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WOS:000632691700001; Freshwater environments host roughly half of the world’s fish diversity, much of which is concentrated in large, tropical river systems such as the Amazon. Fishes are critical to ecosystem functioning in the Amazon River basin but face increasing human threats. The basic biology of these species, and particularly migratory behaviour, remains poorly studied, in part owing to the difficulty associated with conducting tagging studies in remote tropical regions. Otolith microchemistry can circumvent logistical issues and is an increasingly important tool for studying fish life histories. However, this approach is still new in the Amazon, and its potential and limitations to inform fish conservation strategies remain unclear. Here, otolith microchemistry studies in the Amazon are reviewed, highlighting current possibilities, and several key factors that limit its use as a conservation tool in the Amazon are discussed. These include the dearth of spatiotemporal elemental data, poor understanding of environment–fish–otolith pathways, and insufficient funding, facilities, and equipment. A research initiative is proposed to harness the potential of this technique to support conservation in the Amazon. Key aspects of the proposal include recommendations for internal and external funding, which are critical to acquiring and maintaining technical staff, cutting-edge equipment, and facilities, as well as fostering regular scientific meetings and working groups. Meetings can facilitate a systematic approach to investigating environment–otolith pathways, broadening the chemical baseline for most Amazonian tributaries, and exploring potential valuable elements. These outcomes are urgently needed to conserve biodiversity and ecosystem functioning in the Amazon, especially given threats such as widespread hydroelectric damming. The initiative proposed here could make otolith microchemistry an important, cost-effective tool to inform and foster conservation in the Amazon, and act as a template for other imperilled tropical river basins, such as the Mekong and the Congo.

The development of analytical tools to determine the origin of fishes is useful to better understand patterns of habitat use and to monitor, manage, and control fisheries, including certification of food origin. The application of isotopic analyses to study calcified structures of fishes (scales, vertebrae, and otoliths) may provide robust information about the fish geographic origin and environmental living conditions. In this study, we used Sr and C isotopic markers recorded in otoliths of wild and farmed commercialized pirarucu (Arapaima spp.) to evaluate their prediction potential to trace the fishes origin. Wild and farmed fish specimens, as well as food used for feeding pirarucu in captivity, were collected from different sites. Isotope composition of otoliths performed by isotope-ratio mass spectrometry (IRMS; δ13C) and femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (LAfs-MC-ICPMS; 87Sr∕86Sr) were compared to the isotopic composition of water and of the food given to the fishes in the farms. Wild fish specimens that lived in environments with the largest fluctuation of river water Sr isotope ratios over time presented the largest Sr isotope variations in otoliths. A quadratic discriminant analysis on otolith isotopic composition provided 58 % of correct classification for fish production (wild and farmed) and 76 % of correct classification for the fish region. Classification accuracy for region varied between 100 % and 29 % for the Madeira and the Lower Amazon fishes, respectively. Overall, this preliminary trial is not yet fully developed to be applied as a commercial traceability tool. However, given the importance of Arapaima spp. for food security and the generation of economic resources for millions of people in the Amazon basin, further analyses are needed to increase the discrimination performance of these biogeographical tags.

WOS:000630750300001; 1. The Amazon basin hosts the Earth's highest diversity of freshwater fish. Fish species have adapted to the basin's size and seasonal dynamics by displaying a broad range of migratory behaviour, but they are under increasing threats; however, no study to date has assessed threats and conservation of Amazonian migratory fishes. 2. Here, the available knowledge on the diversity of migratory behaviour in Amazonian fishes is synthesized, including the geographical scales at which they occur, their drivers and timing, and life stage at which they are performed. 3. Migratory fishes are integral components of Amazonian society. They contribute about 93% (range 77-99%) of the fisheries landings in the basin, amounting to -US\436 million annually. 4. These valuable fish populations are mainly threatened by growing trends of overexploitation, deforestation, climate change, and hydroelectric dam development. Most Amazonian migratory fish have key ecological roles as apex predators, ecological engineers, or seed-dispersal species. Reducing their population sizes could induce cascading effects with implications for ecosystem stability and associated services. 5. Conserving Amazonian migratory fishes requires a broad portfolio of research, management, and conservation actions, within an ecosystem-based management framework at the basin scale. This would require trans-frontier coordination and recognition of the crucial importance of freshwater ecosystems and their connectivity. 6. Existing areas where fishing is allowed could be coupled with a chain of freshwater protected areas. Management of commercial and subsistence species also needs fisheries activities to be monitored in the Amazonian cities and in the floodplain communities to allow assessments of the status of target species, and the identification of management units or stocks. Ensuring that existing and future fisheries management rules are effective implies the voluntary participation of fishers, which can be achieved by increasing the effectiveness and coverage of adaptive community-based management schemes.

International audience; Amazonian goliath catfishes are widespread in the Amazon Basin. Recently, otolith 87Sr:86Sr analyses using laser ablation–multi‐collector–inductively coupled plasma mass spectrometry (LA‐MC‐ICPMS) revealed a >8,000 km trans‐Amazonian natal homing in Brachyplatystoma rousseauxii among fish caught and hatched in the largest Amazon River tributary, the upper Madeira basin. Although also suspected for fish in the upper Amazon, homing could not be demonstrated owing to less distinct environmental 87Sr:86Sr gradients along the Amazon mainstem. Using scanning X‐ray fluorescence microscopy (SXFM), a separate study provided evidence that Se:Ca and Sr:Ca are useful markers for identifying migration into Andean headwaters and the estuarine environment. We analysed otoliths of known 87Sr:86Sr profiles using SXFM mapping to test if Sr:Ca and Se:Ca patterns could demonstrate natal homing for three fish caught in the upper Amazon, using as reference two individuals that were natal homers and two forced residents (hatched after the construction of hydroelectric dams on the Madeira River) from the upper Madeira River. As hypothesised, although the Sr isotope profiles of the upper Amazon individuals were uninformative, two of them presented similar alternating mirror patterns of Sr:Ca and Se:Ca to those of the upper Madeira natal homers, indicating migrations out of the Andean region and into the estuary area. Both were therefore natal homers from the upper Amazon. The third individual from the upper Amazon presented similar Sr:Ca and Se:Ca patterns to those of the upper Madeira residents, suggesting it was a natural resident from the upper Amazon. By combining the results of 87Sr:86Sr analyses (LA‐MC‐ICPMS) and Sr:Ca and Se:Ca mappings (SXFM) that are completely independent of one another, we demonstrated that B. rousseauxii also performs natal homing in the upper Amazon. Our results indicate that the life cycle of B. rousseauxii is more complex than previous literature hypothesised, with the existence of partial migration, even in absence of physical barriers. Quantifying the relative importance of these different life‐history strategies will have important implications for fisheries management. Our results also lay the groundwork for conservation efforts in the context of hydropower development in the Amazon Basin and set testable hypotheses of the potential impacts of the Madeira River dams.

This paper explores the effects of two run-of-river dams (Jirau and Santo Antônio) built in cascade in the middle Madeira River (Brazil) on the interruption of long-distance migration routes of the gilded catfish (Brachyplatystoma rousseauxii). A participative monitoring system was set up to compare capture by commercial fishers approximately 1500 km upstream of the dams in Bolivia, before (1998-2007) and after (2015-2017) dam closure. A significant decrease in gilded catfish catches and in catch per unit effort was observed after dam closure, whereas no significant difference in mean weight was found. Back-estimation of age suggests that the few individuals remaining after dam closure in 2009 are a mixture of old homers that returned upstream before dam closure, and residents hatched after dam closure and trapped in the upper Madeira. Unless fishways in the Madeira River dams improve their efficiency, the gilded catfish might become rare and in danger of regional extinction in the upper Madeira basin in the next few years, negatively affecting river fisheries., Este estudio explora el impacto de las represas en cascada Jirau y Santo Antônio en el curso medio del río Madeira (Brasil) sobre la interrupción de la ruta de migración del bagre dorado (Brachyplatystoma rousseauxii). Se estableció un sistema de monitoreo participativo para comparar la captura de dorado por pescadores comerciales en Bolivia, aproximadamente 1 500 km río arriba de las represas, antes (1998-2007) y después (2015-2017) de su cierre. Se observó una disminución significativa en las capturas y en la captura por unidad de esfuerzo de dorado después del cierre de ambas represas. No hubo diferencias significativas en el peso promedio antes y después del cierre. La estimación de la edad de los pocos individuos capturados arriba de las represas sugiere que se trata de una mezcla de individuos adultos que han podido pasar las represas antes de su cierre en 2009, y residentes nacidos después del cierre de las represas, atrapados en el alto Madeira. Si los sistemas de traspaso de peces implementados en las represas del rio Madeira no mejoran su eficiencia, el dorado podría volverse escaso y en peligro de extinción regional en la cuenca alta del Madeira en los próximos años, afectando negativamente la pesca de esta especie.

International audience; In the Amazon, migratory catfishes of the genus Brachyplatystoma are apex predators that are important for fisheries and conservation. The life cycle of Brachyplatystoma platynemum Boulenger, 1898 is poorly known, although it has been hypothesized to be very similar to that of Brachyplatystoma rousseauxii Castelnau, 1855, which uses the entire length of the Amazon basin to complete its life cycle (from the Andes to the estuary). This study provides the first data on the migratory patterns of B. platynemum at the individual level using otolith microchemistry. In total, 94 individuals were sampled close to major breeding areas in the Amazon basin (78 fish from the middle and upper Madeira River and 14 fish from the upper Amazon), and their lifetime movements were assessed by measuring variations in 87 Sr/ 86 Sr along transverse sections of their otoliths (ear stones), using laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS). The migrations of B. platynemum are not as extensive as those of B. rousseauxii, and do not involve natal homing. Furthermore, the estuary is not a nursery area, at least for fish hatched in the Madeira. Nevertheless, B. platynemum migrates several thousand kilometres within the Amazon basin, with transboundary displacements between at least Bolivia, Brazil, and Peru. Current and planned hydroelectric development in the Amazon basin will severely disrupt both migration and access to breeding grounds, ultimately affecting the recruitment and population dynamics of these apex predators. The conservation of B. platynemum is crucial for the stability of the Amazonian aquatic food webs. This requires building effective fish passage on the two existing Madeira dams and considering alternative options to the large-scale hydropower development in the Amazon basin

Santo Antonio Energia (SAE) Universidade Federal de Rondonia (UNIR) Instituto de Estudos e Pesquisas Agroambientais e Organizacoes Sustentaveis (IEPAGRO) CAPES [1402376, 047/2012, 6632/14-9] CNPq [204344/2015-8] Foundation of Support to Research of the Amazon [PAREV/FAPEAM 019/2010] FAPESP (Sao Paulo Research Foundation) [2016/07910-0] The goliath catfish Brachyplatystoma rousseauxii has crucial economical and ecological functions in the Amazon basin. Although its life history characteristics have been studied in the Amazon, there is little information in the Madeira River basin, which holds genetically distinct populations and where dams were recently built. Using fish collected in Bolivia, Brazil and Peru, this study provides a validation of growth rings deposition and details the growth patterns of B. rousseauxii in the Madeira before the dams' construction. Age structure and growth parameters were determined from 497 otolith readings. The species exhibits two growth rings per year and sampled fish were between 0 and 16 years old. In the Brazilian portion of the basin, mainly young individuals below 5 years old were found, whereas older fish (> 5 years) were caught only in the Bolivian and Peruvian stretches, indicating that after migrating upstream to reproduce, adults remain in the headwaters of the Madeira River. Comparing with previous publications, B. rousseauxii had a slower growth and 20 cm lower maximum standard length in the Madeira River than in the Amazon River. This study provides a baseline for future evaluation of changes in population dynamics of the species following dams closure. Univ Fed Rondonia UNIR, Dept Biol, Lab Ictiol & Pesca, BR 364,Km 9,5, BR-76801059 Porto Velho, RO, Brazil Programa Posgrad Rede Biodiversidade & Biotechnol, BR 364,Km 9,5, BR-76801059 Porto Velho, RO, Brazil UAGRM, IRD, IIAP, LMI,EDIA, Montpellier, France INPA, Av Andre Araujo 2936, BR-69067375 Manaus, AM, Brazil Univ Fed Alagoas UFAL, Av Lourival Melo Mota,S-N Tabuleiro Martins, BR-57072900 Maceio, AL, Brazil Univ Fed Sao Paulo, Rua Doutor Carvalho Mendonca 144, BR-11070100 Santos, SP, Brazil Univ Fed Amazonas, Av Gen Rodrigo Octavio Jordao Ramos 3000, BR-69077000 Manaus, AM, Brazil IIAP, Vv Jose Quinones Km 2-5,Apartado Postal 784, Iquitos, Peru IRD, UMR BOREA, MNHN, CNRS 7208,SU,UCN,UA,IRD 207, Ave Agropolis 911, F-34394 Montpellier, France UMSS, ULRA, FAUNAGUA, ECOSINTEGRALES SRL, Ave Max Fernandez Final S-N, Cochabamba, Bolivia ECOSINTEGRALES SRL, Res Act, Carlos Muller St 211, Cochabamba, Cercado, Bolivia Inst Amazon Invest Cient SINCHI, Ave Vasquez Cobo Entre Calles 15 & 16, Bogota, Colombia Univ Fed Sao Paulo, Rua Doutor Carvalho Mendonca 144, BR-11070100 Santos, SP, Brazil CAPES [1402376, 047/2012, 6632/14-9] CNPq [204344/2015-8] [PAREV/FAPEAM 019/2010] FAPESP [2016/07910-0] Web of Science

Summary Length–weight relationships (LWRs) are presented for 112 freshwater fish species representing 23 families and five orders captured in the Madeira River, the largest white-water river tributary of the Amazon River. The allometry coefficient (b) of the LWR (Wt = aSLb) ranged from 2.446 to 3.856 with a median value of 3.102. Eight new LWR records are presented for Amazonian species as information for FishBase. LWRs in the present study provide historical data on a and b coefficients prior to the damming of the Madeira River in November 2011, allowing comparison estimates of predicted future population parameters as influenced by human intervention.

International audience; Knowledge 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.

The jatuarana ( Brycon amazonicus ), is an important species for the Madeira River commercial fisheries. The paper aims to characterize the jatuarana fishing dynamics in the middle Madeira River and test whether there are differences dowstreams and upstreams the Teotonio waterfall. Commercial fisheries landings were monitored daily at 15 ports or riverine communities along that stretch, using semi-structured interviews with fishermen. With data from the fishing monitoring program of UHEs Santo Antonio and Jirau we analysed: the yield, catch per unit effort (CPUE), length structure, locations and fishing gear used, between 2009 to 2011.The fishing yield of this species was temporaly analyzed with data from the Fishermen Colony of Porto Velho city (Rondonia state, Brazil), between 1990 to 2012. The yield and the CPUE showed significant differences by area and locations and the capture of the species was carried out primarily in the channel river and banks river through gillnets. In addition, the samples collected in the upstream area have higher distribution and modal lengths than from those collected downstream. These results suggest that the areas require distinct management measures.