Trans‐Amazonian natal homing in giant catfish

Abstract

International audienceKnowledge of fish migration is a prerequisite to sustainable fisheries management and preservation, especially in large international river basins. In particular, understanding whether a migratory lifestyle is compulsory or facultative, and whether adults home to their natal geographic area is paramount to fully appraise disruptions of longitudinal connectivity resulting from damming.In the Amazon, the large migratory catfishes of the Brachyplatystoma genus are apex predators of considerable interest for fisheries. They are believed to use the entire length of the basin to perform their life cycle, with hypothesized homing behaviours. Here, we tested these hypotheses, using the emblematic B. rousseauxii as a model species.We sampled adults close to major breeding areas in the Amazon basin (upper Madeira and upper Amazonas) and assessed their lifetime movements by measuring variations in 87Sr/86Sr along transverse sections of their otoliths (ear stones) using laser ablation multicollector mass spectrometry (LA-MC-ICPMS).We demonstrate that larvae migrate downstream from the Andean piedmont to the lower Amazon, where they grow over a protracted period before migrating upstream as adults. Contrary to prevailing inferences, not all fish spend their nursery stages in the Amazon estuary. By contrast, the passage in the lower or central Amazon seems an obligate part of the life cycle. We further evidence that most adults home to their natal geographic area within the Madeira sub-basin. Such long-distance natal homing is exceptional in purely freshwater fishes.Synthesis and applications. By using otolith microchemistry, we were able to demonstrate a seemingly compulsory basin-wide migratory life cycle of large Amazonian catfishes. This makes them the organisms performing the longest migrations (>8000 km) in fresh waters. This exceptional life history is already jeopardized by two dams recently built in the Madeira River, which block a major migration route and access to a substantial part of their spawning grounds. Major impacts can be anticipated from the current and forthcoming hydroelectric development in the Amazon basin, not only on the populations and fisheries of this apex predator, but also on Amazonian food webs through trophic cascades

Unmasking continental natal homing in goliath catfish from the upper Amazon

“…The section was then ground and polished using polishing papers (1,200 and 2,400 μm) and ultra-pure water until the core was visible on one side, as detailed in Duponchelle et al (2016). The section was then ground and polished using polishing papers (1,200 and 2,400 μm) and ultra-pure water until the core was visible on one side, as detailed in Duponchelle et al (2016).…”

“…The section was then ground and polished using polishing papers (1,200 and 2,400 μm) and ultra-pure water until the core was visible on one side, as detailed in Duponchelle et al (2016). Analyses using LA-MC-ICPMS ( 87 Sr: 86 Sr profiles) were conducted at the Laboratoire de Chimie Analytique Bio-inorganique et Environnement in Pau and at the Laboratoire Cycles Géochimiques et Ressources of IFREMER in Brest (for details see Duponchelle et al, 2016;Hauser, 2018;Hauser et al, 2019). Photos of the prepared otoliths before microchemical analyses, as well as their respective growth marks, are presented in supporting information ( Figure S1).…”

“…Although also suspected for fish caught and hatched in the upper Amazon, this migratory pattern has not been demonstrated owing to less distinct environmental F I G U R E 1 Illustration of the migratory patterns of Brachyplatystoma rousseauxii in the Amazon basin, as revealed by otoliths 87 Sr: 86 Sr profiles, in red on the graphs (based on Duponchelle et al, 2016, andHauser, 2018). (a) Natal homing behaviour of a fish hatched and caught in the Upper Madeira sub-basin (Bolivia), after a prolonged migration down to the lower Amazon River: on the otolith's transverse section, the hatching signature (c. 0.721), characteristic of the upper Madeira waters, quickly drops to a lower value typical of the lower Amazon River (c. 0.710), when the larvae are flushed down to the lower Amazon by the current at a mean size of c. 3.4 cm (Duponchelle et al, 2016). (a) Natal homing behaviour of a fish hatched and caught in the Upper Madeira sub-basin (Bolivia), after a prolonged migration down to the lower Amazon River: on the otolith's transverse section, the hatching signature (c. 0.721), characteristic of the upper Madeira waters, quickly drops to a lower value typical of the lower Amazon River (c. 0.710), when the larvae are flushed down to the lower Amazon by the current at a mean size of c. 3.4 cm (Duponchelle et al, 2016).…”

“…(a) Natal homing behaviour of a fish hatched and caught in the Upper Madeira sub-basin (Bolivia), after a prolonged migration down to the lower Amazon River: on the otolith's transverse section, the hatching signature (c. 0.721), characteristic of the upper Madeira waters, quickly drops to a lower value typical of the lower Amazon River (c. 0.710), when the larvae are flushed down to the lower Amazon by the current at a mean size of c. 3.4 cm (Duponchelle et al, 2016). (c) Otolith 87 Sr: 86 Sr profile of a fish hatched and caught in the upper Madeira after completion of the dams (= forced residents); unlike the pattern observed before the dams (see a), the isotopic values remain within the range of Madeira water vales throughout the fish's life (Hauser, 2018) [Colour figure can be viewed at wileyonlinelibrary.com] 87 Sr: 86 Sr gradients along the Amazon mainstem (Duponchelle et al, 2016). The 87 Sr: 86 Sr profile then starts rising again to come back approximately to the hatching value at the moment of the fish's capture in the upper Madeira subbasin (in the Ichilo River).…”

We need better understanding about functional diversity and vulnerability of tropical freshwater fishes

“…For example, some tropical fish species are morphologically similar but differ in their physiology, ecology and spatial distributions (e.g. Lobón-Cerviá and Bennemann 2000; Nunes et al 2014;Duponchelle et al 2016). In addition, fishes have indeterminate growth influenced by environmental variation and populations with broad size distribution diversity; therefore, FD should have significant intraspecific and seasonal variations (e.g.…”