CASTRO AND ERZINI: COMPARISON OF LENGTH-FREQUENCY PACKAGES 



progression analysis implemented in the LFSA 

 package. 



We feel that length-frequency analysis should not 

 be used in the complete absence of information on 

 growth and recruitment patterns or with very small 

 data sets. Other important information includes data 

 on migration and seasonal patterns in distribution, 

 and such information should be used to guide sam- 

 pling programs. Irregular recruitment both in terms 

 of level and pattern may strongly affect the results. 

 Clearly, length-frequency analysis can be a useful 

 tool when used in conjunction with other methods. 

 However, it seems unreasonable to expect such tech- 

 niques to produce reliable information when the 

 classical methods of fisheries fail or cannot be used. 

 For example, traditionally, growth parameters have 

 been estimated from age-length keys and mortal- 

 ities derived from the age structure of the catch. 

 In cases where the age-length key cannot be ob- 

 tained, there is a temptation to obtain growth 

 parameters at any cost using length-frequency anal- 

 ysis. If this is done, great care should be taken to 

 ensure that a minimum amount of biological infor- 

 mation exists. The use of length-frequency analysis 

 as a "black box" where a length-frequency distribu- 

 tion goes in from one side and a whole set of 

 biological parameters emerge does not seem correct. 

 If as a first step, the data are plotted and there is 

 no visual evidence of progressing modes, then even 

 if biological information is available, length-fre- 

 quency techniques should perhaps not be applied at 

 all. 



To have a more complete picture of the limitations 

 and usefulness of length-frequency techniques, a 

 much wider range of conditions must be tested. For 

 example, the effect of variations in individual 

 parameters particularly M and F, and in combina- 

 tions of parameters must be tested. The effects of 

 size class width on length-frequency analysis is also 

 an area which should be investigated. It is the in- 

 tention of the authors to continue this work in order 

 to examine as wide a range of situations as possible. 



ACKNOWLEDGMENTS 



The authors would like to express their gratitude 

 to Saul Saila for his guidance, advice, and support 

 during the course of this work. The authors would 

 also like to thank D. Pauly, P. Sparre, and an anony- 



mous reviewer for their comments. This work was 

 sponsored in part by USAID Grant No. DAN- 

 4146-G-SS-5071-00 (Fisheries Stock Assessment 

 CRSP). 



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