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Age and Growth Determination of the Bat Ray, Myliobatis californica Gill, in Central California

Linda K. Martin and Gregor M. Cailliet
Copeia
Vol. 1988, No. 3 (Aug. 3, 1988), pp. 762-773
DOI: 10.2307/1445399
Stable URL: http://www.jstor.org/stable/1445399
Page Count: 12
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Age and Growth Determination of the Bat Ray, Myliobatis californica Gill, in Central California
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Abstract

Ages of the bat ray, Myliobatis californica, from central California were determined using two methods-oil-clearing and x-radiography-to enhance the growth bands on the vertebral centra. The annual nature of band deposition was supported by comparison of modal disc widths (DW) from size-frequency analysis of the first three age classes to mean back-calculated DW, and by changes in centrum edge widths and mineralization patterns. Significant differences between mean DW determined by the two ageing techniques occurred in only one age class for each sex. The x-radiography technique produced the most realistic growth curve for males, while for females the oil-clearing technique was best. However, for the sample analyzed, the two techniques produced similar growth curves. The von Bertalanffy growth curves derived from these techniques indicate that female bat rays reach a greater asymptotic size (DW = 1587 mm) and have a lower growth rate (K = 0.0995) than males (DW = 1004 mm, K = 0.229).

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