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Population responses of two omnivorous fish species to impoundment of a Brazilian tropical river

Population responses of two omnivorous fish species to impoundment of a Brazilian tropical river Brycon gouldingi and B. falcatus were the most abundant and widespread of five species of the genus captured in a sampling study encompassing 5 years (1995–2000) in the upper Rio Tocantins, where the river was impounded by the Serra da Mesa hydroelectric dam. Given that impoundments constitute a disturbance to which species will show demographic and biological responses, we assessed such responses of these two omnivorous fishes, whose genus is regarded as vulnerable to impoundments. Both species increased greatly in numbers during the initial reservoir filling period. Brycon gouldingi had higher abundance values than B. falcatus in all sampling months, except in the pre-impoundment period. Both species showed a significant weight increment relative to body length during the time they remained in the reservoir. No reproductive individuals of B. gouldingi were recorded in the study area, but those few of Brycon falcatus were found in both wet and dry seasons, suggesting a more opportunistic strategy of reproduction. Both species were omnivorous and overlapped broadly in diet. The proportions of dietary items, however, varied in relation to fish size class and water dynamics (lotic versus lentic sites). Terrestrial arthropods composed a larger proportion of the diet of smaller-sized individuals and those from lentic sites, whereas seeds and fruits contributed more to the diet of both larger-sized individuals and those from lotic environments. Except for fish and aquatic heteropterans, which were consumed mainly in the reservoir, all other food items were allochthonous, indicating the dependence of these two species of Brycon on the terrestrial environment. The two species responded similarly to the alterations imposed by the impoundment of the upper Tocantins, although reproduction/recruitment pattern was slightly different between species. As observed in other regions of Brazil, impoundments and deforestation appear to produce negative cumulative effects on species of Brycon. These impacts call for greater efforts to conserve and manage members of this diverse and widespread genus. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Hydrobiologia Springer Journals

Population responses of two omnivorous fish species to impoundment of a Brazilian tropical river

Hydrobiologia , Volume 627 (1) – Feb 26, 2009

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References (60)

Publisher
Springer Journals
Copyright
Copyright © 2009 by Springer Science+Business Media B.V.
Subject
Life Sciences; Zoology ; Ecology; Freshwater & Marine Ecology
ISSN
0018-8158
eISSN
1573-5117
DOI
10.1007/s10750-009-9727-7
Publisher site
See Article on Publisher Site

Abstract

Brycon gouldingi and B. falcatus were the most abundant and widespread of five species of the genus captured in a sampling study encompassing 5 years (1995–2000) in the upper Rio Tocantins, where the river was impounded by the Serra da Mesa hydroelectric dam. Given that impoundments constitute a disturbance to which species will show demographic and biological responses, we assessed such responses of these two omnivorous fishes, whose genus is regarded as vulnerable to impoundments. Both species increased greatly in numbers during the initial reservoir filling period. Brycon gouldingi had higher abundance values than B. falcatus in all sampling months, except in the pre-impoundment period. Both species showed a significant weight increment relative to body length during the time they remained in the reservoir. No reproductive individuals of B. gouldingi were recorded in the study area, but those few of Brycon falcatus were found in both wet and dry seasons, suggesting a more opportunistic strategy of reproduction. Both species were omnivorous and overlapped broadly in diet. The proportions of dietary items, however, varied in relation to fish size class and water dynamics (lotic versus lentic sites). Terrestrial arthropods composed a larger proportion of the diet of smaller-sized individuals and those from lentic sites, whereas seeds and fruits contributed more to the diet of both larger-sized individuals and those from lotic environments. Except for fish and aquatic heteropterans, which were consumed mainly in the reservoir, all other food items were allochthonous, indicating the dependence of these two species of Brycon on the terrestrial environment. The two species responded similarly to the alterations imposed by the impoundment of the upper Tocantins, although reproduction/recruitment pattern was slightly different between species. As observed in other regions of Brazil, impoundments and deforestation appear to produce negative cumulative effects on species of Brycon. These impacts call for greater efforts to conserve and manage members of this diverse and widespread genus.

Journal

HydrobiologiaSpringer Journals

Published: Feb 26, 2009

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