Potential Biological Removal (PBR)

The Potential Biological Removal (PBR) level is defined as the maximum number of animals, not including in natural mortalities that may be removed annually from a marine mammal stock while allowing that stock to reach or maintain its optimal sustainable population level.

PBR is calculated as the product of three quantities:

PBR = Nmin * ½ Rmax * Fr


Nmin = minimum population estimate = 20th percentile of a log-normal distribution of the population abundance estimate



N is the best abundance estimate for the population and the CV(N) is the coefficient of variation of the best abundance estimate

Rmax = the maximum theoretical or estimated net productivity rate of the stock at a small population level.  The default values are 0.04 for cetaceans and 0.12 for seals.

Fr = a recovery factor that is between 0.1 and 1.  This factor is to ensure the recovery of the depleted population and takes in account additional uncertainties other then the precision of the abundance estimate.  The default values are 0.1 for endangered stocks and 0.5 for depleted and threatened stocks and stocks of unknown status.

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(File Modified Jan. 11 2018)