Modeling energy flow in a large Neotropical reservoir: a tool do evaluate fishing and stability

Abstract

Recently, there is an increasing perception that the ecosystem approach gives important insights to support fisheries stock assessment and management. This paper aims to quantify energy flows in the Itaipu Reservoir (Brazil) and to simulate increase of the fishing effort of some species, using Ecopath with Ecosim software, which could allow inferences on stability. Therefore, two steady-state Itaipu models were built (1983-87 and 1988-92). Results showed that: a) there are no differences between models, and results on aging trends do not vary over time indicating that fishery does not alter the ecosystem as a whole; b) results of fisheries simulations are approximate to mono-specific stock assessment for the same species and periods; c) many authors believe that tropical ecosystems are environments where biotic and abiotic oscillations are annual and sometimes unexpected, but the results found for the Itaipu Reservoir indicate that stability was met after 16 years.Nos dias atuais, aumenta a percepção que a análise ecossistêmica fornece importantes esclarecimentos na avaliação e manejo de estoques pesqueiros. Este trabalho objetiva quantificar o fluxo de energia na teia trófica do reservatório de Itaipu e simular o aumento de pesca de algumas espécies usando o programa "Ecopath com Ecosim", que permite inferências sobre a estabilidade do sistema. Desta forma, dois modelos de "estado-estacionário" foram construídos (o primeiro para o período 1983-87 e o outro para 1988-92). Os resultados mostraram que: a) não há diferenças entre os modelos e os resultados sobre tendências de amadurecimento não variam com o tempo indicando que a pesca não altera o sistema como um todo; b) os resultados de simulação de pesca se aproximam de avaliações mono-específicas, realizadas por outros autores, com dados de mesmas espécies e períodos; c) muitos autores acreditam que reservatórios tropicais são ambientes submetidos a oscilações antrópicas que alteram grandemente sua dinâmica dificultando a estabilidade, mas os resultados para o reservatório de Itaipu indicam que a estabilidade foi encontrada 16 anos após a sua formação.

Diet and niche breadth and overlap in fish communities within the area affected by an Amazonian reservoir (Amapá, Brazil)

“…The relatively high frequencies of fish, crustaceans, insects, plant material, and detritus in the diets of the species analyzed in the present study are similar to the pattern recorded in other reservoirs in Brazil (Ferreira 1984, Hahn et al 1998 reflecting the typical pattern expected for a fish community in South America, in particular in artificial reservoirs (Mérona et al 2001, Loureiro 2000, Angelini et al 2006 where the opportunistic behavior does not mean that the species are able to use the full diversity of available feeding resources, but that they may shift from one resource to another, according to their needs (Gerking 1994).…”

Estimates of population parameters and consumption/biomass ratio for fishes in reservoirs, Paraná State, Brazil

“…Ecological modeling is under development in tropical regions, such as Brazil (Angelini & Petrere, 1996;Wolff et al, 2000;Angelini & Agostinho, 2005a, 2005bAngelini et al, 2006;Angelini & Gomes, 2008). Pauly (1998b) pointed out to the need for an adaptation or more precisely a "tropicalization" of the parameters from Beverton and Holt models.…”

Application of Ecopath model on trophic interactions and energy flows of impounded Manwan reservoir ecosystem in Lancang River, southwest China

“…Studies on habitat changes (species richness or shortage) associated with food web structure and food availability in complex reservoir ecosystems have received much attention from ecologists (Angelini et al 2006;Amarasinghe & Weerakoon 2009). Modeling approach was considered as an effective way to reveal the food web structure and pathways of energy flows resulted from damming a river.…”