(HP-65) A Simple Iterative Solution to the Catch Equation

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An extract from A Simple Iterative Solution to the Catch Equation, Fisheries and Marine Service, ICNAF Res.Doc. 75/42, JUN 1975.

Abstract: A on simple method of estimating stock size at age and fishing mortality rates based on the near linearity in fishing mortality of the square root of the ratio of catch at age n to the surviving number of fish at age n+1 is presented.
HP 65 Program:
A program has been written fOr the HP65 programmable pocket calculator implementing the above method. The program is stored on two magnetic cards. The first contains the initialization for a year class. The estimated rates of natural and fishing mortalities and the catch of the oldest fish are input and the popUlation size of oldest fish is output and stored for further analysis. The program on the second card calculates Fn and Pn the rate of fishing mortality in year n and population size
of the year class in year n using the catch in year n and the population size in year n+1 for a given year class. The user inputs an underestimate and overestimate of Fn and the program improves these estimates by successive linear interpolations- (method of regula falsi) until sufficient accuracy is obtained.

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ps: see also (HP-25) Resolution of the Catch Equation by a Simple Iterative Method