The bycatch of piramutaba, Brachyplatystoma vaillantii industrial fishing in a salinity and depth gradient in the Amazon estuary, Brazil

ABSTRACT The piramutaba, Brachyplatystoma vaillantii is a freshwater catfish that is the most abundant fishery resource in the Amazon estuary. Piramutaba trawling is done on industrial fishing scale and is characterized by the presence of many freshwater and marine bycatch species, with and without commercial value. Here we describe the bycatch of the industrial fishery of piramutaba in the Amazon estuary and evaluate the relationship of two important environmental factors, depth and salinity, with the accidental capture of freshwater and marine fishes in the Amazon estuary in the rainy and dry seasons. We identified 21 cartilaginous fish species (19.1% freshwater and 80.9% marine) and 125 bony fish species (25.6% freshwater and 74.4% marine). The bycatch included 64 species without commercial value (43% of all bycatch species), which are always discarded. Freshwater and estuarine fishes exhibited significantly higher abundances in shallower environments, while marine fishes were similarly abundant along the entire depth gradient. On the contrary, the abundance of freshwater fishes significantly decreased, and that of estuarine and marine fishes significantly increased with increasing salinity. Regarding the conservation status of the bycatch species, one is classified as vulnerable (VU), and seven as critically endangered (CR). The information on the bycatch of piramutaba fishery in the Amazon estuary is important to subsidize regional fisheries policies and the management of protected areas.摘要：piramutaba（Brachyplatystoma vaillantii）是一种淡水鲶鱼，为亚马逊河口最为丰富的渔业资源。该物种的拖网捕捞以工业化渔业规模开展，其典型特征为伴随大量具有或不具有商业价值的淡水与海洋副渔获物种。本研究描述了亚马逊河口piramutaba工业化渔业的副渔获物情况，并评估了干湿季中，水深与盐度这两个关键环境因子与亚马逊河口淡水、海洋鱼类误捕量之间的关联。本次研究共鉴定出21种软骨鱼类（其中淡水种占19.1%，海洋种占80.9%）及125种硬骨鱼类（淡水种占25.6%，海洋种占74.4%）。副渔获物中包含64种无商业价值的物种（占所有副渔获物种的43%），此类物种均会被直接丢弃。淡水与河口鱼类在浅水环境中的丰度显著更高，而海洋鱼类在整个深度梯度上的丰度分布较为均匀。与之相反，随着盐度升高，淡水鱼类的丰度显著下降，而河口与海洋鱼类的丰度则显著上升。针对副渔获物种的保护现状，其中1种被列为易危（VU），7种被列为极危（CR）。亚马逊河口piramutaba渔业副渔获物相关研究数据，可为区域渔业政策制定及保护区管理提供重要支撑。