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Data from: Dermal denticle shedding rates vary between two captive shark species

Citation

Dillon, Erin et al. (2021), Data from: Dermal denticle shedding rates vary between two captive shark species, Dryad, Dataset, https://doi.org/10.25349/D9K32M

Abstract

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.

Usage Notes

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 (Sphyrna tiburo) and three zebra sharks (Stegostoma fasciatum) 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.

Funding

University of California, Santa Barbara

Schmidt Family Foundation

Alfred P. Sloan Foundation