Search

The abundances of migratory shark species observed throughout the Mid-Atlantic Bight (MAB) during productive summer months suggest that this region provides critical habitat and prey resources to these taxa. However, the principal prey assemblages sustaining migratory shark biomass in this region are poorly defined. We applied high-throughput DNA metabarcoding to shark feces derived from cloacal swabs across nine species of Carcharhinid and Lamnid sharks to (1) quantify the contribution of broad taxa (e.g., invertebrates, fishes) supporting shark biomass during seasonal residency in the MAB and (2) determine whether the species displayed distinct dietary preference indicative of resource partitioning. DNA metabarcoding resulted in high taxonomic (species-level) resolution of shark diets with actinopterygian and elasmobranch fishes as the dominant prey categories across the species. DNA metabarcoding identified several key prey groups consistent across shark taxa that are likely integral for sustaining their biomass in this region, including Atlantic menhaden (Brevoortia tyrannus), Atlantic mackerel (Scomber scombrus), and benthic elasmobranchs, including skates. Our results are consistent with previously published stomach content data for the shark species of similar size range in the Northwest Atlantic Ocean, supporting the efficacy of cloacal swab DNA metabarcoding as a minimally invasive diet reconstruction technique. The high reliance of several shark species on Atlantic menhaden could imply wasp-waist food-web conditions during the summer months, whereby high abundances of forage fishes sustain a diverse suite of migratory sharks within a complex, seasonal food web., (© 2023 Fisheries Society of the British Isles.)

Recent spikes in interactions between humans and sharks in the New York Bight have sparked widespread reporting of possible causalities, many of which lack empirical support. Here we comment on the current state of knowledge regarding shark biology and management in New York waters emphasizing that the possible drivers of increased human-shark interactions are confounded by a lack of historical monitoring data. We outline several key research avenues that should be considered to ensure the safe and sustainable coexistence of humans, sharks, and their prey, in an era of accelerated environmental change., (© 2023 Fisheries Society of the British Isles.)

Measures of trophic position (TP) are critical for understanding food web interactions and human-mediated ecosystem disturbance. Nitrogen stable isotopes (δ(15) N) provide a powerful tool to estimate TP but are limited by a pragmatic assumption that isotope discrimination is constant (change in δ(15) N between predator and prey, Δ(15) N = 3.4‰), resulting in an additive framework that omits known Δ(15) N variation. Through meta-analysis, we determine narrowing discrimination from an empirical linear relationship between experimental Δ(15) N and δ(15) N values of prey consumed. The resulting scaled Δ(15) N framework estimated reliable TPs of zooplanktivores to tertiary piscivores congruent with known feeding relationships that radically alters the conventional structure of marine food webs. Apex predator TP estimates were markedly higher than currently assumed by whole-ecosystem models, indicating perceived food webs have been truncated and species-interactions over simplified. The scaled Δ(15) N framework will greatly improve the accuracy of trophic estimates widely used in ecosystem-based management., (© 2013 The Authors. Ecology Letters published by John Wiley & Sons Ltd and CNRS.)