Landscape variables affecting fishery yield in lake systems of the Central Amazon region, Brazil

Abstract

According to fisheries data, lakes are important systems for fish production in the Amazon basin. However, there is no information about the relationship between landscape variables and fishing yield that allows foresight into potential resource exploitation in this environment. The present study aims to evaluate this relationship with the hypothesis: lakes of different shapes give the same fishery yield in the Amazon, after considering the effects of lake size, distance to the river, fishing effort, fuel and ice used. Fishery data from 1994 to 1996 were analyzed with regard to 3228 trips on 50 lakes of the main white water tributaries of the Amazon basin. Analysis of covariance was applied to test this hypothesis. With variables such as fishing grounds access, fishing effort and lake shape the model explained a significant 72% of variabilities in the fisheries yield. Fishing yields among lake systems were different, thus the null hypothesis was rejected (P < 0.05). Results indicate that dendritic lakes far distant from the main river have greater productivity than floodplain lakes because there are more habitats of fish refuge for reproduction and feed available to the fish; there are also more limitations to access by predators.

Trophic Ecology ofArapaimasp. in a ria lake—river–floodplain transition zone of the Amazon

“…Therefore, the ria lake may provide better conditions as an appropriate refuge for fish during extreme drought events for both prey and predators. The dendritic morphology of ria lake environments and the large terrestrial–aquatic interface perimeter may result in increased nutrient inputs and enhancement of lake productivity (Nolan et al., ). Although predation and predator–prey encounter rates are affected by water transparency (Turesson & Brönmark, ), one of the studied floodplain lake with a transparency that exceeded the study ria lake (150 cm vs. 80 cm) only yielded adult arapaima with empty stomachs.…”

“…Although the warmer waters of floodplain lakes could increase digestion rates and thereby affect the frequency of empty stomachs, a 4°C difference between habitat types is unlikely to account for the notable between-habitat differences in empty stomachs observed here. The connectivity of ria lake environments to tributary stream networks and the main river channels may provide a better explanation of higher prey availability in ria lakes at the end of the dry season (Freitas, Siqueira-Souza, Florentino, & Hurd, 2013;Nolan et al, 2009). For example, Arantes et al (2013) found that floodplain lakes with more connectivity have a higher arapaima density than lakes with low connectivity, suggesting a greater availability of food resources in the better-connected lake habitats.…”

“…The Purus River has high nutrient and suspended sediment concentrations (Junk, Soares, & Carvalho, ), is highly productive and is the main source of fishes found in the markets of Manaus (Batista & Petrere, ). Within the Purus River basin, floodplain lakes usually occur in a horseshoe shape (Figure ; Nolan et al., ). The lakes vary in pH (5.0–7.2), conductivity (9‐45μS/cm), transparency and water colour and remain isolated from other water bodies during the dry season.…”

“…To date, most of the Amazonian trophic ecology literature has focused on these river-floodplain habitats (Araújo-Lima et al, 1986;Bayley, 1995;Benedito-Cecílio et al, 2000;Forsberg et al, 1993;Junk et al, 1989;Martinelli et al, 1991). In contrast, the trophic ecology of Amazonian ria lakes' habitats has not been adequately studied even though they exhibit high fishery yields and serve as critical nursery and/or feeding habitats for many fishes (Nolan, Fabré, & Batista, 2009). Ria lakes were formed by eustatic changes.…”

“…The dendritic morphology of ria lakes increases the perimeter of the terrestrial-aquatic interface, increasing the potential for allochthonous inputs to the water (e.g. terrestrial material; Henderson & Crampton, 1997;Irion, Junk, & Mello, 1997;Nolan et al, 2009). The nutrient-poor catchment of ria lakes typically yields waters with high oxygen levels in comparison with floodplain lakes (Henderson & Crampton, 1997).…”