Techniques for enhancing vertebral bands in age estimation of California elasmobranchs
Vertebrae from 1,152 elasmobranchs representing 22 species were collected between 1979 and 1981 to assess methods of enhancing incremental growth bands for age estimation. Thus far, we have tested methods previouslyreported in the literature, and have developed new procedures to enhance growth increments on 684 individuals of 14 species of elasmobranchs. Silver nitrate impregnation, X-radiograpby, and cedarwood oil clearing were the most successful techniques. Less effeetive were alizarin red staining, paraffin impregnation, alcohol immersiorn, and formic acid etching. Methods for preparing vertebrae and enhancing and counting growth increments are presented, and the problems associated with interpreting tile annual nature of such counts are discussed.
Preliminary studies on the age and growth of blue (Prionace glauca), common thresher (Alopias vulpinus), and shortfin mako (Isurus oxyrinchus) sharks from California waters
Two methods of enhancing growth bands on vertebral centra-silver nitrate impregnation and X -radiography have proven to be successful when used on centra from 130 blue, Prionace glauca, 143 common thresher, Alopias vulpinus, and 44 shortfin maim, Isurus oxyrinchus, sharks. Bands were counted and measured, and these data were used to construct growth curves based on the von Bertalanffy and logistic growth models. The problems of verification of these counts, and validation of the periodicity of band formation, have been identified and are discussed in relation to the growth curves generated for each of these three species. Our results and other available information indicate that these elasmobranchs grow relatively slowly, reaching their asymptotic lengths at 20 yr of age for blue sharks, and between 45 and 50 yr for shortfin mako and common thresher sharks. They have a large size but relatively
early age of ilrst reproductive maturity, and low fecundities. This combination of traits could make them susceptible to overfishing.