20 



Fishery Bulletin 103(1) 



2500 



2000  



£ 1500 



1000 



500 



Alaska and West Coast combined 



Linear regression 



(Alaska and West  



Coast combined) 



2000 4000 6000 



Somatic weight (g) 



8000 



Figure 4 



Fecundity at somatic weight for combined Alaska 

 and West Coast shortspine thornyhead rockfish 

 iSebastolobus alascanus). 



regression lines intersected, and the February-March 

 group was not lower than the October-December group. 

 The February-March group did have lower fecundity 

 than the October-December group for lengths smaller 

 than 27 cm; however the sample size was very small. No 

 significant difference existed between the two groups 

 when the single, large fecundity observation late in the 

 spawning season was ignored (P=0.34). 



Discussion 



Emerson et al. (1990) cited the ability to distinguish 

 borderline vitellogenic oocytes from nonvitellogenic 



oocytes as an advantage of the stereological method, and 

 this was a clear benefit in our study. The stereological 

 method allowed us to differentiate between vitellogenic 

 and nonvitellogenic oocytes at an earlier stage of ovary 

 development than was possible with the gravimetric 

 method. However, the use of ovaries in earlier stages of 

 development increases the potential magnitude of fecun- 

 dity overestimates due to atresia. Atresia, or the resorp- 

 tion of oocytes, is a potential source of error for fecundity 

 estimates (Hunter et al., 1992). Although atretic oocytes 

 can be identified with the stereological method, oocytes 

 that are destined for atresia will be counted, causing 

 fecundity to be overestimated. The amount of atresia will 

 determine the magnitude of this overestimate. Samples 



