Deficient downstream passage through fish ladders: the case of Peixe Angical Dam, Tocantins River, Brazil

Fernando Mayer Pelicice,Carlos Sérgio Agostinho

doi:10.1590/s1679-62252012000400003

Fernando Mayer Pelicice, Carlos Sérgio Agostinho

Open Access

https://doi.org/10.1590/s1679-62252012000400003

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Journal: Neotropical Ichthyology	Publication Date: Oct 1, 2012
Citations: 16	License type: cc-by

Affiliation: Universidade Federal do Tocantins

Abstract

Downstream passage through fish ladders and other facilities remains largely uninvestigated in South America. In view of this concern, we monitored ascending and descending fish movements through the fish ladder at Peixe Angical Dam, upper Tocantins River, Brazil, between September 2009 and August 2010. To investigate the extent of downstream passage, the fish fauna was sampled monthly (i) at sites upstream and downstream from the dam and (ii) inside the ladder. To distinguish between ascending and descending movements, the fish ladder remained open (permanent water flow), but a screen blocked the complete passage of fish in both directions. The results of the study indicated that the ladder restricts fish movements in both directions. Few species were found to use the ladder (31 out of 119 species recorded in the area). Moreover, monitoring revealed that downstream passage is even more limited. Only 18 species were recorded moving downstream. In addition, few fish attempted to move downstream during the year; of all fish captured in the ladder (n = 17,335), only 4% were descending. Species performing exclusive downstream movements were numerically rare or infrequent. Most downstream captures involved only four species. We emphasize that several species performed one-way upstream movements or showed a high density of ascending fish. Consequently, the numerical ratio between ascending and descending fish (ind./m²) showed high positive values throughout the year (644:1 on average, considering all species); migratory species showed higher ratios (1069:1). The results of the study show that the facility fails to support the downstream passage of migratory and non-migratory fishes. We conclude that the fish ladder at Peixe Angical Dam does not play a conservation role and may complicate alternative conservation efforts.

Highlights

Fish passages have been installed in many Brazilian dams (Agostinho et al, 2008) in an attempt to restore fish movements in rivers fragmented by dams
Our results indicated that the ladder at Peixe Angical Dam is very selective
The principal finding of the study is that downstream passage through the ladder is extremely limited, considering that few downstream migrants were captured in the ladder during the study

Summary

Introduction

Fish passages have been installed in many Brazilian dams (Agostinho et al, 2008) in an attempt to restore fish movements in rivers fragmented by dams. Fish (adult and young) would migrate or drift downriver, dispersing throughout the basin In view of this belief, more than 50 fish passages, ladders, were installed in the country. The mere presence of fish passages was synonymous with successful fish conservation As a result, these facilities were never evaluated; their functional aspects and effectiveness remained largely unknown, and the facilities acquired intrinsic value and prestige among laymen and managers. Studies have identified important problems during upstream passage (Oldani & Baigún, 2002; Fernandez et al, 2004; Agostinho et al, 2007a; Makrakis et al, 2007; Volpato et al, 2009) The basis of these problems is that few species are able to ascend ladders and other facilities. Downstream passage, would occur naturally as fish passed through the ladder

Methods

Results

Conclusion