“…By contrast, strontium (Sr) isotopic ratios in otoliths, which depend almost exclusively on the age and bedrock geological composition of watersheds, and thus barely vary across years, represent accurate habitat signatures in freshwaters (Kennedy, Folt, Blum, & Chamberlain 1997;Kennedy, Blum, Folt, & Nislow 2000;Barnett-Johnson, Pearson, Ramos, Grimes, & MacFarlane 2008). Recently, the use of 87 Sr: 86 Sr has proved effective in determining migratory patterns of freshwater fishes in complex and extensive river systems, such as the Amazon Basin (Pouilly, Point, Sondag, Henry, & Santos 2014;Garcez, Humston, Harbor, & Freitas 2015;Souza, Humston, & Freitas 2016), including in goliath catfishes (Hegg, Giarrizzo, & Kennedy 2015;Duponchelle et al, 2016). Otolith 87 Sr: 86 Sr analyses using laser ablation-multi-collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) have confirmed a >8,000-km migration and revealed natal homing in populations of B. rousseauxii from the largest white-water Amazon River tributary-the Madeira River (Duponchelle et al, 2016; Figure 1).…”