Pre-exploitation shark baselines and the history of human impact on coral reef-associated shark communities in the Caribbean are poorly understood. We recovered shark dermal denticles from mid-Holocene (~7 ka) and modern reef sediments in Bocas del Toro, Caribbean Panama to reconstruct an empirical shark baseline before major human impact and quantify how much the modern shark community in the region had shifted from this historical reference point. We found that denticle accumulation rates, a proxy for shark abundance, declined by 71% since the mid-Holocene. All denticle morphotypes, which reflect shark community composition, experienced significant losses, but those morphotypes found on fast swimming, pelagic sharks (e.g., families Carcharhinidae and Sphyrnidae) declined the most. Analysis of historical records suggested that the steepest decline in shark abundance occurred in the late 20^th century, coinciding with the advent of a targeted shark fishery in Panama. Although the disproportionate loss of denticles characterizing pelagic sharks was consistent with overfishing, the large reduction in denticles characterizing demersal species with low commercial value (i.e., the nurse shark Ginglymostoma cirratum) indicated that other stressors could have exacerbated these declines. We demonstrate that the denticle record can reveal changes in shark communities over long ecological timescales, helping to contextualize contemporary abundances and inform shark management and ecology.

DillonPNAS_SupData_Bocas_Denticles

This dataset includes: (1) mid-Holocene and modern shark dermal denticle (shark scale) assemblage data; (2) recent shark catch data; and (3) semi-quantitative perceptions of shark abundance through time based on historical records in Caribbean Panama. Denticles were recovered from bulk samples of fine sediments collected from a subaerially exposed ~7000-year-old coral reef and from nearby modern reefs within a sheltered, semi-enclosed lagoonal system in Bocas del Toro, Panama. The rate of denticle accumulation in these sediments serves as a proxy for shark abundance. These data were collected to reconstruct a shark baseline before major human impact in this region of Caribbean Panama and quantify how much the modern shark community had changed over time. Insight from the denticle record was supplemented with archaeological evidence, historical narratives, and modern ecological and fisheries data to independently reconstruct the ecological history of sharks in the region, help constrain the timing of shark declines, and make inferences about the drivers and ecological consequences of those declines.

This dataset contains five csv files: "abundances", "taphonomy", "sorting", "ecol_state_scores", and "shark_catches". Field attributes for each csv file are described in the accompanying Metadata ReadMe file.