Fig 1.
Water sampling points and geology of the Amazon River basin.
Maps show (A) the location of 87Sr/86Sr water samples within the Amazon River basin digitized by the authors from location descriptions in the literature [51–53] and points predicted from Eq 1. The geological age and composition of the basin (B) used to predict the 87Sr/86Sr signatures of unsampled watersheds is also shown. Maps created using USGS datasets [59–61].
Table 1.
Brachyplaystoma spp. sample information.
Fig 2.
Otolith sectioning and analysis.
Representative transverse section from a dourada lapillus otolith showing the analysis area (in red) used for all otoliths with the laser-ablation tracks indicated. All analyses were performed approximately perpendicular to the growth rings.
Fig 3.
River isotopic signatures throughout the Amazon River basin.
Strontium ratio values (y-axis) for each sampled and predicted watershed (x-axis) in the current study. Color indicates the classification to three river groups using quadratic discriminant function analysis. Solid error bars indicate the standard deviation where samples were repeated over time (See Table 1 for sample sizes). Dashed error bars indicate the prediction intervals from the geologic regression (Eq 1) used to predict that point. Points bordered in black were misclassified during cross validation of the quadratic discriminant function.
Table 2.
Isotopic and geologic makeup of major watersheds of the Amazon River basin.
Fig 4.
Location classification of 87Sr/86Sr signatures in otolith transects.
Plots show the variation in 87Sr/86Sr (y-axis) over the life of sampled fish, represented as distance from the otolith core in microns (x-axis). Horizontal colored lines indicate stable signatures identified using changepoint analysis, with colors representing inclusion in one of three statistically distinguishable river groups based on quadratic discriminant analysis. Fourteen samples of dourada (A) were collected in Belém and Manaus fish markets. Five samples of piramutaba (B) were collected in Manaus. Three samples of piraíba (C) were collected in Belém. Dark grey chart labels indicate a different y-axis scale was used to accommodate large variations in 87Sr/86Sr. The x-axis scale differs for all fish depending on the width of the otolith, which varies based on age, growth and species specific factors.