418 



Abstract-From 1995 to 1998. we col- 

 lected female black rockfish (Sebastes 

 mt'lanops) off Oregon in order to 

 describe their basic reproductive life 

 history and determine age-specific 

 fecundity and temporal patterns in 

 parturition. Female black rockfish had 

 a 50^ probability of being mature at 

 394 mm fork length and 7.5 years-of- 

 age. The proportion of mature fish age 

 10 or older significantly decreased each 

 year of this study, from 0.511 in 1996 

 to 0.145 in 1998. Parturition occurred 

 between mid-January and mid-March, 

 and peaked in February. We observed a 

 trend of older females extruding larvae 

 earlier in the spawning season and 

 of younger fish primarily responsible 

 for larval production during the later 

 part of the season. There were dif- 

 ferences in absolute fecundity at age 

 between female black rockfish with 

 prefertilization oocytes and female 

 black rockfish with fertilized eggs; 

 fertilized-egg fecundity estimates were 

 considered superior. The likelihood 

 of yolked oocytes reaching the devel- 

 oping embryo stage increased with 

 maternal age. Absolute fecundity esti- 

 mates ( based on fertilized eggs) ranged 

 from 299,302 embryos for a 6-year-old 

 female to 948,152 embryos for a 16- 

 year-old female. Relative fecundity 

 (based on fertilized eggs I increased 

 with age from 374 eggs/g for fish age 6 

 to 549 eggs/g for fish age 16. 



Maturity, ovarian cycle, fecundity, and 

 age-specific parturition of black rockfish 

 (Sebastes melanops) 



Stephen J. Bobko 

 Steven A. Berkeley 



Department of Fisheries and Wildlife 



Hatfield Marine Science Center 



2030 SE Marine Science Drive 



Oregon State University 



Newport, Oregon 97365 



Present address (for S. A. Berkeley, contact author): Long Marine Laboratory 



University of California, Santa Cruz 



100 Shaffer Rd 



Santa Cruz, California 95060 



E-mail address (for S A Berkeley, contact author): stevenab@cats.ucsc.edu 



Manuscript submitted 13 March 2003 

 to Scientific Editor's Office. 



Manuscript approved for publication 

 30 March 2004 bj the Scientific Editor. 



Fish Bull. 102:418-429(2004). 



Many fish species in the North Pacific 

 have a long reproductively active life 

 span, which increases the likelihood 

 of producing offspring during peri- 

 ods of favorable environmental condi- 

 tions. This bet hedging reproductive 

 strategy reduces the impact of envi- 

 ronmental variation on reproductive 

 success (Goodman, 1984; Leaman 

 and Beamish, 1984; Schultz, 1989). 

 In species with age-structured spawn- 

 ing schedules, a broad age distribu- 

 tion will maximize the length of the 

 spawning season. The more protracted 

 the reproductive period, the greater 

 the likelihood that some spawning 

 will occur during conditions favorable 

 for larval survival (Lambert, 1990). 

 Age-related differences in the timing 

 of spawning have been observed in 

 many fishes; usually larger, older fish 

 spawn earlier (Simpson, 1959; Bage- 

 nal, 1971; Berkeley and Houde, 1978; 

 Shepherd and Grimes, 1984; Lambert, 

 1987), but in some cases younger fish 

 spawn earlier in the season (Hutch- 

 ings and Myers, 1993). 



Age truncation, an inevitable result 

 of fishing, can increase recruitment 

 variability by reducing the length of 

 the spawning season or by selectively- 

 removing older, more fit individuals 

 from the population. Factors that 

 might affect individual reproductive 

 success include the number of eggs 

 produced, the quality of eggs (e.g., 

 yolk or oil globule volume), and the 

 size or health of eggs and larvae. Off 



the coast of Oregon, widow rockfish 

 (Sebastes entomelas) have exhibited 

 increased absolute fecundity, and 

 more importantly have increased rela- 

 tive fecundity, with age (Boehlert et 

 al., 1982). Individual populations of 

 shortbelly rockfish (Sebastes jordani), 

 have been found to produce larvae 

 with differing lipid and protein com- 

 positions and consequently potentially 

 differing rates of survival (MacFar- 

 lane and Norton. 1999). Zastrow et 

 al. (1989) reported that striped bass 

 eggs stripped from wild fish increase 

 in quality with maternal age due to 

 increased amounts of proteins and 

 lipids, although relative concentra- 

 tions remain unchanged. 



Black rockfish ( Sebastes melanops), 

 like most other rockfish, are long- 

 lived, moderately fecund livebearers 

 with long reproductive life spans. Al- 

 though their longevity and low rate 

 of natural mortality is presumed to 

 be an adaptation to allow success- 

 ful reproduction over their lifespan 

 despite long periods between favor- 

 able environmental conditions, it al- 

 so makes them more susceptible to 

 overexploitation. The objective of our 

 research presented in the present 

 article is twofold. First, we describe 

 the basic reproductive life history 

 of black rockfish. with an emphasis 

 on the ovarian developmental cycle 

 and maturity schedule. Second, we 

 investigate age-specific fecundity and 

 temporal patterns in parturition and 



