A NEW RECORD OF Carcharhinus leucas IN AN AMAZONIAN RIVER SYSTEM

Carcharhinus leucas is a cosmopolitan shark species in tropical and subtropical waters. Normally, individuals are found in most of the major rivers in the world but records in the Amazon basin are somewhat scarce. Here we provide a new record of a young of the year female bull shark caught in Cametá (PA) as bycatch of the bottom longline fi shery, weighing 8 kg and measuring 90 cm total length. The Brazilian Amazon coast and its freshwater systems are one of the only areas where records of small young of the year and juveniles exist for the Atlantic Ocean on the Neotropical region. Therefore, this information is important to direct future research on habitat use and reproductive patterns for the species in this region, since this could be a crucial area for the species conservation.

The bull shark is considered to be near threatened with extinction by the International Union for the Conservation of Nature (IUCN), but its current population trends are unknown (Simpfendorfer & Burgess, 2009). However, it is important to notice that species inhabiting both marine and freshwater environments are subjected to a greater interaction with fi sheries. In fact, the major threat to C. leucas is fi shing (Ferreira et al., 1996;Karl et al., 2011) and possibly dams as a barriers to up and downstream migrations in freshwater systems (Lees et al., 2016;Winemiller et al., 2016). Besides that, this shark species is extremely resilient to habitat modifi cation and extreme environmental conditions .
Therefore, records of C. leucas in freshwater systems are important to provide a greater understanding of how this species uses non-marine habitats (Heupel et al., 2010). Many records from the Amazon basin comprise a lot of juvenile bull sharks (Starks, 1913;Thorson, 1972;Ferreira et al., 1996;Feitosa et al., 2016;Goulding et al., 2018), suggesting the region might be an important area

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for this life stage. Thus, these records provide better understanding of how the species uses the Amazon biome's waters, especially since it is an important area in the Atlantic, one of the few parts of the Neotropical region where young of the year and neonates are captured.
The present study aimed at reporting the fi rst capture of a young of the year bull shark in the Tocantins river basin, one of the largest rivers comprising the Amazon region, extending the records of this species in the Amazon River basin. We also provide a review of bull shark records in the Amazon basin based on published and on gray literature review.
The Tocantins River basin is associated with the Araguaia River basin, which together form the Tocantins-Araguaia system corresponding to the second largest drainage in the Amazon, totaling 767,164 km2 (Ribeiro et al., 1995). It is located in a region with tropical climate, an annual rainfall average of 1,752 mm, and evapotranspiration potential of 768 mm (Ho et al., 2016). The average river downstream fl ow near Marabá city, Pará state, is of around 11,000 m 3 s-1 (Ho et al., 2016), and the hydrological regime is defi ned by rain caused by the Intertropical Convergence Zone (Marengo, 2006;Valverde & Marengo, 2014).
Additionally, the Tocantins River has been under constant human induced changes from the urban agglomerations (e. g. Cametá city) and mainly for the construction of dams along its course (Akama, 2017). Currently, seven hydroelectric plants operate in the area, with a potential of energy generation up to 11,500 MW, the third largest in Brazil (https:// www.ana.gov.br/sala-de-situacao/tocantins/saibamais-tocantins). However, the dams' catchments have been continually experiencing less rainfall, which has both decreased the plants' capacity of energy production and the volume of water fl owing on the river (ANA, 2020). These human induced impacts have a profound eff ect of freshwater fi shes.  (Santos et al., 2004;Lasso et al., 2013), but the impacts of dams and other anthropogenic developments on these species are mostly unknown.
In addition to these freshwater stingrays, the bull shark would be expected to occur in this habitat, although there are no documented records of a shark in this river basin so far.
In 10 August 2019 a young of the year female bull shark was caught in the Cametá municipality, Pará State (Figure 1). The specimen was captured as bycatch of the bottom longline fi shery targeting the Gilded catfi sh (Brachyplatystoma rousseauxii (Castelnau, 1855). Since the only information obtained from this specimen comes from photographic records, video and personal communications with the fi shers, no samples from the specimen could be collected. The distance from a general point of capture to the river mouth was calculated using Google Earth Pro software.
Fishers in the Tocantins River caught a young of the year specimen of Carcharhinus leucas weighting 8 kg and measuring 90 cm total length (Figure 2). The individual was caught at 6 m depth and 273 km away from the estuary in an area with high incidence of small islands. In addition, the capture occurred in the dry season, when freshwater fl ow decreases, and saltwater intrusion occurs. The local community consumed the fi sh. Finally, the catch was shared in social media outlets generating a journalistic report by the local media posted on YouTube (https://bit. ly/2mIphUW).
Although commonly encountered in tropical estuaries and rivers, this record represents the fi rst shark ever recorded in the Tocantins River basin. In fact, records of the bull shark in the Amazon basin are scarce. Thorson (1972) provides 20 records for the species in the Amazon River and its tributaries comprising juveniles and adults from both sexes. Werder & Alhanati (1981) provide three more records of sharks captured well within the river. Further records come from Soto & Nisa-Castro-Neto (1998), Karl et al. (2011), Gausmann (2018, and a record of a specimen captured in Santarém, Pará state in 2018 (https://glo.bo/31HBxnK). When examining records in the Brazilian Amazon biome on a wider scale, this list increases with records from the Mearim River, Maranhão state (Feitosa et al, 2016), and the present study. Therefore, we consider that there are 29 records of bull shark specimens in the Amazon biome in a span of over 50 years. From those, the vast majority comprise young of the year and juvenile specimens   Despite the sparse historical record, Brazil's Amazon coast and freshwater systems seem to have the most consistent record of young of the year and juvenile specimens of C. leucas. Other records for these life stages in Brazil come from southearstern Brazil (Cananeia, São Paulo) (Sadowsky, 1967), but no recent records exist to our knowledge. Although not enough to support a hypothesis of nursery area.
For C. leucas, this information is important to direct future research on habitat use and reproductive patterns for the species in the Amazon biome, including its coastal waters. In fact, this is especially consistent with C. leucas behavior, since several rivers in the world are known to be nurseries for this species (Tillet et al., 2011).
Therefore, the existence of a nursery for the bull shark in the Amazon biome must be investigated to better understand this area's role on the species dynamics in the Neotropical region. We also reinforce the need to study the effects of fisheries in its population, since several records also exist from these juveniles on the estuarine area, where intense gillnet and longline fi sheries targeting Cynoscion acoupa and Scomberomorus brasiliensis occur (Mourão et al., 2014;Almeida et al., 2014). Furthermore, Alencar et al (2001) provide records of elevated biomass of C. leucas on the Amazon coastal waters, especially near the Amapá state's coast, which is strongly infl uenced by the Amazon River discharge (Coles et al., 2013). Finally, we suggest employing vertebrae microchemistry to study habitat use and juvenile residency patterns in the area.