Inferring age from otolith measurements: A review and a new approach

In 1985, Boehlert (Fish. Bull. 83: 103-117) suggested that fish age could be estimated from otolith measurements. Since that time, a number of inferential techniques have been proposed and tested in a range of species. A review of these techniques shows that all are subject to at least one of four types of bias. In addition, they all focus on assigning ages to individual fish, whereas the estimation of population parameters (particularly proportions at age) is usually the goal. We propose a new flexible method of inference based on mixture analysis, which avoids these biases and makes better use of the data. We argue that the most appropriate technique for evaluating the performance of these methods is a cost-benefit analysis that compares the cost of the estimated ages with that of the traditional annulus count method. A simulation experiment is used to illustrate both the new method and the cost-benefit analysis.