Estimating Natural Mortality (M)

This tool employs various empirical estimators of natural mortality.

As the user enters values for the below input parameters,

estimates will be displayed in the main panel.

Uncertainty can also be added to the estimates by chosing

a coefficient of variation (CV) value and error distribution type.


References for each method can be found here

Parameters inputs

Provide a value for the CV and choose an error type to add additional uncertainty to the point estimates. The CV will be applied to all methods.

CV = 0 means only point estimates will be reported

Provide inputs below. You do not need values for all inputs; natural mortality will only be estimated for a given methods when all input requirements are met.

Scientific name calls the FishLife M estimator

Input requirements for other methods can be found here

Composite M: method weighting

Allows for weighting of the contribution of each method in the composite M distribution

Values range from 0 to 1. A value of 0 removes the contribution; a value of 1 is full weighting.
Default values are based on redundancies of methods using similar information. For instance,the four longevity-based methods are given a weight of 0.25, so all weighted together equal 1.
The prior sample number generates a prior based on the number of specified samples. This value also defines the binwidth in the density plot, thus lower sample numbers will give a more diffuse prior.

M prior control parameters

Composite M prior downloads

Downloads are DMP files that can be loaded directly into R

Higher sample sizes create a composite distribution truer to the component distributions

Adjusting bandwidth >1 creates a more diffuse composite distribution

Natural mortality (M) estimates by method

Legend color indicate inputs used by each method.
Downloadable R object contains paramter inputs, estimted M point estimates, and age-specific M values.

Natural mortality (M) point estimates

Download M values plot Download M table csv file Download parameter inputs and M values R object


Natural mortality (M) by age

Download M at age plot Download age-specific M values csv file

Method density and weights

When no uncertainty is expressed, point estimates with weights are shown
When uncertainty is expressed, the distribution of each method is given, with its frequency (determined by the weighting) plotted on the y-axis
Download M density plot Download M density inputs as R object


Composite natural mortality

Blue vertical line indicates median value

First composite M object is based on the number of specified samples

Second composite M object is based on th adjusted bandwidth

Download composite M density plot