DOI: 10.25349/d9k32m
title: Data from: Dermal denticle shedding rates vary between two captive shark species

description: Shark dermal scale (denticle) accumulation in the fossil record can
 provide information about the abundance and composition of past shark
 communities. Denticles are shed continuously, such that a single shark
 leaves a scattered composite of many isolated denticles in sediments.
 However, the rate of denticle shedding as well as how these rates vary
 among shark species with different life modes and their consistency over
 time are unknown, limiting the interpretation of denticle assemblages. To
 better understand the process of denticle shedding and calibrate the
 relationship between absolute shark abundance in the environment and
 denticle deposition in sediments, we captured denticles shed by two shark
 species in a large aquarium over nine months. We then simulated how these
 aquarium-derived shedding rates shape the relationship between shark
 abundance and denticle accumulation. Bonnethead sharks (Sphyrna tiburo) –
 a more active, benthopelagic species with small, thin denticles – shed 3.6
 times faster on average than zebra sharks (Stegostoma fasciatum) – a more
 sedentary, demersal species with large, robust denticles. This pattern
 persisted when shedding rates were corrected by estimated denticle
 quantities, shark space use, and methodological factors (2.2- to 3.8-fold
 difference). Over the study, bonnethead shark shedding rates declined
 while zebra shark shedding rates increased slightly. Finally, denticle
 assemblage composition corresponded with the relative abundance of
 denticles on each species’ body, consistent with natural shedding rather
 than selective loss. Overall, we show that shark taxa contribute unevenly
 to the denticle record, indicating that shedding rate measurements can
 help inform and constrain ecological interpretations of denticle
 assemblages.
description: This dataset includes: (1) shark dermal denticle (scale) and
 tooth accumulation measurements in a controlled aquarium tank containing
 five sharks and (2) accompanying observations of shark behavior in the
 same aquarium tank. Data were collected from captive sharks in the
 Tropical Pacific Gallery at the Aquarium of the Pacific (Long Beach, CA)
 between 2018 and 2020. The ~1,325,000 L tank housed two bonnethead sharks
 (<i>Sphyrna tiburo</i>) and three zebra sharks
 (<i>Stegostoma fasciatum</i>) during the study, permitting
 measurements of denticle shedding rates from two shark species with
 different life modes and denticle morphologies. Shark denticles (and
 teeth) were recovered from replicate sand-filled trays placed in three
 locations in the tank over a nine-month-long period. Denticle accumulation
 was collected at multiple time points to measure sub-annual temporal
 variability in shedding rates. Denticles were classified to species and
 functional morphotype to compare shedding rates between the two shark
 species in the tank and examine whether certain denticle morphotypes were
 preferentially shed. Denticle preservation was scored to document their
 condition around the time of shedding. Lastly, behavioral surveys were
 conducted to assess how patterns of shark activity, space use, and
 interactions with the tank environment varied between species and, in
 turn, might have influenced denticle shedding. Together, these data
 provide insight into the process of denticle shedding and can be used to
 explore the relationship between absolute shark abundance and denticle
 deposition in sediments. This dataset contains five csv
 files: “counts”, “weathering”, “morphotype_id”, “teeth”, and “behavior”.
 Field attributes for each csv file are described in the accompanying
 Metadata ReadMe file.