Hannah et a\ Length and age at maturity foi Eopsctta /oidani 



715 



mature fish were sampled, even though the commercial 

 fishery samples showed a similar lower size range to the 

 fish collected in our study (Fig. 6). The lack of immature 

 fish was most evident in the 1986-91 November-February 

 samples from Charleston. Oregon, where 170 fish were 

 sampled for maturity, and only one fish was reported as 

 immature. The 1992-2000 Charleston data also showed 

 low numbers of immature fish. These samples also showed 

 groups of very small fish, and most or all of them were 

 classified as mature (Fig. 5). This kind of bias, where small 

 fish encountered are more likely to be reported as mature 

 than similar-size fish sampled from a well-mixed popula- 

 tion, would also act to flatten the resultant maturity curve. 

 The Astoria winter data included more immature fish, and 

 accordingly produced steeper maturity curves. However it 

 was unclear to what degree bias from sampling spawning 

 aggregations may have influenced these curves. 



Discussion 



Although it is known that late fall and winter is a better 

 time for visually assessing female maturity status for 

 petrale sole, our data showed clearly that late summer and 

 early fall maturity samples, for which there was a visual 

 determination of maturity, should not be used for estimat- 

 mg maturity in this species. Although our study did not spe- 

 cifically examine ovaries from spring collections, the general 

 timing of ovarian development in this species suggests that 

 this caution can be extended to all late spring and summer 

 samples. Our results are similar to the findings of Ramsay 

 and Witthames ( 1996), who suggested that visual maturity 

 evaluations of the common sole iSolea solea) are generally 

 only reliable during a limited portion of the year. 



The maturity data developed in our study (Figs. 3 and 4) 

 suggest a larger size at 50'7f maturity (33.1 cm vs. 30.7 cm) 

 and a much steeper maturity curve for petrale sole than 

 indicated by the 1986-91 sample data used in the last two 

 petrale sole stock assessments (Turnock et al.^). Although 

 the curves appeared to be quite different, the length at 

 SOVc maturity increased by only 2.4 cm. The most recent 

 stock assessment model indicates an annual fishing mor- 

 tality rate, for fully exploited size groups, of 0.285 (Samp- 

 son and Lee' ). Incorporating a revised maturity ogive from 

 our study decreased the equilibrium fishing rate to 0.268, 



20 23 26 29 32 35 38 41 44 47 50 53 56 59 

 Length 



1,25-, 



jmr"~^ 



1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 

 Age 



Figure 3 



Proportion mature for female petrale sole, by age and 

 length (FL,cni), from September samples. Maturity status 

 was determined by histological examination by using pres- 

 ence and absence of vitellogenesis to determine maturity. 

 Fitted curve is also shown (Table 3). 



a change of about 6% (Sampson'*). This modest effect on 

 harvest rate seems odd, given the large apparent differ- 

 ence between the curves in Figure 3. A possible explana- 

 tion for this discrepancy is that the results depend heav- 



^ Sampson, D. B. 2000. Personal commun. Coastal Oregon 

 Marine E.xperiment Station and Department of Fisheries and 

 Wildlife, Oregon State University, Hatfield Marine Science 

 Center, Newport, OR 97365. 



