A large stingray with an acoustic transmitter attached to her pectoral fin.

A stingray barb without the mucus covering.

The round stingray, Urolophus halleri, is the most common stingray found in Southern California waters. It typically inhabits sand or mud substratum off coastal beaches, bays, and sloughs (Eschmeyer, et. al. 1983). The stingray gains its name from the poisonous serrated spine located towards the base of its tail, which it uses to defend itself, such as when it is stepped on by an unsuspecting human. Because of human population increases along coastal areas, more people are participating in ocean recreation activities and are going to the beach. As the result of these apparent overlaps in habitat use between stingrays and humans, increased numbers of stingray-related injuries have been reported from beaches in Orange County, California.
 

Injury caused by barb

The average frequency of stingray related injuries to beach goers at Seal Beach by month over the last three years.

Seal Beach, California is a popular beach destination located immediately south of the San Gabriel River mouth and Alamitos Bay, which are both areas of warm water discharge via power plant effluent. This beach is frequently used by local residents for swimming and bodyboarding. In 1998, approximately 450 stingray-related injuries were treated by City lifeguards from the Seal Beach area alone (Steve Cushman, pers. comm.). Because of the high number of stingray-related injuries, City Public Safety officials are interested in finding ways of reducing this hazard, without impacting the environment. Unfortunately, very little is known about biology and behavior of these stingrays, thus, making it extremely difficult to develop measures to protect the public from stingray encounters.

Large-scale removal of rays along these beaches has been suggested as a means of reducing stingray injuries. However, because the round stingray is an important benthic predator, depletion of the population could cause adverse ecological effects to coastal benthic communities. In addition, large-scale removal may be ineffective due to seasonal coastal movements.

We are presently conducting a spine regeneration study in both the laboratory and field to determine whether spine clipping will reduce the chances of stingray-related injuries to beach goers. The success of this procedure, however, is largely dependent on the movement patterns of the rays. For example, if rays were constantly moving along the shoreline, then the population would have to be "clipped" continuously. Unfortunately, nothing is known about the movement patterns of the round stingray. In addition, Babel (1967) found a positive correlation between water temperature and stingray occurrence at the outlet to the Seal Beach Power Plant, concluding that rays prefer warmer water. Unfortunately, little is known about how water temperature and tide may affect movement patterns of rays along the coast. Thus, a more detailed understanding of how urban influence of oceanographic features may aid in reducing stingray related injuries along popular beaches.

To quantify the movement patterns and densities of round stingrays off Seal Beach we are using a combination of acoustic telemetry tracking, monitoring and diver surveys.
 

A bathymetry map of the Seal Beach area. The dots and star represents the locations where stingray tagged at the San Gabriel River mouth (star) have been recaptured.

Students measuring and tagging a stingray

Stingrays are followed from a small Boston Whaler customized for coastal tracking and small acoustic transmitters. Rays are followed continuously for up to 72 hours and then periodically relocated. To further augment long shore movements, acoustic listening stations have been placed along the Seal Beach shoreline to listen for rays carrying transmitters as they may move by. Densities of stingrays in relation to the San Gabriel River are being determined using beach seines and diver surveys.
So far we’ve tagged over 2600 stingrays at Seal Beach and have only recaptured 14! That means there are a lot of stingrays off Seal Beach, but they do not seem to remain at this site for very long. We’ve tracked 5 rays and have found that they can move over a mile in several hours or can remain in the same small area for several days.

Students removing stingrays from the beach seine.

Using the Seal Beach Life Guard truck and jetski to deploy the 300’ long beach seine at Seal Beach.

However, this research is still on-going so we cannot conclude anything just yet. Stay tuned for more information - we’ll make it available as we continue to better understand the movement patterns of this interesting stingray. This research is funded by the City of Seal Beach Life Guards, USC Sea grant (http://www.usc.edu/go/seagrant), and the Surfrider Foundation - Seal Beach chapter. This work couldn’t be done without the assistance of the many graduate and undergraduate students from CSU Long Beach and local community.