O uso de isótopos estáveis de nitrogênio (δ15N) evidencia a posição trófica do pirarucu (Arapaima sp.)?

Abstract

Trophic studies are essential to understand the regulation and transfer of energy among individuals and ecosystems. We explored estimates of trophic position using stomach-content analysis and δ15N in liver and muscle in a broad size range of arapaima from lakes in the middle Juruá River, Amazonas. We also combined stomach-content analysis with the empirical knowledge of local dwellers to expand the understanding of arapaima feeding in the study area. Arapaima total length explained most of the variation in trophic-position values estimated from liver and muscle δ15N, showing that body size has more effect than prey trophic position on δ15N values. This highlights the need for a better understanding of the factors that affect values of δ15N that are unrelated to diet trophic position. Stomach content analysis combined with empirical knowledge provided complementary information indicating that young arapaima eat fish and invertebrates and adults feed exclusively on fish, but from a wide range of species and mainly from low trophic positions. The interviewees had consistent ecological knowledge of the arapaima feeding and could contribute to the implementation of future management projects in the region. Stable isotopes may add supplementary information in trophic studies, but stomach-content analysis is still needed to unravel the trophic ecology of predatory fishes in each area of interest.