| Resumo: |
Striped weakfish (Cynoscion guatucupa)and whitemouth croaker(Micropogonias furnieri)are one of the most important coastal resources of Bahia Blanca Estuary (Buenos Aires Prov., Argentina). The aims of this thesis were: 1, to analyze the population and morphological characteristics of the juveniles stages of the striped weakfish and the whitemouth croaker living in Bahia Blanca Estuary; 2, to describe the dietary habits of the juveniles of these two species; 3, to analyze the ontogenetic and seasonal diet changes in both species, and 4, to study the feeding interrelationships between both species as well as the interrelationships between each species and its prey. In view of the mentioned objectives, diet was evaluated taking into account the following parameters: frequency of occurrence (FO),numerical abundance (N), and biomass (B)of the prey found in the stomach contents. In addition, the following multivariate methods were used to pinpoint dietary size-related and seasonal shifts: non-metric multidimensional scaling analysis (NMDS)and cluster analysis. Feeding selectivity was evaluated seasonally using Vanderploeg and Scavias relativized electivity index. Interspecific diet differences were analyzed using the Specific Overlap index (SO)as well as the Schoeners index (S)based on prey numerical abundance and biomass. Feeding strategy analysis of the whole juvenile populations of striped weakfish and whitemouth croaker are indicative of both species as generalist feeders with a broad dietary niche width. The seasonal dietary shifts observed both in the striped weakfish and whitemouth croaker evidenced changes in the availability of organisms, thus corroborating the opportunistic behavior of these species. The dietary overlap analysis between both species indicates differences in the use of the available resources. However, in two seasonal periods (beginning of autumn and summer)the proportions of the main prey items consumed by each species were very similar and diet overlap was high. High overlap values during these two seasonal periods coincide with the peak abundances of the prey consumed, and they evidence no negative effects in the feeding condition of the juveniles of bothspecies. As a result, and although diet overlap was high at the beginning of autumn and in summer, no evidence of food competition was found in the present study between the young striped weakfish and white mouth croaker.
Universidad Nacional del Sur, Departamento de Biologia, Bioquímica y Farmacia, (Bahía Blanca, Argentina)
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