimation of appendicularians abundance and biomass with the tick mesh was higher than 86 in individuals with trunk length smaller than 600 µm. Small species dominated the area with non significant interannual differences of their abundance, in most of cases. Three faunistic areas were defined, which were characterized by key species. Acartia tonsa, P. crassirostris, P. parvus y Podon polyphemoides caracterized the Estuarine Area. O. nana, Microsetella norvegica, Evadne nordmanni y Oikopleura dioica, defined the Coastal Area, and the large copepods ( 1 mm of total length) such as Calanoides carinatus, Drepanopus forcipatus, Centropages brachiatus, Clausocalanus brevipes, Ctenocalanus vanus, and the cyclopoid O. helgolandica defined the Shelf Area. High abundance of potential zooplanktonic prey in sectors where highest densities of Engraulis anchoita larvae were recorded, allow to suppose that food is not limitant for larval growth and survival. ZooImage method, employed for the first time in the Argentine Sea, presented an accuracy similar to the traditional optical method for the abundance and biomass estimation of copepods and appendicularians. Due to the quicky obtention of results, this kind of analysis represent a very useful tool, adequate to the fisheries programs requirements. Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/1834/4204 2011-01-01T00:00:00Z http://hdl.handle.net/1834/4205 Title: Estrategias de vida de los copépodos Drepanopus forcipatus y Calanus australis en relación con los recursos tróficos en la plataforma patagónica austral (Argentina, 47°- 55°S) Authors: Antacli, J.C. Abstract: This Thesis contributes to elucidate the life cycle strategies of two copepod species, the medium-size clausocalanid Drepanopus forcipatus Giesbrecht, 1888 and the large calanid Calanus australis Brodsky, 1959, in relation to the environmental conditions in the southern Patagonian shelf (47°-55°S). This research was mainly carried out with samples collected in late summer/early autumn (March/April, 2004) onboard RV "Dr. E. L. Holmberg" (INIDEP, Mar del Plata). An additional sampling performed during early spring (October, 2005) with RV "Puerto Deseado" (CONICET) was also utilized. The present study was based on the following research questions: 1) Which is the available food for copepod populations by late summer? 2) Which is the relative contribution of D. forcipatus and C. australis to the summer mesozooplankton community conformation in the southern Patagonian shelf when it is determined from samples collected by a fine mesh size net? 3) Which feeding and reproductive activity levels do D. forcipatus and C. australis have by late summer? 4) Which are the strongest trophic links of D. forcipatus and C. australis to lower trophic levels by late summer in the region? 5) Which are the adaptive strategies of D. forcipatus and C. australis to cope with seasonal food variability? In the southern Patagonian shelf, the mesozooplankton overall structure and that of its populations have been historically misinterpreted because of sampling with coarse nets. Environmental conditions during late summer in the study area corresponded with a post phytoplankton bloom stage and, consequently, food availability in the size range efficiently ingested by copepods ( 10 ìm) was low. Both species revealed a seasonal pattern in feeding and reproduction, low in summer and high in spring, in coincidence with food availability in situ. D. forcipatus and C. australis may have diminished metabolism as an adaptation to poor food conditions, although apparently had not fully entered yet in a resting stage (dormancy). D. forcipatus may perform an opportunistic and rather flexible strategy when facing low concentrations of optimal food. This copepod would be capable of exploiting the actually available resources, and to sustain reproduction under low food availability. C. australis would be adapted to seasonally variable trophic conditions, would select food by particle size and would be able to reproduce with low or no food, at the expense of a combination of ingestion and assimilation of the lipid reserves stored during development Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/1834/4205 2011-01-01T00:00:00Z