LENARZ ET AL.: YIELD PER RECRUIT OF ATLANTIC YELLOWFIN TUNA 



Table 5. — Estimates of yield per recruit per effort (kg) when M = 



LeGuen and Sakagawa ( 1973) is used. 



0.8, initial F 

 -Continued. 



= 0.2, and growth curve of 



the examination of hard parts, are extremely 

 difficult and not easily interpreted for tropical 

 species such as the yellowfin tuna. 



The marked increase in estimates of size-speci- 

 fic F beyond 130 cm for the purse seine gears is 

 a possible result of underestimating ages of older 

 yellowfin. To examine this possibility, the 

 growth curve of LeGuen and Sakagawa (1973) 

 was modified. It was hypothetically assumed 

 that the percentage of underestimation of the 

 time interval within a size interval increased 

 linearly from 0% at 135 cm to 100% at 180 cm. 

 The resulting growth curve is compared to the 

 original in Figure 14. 



Values of size-specific F were then estimated 

 as before with initial values of 0.2 and 0.8. The 

 value of 0.2 gave the most reasonable results 

 for reasons similar to those given before. Values 

 of size specific F for each gear are shown in 



o LE GUEN a SAKAOAWA 

 • HYPOTHETICAL 



5 6 

 AGE (YEARS) 



Figure 14. — Growth curves of Atlantic yellowfin tuna. 

 Upper curve is from LeGuen and Sakagawa (1973). Lower 

 curve is a modification of the upper curve (see text). 



53 



