Fish composition and prey utilization of the black skimmer (Rynchops niger) in mar Chiquita coastal lagoon, Argentina

Abstract

A B S T R A C TLagoons along the western coast of the South Atlantic Ocean shelter high densities of juvenile fish and are key areas for several seabirds that rely on the resources offered by this kind of ecosystem. The objective of this study was to analyze fish composition and abundance in shallow-water areas of the estuarine region of Mar Chiquita Coastal Lagoon (Argentina) and the diet composition of the Black skimmer (Rynchops niger) during its non-breeding season as well as evaluating its inter-annual variations. Fish were sampled with a beach-seine net and the skimmers' diet was analyzed from their pellets. The estuarine-dependent marine fishes were the best represented bio-ecological category followed by freshwater fishes. Significant differences were observed in fish abundance and composition between and within years. Species richness was higher during the summer season and during the first year sampled. The occurrence of freshwater fishes as an important and diverse group of the Mar Chiquita estuarine area contrasted with previous reports. The diet of the Black skimmer included freshwater, estuarine and marine fish species. Skimmers forage in the shallow waters of the estuarine area of the Mar Chiquita Coastal lagoon though little similarity was observed between its diet and local fish abundance. These results emphasize the importance of performing these evaluations in order to improve the quality of studies and the interpretations of top predators foraging ecology. R E S U M OAs lagoas costeiras do Oceano Atlântico Sul abrigam altas densidades de peixes juvenis e são áreas-chave para diversas aves marinhas que dependem dos recursos oferecidos por esses ecossistemas. O objetivo do presente trabalho foi analisar a abundância e a composição de peixes na região estuarina da Lagoa Costeira Mar Chiquita (Argentina), a dieta do talha-mar (Rynchops niger) e as variações interanuais. Os peixes foram coletados com uma rede de praia tipo picaré e a dieta do talha-mar analisada a partir de suas fezes. O peixe-marinhos dependentes do estuário foram a categoria bioecológica melhor representada, seguido por peixes de água doce. Foram observadas diferenças intranuais e interanuais significativas na abundância e composição da ictiofauna. A riqueza de espécies foi maior durante o verão e no primeiro ano da amostragem. A ocorrência de peixes de água doce como um grupo importante e diversificado na área estuarina do Mar Chiquita contrasta com resultados de estudos anteriores realizados na área. A dieta do talha-mar incluiu peixes de água doce, estuarinos e marinhos. Apesar dessa ave se alimentar em águas rasas da área estuarina do Mar Chiquita, uma baixa similaridade entre sua dieta e abundância local de peixes foi observada. Esses resultados reforçam a importância da realização de avaliações a fim de proporcionar avanço nos estudos e melhorar as interpretações sobre a ecologia alimentar de predadores de topo.

Rainy cycles in South America as a driver for the breeding of the Black Skimmer (Rynchops niger) and the Large-billed Tern (Phaetusa simplex) (Aves, Charadriiformes)

“…Rynchops n. cinerascens migrate mostly to coastal regions and can be found on the N Atlantic coast of Brazil, on the Pacific coast of Ecuador, Panama, Colombia, Peru, and Chile, with large flocks at the mouth of the Aconcagua River (Concon) and the Elqui River (La Serena), N and W of Argentina and in large lakes such as Titicaca in Peru and Bolivia (Davenport et al, 2016). Rynchops n. intercedens migrates to the W Atlantic coast from the central/eastern portion of the Northern Brazilian coastline (Maranhão state) easternward to Rio Grande do Norte state, and from Bahia (Brazil) to Argentina, and also to lakes and river courses in Brazil, as well in the Mar Chiquita lagoon, Mar del Plata, which is probably the main nonbreeding concentration of R. n. intercedens, with around 12,000 individuals counted from late February to May (Favero et al, 2001;Mariano-Jelicich et al, 2003). On the other hand, Phaetusa simplex spp.…”

Interaction strength varies in relation to tidal gradient and spatial heterogeneity in an intertidal Southwest Atlantic estuarine food web

“…Birds can use all intertidal and their abundances increase in summer (e.g. Mariano-Jelicich et al, 2003), while fishes have the access for food limited by tidal cycle and their abundances do not change along the year. Moreover both predators use in different ways areas with and without crab bioturbation (see Martinetto et al, 2005).…”

“…The south-western Atlantic estuaries are important nursery and feeding areas for migratory and local birds (e.g. Botto et al, 1998;Mariano-Jelicich et al, 2003) and fishes (e.g. Cousseau et al, 2001;Valiñas et al, 2010).…”