Virginia Institute of Marine Science
MARINE AND COASTAL FISHERIES
The Cownose Ray Rhinoptera bonasus is an opportunistic predator of benthic invertebrates and has had a long history of negative interactions with commercial shellfish industries. Most recently, Cownose Rays have been implicated in negatively affecting the recovery of bay scallop Argopecten irradians stocks in North Carolina and oyster restoration and commercial aquaculture efforts in Chesapeake Bay. A mitigation attempt to decrease predation on shellfish has resulted in an unregulated fishery for Cownose Rays. Cownose Ray life history suggests that they are highly susceptible to overexploitation. We determined age, growth, and size at maturity for Cownose Rays collected in Chesapeake Bay. In total, 694 rays were used for the study: 246 males ranging in size from 30.0 to 98.0cm disc width (DW) and 448 females ranging from 30.0 to 110.5cm DW. The oldest individual observed was a female (107cm DW) estimated at age 21. Our data suggested that Cownose Rays grow considerably faster during the first few years than has been previously reported, thus producing higher estimates of the growth coefficient k. The best-fit growth models (three-parameter von Bertalanffy models) estimated k-values of 0.2741 for males and 0.1931 for females. The large sample size and inclusion of many older animals (n = 119 rays over age 10) resulted in theoretical maximum size estimates that matched the observed sizes well. The median size at 50% maturity was 85-86cm DW for males and females (corresponding to ages of approximate to 6-7 for males and approximate to 7-8 for females). Fecundity in Cownose Rays was typically one embryo per mature female, with a gestation period of 11-12 months. Our study confirms that the Cownose Ray is a K-selected species with late maturity, long gestation, and low reproductive potential, indicating that it could be highly susceptible to overexploitation.
GULF-OF-MEXICO; RHINOPTERA-BONASUS; LIFE-HISTORY; MOVEMENTS; SHARKS; CALIFORNICA; POPULATION
We are grateful to Janet Krenn for editorial review of drafts of this paper and to David Rudders for statistical analysis assistance. We also thank the many Virginia fishermen and seafood processors for assistance with the collection and processing of rays. This work is a result of research sponsored by National Oceanic and Atmospheric Administration (NOAA) Award Number NA07NMF4570324 and in part by NOAA Award Number NA10OAR4170085 to Virginia Sea Grant. This is Virginia Institute of Marine Science Contribution Number 3252.
Robert A. Fisher , Garrett C. Call & R. Dean Grubbs (2013) Age, Growth, and Reproductive Biology of Cownose Rays in Chesapeake Bay, Marine and Coastal Fisheries, 5:1, 224-235, DOI: 10.1080/19425120.2013.812587