ON THE TAGGED RATIO METHOD FOR ESTIMATING THE NAURAL MORTALITY COEFFICIENT

Abstract

When two-release tagging design, such that the first tagged fish (X₁) are released some time (τ unit intervals) before fishing starts and the second release (X₂) is done just before fishing starts, is used, the natural mortality coefficient (M) may be estimated by the tagged ratio method as follows.
M=(A₂-A₅)+ln(X₂/X₁)/τ-T
Where A₁ and A₂ are Y-intercepts of linear regression lines of logarithmic value of sample tagged ratios on time respectively, and T is the tag diminution coefficient which is supposed to be constant and is also estimated simultaneously.
An example for calculation by this method is also shown.