Age and growth of the round stingray, Urobatis halleri, at Seal Beach, California

Lori Hale

A round stingray swimming at Seal Beach, California.

My research focuses on the population dynamics of the round stingray, Urobatis halleri, specifically the age and growth structure of the population of round stingrays at Seal Beach, California. Age and growth analyses of fish species are the first step in examining fundamental biological processes of a population (Goldman 2004). Estimations of the age structure of a population and growth rates of a species are applied to determine longevity, mortality, productivity, yield, and population dynamics which in turn are essential for responsible fisheries management. Responsible management of species is imperative for preventing exploitation and overfishing, which can lead to the collapse of a fishery and possible extinction of a population or species.

The round stingray is one of the most common nearshore elasmobranch species in southern California. Round stingrays are especially abundant at Seal Beach, California, where power plant effluent at the confluence of the San Gabriel River and Alamitos Bay has caused a substantial increase in water temperature. Seal Beach is a popular recreation and residential area for many people. Round stingrays can cause severe injuries to humans when these animals are stepped on; consequently, there were over 1500 stingray-related injuries reported at Seal Beach from 1999-2002 (Seal Beach Lifeguards pers. comm.) The high incidence of stingray-related injuries at Seal Beach has led public safety officials to seek methods to control the round stingray population.

In fish, bony structures such as otoliths, fin rays, and spines are used in age estimation (Cailliet et al. 1983). In elasmobranchs, the cartilage of the vertebral centra becomes calcified via deposition of calcium ions into the intercellular matrix of the cartilage (Ridewood 1921). This calcification is seen as longitudinal concentric rings, and subsequent rings are deposited with growth. These growth rings appear as a thin ring applied during winter, and a wider ring applied during summer. The pair of rings deposited each year is referred to as an annulus (Cailliet et al. 1983). The enumeration of annuli deposited in vertebral centra provides the most reliable method of estimating age at length in elasmobranchs (Cailliet et al. 1983).

Round stingray vertebrae showing growth rings.

I am currently estimating the ages of round stingrays collected at Seal Beach in monthly beach seines. It appears that the round stingray lives for 7-10 years and may grow slower than related species like Urolophus lobatus and Urolophus paucimaculatus.

My project is part of a larger Seal Beach stingray project, and more information on other data collected on this species at Seal Beach can be found here: Seal Beach Stingray Project

This project has been funded by Sigma Xi Grants-In-Aid of Reseach and the International Women's Fishing Association. Additional support was provided by numerous volunteers and the Seal Beach Lifeguards.


 

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