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Universidad de Buenos Aires (2001)

Fishery ecology of patagonian lakes and reservoirs (Argentina)

Baigun, Claudio Rafael Mariano

Titre : Fishery ecology of patagonian lakes and reservoirs (Argentina)

Ecología pesquera de lagos y embalses patagónicos (Argentina)

Auteur : Baigun, Claudio Rafael Mariano

Université de soutenance : Universidad de Buenos Aires

Grade : Doctor en Ciencias Biológicas 2001

This thesis presents an analysis of fisheries ecology on 54 Argentine patagonian lakes and reservoirs. An ordination of lakes and reservoirs based on different limnological characteristics was performed using Principal Component Analysis. Three basic types of environments : located on the ecotone, Andean mountains and plateau were defined, having the last two types subcategories. Patagonian lakes and reservoirs exhibited differences across a gradient defined mainly by trophic and edaphic characteristics, and secondarily by morphometry and climatic factors. Species composition and relative abundance were obtained by extensive and intensive sampling designs using experimental gill net gangs. Gill net captures were analyzed as function of length and weight and for those lakes with seasonal information, length structures were corrected by selectivity for the different species. A total 10 species were identified : Odontesthes hatcheri (pejerrey patagónico), O. bonariensis (pejerrey bonaerense), Percichthys trucha (perca boca chica), P. colhuapiensis (perra bocona), Oncorhynchus mykiss (trucha arco iris), Salmo trutta (trucha marrón), Salvelinus fontinalis (trucha de arroyo), S. namaycush (trucha de lago), Salmo salar sebago (salmón encerrado), Galaxias platei (puyen grande) and Aplochiton sp. (peladilla). Salmonids are exotic species in Patagonia and represented 53 % of experimenta capturas. In turn, percictids comprised 22 %, whereas 19 % corresponded to Patagonian pejerrey. Due to the importance of salmonids in Patagonia, the introduction process and stocking characteristics in dfferent waterbodies types (large and small lakes, rivers and creeks) were analyzed. Using Corrrespondence Analysis it was found that S. namaycush and S. salar sebago were strongly associated with large lakes, whereas S. trutta was mostly related to small lakes size. In turn. S. fontinalis appeared mostly associated with creeks, while O. mykiss was the most ubiquitous of the salmonid species. Species mean length and mean weight were estimated for all lakes and reservoirs where extensive information was available and relative condition was determined in those environments with intensive samplings. Using length structure analysis growth parameters, natural mortality rates and critical age and length were estimated. Both mean and infinite length were related to total nitrogen, total phosphorous, transparency and mean depth, although not linearly in all cases, suggesting the existence of ecological optima. It was noted that for same species, natural mortality and critical length varied among environments. Community patterns were analyzed using Correspondence Analysis and showed that several communities were dominated by only salmonids and atherinopsids-percicitids respectively, but other were mixed. Species richness was related to surface lakes and fish abundance was correlated with total organic nitrogen, total phosphorous and clorophyil and negativer with mean depth and transparency. Use of Discriminant Analysis showed that conductivity, mean annual air temperature, transparency and mean depth were the variables that accounted by for 81 % of differences between mean species abundance at each community type. Discriminant function correctly classified 74 % of environments Fish yield were estimated applying empirical models derived from sport and commercial fisheries from Northern Hemisphere lakes and reservoirs. Also production models were used and maximum sustainable yield was estimated for those environments with suitable fishery information. Such estimations allowed to predict that Andean lakes yield up to 5 kg/ha, ecotone lakes may range between 20 and 40 kg/ha and plateau lakes and reservoirs will yield between 20 to 30 kg/ha on annual basis. Based on lake typology and community types, several guidelines were proposed to develop strategies for resource exploitalion, to maintain sustainable use of those fisheries with high fishing pressure and to preserve and enhance natives pecies populations. It was concluded that management of Patagonian fisheries resources requires the application of environmental criteria at a regional scale and use of population parameters and fishery information at a local scale. It is also necessary to modify traditional management paradigms, encompassing the conservation of biodiversity as a main goal for a sustainable resource use and for developing sound management strategies.


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