Hypothesis
The chemistry of ear bones (otoliths) in young skipjack tuna would differ enough between the three main Indian Ocean nursery areas to tell where an unknown fish was born.
What failed
Some single elements differed between nurseries, but the overall chemical signatures largely overlapped. The best classifier assigned fish to the correct nursery only 51% of the time, and the Central and Eastern nurseries were hard to separate.
Broken assumption
Otolith chemistry is distinct enough between Indian Ocean nursery areas to identify the birthplace of skipjack tuna.
Why
The nursery signatures overlap, and the signatures also changed between the 2018 and 2019 cohorts, which makes a fixed reference signature unreliable.
From the published paper: Artetxe-Arrate et al. PLoS ONE, 2021. ↗CC BY