Brodziak and Mikus: Variation in life histoid parameters o\ Microstomas paaficus 



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during spring and an offshore spawning migi-ation in late 

 autumn. Westrheim et al. (1992) inferred from tag recov- 

 eries that two major concentrations of Dover sole were 

 present during summer: an inshore group composed of 

 females and small males and an offshore group primarily 

 composed of large males. Jacobson and Hunter ( 1993) also 

 found that Dover sole segregated by sex in their analysis 

 of bathymetric patterns in population structure. Overall, 

 if large male Dover sole undertake seasonal movements 

 less frequently than females, their growth rates may be 

 expected to be less heterogeneous than those of females 

 that move from the continental slope to the more produc- 

 tive waters of the continental shelf during spring. Sea- 

 sonal sampling of Dover sole population structure at depth 

 would improve understanding of the relative movements 

 of male and female Dover sole. 



As others have suggested (Hagerman. 1952; Hunter et 

 al., 1990; Turnock et al., 1994), we found that Dover sole 

 exhibit sexual dimorphism in growth. In particular, there 

 was a significant difference between male and female 



growth curves because females attain larger sizes. Mean 

 length of females increased more rapidly than that of 

 males at roughly 5 years of age. The result that females 

 attain greater lengths than males is consistent with 

 Hunter et al. ( 1990) who also found that values of L . were 

 greater for females. Although our results were not directly 

 comparable to those of Hunter et al. ( 1990) because of dif- 

 ferences in otolith aging technique and sampling design, 

 asymptotic lengths of females were estimated to be S'^ 

 greater than those for male samples in both studies. 

 Some of the growth differences between sexes may result 

 from behavioral differences in feeding and habitat use. 

 Although Dover sole feed more intensively and less selec- 

 tively on the continental shelf during summer (Pearcy and 

 Hancock, 1978). some older fish may remain in deeper 

 water year round (Hunter et al.. 1990). Sexually mature 

 Dover sole are commonly found in the oxygen minimum 

 zone at depths of 600-1000 m (Hunter et al.. 1990; Jacob- 

 son and Hunter, 1993), where low food and oxygen levels 

 depress metabolism and growth potential (Vetter et al., 

 1994). Differences between male and female patterns of 



