FISHERY BULLETIN: VOL. 79, NO. 1 



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VON BERTALANFFY CURVE (BGC 3, N' 51, FL 3.7 -80.3cm) 102.0cm 0,55 -0.02 yr 

 LINEAR GROWTH STAGES 



12 



15 18 21 



AGE ( MONTHS ) 



24 



27 



30 



33 



36 



Figure 2. — Growth curve of skipjack tuna in the central Pacific as determined by otolith examination. Linear growth stanzas 



determined by LINFIT (see text). For parameters of growth stanzas, see Table 2. 



rates up to 65 cm FL; beyond 65 cm FL, Brock's 

 curve departs from ours and approaches an 

 asymptote more rapidly. The difference in the 

 growth rates above 65 cm may be due to two factors 

 which would affect the modes of large (>6.8 kg) 

 skipjack tuna: differential fishing or total mortal- 

 ity and temperature requirements of skipjack 

 tuna. Barkley et al. (1978) hypothesized that large 

 ( >6.8 kg) skipjack tuna required cooler water than 

 small skipjack tuna and therefore could tolerate 

 the warmer surface water for relatively short 

 periods. If so, the catchability of large skipjack 

 tuna would be altered in the surface fishery and 

 length-frequency modes of large skipjack tuna 

 would be underestimated. Our otolith age deter- 

 minations are not affected by these factors. 



Otolith readings were also used to examine the 

 age-length relationship of eastern Pacific skipjack 



tuna (Figure 5). Of the 20 specimens examined, 11 

 were caught off Baja California, Mexico. The other 

 nine were caught in the eastern Pacific west of the 

 Inter-American Tropical Tuna Commission's Yel- 

 low^n Regulatory Area. Most of these nine speci- 

 mens had age-length relationships similar to 

 those offish caught off Baja California, but several 

 had relationships similar to specimens taken in 

 the central Pacific. Indications are that skipjack 

 tuna in the eastern Pacific Ocean off Baja Califor- 

 nia grew at a slower rate than those in the central 

 Pacific. 



Our eastern Pacific skipjack tuna growth curve 

 was compared with those of earlier studies from 

 the eastern Pacific (Figure 5). A growth curve 

 based on the progression of modes in length fre- 

 quencies (Joseph and Calkins 1969) is similar to 

 our curve; both show good agreement between 40 



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