Quantifying shark predation effects on prey: Dietary data limitations and study approaches

Abstract

Understanding the ecological impacts of sharks on prey populations has become a research priority given widespread shark population declines due to overfishing, combined with significant conservation efforts. Accordingly, many studies have conducted analyses of shark stomach contents and/or used biomarkers, such as stable isotope signatures, to assess dietary patterns in order to infer ecological roles. Here, I summarize how relying on stomach contents and/or stable isotope signatures to assess the potential for sharks to initiate trophic cascades can be misleading and may significantly underestimate the strength of shark top-down predation effects on prey. However, a study approach that measures attributes of the sharks (e.g. hunting mode), potential prey (e.g. escape speed) and the environment (e.g. habitat rugosity) can provide greater insights for quantifying the magnitude of top-down predation effects of sharks and the potential for their population declines or recoveries to trigger trophic cascades. To aid future investigations, I provide a set of predictions, based on ecological theory, which would specifically lead to in - creases in the magnitude of shark predation effects on prey populations. I also present key study approaches currently being employed by researchers to test such predictions.