FISHERY BULLETIN: VOL. 83, NO. 4 



Table 5. — Percentage of pregnant dolphins that were lac- 

 tating (1971-83) grouped by 1) the area in which the speci- 

 mens were collected; 2) the quarter of the calendar year; 

 3) the length of time between sighting the school and 

 release of the net; 4) the observer's estimate of the total 

 school size; 5) the number of dolphins known to be killed 

 in the set; and 6) the tons of tuna caught in the set. 

 Note that total sample size varies with the availability of data 

 on the stratifying variable. Probabilities are based on chi- 

 square contingency tests. Only samples from the northern 

 offshore stock of spotted dolphins are included. CYRA = 

 Commission Yellowfin Regulatory Area. 



DISCUSSION 



Changes in the reproductive status of the female 

 segment of a population can be monitored using a 

 variety of reproductive indices: 1) mean age at sexual 

 maturation, 2) mean length (or weight) at sexual 

 maturation, 3) annual pregnancy rates, 4) calving 

 interval, 5) percentage of mature females that are 

 pregnant, 6) percentage of females that are lactating, 

 and 7) percentage of females that are sexually 

 mature Changes in each of these are examined 

 below. 



Changes in Maturation Parameters 



Myrick et al. (1984) have found no significant dif- 

 ference in the age at sexual maturation (ASM) 

 between a sample from 1973 to 1978 and another 

 sample from 1981. In the present study, length at 

 attainment of sexual maturity is estimated to have 

 increased 4.4 cm from 1974 to 1983. If these results 

 hold, dolphins must be growing faster in recent 



Table 6. — Multiway tests of factors affecting 

 the percentage of pregnant females that are 

 lactating. Log-likelihood chi-square was 

 used to calculate the probability that per- 

 cent lactating is independent of the stated 

 factor(s) using the log-linear model. Lacta- 

 tion state (lactating/not lactating) is implicit 

 as the first factor in each comparison. 



Table 7. — Percentage of female dolphins that were sexual- 

 ly mature (1973-83) grouped by 1) the area in which the 

 specimens were collected; 2) the quarter of the calendar 

 year; 3) the length of time between sighting the school 

 and release of the net; 4) the observer's estimate of the 

 total school size; 5) the number of dolphins known to be 

 killed in the set; and 6) the tons of tuna caught in the set. 

 Note that total sample size varies with the availability of data 

 on the stratifying variable. Probabilities are based on chi- 

 square contingency tests. Only samples from the northern 

 offshore stock of spotted dolphins are included. CYRA = 

 Commission Yellowfin Regulatory Area. 



Mature 

 (%) 



N 



Prob- 

 ability 



1) Geographic area 



Inside CYRA 55.7 6,329 0.19 



Outside CYRA 57.5 1 ,625 



2) Season 



1st quarter 54.2 3,495 



2d quarter 57.2 1 ,738 0.02 



3d quarter 58.2 1,580 



4th quarter 57.6 1,155 



3) Chase time (min) 



<20 54.4 2,067 



20-40 56.1 3,084 0.36 



>40 56.5 1 ,689 



4) School size 



<500 53.5 1,183 



500-1,500 56.8 1,970 0.19 



>1,500 56.0 1,753 



5) Number killed 



1-10 57.9 2,465 



11-30 54.9 2,068 0.02 



>30 54.0 2,321 



6) Tuna caught (tons) 



0-5 53.3 920 



6-15 55.1 1,779 0.05 



16-30 54.5 1,668 



>30 57.7 2,482 



years. Given small sample sizes of aged individuals, 

 significant changes in ASM may be difficult to 

 detect. Previous studies have shown that the age at 

 sexual maturation is quite responsive to population 

 changes in marine mammals (Fowler 1984), while 

 length at maturation tends to show little change For 

 fin whales, Balaenoptera physalus, Lockyer (1972) 



664 



