The shell microstructure and chronology of the abalone Haliotis corrugata

Abstract

The abalone Haliotis corrugata deposits fine and dark rings in the shell near the spire and the dark rings can be used to age the shell. Each dark ring has two distinct microstructural elements; a layer of prismatic structure, possibly calcite, and a juxtaposed narrower layer of granular structme. The crystalline ultrastructure of aragonite between the rings shows seasonal changes in thickness of laminae apparently correlated with seasonal temperature changes. Examination of shells grown in culture showed that three fine rings are deposited during the first year, the first dark ring at an age of about 20 months, and the second between 2 and 2 ½ years; thereafter a dark ring is deposited annually. This aging technique was validated up to about 12 years of age by using growth checks laid down in the shell in about October 1991 during the El Niño as a time-stamp from which growth rates and age could be estimated. Using the aging technique the von Bertalanffy growth equation was fitted to age-length data from La Natividad, Baja California and the following parameters obtained: K = 0.33; L_∞ =160 mm. Catch curve analyses of commercial catch data gave Z = 0.28 for a sample in the late 1970s, and 0.66 for one in 1995.

Keywords:

• Haliotis corrugata
• rings
• shell-aging
• shell ultrastructure
• El Niño
• growth check