(HP-67/97) Length-Based Methods in Fisheries Research

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An extract from Length-Based Methods in Fisheries Research, Proceedings of the International Conference on the Theory and Application of Length-Based Methods for Stock Assessment, 11-16 February 1985, Mazzara del Vallo, Sicily, Italy; ICLARM Conference Proceedings 13: 1987 (463 pgs)

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b. Sex Ratio 2

DESCRIPTION: The program estimates the fishing and natural mortality coefficients (F and M) from knowledge of the catch numbers by length (or age) class, the total mortality coefficient (Z), the age at first capture (t,), and the age at the end of the first fishing season (t1), for each sex. Also required is the fishing season duration (t2) which is taken as being the same for each sex. When the catch numbers are by length, class, the lower length limit for each class (Ld) is required to be converted to age (td), using pre-determined values for the growth constants in the 'standard' von Bertalanffy equation.
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The program has two options:
 OPTION 1 when MA = MB = M assumed
 OPTION 2 when FA = FB = F assumed

Catch number ratios are estimated, after assuming a value of M (OPTION I ) or F (OPTION 2), for each pair of t i and tz. The extent of proportional 'correlation' between the estimated and observed catch number ratios is then used to identify whether the trial value of M or F is a 'best choice' value. This involves determining the linear (geometric means) correlation and regression parameters; the coefficient of determination (r2), the y-intercept (u), the slope (v); as well as the sum of the
squared differences between the observed and estimated catch number ratios (X D2). The ideal 'best choice' is taken as when the r2 is maximized, u is zero, v is unity, and X D2 is minimized.
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Listing Notes
a.  Language                      HP 67/97 programming language
b.  Implementation              Hewlett Packard
                                       HP 67/97
c.  Hardware Requirements   Nil
d.  RAM Requirements          About 12K each program

Listing
       A complete listing is given in Fig. 22
              Sex Ratio 1              Option 1
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              Sex Ratio 1              Option 2
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              Sex Ratio 1              Option 1
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              Sex Ratio 2              Option 2
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              Sex Ratio 1              (Card 1)
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              Sex Ratio 2              (Card 2)
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              Sex Ratio 2              (Card 3)
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