I 08 



Fishery Bulletin 94( 



1996 



o 1 



Canonical variable 



Figure 8 



Histogram of the canonical variable from discriminant 

 analysis of the data for the two groups and six character- 

 istics of the vas deferens. The shaded portion represents 

 group 1 (sampled between 0001 and 1200 h) and the white 

 area outlined in bold represents group 2 (sampled between 

 1201 and 2400 h). The group centroids are also plotted. 



1.24 days in 1987 (1.22 days for the pooled data). In 

 other words, spawning occurred nearly every day for 

 males, as was the case for females. 



Batch fecundity 



The estimated mean relative fecundity and standard 

 deviation for 12 fish was 68.0 ±20.7 oocytes per gram 

 of body weight (Table 4). The relationship between 

 batch fecundity and length (Fig. 9) can be described 

 by the following equation: 



BF = ( 1.1015 x 10" 8 )L 4679 , 



[r 2 = 0.76] 



where BF = batch fecundity in number of oocytes; 

 and 



L = length in millimeters. 



The predicted batch fecundities and 95% prediction 

 intervals from this equation for yellowfin tuna of 

 1,000 mm and 1,200 mm FL are 1,199,841 (991,129; 

 1,452,359) and 2,815,639 (2,025,445; 3,913,724), re- 

 spectively. 



Cost of spawning 



Yellowfin tuna oocytes in the most advanced group 

 enter the migratory-nucleus phase about 6 to 8 h 

 before spawning and begin to hydrate about 4 to 6 h 



before spawning (Fig. 3; Table 1). The hydration pro- 

 cess results in a rapid increase in size of the oocytes 

 and in wet weight of the ovary but there is no in- 

 crease in dry weight (LeClus, 1979). The mean size 

 of oocytes in the migratory-nucleus stage just before 

 the hydration process begins is 0.75 to 0.80 mm (Fig. 

 3; Table 1 ). The mean wet weight of a yellowfin tuna 

 oocyte in the migratory-nucleus stage was estimated 

 to be 0.157 mg. This estimate was based on two fe- 

 males of 945 and 1056 mm FL whose oocyte diam- 

 eters were x = 0.78 mm [SD=0.01 mm| and x - 0.79 

 mm [SD=0.01 mm| and whose oocyte weights were x 

 = 0.156 mg ISD=0.015 mg] and x = 0.158 mg 

 |SD=0.011 mg], respectively. The mean relative fe- 

 cundity of yellowfin tuna, from this study, is 68.0 

 oocytes per gram of body weight. The cost of a single 

 spawning (excluding behavioral activities) is thus 

 about 1.1% of body weight. If a female spawns every 

 1.14 d, the average daily cost of spawning a batch of 

 eggs is 0.97% of the body weight per day. 



The costs of a single spawning (excluding behav- 

 ioral activities ) for both females and males were also 

 estimated by subtracting the percentage of calculated 

 body weight of the gonads just after spawning (0001- 

 0400 h) from the percentage of body weight of the 

 gonads just before spawning occurs (1600-2000 h). 

 For females, the average weight of the ovaries with 

 oocytes in the migratory-nucleus stage (preceding 

 spawning) was 2.12% of body weight, and just after 

 spawning was 0.78%, which yields an estimate for 

 the cost of spawning of 1.34% of body weight. For 

 the males, the average weight of the testes preced- 

 ing spawning was 1.43%, and just after spawning 



