Sawfish, read in tooth and saw: Rostral teeth as endogenous chemical records of movement and life-history in a critically endangered species

Abstract The ecology of endangered and rare species can be difficult to study due to their low abundances and legal limits on scientist’s ability to catch, sample, and track them. This is particularly true of sawfish (family Pristidae) whose numbers have declined precipitously, placing all five species on the CITES list of critically endangered species worldwide. Best known for their distinctive, toothed rostrum the ecology, movement, and life-history of sawfish is poorly understood. Sawfish rostral teeth are modified placoid scales, which grow continuously throughout the life of the fish. This continuous growth, combined with their stable calcified makeup, makes sawfish teeth a potential source of temporal records of chemical and isotopic changes through the life of the fish. Rostral teeth can be removed non-lethally from living animals and are also often preserved in rostra housed in museums and as curios, potentially allowing both contemporaneous and historical sources of life-history data. Study of the potential for sawfish rostral teeth as endogenous chemical and structural records is extremely limited, however. Using archived samples of largetooth sawfish (Pristis pristis) we show that multiple chemical tracers can be recovered from sawfish teeth, and that these tracers can be used to understand movement across salinity gradients and between freshwater and the ocean. We further show that sawfish teeth contain repeated structures and indistinct banding which could potentially be used for aging or growth analysis of fish.