I20r 



PRESENT STUDY 

 POINSARD (v^l 

 CHATWIN 



100 120 140 



FORK LENGTH (cm.) 



160 



Figure 3. — Estimated length-weight relations for yellowfin 

 tuna (Chatwin, 1959; Poinsard, 1969). Poinsard's relation based 

 on square root relation between predorsal and fork length. 

 Chatwin's study did not include fish longer than 115 cm. 



Since it is desirable to utilize the function which 

 was estimated directly from either predorsal or 

 fork length data, the results of Poinsard should be 

 used when predorsal lengths are measured and 

 the results of the present study should be used 

 when fork lengths are measured. 



Beardsley^ (pers. commun.) allowed me to 

 examine length and weight measurements of 

 more than 2,000 yellowfin tuna captured in the 

 western Atlantic. These data are very similar to 

 the data used in the present study. 



Beardsley and Richards (1970) estimated the 

 parameters of Equation (1) for skipjack tuna and 

 little tunny captured off the coast of Florida. Their 

 estimate of the equation for skipjack tuna is 



W = 0.00007927L3-22750 

 and for little tunny is 



W = 0.0000181L3-02838 



100 120 140 



FORK LENGTH (cm.) 



160 



180 



200 



Figure 4. — Estimated length-weight relations for yellowfin 

 tuna (Poinsard, 1969). Poinsard's relation based on logarithmic 

 relation between predorsal and fork length. 



These results are quite similar to the results of the 

 present study. The range in fork length of skip- 

 jack tuna in their study was 38-78 cm and for little 

 tunny 34-87 cm. Since these size ranges exceed 

 the ranges encountered in this study their results 

 should be used. Chatwin (1959) obtained similar 

 results for skipjack tuna from the Pacific, and 

 Batts (1972) for skipjack tuna from the western 

 Atlantic. 



The number of frigate mackerel used in this 

 study is too small to produce very meaningful 

 results. The results are presented here only to 

 make them available to other workers. 



Several authors including Pienaar and Thom- 

 son (1969) have questioned the validity of assump- 

 tions made about the error term in Equation 

 (1). Also, the logarithmic transformation results 

 in weight being slightly underestimated even if 

 Equation ( 1) is correct. Results of simulations by 

 Fox (1973)^ indicate that 6 is unbiased and an 

 unbiased estimate of a is given by 



a' =a exp (1/2 (s^^,;)) (3) 



^Southeast Fisheries Center, National Marine Fisheries 

 Service, NOAA, Miami, FL 33149. 



■■'Fox, W. W., Jr. 1973. Some simple biologically useful 

 functions and multiplicative error regression models. Unpubl. 



manuscr. Southwest Fish. Cent. 

 La Jolla, CA 92037. 



Natl. Mar. Fish. Serv., NOAA, 



850 



