Is fish passage technology saving fish resources in the lower La Plata River basin?

Abstract

Over 450 dams have been constructed in the upper Paraná River basin in Brazil during the past 40 years. River regulation by these dams is considered a primary factor in the reduction of fish diversity and depletion of migratory species. In contrast to the upper Paraná Basin, only two large dams (both with upstream fish passage) have been constructed in the lower La Plata River basin. Fishery managers in the lower basin are concerned that existing and planned dams will further deplete populations of migratory fish species that constitute important recreational and commercial fisheries as has occurred in the upper basin. We assessed the sustainability of fisheries in the lower basin in the face of increased river regulation by using literature information to describe the efficiency of the fish passage systems used to mitigate river regulation impacts on fisheries. Our analysis shows that fish passage systems at both lower basin dams, Yacyreta and Salto Grande, fail to transfer sufficient numbers of upstream migrants to sustain populations of migratory species. Fish passage efficiency of target species in the fish elevators at Yacyreta is less than 2%. Fish diversity in the fish elevators is low because about 85% of the fish belong to only three nonmigratory species (Pimelodus maculatus, Oxydoras kneri and Rhinodoras dorbignyi). Large migratory species targeted for passage rarely comprise even 5 % of the fish number in the passage system. The two Borland locks at Salto Grande Dam cannot dependably pass large numbers of migratory species because passage efficiency is dependent upon interactions of powerhouse and spillway operation with tailrace elevations. Most species in the Borland system were either a small catfish (Parapimelodus valenciennis) or a engraulid (Lycengraulis grossidens). Again, the targeted migratory species were not abundant in the passage system. We conclude that existing fish passage technology in the lower basin is inadequate and that improved fish passage designs are required to conserve migratory species. These designs must be based on integrated information from geomorphology (habitat), natural fish behavior, fish swimming capabilities, and detailed population studies.Mais de 450 barragens foram construídas no alto rio Paraná, Brasil, nos últimos 40 anos. A regulação dos rios por barragens é considerada um dos fatores primários de redução da diversidade de peixes e depleção de espécies migratórias. Em contraste, somente duas grandes barragens foram construídas nos trechos mais inferiores da bacia do rio da Prata. No momento, há uma grande preocupação acerca do impacto dos represamentos sobre espécies que se constituem a base da pesca comercial e esportiva na bacia. Este artigo aborda o desempenho das passagens de peixes das barragens de Yacyreta e Salto Grande, monstrando que as mesmas falham na transferência de grandes quantidades de espécies migratórias para os trechos a montante. A barragem de Yacyreta tem dois elevadores com problemas importantes de projeto. Como resultado, a eficiência n...

Fish passages in South America: an overview of studied facilities and research effort

“…Fluvial ecosystems are increasingly vulnerable to river regulation and impoundments, and FPF will continue to be installed with the intent of mitigating impacts. However, controversies and skepticism about their conservation role is growing (e.g., Agostinho et al, 2002Agostinho et al, , 2007aOldani et al, 2007;McLaughlin et al, 2012;Pompeu et al, 2012;Pelicice et al, 2015;Kemp, 2016), and the present study revealed that we have limited understanding about the functioning, management success and conservation value of fishways in South America. We hope that our study will guide future research to take place in a broader context, considering issues that range from fish passage efficiency to recruitment and population persistence.…”

“…These facilities are usually seen as efficient management actions, and received support from authorities, stakeholders and the general public. Recent studies, however, have elicited discussions about the value of FPF to foster migratory fish conservation in South America, because several aspects concerning their functioning and management role remain poorly known (e.g., Agostinho et al, 2002;Oldani et al, 2007;Pelicice, Agostinho, 2008;Pelicice et al, 2015). These studies argue that evaluations rarely preceeded or followed the construction of FPF, while monitoring programs traditionally focused on variables with partial relevance for conservation plans (e.g., upstream passage), while neglecting other important issues (e.g., population dynamics, spawning, recruitment and dispersion).…”

Dams and the fish fauna of the Neotropical region: impacts and management related to diversity and fisheries

“…Information in this document clarified some relevant weaknesses in fish conservation, such as high selectivity and favoring the promotion of few species and not always the target ones (Agostinho et al, 2007d;Hahn et al, 2007;Makrakis et al, 2007;Oldani et al, 2007;Fernandez et al, 2007). It was also clear the difficulties in descending migration, passage through dams and the unlikely downstream drift of offspring along a reservoir body, which ultimately will reduce recruitment below dams (Agostinho et al, 2007d;Lopes et al, 2007).…”

Passage of fish larvae and eggs through the Funil, Itutinga and Camargos Reservoirs on the upper Rio Grande (Minas Gerais, Brazil)

“…However, the efficiency of fish passes has been questioned because of their failures or negative effects on fish populations (Agostinho et al, 2002;Agostinho et al, 2007b;Agostinho et al, 2007c;Fernandez et al, 2004;Oldani et al, 2007;Makrakis et al, 2007). One reason fish passes have failed to preserve migratory fish populations is that it is difficult for eggs and larvae to pass through reservoirs (Agostinho & Gomes, 1997;Agostinho et al, 2007a;Agostinho et al, 2007b).…”