Fish bycatch of the laulao catfish Brachyplatystoma vaillantii (Valenciennes, 1840) trawl fishery in the Amazon Estuary

Abstract

This study aimed to analyse the composition and seasonal variation in the fish bycatch of the Brachyplatystoma vaillantii trawl fishery in the Amazon Estuary in 2009 by monitoring the trips of 48 vessels. The bycatch represented 29% of the catches, totalling 22,228 specimens and 52 taxa, distributed in 22 families (the principal families were Ariidae, Pimelodidae, and Sciaenidae). Brachyplatystoma rousseauxii, Plagioscion squamosissimus, and Sciades herzbergii together contributed 69% of the bycatch and were considered consistent bycatch species. Although a higher proportion of bycatch was captured during the rainy season, the seasonal difference was not significant. A multidimensional scaling (MDS) ordination analysis and an analysis of similarity (ANOSIM) indicated that the species composition of the bycatch was similar across the seasons. However, larger numbers of B. rousseauxii and P. squamosissimus were captured during the rainy season, whereas S. herzbergii predominated during the dry season. The marine migrants and estuarine species guilds showed the greatest richness, whereas freshwater migrants were the most numerous. Among the feeding guilds, the zoobenthivores were the most diverse, whereas the piscivores were the most abundant. The results indicate that fishing pressure primarily affects small- (20-30 cm) and medium-sized (30-50 cm) individuals, although the catch of P. squamosissimus was composed primarily of adults. However, the catches of both B. rousseauxii and B. vaillantii were composed primarily of juveniles.

Translated abstract

Este estudo objetivou analisar a composição e variação sazonal da ictiofauna acompanhante da pesca de arrasto de Brachyplatystoma vaillantii no estuário amazônico, em 2009, através do monitoramento de viagens de 48 embarcações. A ictiofauna acompanhante representou 29% das capturas, totalizando 22.228 indivíduos e 52 táxons pertencentes a 22 famílias, sendo estas as principais: Ariidae, Pimelodidae e Sciaenidae. Brachyplatystoma rousseauxii, Plagioscion squamosissimus e Sciades herzbergii representaram juntas 69% da captura e foram consideradas constantes. Embora o maior percentual de captura tenha ocorrido no período chuvoso, as diferenças sazonais não foram significativas. Análises de ordenação (MDS) e de similaridade (ANOSIM) mostraram que a composição da captura entre os períodos é semelhante; entretanto, maiores capturas de B. rousseauxii e P. squamosissimus foram observadas no período chuvoso, enquanto S. herzbergii foi dominante no período seco. As guildas migrantes marinhas e espécies estuarinas apresentaram maior riqueza, enquanto as migrantes dulcícolas predominaram em percentual de indivíduos. Considerando as guildas alimentares, as zoobentívoras apresentaram a maior riqueza, enquanto as piscívoras predominaram em abundância relativa. Os resultados indicam que a pressão pesqueira atua sensivelmente sobre os indivíduos de pequeno (20-30 cm) e médio (30-50 cm) porte, embora a captura de P. squamosissimus seja composta predominantemente por adultos. A captura de B. rousseauxii e B. vaillantii, entretanto, foi composta predominantemente por juvenis.