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RESEARCH ARTICLE
Contents Vol 58(1)

Hard prey specialists or opportunistic generalists? An examination of the diet of the cownose ray, Rhinoptera bonasus

A. B. Collins A B C D , M. R. Heupel B , R. E. Hueter B and P. J. Motta A
+ Author Affiliations
- Author Affiliations

A University of South Florida, Department of Biology, 4202 East Fowler Avenue, Tampa, Florida 33620, USA.

B Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, Florida 34236, USA.

C Current address: Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, 100 8th Avenue SE, St. Petersburg, Florida 33701, USA.

D Corresponding author. Email: angela.collins@myFWC.com

Marine and Freshwater Research 58(1) 135-144 https://doi.org/10.1071/MF05227
Submitted: 22 November 2005  Accepted: 27 July 2006   Published: 30 January 2007

Abstract

Atlantic cownose rays (Rhinoptera bonasus) are benthic, suction feeders whose foraging activities have been implicated in severe damage to commercial shellfish industries. With jaws highly modified for durophagy, it has been assumed that R. bonasus are crushing specialists that feed primarily upon hard molluscan prey. Stomach contents from R. bonasus caught within Florida’s Charlotte Harbor estuary between July 2003 and July 2004 were analysed using the index of relative importance (IRI) to determine most important prey types. Prey items were identified from 38 families and fell into nine distinctive groups. The three most dominant prey groups were crustaceans (%IRI = 55.31), polychaetes (%IRI = 25.20) and bivalves (%IRI = 12.58). Shoalmates had more similar diets than non-shoalmates, suggesting group feeding. Most small or softer-bodied prey consumed were relatively intact, indicating lack of prey processing and capture through suction feeding. All larger, harder-bodied prey showed evidence of crushing (fractured and broken shells). Although R. bonasus has been characterised as a hard prey specialist, these results suggest it may behave as an opportunistic generalist, modifying feeding behaviour to consume readily available prey.

Additional keywords: benthic feeding, durophagy, feeding ecology, Myliobatiformes, stingray.


Acknowledgements

This work was supported in part by grants from the Mote Scientific Foundation, the University of South Florida, Charlotte Harbor National Estuary Program, PADI Foundation, PADI Project Aware and NOAA/NMFS through the National Shark Research Consortium. Thanks to Florida Fish and Wildlife Research Institute’s Fisheries-Independent Monitoring Program, especially Gregg Poulakis, Phil Stevens, and the Charlotte Harbor field laboratory staff for collecting samples, and to Bob McMichael, Tim MacDonald and Chuck Idelberger for allowing A. B. Collins to review historical sampling data. Thanks to Jay Leverone, Anamari Jayo Boyes and Debi Ingrao for their assistance in identification of benthic organisms; to Colin Simpfendorfer, Susan Bell and Beau Yeiser for their help and guidance; and to Tony Tucker, Jack Morris, Adam Summers, Jim Gelsleichter, John Tyminski, Julie Neer and numerous student interns for their assistance throughout the duration of this project. A. B. Collins was the recipient of the Mote Marine Laboratory and University of South Florida Graduate Fellowship in Elasmobranch Biology during the course of this work. All research was conducted under the guidelines of the University of South Florida’s Institutional Animal Care and Use Committee (IACUC certification No. 2331).


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