ABSTRACT
The ability to perform age determinations based on the examination of hard anatomical parts is of fundamental importance in sheries research. Precise and accurate age information is the key to obtaining quality estimates of growth and other vital rates such as natural mortality and longevity and is essential for successful sheries management. The effect of inaccurate age determinations on our understanding of population dynamics can lead to serious errors in stock assessment, often resulting in overexploitation (Beamish et al., 2006;
Cailliet and Andrews, 2008; Campana, 2001; Heppell et al., 2005; Hoenig and Gruber, 1990; Hoff and Musick, 1990; Longhurst, 2002; Musick, 1999; Ofcer et al., 1996). Fish age and growth are also critical correlates with which to evaluate many other biological (and pathological) processes, such as productivity, yield per recruit, prey availability, habitat suitability, and even feeding kinematics (Campana, 2001; DeVries and Frie, 1996; Robinson and Motta, 2002). Whereas age and growth are usually used together in phraseology, it is important to remember that each term has its own distinct meaning, which was eloquently stated by DeVries and Frie (1996):
It is important to understand the ages, growth characteristics, maturation processes, and longevity of shes to assess their current population status and to predict how their populations will change in time (Cailliet et al., 1986a; Ricker, 1975). 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 (Beamish et al., 2006; Cailliet and Andrews, 2008; Cortés, 1997; Heppell et al., 2005; Longhurst, 2002; Ricker, 1975). Over the past several decades, it has become obvious that many sheries for chondrichthyan shes are not sustainable at current exploitation rates or at all. As early as 1974, Holden suggested that these shes had life histories, including late age at maturity, few offspring, and lengthy gestation periods, that made them vulnerable to overexploitation. Since then, shing mortality on elasmobranchs, both as directed and as non-target catch in sheries has increased (Baum et al., 2003; Bonl, 1994; Casey and Myers, 1998; Stevens et al., 2000), and discards at sea are either underestimated or unknown (Camhi, 1999). These facts make the study of their life histories, including age, growth, and reproduction, even more important.
