true

ISRA FACTSHEETS

SOUTH AMERICAN INLAND WATERS

ISRA FACTSHEETS

SOUTH AMERICAN INLAND WATERS

Amazon River Mouth ISRA

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Amazon River Mouth ISRA

Amazon River Mouth

Summary

Amazon River Mouth is located in northern coastal Brazil, along the Amapá and Pará states. This area is formed by the confluence of the Amazon and Tocantins rivers with the Atlantic Ocean, creating a complex estuarine system. It is influenced by tides, river discharge, ocean currents, and seasonal variations, which impact water salinity, sedimentation, and biodiversity. This area overlaps with Amazon Estuary and its Mangroves Ramsar Site and Reserva Biológica do Parazinho. Within this area there are: reproductive areas (e.g., Whitespotted Freshwater Stingray Potamotrygon scobina) and the area sustains a high diversity of rays (four species).

Amazon River Mouth

Amazon River Mouth

DESCRIPTION OF HABITAT

Amazon River Mouth is located in northern Brazil. It is situated along the Amapá State and Pará State on the northeastern coast of South America. This region is formed by the confluence of the Amazon and Tocantins rivers with the Atlantic Ocean, creating a complex estuarine system. The freshwater from the Amazon River mixes with saline waters from the Atlantic Ocean, influenced by tides, river discharge, ocean currents, and seasonal variations, which impact water salinity, sedimentation, and biodiversity. The main marine current affecting this area is the South Equatorial Current, also known as the Brazil Current (Almeida 2008).

This area experiences two distinct seasonal phases. The rainy season (January–June) is characterised by heavy rainfall that causes widespread flooding, with peak precipitation between February–May. Freshwater discharge from the Amazon River is at its highest, increasing sediment deposition, reducing water clarity, and altering habitat availability. During the dry season (July–December), rainfall is reduced, leading to receding water levels and drier conditions (Almeida 2008). The lower Amazon River discharge allows saline water to penetrate further inland.

Tidal fluctuations can reach four meters, significantly altering the landscape. High tides push saline water inland, while low tides expose mudflats (Almeida 2008). Persistent trade winds drive water circulation and redistribute nutrients, supporting high biological productivity (Almeida 2008). Seasonal flooding and drought cycles shape the ecosystem, influencing species distribution and habitat structure (Goulding 1980). The outer Amazon River Mouth is marked by a shallow, muddy bottom, where freshwater and marine waters dynamically mix (Eisma & Marel 1971; Curtin & Legeckis 1986).

Marajó Island is located within this area, the largest fluvio-marine island in the world. Within the Bailique Archipelago, Parazinho Island is one of the outermost fluvial islands of this vast river delta and is shaped by tidal flooding, which forms a network of drainage channels (de Souza Gama & Rosa 2020).

This area overlaps with Amazon Estuary and its Mangroves Ramsar Site (Ramsar 2025) and Reserva Biológica do Parazinho (UNEP-WCMC 2025).

This Important Shark and Ray Area is benthic and is delineated from surface waters (0 m) to 50 m based on the bathymetry of the area.

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Amazon River Mouth is an important reproductive area for four ray species.

Between March 2011–January 2013, 42 Marques’ Freshwater Stingrays (23 males, 19 females) were sampled in this area using longlines, gillnets, spears, and traps (de Souza Gama 2013). Of these, 12 were pregnant females based to the presence of embryos (63% of the total females sampled). Seven males were reproductively active. The body sizes of the 42 rays ranged between 8.9–59.3 cm disc width (DW). As size-at-birth is ~12 cm DW (Araujo et al. submitted), some individuals were neonates/ young-of-the-year (YOY) (de Souza Gama 2013).

In 2005 (April–June and October–December), 2006 (May, July, August, September, and November), and 2007 (January and March), 138 Ocellate Freshwater Stingrays (82 females and 56 males) were captured in Marajó Island, through independent fishery surveys that used bottom longlines, gillnets, beach seines, and spears (Almeida 2008). A total of 54 pregnant females (presence of eggs or embryos) were collected (66% of all females sampled). Forty-seven males were adults displaying reproductive behaviour (i.e., presence of semen) (Almeida 2008). Based on the individuals sampled in this area, it was determined that the reproductive cycle of Ocellate Freshwater Stingray follows an annual pattern closely tied to seasonal changes in rainfall and water levels. Copulation occurs during the transitional rainy-dry season (May–June). Gestation takes place during the dry season (June–October). Birth occurs at the beginning of the rainy season (November–December) and lasts around four months. During this period, newborn Ocellate Freshwater Stingray are observed using flooded areas as nurseries. This reproductive cycle ensures that newborns emerge during the wet season, when habitat availability increases due to rising water levels, reducing predation risk, and improving survival chances (Almeida 2008). Between March 2011–January 2013, 54 Ocellate Freshwater Stingrays were captured using longlines, gillnets, spears, and traps of which 18 were sampled (females = 6, males = 12) (de Souza Gama 2013). Sizes ranged between 10.5–48 cm DW. Since size-at-birth is between 10–14 cm DW, and size-at-maturity is ~39 cm DW for males and ~44 cm DW for females (Torres et al. submitted a), the individuals sampled included neonates, YOY, juveniles, and adults. Three pregnant females, assessed based on the presence of embryos, were captured (25.9–48 cm DW).

In 2000 (May, August, October, and December), 2001 (December), and 2002 (March), 281 Reticulate Freshwater Stingrays were collected using longlines and bottom nets (Almeida 2003). Of these, 276 (98% of the total individuals sampled) were neonate, YOY, or juvenile (Almeida 2003). Between March 2011–January 2013, bimonthly sampling using longlines, gillnets, spears, and traps was undertaken across 82 days (de Souza Gama 2013). Reticulate Freshwater Stingrays were captured (n = 18) of which 15 were sampled (9 females, 6 males) (de Souza Gama 2013). Sizes ranged between 10.9–32.8 cm DW. Since size-at-birth is between 8–14 cm DW, and size-at-maturity is ~23 cm DW for males and ~24 cm DW for females (Torres et al. submitted b), the individuals sampled included neonates, YOY, juveniles, and adults. Three pregnant females, assessed based to the presence of embryos, were also captured (de Souza Gama 2013).

Between 1996–2005, 343 Whitespotted Freshwater Stingrays (130 males, 107 females) were sampled   in this area. From these, 31 were pregnant females, due to the presence of embryos (29% of the total females sampled) (Charvet-Almeida et al. 2005). In 2000 (May, August, October, and December), 2001 (December), and 2002 (March), 398 Whitespotted Freshwater Stingrays were captured using longlines and bottom nets (Almeida 2003). Of these, 80 (20% of all individuals sampled) were neonate or YOY (10–20 cm DW).  Females and males mature at 40 and 35 cm DW, respectively (Charvet-Almeida et al. 2005). Between March 2011–January 2013, 11 Whitespotted Freshwater Stingrays were captured of which five females were sampled, measuring 28.8–55 cm DW. One pregnant female was captured, carrying four embryos (de Souza Gama 2013).

CRITERION D

SUB-CRITERION D2 – DIVERSITY

Amazon River Mouth sustains a high diversity of Qualifying Species (four species). This exceeds the regional diversity threshold (three species) for the South American Inland Waters region (Almeida 2003, 2008; Charvet-Almeida et al. 2005; Almeida et al. 2008; de Souza Gama 2013; Marceniuk et al. 2023).

Amazon River Mouth

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