Life History Aspects of a Commercially Exploited stingray, Dasyatis brevis, from the Magdalena Bay Complex, B.C.S., Mexico
Wade Smith with a 61 cm disc width
female Dasyatis brevis.
Life History Aspects of a Commercially Exploited stingray, Dasyatis brevis, from the Magdalena Bay Complex, B.C.S., Mexico |
Wade Smith with a 61 cm disc width female Dasyatis brevis. |
Wade D. Smith |
Mexican elasmobranch fisheries have expanded to become the largest in the Americas, raising concerns that overfishing of these resources may occur in the near future. Rays dominate the catch composition at many locations throughout the Pacific and Gulf of California. The Magdalena Bay complex is believed to be the most important developing fishing region in Baja California Sur and is home to an established, directed fishery for rays. Dasyatis brevis, the diamond stingray, is a primary component of these landings. Dasyatis brevis is reported to occur from southern California to Chile, including the Galapagos and Hawaiian Islands. Disc widths up to 1.2 m have been recorded. A pilot study for this project completed during the summer of 1998 indicated that D. brevis frequently moves in loosely aggregated schools segregated by both size and sex. Females were observed to reach considerably larger disc widths than males. Mature adults of both sexes tended to occupy deeper water.
If D. brevis also exhibits the long life span, slow growth, and late age of maturity, and low fecundity described for other elasmobranchs, depletion or collapse of the targeted population is possible. Because sharks and rays tend to serve as apex predators, their removal may have considerable impact upon the intricate food webs found in marine environments. It has been determined that rays regulate the populations of benthic organisms such as clams and polychaetes through their feeding habits. Additionally, rays modify and enhance habitat in sandy and muddy environments by creating large feeding pits. As a result, the removal of rays may have significant and unpredictable effects on the biological diversity of entire marine communities. The proposed investigation will provide the first details of the life history characteristics of this virtually unknown but widely distributed large stingray. An improved understanding of the biology and population dynamics of commercially important species is crucial for formulating effective, sustainable management strategies for exploited populations.
The objectives of this study are to: 1) determine the growth characteristics of D. brevis by analyzing the banding patterns deposited within the vertebral centrum; 2) validate the periodicity of vertebral banding through marginal increment analysis; 3) predict the reproductive status as related to age estimates; and 4) describe the age composition of D. brevis in the Magdalena Bay complex.
Funding: Support for this project has been provided in part by a partial California Sea Grant College System Traineeship, California Sea Grant College System Rapid Response Grant, the Dr. Earl H. Myers and Ethel M. Myers Oceanographic and Marine Biology Trust, the PADI Foundation, and Project AWARE.