chapter  14
50 Pages

Age Determination and Validation in Chondrichthyan Fishes

ByGregor M. Cailliet, Kenneth J. Goldman

CONTENTS 14.1 Introduction .................................................................................................................................. 399 14.2 Methodology................................................................................................................................. 400

14.2.1 Structures......................................................................................................................... 400 14.2.1.1 Vertebrae........................................................................................................... 400 14.2.1.2 Spines ............................................................................................................... 401 14.2.1.3 Neural Arches................................................................................................... 401 14.2.1.4 Caudal Thorns and Other Structures ............................................................... 402

14.2.2 Sampling and Processing Specimens ............................................................................. 402 14.2.2.1 Taking Samples ................................................................................................ 402 14.2.2.2 Centrum Cleaning and Sample Preparation .................................................... 403

14.3 Age Determination ....................................................................................................................... 404 14.3.1 Centrum Staining ............................................................................................................ 407 14.3.2 Precision and Bias........................................................................................................... 408 14.3.3 Back-Calculation ............................................................................................................. 408

14.4 Verification and Validation ........................................................................................................... 409 14.4.1 Size Mode Analysis ........................................................................................................ 410 14.4.2 Tag-Recapture.................................................................................................................. 410 14.4.3 Marking, Field Tag-Recapture, and Laboratory Studies ................................................ 411 14.4.4 Centrum Edge and Relative Marginal Increment Analysis............................................ 412 14.4.5 Captive Rearing............................................................................................................... 413 14.4.6 Bomb Carbon .................................................................................................................. 414

14.5 Review and Status of Chondrichthyan Age, Growth, Verification, and Validation Studies ....... 414 14.6 Growth Models............................................................................................................................. 424 14.7 Comparative Growth Coefficients (k in the von Bertalanffy) ..................................................... 425 14.8 Comparative Ages of Maturity and Longevity among Studies................................................... 425

14.8.1 Age of Maturity Estimates.............................................................................................. 425 14.8.2 Longevity Estimates........................................................................................................ 438

14.9 Implication of Growth, Longevity, and Demography to Fisheries Management ....................... 438 Acknowledgments.................................................................................................................................. 439 References .............................................................................................................................................. 439

14.1 Introduction It is important to understand the ages, growth characteristics, maturation processes, and longevity of fishes to assess their current population status and to predict how their populations will change in time (Ricker, 1975; Cailliet et al., 1986b). Fishery biologists have used age, length, and weight data as

important tools for their age-based population models. Especially important are details about growth and mortality rates, age at maturity, and life span (Ricker, 1975; Cortés, 1997). Over the past several decades, it has become obvious that fisheries for chondrichthyan fishes have not been easily sustainable. In 1974, Holden suggested that these fishes had life histories that made them vulnerable to overfishing. Included in the characteristics he cited were slow growth, late age at maturity, few offspring, and lengthy gestation periods. Since then, fishing pressure on elasmobranchs, both as directed and as bycatch fisheries (and discards) has increased (Bonfil, 1994; Casey and Myers, 1998; Stevens et al., 2000; Baum et al., 2003), stimulating many studies on many important aspects of their life histories, such as age, growth, and reproduction.