Bobko and Berkeley: Maturity, ovarian cycle, fecundity, and parturition of Sebastes melanops 



427 



estimates of reproductive potential, in which fe- 

 cundity for prefertilization females is used, may 

 overestimate actual larval production because 

 an increasing proportion of the stock consists of 

 young fish. 



We observed a recurring trend of older, larger 

 fish extruding larvae earlier in the reproductive 

 season and larval output being increasingly domi- 

 nated by younger and younger fish. Eldridge et al. 

 (1991) reported that larger (and most likely older) 

 yellowtail rockfish {Sebastes flavidus) spawned 

 earlier in the season than smaller fish — a pat- 

 tern also reported for darkblotched rockfish (S. 

 crameri) by Nichol and Pikitch (1994). Reduced 

 food availability has been suggested as a poten- 

 tial cause for delayed reproduction in Sebastes for 

 smaller, younger individuals with high metabolic 

 requirements for somatic growth (Larson, 1991). 

 We feel that limiting the amount of energy that 

 can be spent on reproductive development would 

 cause lower fecundity or reduced yolk content, but 

 not necessarily a delay in reproductive develop- 

 ment that would result in suboptimal timing of 

 parturition. 



Stock assessments rarely consider changes in 

 population age composition resulting from the 

 removal of older age classes except to the extent 

 that total egg and larval production is reduced. 

 The decreasing representation of mature female 

 black rockfish age 10 and older in the three years 

 of our study indicates that age truncation is oc- 

 curring in black rockfish in Oregon. This trun- 

 cation not only removes biomass and potential 

 larval production, but truncation of the upper 

 end of the age distribution eliminates mature 

 females with higher fecundity per individual, a 

 greater success in carrying eggs through to the 

 larval stage, and an age group that extends the 

 overall parturition season. Further research is 

 necessary to explore the controlling mechanisms 

 of differential reproductive success with age and 

 to determine how best to incorporate these find- 

 ings into stock assessment models. 



Acknowledgments 



Many individuals contributed to the completion of 

 this study. Tom Rippetoe provided many hours of 

 expert assistance in all aspects of this research. 

 Bob Mikus aged all of the adult black rockfish 

 for this study. We thank him and the Oregon 

 Department of Fisheries and Wildlife for all their 

 support. We thank Dan Detman for his help and 

 time in collecting black rockfish. We also thank 

 Brock McLeod, Jason Castillo, David Stewart, and 

 Michael Hogansen for all their help. We are espe- 

 cially grateful for all those unpaid volunteers who 

 helped with fieldwork: Joe O'Malley, Mark Amend, 

 Bill Pinnix, Wolfe Wagman, and Pat McDonald. 



I I Age 6 - 8 



^M Age 9 - 1 1 



I I Age 12-14 



^mm Age 15 + 



^ ^ <e? <eP ^ <eP ^ ^ ^ 



«£>' & K*' ^' </ t^' #' ^' ^' 



Week-month 



Figure 11 



Percent relative larval production estimated from observations 

 of larval development and age-group-specific absolute fecundity 

 (based on fertilized eggs) for all mature females belonging to each 

 age group of black rockfish collected in Oregon during 1996-98. 



