The authors consider a method to estimate the age composition of released fish which are recaptured and landed at fish markets, by use of the mean lengths and SDs of tagged fish, the ages of which are precisely known. Since 1988, brand tagged flounder have been released in Miyako Bay simultaneously with those without tags and these data are used to examine the practicality of the method. For the first step of the procedure, the total number of fish by age is estimated employing a normal length distribution by use of the mean lengths and SDs of tagged fish which are h and younger are groups, and then the number of fish by age is calculated for each length class. For the second step, the number of fish older than age h is estimated as the residual number of h and younger age for each length class. The difference between this method and conventional methods is that a normal distribution for the length frequency of fish older than the h age group is not assumed. The cumulative estimated length frequency of age groups fit well the original length frequency and this suggests the method is applicable.
