356 



Fishery Bulletin 104(3) 



W=0.000762L3 6127 (n=573, r-=0.963, P<0.0001). Param- 

 eters for the ovary- free weight to total length (cm I rela- 

 tionship were W=0.001277L3 "8° (n = 568, r2 = 0.969, 

 P<0.0001). Parameters of the von Bertalanffy growth 

 model for female rex sole in the GOA were L^ = 41.824, 

 ;fe=0.388, and ?o=-0.022 (n=556, r2=0.480, P<0.0001). 

 All GOA parameters of the von Bertalanffy growth 

 model differed from those off the coast of Oregon: 

 L^ (Z = 8.01, P<0.0001), k (Z=5.61, P<0.0001), and /g 

 (Z=2.29, P=0.0110). Female rex sole age 1-15 years 

 grew much more quickly in the GOA than off the Oregon 

 coast (Fig. 8). 



Discussion 



A representative sample of fish can be challenging to 

 collect during the spawning season, because samples 

 from spawning aggregations may produce dispropor- 

 tionately large numbers of mature fish whereas samples 



45 

 40 

 35 - 

 30  

 25- 

 20 

 15 

 10 

 5 -I 



D Immature (274) 

  Mature (320) 



", w. S. 



170 215 260 305 350 395 440 485 530 

 Length (mm) 



100 -1 

 90 

 80 

 70 - 

 60  

 50 - 

 40 

 30 

 20 

 10 -I 







D Immature (256) 

  Mature (301) 



dU 



JL 



n. H. 



23456789 10 

 Age (yr) 



13 14 15+ 



Figure 5 



The number of immature and mature female rex sole {Glypto- 

 cephalus zachirus) by total length (upper graph) and age (lower 

 graph). Sample size is given in parentheses. Lengths are binned 

 at 15-mm increments and "age 15+" includes all females from 15 

 to 29 years old. Minimum size at maturity occurred in a fisb with 

 total length of 287 mm, and minimum age at maturity occurred 

 at 3 years. 



from elsewhere may yield unusually large numbers of 

 immature fish (Sampson and Al-Jufaily, 1999). The 

 combination of samples from commercial trawls and ran- 

 domly chosen trawls taken on research surveys provide 

 a reasonable representation of the GOA population and 

 are suitable for estimating spawning season, length and 

 age at maturity, and growth rate. Shore-side sampling 

 of the commercial catch enabled the annual cycle of rex 

 sole sexual maturation to be monitored, and although a 

 common problem in obtaining samples from commercial 

 fishing gear is that the size-selectivity of trawls may 

 produce biased estimates of size frequency and size at 

 age (Sampson and Al-Jufaily, 1999), this concern was 

 alleviated because small rex sole (minimum length = 172 

 mm) were collected from processing plants. 



One limitation in the sampling effort was that sam- 

 ples could not be obtained in August and September. 

 This raises two concerns. First, the onset of the GOA 

 spawning season was estimated to be October by the 

 presence of POFs in mature ovaries; but, in all prob- 

 ability, it may begin earlier. Second, Hunter 

 et al. (1992) argue that length and age at ma- 

 turity are best estimated from fish collected 

 prior to the spawning season, because dur- 

 ing the spawning season the ovaries of some 

 postspawning females are reabsorbed to the 

 extent that they are indistinguishable from 

 those of immature females. Their estimates 

 of Dover sole (Microstomus pacificus) length 

 at maturity from samples taken during the 

 spawning season were 1.6-5.7 cm higher than 

 estimates from samples taken prior to the 

 onset of spawning (Hunter et al., 1992). Given 

 that GOA collections were unavailable prior 

 to the spawning season, estimates of ML^q in 

 the present study may have been biased high. 

 However, because 1) all postspawning females 

 had POFs present and 2) there were no fe- 

 males that had atretic yolked oocytes without 

 POFs, it is unlikely that mature females were 

 misclassified as immature in this study. 



Spawning season 



The spawning season for the population of 

 female rex sole in the GOA ends in May and 

 appears to commence in October, although it 

 may begin earlier (see above). Castillo (1995) 

 estimated the spawning season for rex sole in 

 the GOA lasts from April through September, 

 which differs markedly from results in the 

 present study which are based on year-round 

 histological examination of ovaries. Castillo 

 (1995) based his estimation on the seasonal 

 occurrence of rex sole larvae near Kodiak 

 Island (Kendall and Dunn, 1985) rather than 

 on collections of adult rex sole in spawning 

 condition. Because rex sole larvae attain an 

 exceptionally large size (up to 89 mm standard 

 length) and have a prolonged pelagic life of 



