HOSIE and HORTON: BIOLOGY OF REX SOLE 



TABLE 4. — Computed mean length at age and mean length at age estimated by von 

 Bertalanffy growth equation for 45 unsexed, 189 male, and 212 female rex sole collected off 

 northern Oregon in September-October 1969 and September 1971. 



Age' 

 (yr) 



No. 



Male 



Computed mean Estimated mean 

 length (cm) length 2 (cm) 



9.20 

 12.61 

 17 00 

 19.52 

 21 66 

 24.55 

 2539 

 2582 

 27.37 

 28.90 

 29.33 

 27.00 



9.44 

 13.36 

 16.65 

 19.39 

 21 69 

 23.62 

 25.22 

 26.57 

 27.69 

 28 63 

 2942 

 30.07 



No 



3 45 



7 



33 



11 



19 



14 



9 



17 



24 



28 



20 



14 



4 



2 



6 



1 







3 



Female 



Computed mean Estimated mean 

 length (cm) length 2 (cm) 



920 

 12.71 

 16.64 

 20.45 

 24.95 

 25.64 

 26.33 

 28.05 

 3037 

 31.03 

 33.35 

 3245 

 33.75 

 33.50 

 37.00 

 47.00 



0.00 

 47.30 



891 

 13.44 

 17.25 

 2045 

 23.14 

 25.39 

 27.29 

 28 88 

 30.21 

 31 34 

 32.28 

 33.07 



33 73 



34 29 

 34.76 



'These fall-caught fish were assumed to be about one-half way through the growing season, based upon 

 otolith readings. 



2 Von Bertalanffy growth equations were based on 1- to 10-yr-old males (L a = 33.43 cm, K 

 -0 8551 yr), and 1- to 12-yr-old females (L x = 37.21 cm, K = 0.1747, ( = -0.5667 yr) 

 3 Sexes were not separated for age 1 fish (45 specimens) 



= 0.1778, t n 



37.21 cm fit observed data through age 15.5, but 

 was far below the maximum computed mean TL of 

 47.30 cm. The apparent discrepancy does not in- 

 validate the data because Knight (1968) noted 

 that L x is not the maximum obtainable length, 

 but rather a mathematical tool needed in compu- 

 tations for the von Bertalanffy growth equation. 

 This is exemplified by our collection of a 23-yr-old 

 ( ± 1 yr), 59-cm female rex sole off northern Oregon 

 in February 1970, which we consider as about the 

 maximum length and age of rex sole. Hart (1973) 

 reported a 24-yr-old rex sole was collected off 

 British Columbia, but no length was given. 



Mortality Rate 



Estimates of the total instantaneous mortality 

 rate (Z) derived from data in Table 5 and using the 

 catch curve method varied from 0.53 to 0.70 for 

 males and from 0.44 to 0.55 for females (Table 6). 

 In this analysis the natural logarithm of the 

 numbers of males and females caught at each age 

 was plotted against the respective age class 

 (Figures 4, 5). The total mortality rate was the 

 best fitted slope on the right side of the catch curve, 

 determined by linear regression using ages rang- 

 ing maximally from 6 to 16 yr (Table 5). 



Estimates of Z using the Jackson method 

 ranged from 0.43 to 0.61 for males and from 0.20 to 

 0.52 for females (Table 6). In this method annual 

 survival rate (S) is: 



TABLE 5. — Numbers of rex sole per age group caught during 

 groundfish surveys off northern Oregon in 1971 and 1973 and 

 central Oregon in 1972. 



TABLE 6. — Estimates of the total instantaneous mortality rate 

 (Z) of rex sole collected off northern Oregon in September 1971 

 and 1973 and off central Oregon in September 1972. 



'Based on simple average of Z's for the 3 yr. 



55 



