Simultaneous selachians: characterizing the ecological role of apex predators in Delaware Bay, USA
Date
2023
Authors
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Publisher
University of Delaware
Abstract
The Delaware Bay provides crucial nursery grounds for various teleosts, invertebrates, and elasmobranchs. Among elasmobranchs, Sandbar and Sand Tiger sharks represent apex predators within the Delaware Bay and mid-Atlantic estuarine ecosystems. These apex predators play a crucial role in the Delaware Bay ecosystem, impacting food web structure and function through predation. Despite their important role and potential increases in abundance relatively, little is known about the diet of these species across size classes. To address this lack of information, and better facilitate ecosystem-based management by the state, we used stable isotope analysis of multiple tissues (plasma and red blood cells) with varying turnover rates to characterize the trophic ecology of these species across size classes. A significant increase in blood plasma δ15N over time was evident for both Sandbar and Sand Tiger Sharks. Additionally, δ15N values between species were significantly different, in both blood plasma and red blood cells (RBC), with Sand Tiger sharks having lower δ15N values. We used Bayesian isotope mixing models to estimate relative importance of major prey groups (which included managed species such as Blue crab, Callinectus sapidus, Weakfish, Cynoscion regalis, and Atlantic Menhaden, Brevoortia tyrannus)., allowing us to identify clear niche partitioning of resources amongst species and ontogenetic stages in the Delaware Bay. This information will be used to enhance our understanding of the ecological role of sharks in Delaware Bay and inform management of marine resources of the Mid-Atlantic Bight as shark populations recover from historic overfishing.
Description
Keywords
Apex predators, Elasmobranchs, Isotope analysis, Ecosystem