Abookire; Biology, spawning season, and growth of Glyptocephalus zachirus 



357 



at least 12 months (Pearcy et aL, 1977), the 

 indeterminate pelagic larval phase may have 

 confounded Castillo's (1995) estimates. 



Fish may adjust their spawning season to syn- 

 chronize larval hatching date with the season 

 that is most favorable for larval feeding (Qasim, 

 1956). Because primary production at northern 

 latitudes is restricted to a short, intense period 

 during early summer, fishes at higher latitudes 

 often delay and shorten their breeding season 

 as an adaptation to synchronize the feeding of 

 fish larvae with the zooplankton bloom (refer- 

 ences in Qasim, 1956; Castillo, 1995). How- 

 ever, rex sole in the GOA spawn earlier in the 

 year and for a longer duration than those off 

 the Oregon coast, which spawn from January 

 to June (Hosie and Horton, 1977). Hence, rex 

 sole do not fit the typical pattern of geographic 

 variation found in other pleuronectids, such as 

 English sole (Pleuronectes vetulus; Kruse and 

 Tyler, 1983; Sampson and Al-Jufaily, 1999), 

 Dover sole (Abookire and Macewicz, 2003), 

 and yellowtail flounder {Limanda ferruginea; 

 Zamarro, 1991). 



Maturity and growth 



Size and age at sexual maturity are two impor- 

 tant parameters offish stock assessment models 

 used to estimate spawning biomass and annual 

 catch quotas, but these parameters may vary 

 throughout the geographic distribution of a spe- 

 cies (Roff, 1981; Nichol, 1997; Bromley, 2000) 

 and can be influenced by food availability (Cas- 

 tillo, 1995; Sampson and Al-Jufaily, 1999), 

 oceanographic conditions (Kruse and Tyler, 

 1983; Brodziak and Mikus, 2000), or popula- 

 tion size (Morgan and Colbourne, 1999). Along 

 the west coast of North America both English 

 sole (Sampson and Al-Jufaily, 1999) and Dover 

 sole (Brodziak and Mikus, 2000; Abookire and 

 Macewicz, 2003) exhibit geographic variation in 

 length at maturity and growth. 



There is some indication that female rex sole 

 mature at a smaller size in the southern por- 

 tion of their range: off San Francisco, Cali- 

 fornia, females were fully mature at 22.8 cm 

 (in Hosie and Horton, 1977), and off the Or- 

 egon coast ML^„ was 24 cm (Hosie and Horton, 



GOA logistic 

 regression 



— OR logistic 

 regression 

 (Hosie and 

 Horton, 1977) 



110 160 210 260 310 



360 



III iitiiiiiiii ri I 



410 460 



rill I II I II II II ill! 



510 560 



Total lengtti (mm) 

 Figure 6 

 Proportion of female rex sole {Glyptocephalus zachirus) that were 

 sexually mature in the Gulf of Alaska (GOA) as a function of 

 total length (mm). Data points along the GOA curve represent 

 the proportion of mature females in each 15-mm length-class 

 interval. Logistic model parameter estimates are listed in Table 

 3. The dashed line denotes the length at which 50% of females are 

 mature, and the actual size (mm) of ML^q is given. A maturity 

 curve for female rex sole off the Oregon (OR) coast (from Hosie 

 and Horton, 1977) is graphed for comparison. Female rex sole 

 in the GOA mature at a significantly larger size than off the 

 Oregon coast (P<0.0001l. 



o 



10 

 0.8 - 

 0,6 - 

 0,4 - 

 0,2 - 

 0,0 



oooooo ooooooo 



20 



25 



30 



15 

 Age (yr) 



Figure 7 



Proportion of female rex sole {Glyptocephalus zachirus) in the 

 Gulf of Alaska that were sexually mature as a function of age 

 (years). Datapoints along the curve represent females grouped 

 in intervals of one year. Logistic model parameter estimates 

 are listed in Table 3. 



