Review on studies of age and growth of sharks

Sharks,as an important group of elasmobranches,play a vital role in keeping stability and diversity of marine ecosystem.Understanding of age and growth characteristics of sharks helps us know their life history and estimate the population dynamics and stock status.The main issues derived from previous studies of age and growth of sharks are as follows:(1)What is the most appropriate sample for aging sharks?(2)Which methods are the best for age determination and validation?(3)How to select the best model to describe growth.These issues are reviewed in this study.We compare the advantages,disadvantages and application limitations of two age determination methods(hard tissue identification,length frequency analysis)and three age validation methods(margin increment analysis,chemical markers,and bomb carbon dating).Applications of various growth models for different shark species are also analyzed.Our review indicates that vertebra close to the first dorsal fin are the best samples for determining age of sharks; chemical methods need to be used to increase the visibility of annuls; validation techniques are important for reducing systematic error in determining age of sharks; and multiple candidate models should be tested for choosing the optimal model.This study will provide guide and reference for further studying the age and growth of sharks.