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Aspects of the Life History of the Pacific Electric Ray, Torpedo californica (Ayres)
Julie A. Neer and Gregor M. Cailliet
Vol. 2001, No. 3 (Aug. 6, 2001), pp. 842-847
Stable URL: http://www.jstor.org/stable/1448311
Page Count: 6
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Pacific electric rays (n = 198) were collected from central and southern California from July 1994 through January 1996 for studies on their age and growth, reproduction, and demography. Whole vertebral centra with graphite microtopography band enhancement were used for ageing. Average percent error and percent error were 6.5% and 4.9% among readings. Maximum age was an estimated 16 yr. The von Bertalanffy growth model provided the best fit and predicted an asymptotic total length of 1372 mm for females and 921 mm for males, and K was estimated to be 0.073 for females and 0.137 for males. Female and male reproductive status was determined using two and three criteria, respectively. Median total length-at-maturity, determined using a logistic response function, was 645 mm (age estimate, 6 yr) for males and 731 mm TL (age estimate, 9 yr) for females. Fecundity of one female was estimated at approximately 17 young per litter. Time of parturition could not to be determined. Instantaneous mortality estimates ranged from 0.096-0.277, depending on longevity estimates. Best age-based demographic analyses indicate that the Pacific electric ray population has a net reproductive rate per generation of 2.6-8.9, a generation time of 11.2-13.0 yr, instantaneous rates of change of 0.09-0.18, and finite rates of change of 1.09-1.20.