Temporal variability of fish larvae assemblages: influence of natural and anthropogenic disturbances

Abstract

Natural and induced disturbances greatly influence the temporal distribution of ichthyoplankton abundance. This study assesses and compares the temporal variability of fish larvae assemblages in controlled and free environments to determine the influence of environment variables on the main taxa in these systems. The study was conducted at the Chapecó (without dam impact) and Ligeiro (with dam impact) river mouths, which are located in the upper Uruguay River. Samples were made between October 2001 and March 2004 during three reproductive periods. The larvae assemblages were composed of small and medium-sized Characiformes and Siluriformes. The variation in the distribution of larvae was mainly temporal (>85%). When the three reproductive periods were compared, it was observed in the second period, characterized by a larger water flow and a lower temperature, that there was a reduction in abundance, a lower number of taxa, an absence of stages in post-flexion and a high dissimilarity in larvae assemblage structure. In general, the environmental variables of water flow and temperature most influenced the distribution of egg and larvae abundance. In the studied area, a smaller temporal variability was observed in the structure of larvae assemblages at the sampling sites in the Chapecó River mouth than in in the Ligeiro River mouth under the influence of dams.Os distúrbios naturais e induzidos têm notável influência na distribuição temporal da abundância do ictioplâncton. Este estudo visa avaliar e comparar a variabilidade temporal das assembleias de larvas de peixes, entre ambientes regulados e ambientes livres, bem como, determinar a influência das variáveis ambientais sobre os principais táxons presentes nestes ambientes. O trabalho foi conduzido na foz dos rios Chapecó (sem impacto de barramento) e Ligeiro (impactado por barragens), ambos localizados no alto rio Uruguai. As coletas foram realizadas entre outubro de 2001 e março de 2004 durante três períodos reprodutivos. As assembléias de larvas estiveram compostas principalmente por Characiformes e Siluriformes de pequeno e médio porte. A variação na distribuição de larvas foi principalmente temporal (>85%). Quando comparados os três períodos reprodutivos, foi observado que no segundo período, caracterizado por uma maior vazão da água e menor temperatura, houve redução na abundância, menor número de táxons, ausência de estágios em pós-flexão e elevada dissimilaridade na estrutura da assembléia de larvas. Em geral, as variáveis ambientais vazão e temperatura da água foram as que mais influenciaram a distribuição da abundância de ovos e larvas. Nos ambientes estudados, foi observado que existe uma menor variabilidade temporal na estrutura das assembléias de larvas das estações presentes na foz do rio Chapecó do que naquelas presentes na foz do rio Ligeiro, o qual esta sob influência dos barramentos.

Pools and rapids as spawning and nursery areas for fish in a river stretch without floodplains

“…Despite the difference in the number of captured species between the two environments, the primary fish orders found both in the pool and in the rapids were the Characiformes and Siluriformes. The dominance of these two orders has also been described by several authors for the neotropical freshwater region (Agostinho et al, 1997;Lowe-McConnell, 1999;Agostinho et al, 2003;Reynalte-Tataje et al, 2012b). The larvae assemblage found in the Peixe River was primarily composed of sedentary species, which tend to exhibit opportunistic features, i.e., small and medium sized, few eggs, do not perform large migrations and have no parental care (Vazzoler, 1996).…”

Importance of Reservoir Tributaries to Spawning of Migratory Fish in the Upper Paraná River

“…The net was maintained against the direction of flow facing the fastest current. Surface tows have consistently captured larvae of diverse migratory fish species in the Upper Paraná River Basin (Sanches et al , ; Baumgartner et al , ; Daga et al , ; Reynalte‐Tataje et al , ; Gogola et al , ) and neighbouring Uruguay River Basin (Hermes‐Silva et al ., ; Corrêa et al , ; Reynalte‐Tataje et al , , ).…”

Effects of reservoirs water level variations on fish recruitment

“…The region of the upper Uruguay River is formed by well-embedded and rather steep valleys, with absence of floodplain (Reynalte-Tataje et al, 2012b). This environment favors a flash floodongs with rapid rise in hours during periods of heavy rainfall (Corrêa et al, 2011).…”