SIX and HORTON: ANALYSIS OF AC.K DETERMINATION MIIIK IDS 



S tlavidus 



READER I 



READER 2 

 S pirtmg»r 



READER I 



READER 2 



S mtlonops 



READER I 



READER 2 



13 18 



ESTIMATED AGE (yr) 



FIGURE 5. — Mean (vertical line), range (horizontal line), 

 standard deviation of the mean (white bar), and 95% confidence 

 intervals about the mean (black bar) for two otolith age readings 

 of yellowtail rockfish, canary rockfish, and black rockfish landed 

 in Oregon, 1973-74. 



distributions are approximately normal with 

 means of 11.1 and 10.2 yr, respectively, for first 

 and second readings. Figure 3 shows the means to 

 be significantly different at the 959c level. The 

 standard deviations of the two distributions differ 

 more for this species than for yellowtail and 

 canary rockfishes. Ranges of the two distributions 

 are similar (Figure 5). 



Survival 



Estimates of survival obtained by two methods 

 generally correspond for all species and readings, 

 although Chapman-Robson estimates were con- 

 sistently lower than catch curve estimates (Table 

 6). At the 957c level none of the paired estimates 

 from the two readings were significantly different, 

 as shown by the overlap of confidence intervals. 

 Differences between survival estimates calcu- 

 lated from readings of the same otoliths were 

 greatest for yellowtail rockfish and smallest for 

 canary rockfish by either the catch curve or the 



Chapman-Robson method; yet, on the average, 

 differences between catch curve estimates for the 

 two readings were greater than those obtained by 

 the Chapman-Robson method (Table 6). The 

 differences between catch curve estimates were 

 0.11, 0.015, and 0.093 for yellowtail, canary, and 

 black rockfishes, respectively, while differences 

 between Chapman-Robson estimates were 0.051, 

 0.031, and 0.051, respectively. 



Age-Length Relationship 



The age-length relationships derived from two 

 otolith readings for yellowtail rockfish were 

 described by the equation L = cA h (Figure 6). 

 Fitted lengths-at-age for the first reading were 

 slightly higher than those for the second reading, 

 but 959c confidence limits of the estimates of 

 constants c and b overlap considerably for the first 

 and second readings (Table 7). Little or no overlap 

 of confidence limits for constants c and b exists for 

 males and females for either the first or second 

 readings (Table 7), indicating a significant differ- 

 ence between the age-length relationships by sex 

 for yellowtail rockfish. Age-length data for yellow- 

 tail rockfish were initially applied to the von 

 Bertalanffy growth-in-length equation, but were 

 not well described by this equation due to the 

 lack of young fish in the samples. 6 



Age-length relationships for male canary rock- 

 fish based on two independent readings are nearly 

 identical (Figure 7). Growth curves for females 

 are similar (Figure 7), but discrepancies exist at 

 older ages where fitted lengths for the first 

 reading were higher than those for the second. 



6 The von Bertalanffy equations derived from two readings of 

 yellowtail rockfish otoliths were: 



Males— Reading 1: l t = 47.96[1 - exp( -0.16(^ + 4.01))] 

 Reading 2: I, = 46.34 [1 - exp( -0.27U - 1.03))] 

 Females— Reading 1: /, = 55.47 [1 - exp( -0.14(^ + 3.19))] 

 Reading 2: /,= 53.81 [1 - exp( -0.19U - 0.24))]. 



TABLE 6. — Survival estimates based on two independent readings of the otoliths of yellowtail rockfish, canary rockfish, 



and black rockfish landed in Oregon, 1973-74. 



411 



