Fisheries for elasmobranch fishes, especially for use as human food, are increasing at a tremendous rate in California waters. Unfortunately, critical aspects of their life histories, such as their age structure, growth rates and reproductive habits, are unknown for a majority of the species presently being fished. The evidence that does exist suggests that elasmobranchs have relatively slow growth rates, a late age of first reproductive maturity, low fecundities, and long gestation periods. This combination makes them susceptible to over-fishing due to the close relationship between stock and recruitment and the paucity of catch statistics relating to size, age and state of reproductive maturity. Since elasmobranchs lack hard, bony parts used to age other fishes, little is known about their age or growth rates. This has led Holden (1977) to plead for "establishing acceptable techniques in age determination of e1asmobranchs". Alternating hyaline and opaque zones (circuli) deposited in their vertebral centra appear to be promising tools for aging, much like those in teleost scales, otoliths and bones. However, the amount of calcification varies considerably among elasmobranch vertebrae, and it is necessary to determine which methods are best at discerning these circuli. Since 1979, we have collected more than 700 specimens of at least 25 species, taken several body measurements on them, examined their reproductive tracts, and removed a section of their vertebral columns. From more than 300 individuals of 8 species, we have attempted to discern circuli using several techniques from the literature, modified versions of these techniques, and independently developed methods. Here, we report on three methods which worked well for select species: silver nitrate impregnation, x-radiography and cedarwood oil clearing. We also discuss those methods which have either proven ineffective or which we have not yet been able to evaluate. Finally, we discuss ways of approaching preparation and counting procedures objectively, and the problems associated with interpreting the annular nature of such counts.
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