Document Type

Article

Publication Title

PLoS ONE

Abstract

Declines of large sharks and subsequent release of elasmobranch mesopredators (smaller sharks and rays) may pose problems for marine fisheries management as some mesopredators consume exploitable shellfish species. The spotted eagle ray (Aetobatus narinari) is the most abundant inshore elasmobranch in subtropical Bermuda, but its predatory role remains unexamined despite suspected abundance increases and its hypothesized specialization for mollusks. We utilized a combination of acoustic telemetry, benthic invertebrate sampling, gut content analysis and manipulative experiments to assess the impact of spotted eagle rays on Bermudian shellfish resources. Residency and distribution of adult spotted eagle rays was monitored over two consecutive summers in Harrington Sound (HS), an enclosed inshore lagoon that has historically supported multiple recreational and commercial shellfish species. Telemetered rays exhibited variable fidelity (depending on sex) to HS, though generally selected regions that supported relatively high densities of potential mollusk prey. Gut content analysis from rays collected in HS revealed a diet of mainly bivalves and a few gastropods, with calico clam (Macrocallista maculata) representing the most important prey item. Manipulative field and mesocosm experiments with calico clams suggested that rays selected prey patches based on density, though there was no evidence of rays depleting clam patches to extirpation. Overall, spotted eagle rays had modest impacts on local shellfish populations at current population levels, suggesting a reduced role in transmitting cascading effects from apex predator loss. However, due to the strong degree of coupling between rays and multiple protected mollusks in HS, ecosystem-based management that accounts for ray predation should be adopted.

First Page

e40227

DOI

https://doi.org/10.1371/journal.pone.0040227

Publication Date

7-3-2012

Department

Marine and Environmental Sciences

Comments

Must use original publisher's citation to cite this work.

Copyright: 2012 Ajemian et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: Much of the research was funded by the Eric Clee Environmental Fellowship via the Bermuda Zoological Society. The Bermuda Institute of Ocean Sciences, University of South Alabama (USA), and the Mobile Jayce provided additional logistical and financial support. The Mobile Jaycees are a civic leadership organization and are a nonprofit. They donate annually to the Department of Marine Sciences. Their donation has absolutely no obligations on the department’s part. The department chooses to use these funds to assist graduate students with their research projects, there is no potential for conflict of interest. MJA was supported by fellowships from both the University of South Alabama and Dauphin Island Sea Lab. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interest sexist.

*E-mail:Matt.Ajemian@tamucc.edu

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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