Abstract
Aim:To evaluate possible nycthemeral and seasonal temporal patterns in fish assemblage associated with limnological aspects and biotic factors in two reservoirs in semarid Northeastern Brazil.MethodsFish were sampled with gillnets in nycthemeral cycles throughout the dry and rainy season in two reservoirs (Paulo Sarasate/PS and Edson Queiroz/EQ). The stomach contents of the predator species were surveyed. The limnological variables were submitted to principal components analysis, while their relation to fish abundance was determined by canonical correspondence analysis. Temporal patterns in relative fish species abundance were detected with nMDS.ResultsTemperature and dissolved oxygen levels segregated the reservoirs physico-chemically. Turbidity and chlorophyll-a levels differed between seasons, and the relative abundance of species differed between the reservoirs. Predators were more abundant in PS, while detritivores were more abundant in EQ. Triportheus signatusand Plagioscion squamosissimus were the most abundant species in both reservoirs. In general, predator abundance was positively associated with high temperature and dissolved oxygen (PS>EQ) and negatively associated with turbidity. The activity patterns of P. squamosissimus could not be explained by fluctuations in environmental variables. Non-predators tended to cluster around the vectors chlorophyll-a, pH and turbidity. Predators had a more diversified diet in PS in accordance with food availability, while predators in EQ ate only fish and shrimp. Nycthemeral patterns varied for the same species depending on the reservoir. Generally, in PS predators were more active during daylight hours while non-predators were more active after dark. However, in EQ predators and non-predators displayed similar nycthemeral activity patterns. Regardless of the reservoir, predators were more abundant in the rainy season. No seasonal trend was observed for non-predators.ConclusionsLimnological differences between PS and EQ influenced temporal species abundance patterns. The species distribution was determined by predation conditions and physiological attributes.
Highlights
Covering 969,000 km2, the semiarid region of Northeastern Brazil is subject to recurrent and severe droughts (Ab’Sáber, 2003)
The study was conducted in two major reservoirs in the middle Acaraú River basin (Ceará, Brazil): the Paulo Sarasate reservoir (PS), located in the Varjota municipality, and the Edson Queiroz reservoir (EQ), located in the municipality of Santa Quitéria
Temperature and dissolved oxygen (DO) appeared to promote physical and chemical segregation between the reservoirs since these variables were generally higher for PS than for EQ (Table 1 and Figure 3a)
Summary
Covering 969,000 km, the semiarid region of Northeastern Brazil is subject to recurrent and severe droughts (Ab’Sáber, 2003). The fish assemblage of these reservoirs is the result of the adaptation of the original community (of the caatinga, Rosa et al, 2003) to the new environment (Agostinho et al, 1999; Loureiro‐Crippa & Hahn, 2006; Cantanhêde et al, 2008) and of the introduction of new species. Fish move within a reservoir in accordance with temporal factors (diurnal/nocturnal habits, seasons, and fluctuations in water level) and spatial factors (lotic, lentic, littoral and pelagic zone). Fish assemblages in reservoirs are regulated by environmental fluctuations (abiotic factors) and/or by biotic interactions (Coutant, 1985; Gido & Matthews, 2000; Jackson et al, 2001)
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