FISHERY BULLETIN: VOL. 8(5, NO. 4 



are the minimum requirements for each one of the 

 length-frequency analysis methods? We hope this 

 paper can contribute to providing some understand- 

 ing of this problem. 



MATERIALS AND METHODS 



The Simulation Program: SIMULPOP^ 



SIMULPOP was developed in BASIC, for IBM 

 microcomputers and compatibles. Populations are 



^The program SIMULPOP is available from Margarida Castro 

 upon request. 



simulated by following cohorts in time and the gen- 

 eral characteristics and assumptions of the program 

 include 1) individual growth described by a von 

 Bertalanffy growth curve, no seasonality consi- 

 dered; 2) recruitment: different patterns and ran- 

 dom in numbers; 3) natural mortality: random and 

 normally distributed; 4) fishing mortality: random 

 and normally distributed, and corrected for incom- 

 plete selectivity in younger ages; 5) selectivity: 

 logistic equation considered to represent selectiv- 

 ity of the fishing gear; and 6) length distribution 

 for each age normally distributed, with a mean given 

 by the von Bertalanffy growth curve. The shapes 

 of the frequency distributions are independent of 



CO 

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0) 



0) 



c 



0) 



20.004 



15.00 



10.004 



5.00 



0.00 



20.00 



15.00 



10.00 



5.00 



0.00 



25.00 

 20.00 

 15.00- 

 10.00 

 5.00 

 0.00 



25.00 



20.00 



15.00 



10.00 



5.00 



0.00 



30.00 



25.00 



20.00 



15.00 



10.00 



5.00 



0.00 



Itl^ 



Jan 



Jlllllu^ 



Mar 



May 



Jul 



Sep 



JllUu 



Nov 



3 5 7 9 11 13 15 1719 



Length classes (1 cnn) 



10.00 



4 7 10 13 16 19 22 25 28 31 

 Length classes (1 cm) 



Figure la.— Example of simulated length-frequency distributions for situation 1, the sardine-type species with one recruitment peak 



a year. Only 6 of the 12 months are represented. 

 Figure lb.— Example of simulated length-frequency distributions for situation 2, the sparid/lutjanid-type species with one recruitment 



peak a year. Only 6 of the 12 months are represented. 



646 



