The impact of a hydroelectric dam on Neotropical fish communities: A spatio‐temporal analysis of the Trophic Upsurge Hypothesis

Abstract

We employed the trophic upsurge hypothesis as an analytical framework to describe the response of Neotropical fish communities to terrestrial inundation associated with river damming. Data were collected for the impact assessment of the Peixe Angical Dam, Tocantins River, Brazil. Monthly surveys were conducted at nine sites (seven upstream, two downstream) from 15 months before to 20 months after dam closure and a follow‐up survey 60–83 months after closure. Fish responses differed in timing and magnitude across sites. In the new reservoir, populations peaked 8–13 months after flooding, demonstrating increases in richness (84 ± 52%), biomass (329 ± 266%) and abundance (681 ± 348%) with the maxima for richness and abundance tending to precede biomass maxima. Populations of all families increased but were greatest for Engraulidae, Hemiodontidae, Serrasalmidae and Characidae, and lower for the benthic catfish: Sciaenidae, Dorididae, Pimelodidae. Downstream populations peaked 5–12 months after closure or showed consistent decline. Five years after dam‐closure richness and abundance were lower compared to predam levels, with populations at all sites demonstrating an ongoing decline. Reservoir creation triggers reproductive recruitment and otherwise pools spatially disparate populations from across the flooded valley. If the rise in richness is largely explained by the increased catchability of species otherwise present prior to flooding, it may be more appropriate to estimate species loss with reference to upsurge data. As peak biomass coincides with declining richness, modelling fisheries production from annually aggregated data may risk overestimating the potential for sustainable harvests. Upsurge–response curves can help identify the timing of critical ecological thresholds for flood‐managed fisheries.

Functional erosion and trait loss in fish assemblages from Neotropical reservoirs: The man beyond the environment

“…Newly formed reservoirs usually carry high species richness, sometimes even higher than the natural river, at least during the years immediately after the reservoir is filled. This discrete phase has been described as the “trophic upsurge” period, in which the primary productivity is high and there is considerable biomass input from the flooded vegetation (Agostinho et al., 2016; Monaghan et al., 2019; Thornton et al., 1990). This enhanced but transient trophic state can thereby sustain higher biodiversity for fishes and other organisms.…”

Conservation of migratory fishes in the Amazon basin

“…The same was observed below (Santos, Pinto‐Coelho, Fonseca, Simões, & Zanchi, 2018) and above (Van Damme et al, 2019) the Jirau and Santo Antonio dams in the Madeira River. The fisheries of smaller, mid‐distance detritivorous and frugivorous migratory species first increased in the river channels upstream and downstream of the Tucuruí (Ribeiro et al, 1995) and Peixe Angical dams in the Tocantins River shortly after their construction but declined afterwards (Monaghan, Agostinho, Pelicice, & Soares, 2020). In the Jamari River, fisheries of migratory Characiformes also strongly declined after construction of the Samuel dam (Santos, 1995).…”

The effects of river impoundment on artisanal fishers in the Middle Tocantins River, Brazil

“…River damming causes large-scale environmental impacts, promoting profound changes in fish diversity and fishing resources (Agostinho et al, 2016). Fish biomass and yield usually increase in the first years of the impoundment, but they decline sharply in the following years (Petrere Junior, 1996;Agostinho et al, 1999;Monaghan et al, 2020). Impacts affect mainly migratory fishes, which have high commercial value and are appreciated by artisanal and commercial fisheries (Junk et al, 2007;Castello et al, 2013;D'Avilla et al, 2021;Duponchelle et al, 2020) -but decline dramatically in impounded areas (Loures & Pompeu, 2018;Pelicice et al, 2018;Smith et al, 2019).…”