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



419 



discuss their effect on reproductive success in a 

 population undergoing truncation of the upper end 

 of its age distribution. 



Materials and methods 



We collected female black rockfish during the 

 months of peak female reproductive development, 

 November through March, for three successive 

 years from 1995-96 through 1997-98. Female black 

 rockfish were primarily obtained from recreational 

 charter boat landings in Newport, Depoe Bay, and 

 Charleston, Oregon, in addition to some fish from 

 commercial landings from Port Orford, Oregon 

 (Fig. 1). We also collected fish by rod and reel and 

 spearfishing. When possible, the sex of all avail- 

 able black rockfish was determined, and females 

 were staged as immature or mature. Immature 

 females were measured (FL), and mature females 

 were returned to the laboratory. On extremely busy 

 days when numerous charter boats were fishing, 

 all mature females were collected, but immature 

 fish were not measured. In total we collected 1643 

 female black rockfish. Immediately upon return 

 to the laboratory, we recorded fork length, total 

 weight when possible (most samples from charter 

 boats were carcasses only), liver weight, and ovary 

 weight. Ovaries were assigned a maturity stage 

 based on macroscopic appearance and preserved in 

 10% buffered formalin. We initially followed the gross 

 maturity stage scheme of Nichol and Pikitch (19941 for 

 darkblotched rockfish ( Sebastes crameri) but ultimately- 

 abandoned their classification of maturity stages in favor 

 of the simplified maturity stages reported by Gunderson 

 et al. (1980) (Table 1). Sagittal otoliths were removed 

 and stored dry for age determination. All aging was done 

 by an expert age reader from the Oregon Department of 

 Fish and Wildlife (ODFW), who used the break-and-burn 

 technique (Beamish and Chilton, 1982). Ten percent of 

 the otoliths were randomly selected for a second read- 

 ing to ensure consistency in interpretation of annuli. 

 It should be noted that black rockfish ages have not 

 been validated. However, ages have been validated for 

 yellowtail rockfish (Sebastes flavidus), a closely related 

 species (Leaman and Nagtegaal, 1987), by using otoliths; 

 moreover, the break-and-burn aging method is widely 

 accepted as valid for aging rockfish (MacLellan, 1997), 

 and ages thus derived are routinely used in rockfish 

 stock assessments. Because our sample included all 

 mature females that we encountered, we used these data 

 to estimate the age distribution of mature females in 

 each time period, and the age distribution of parturition 

 during each time interval. 



Histological preparations were made from the ova- 

 ries of 175 females collected monthly from March 1996 

 through March 1997 to track seasonal ovarian devel- 

 opment. Females collected in March 1996 and Novem- 

 ber 1996 through March 1997 were from our regular 

 sampling program, whereas fish collected from April 



45° 00'N " 



42° 50' ' 



124° 30' 120°00'W 



Figure 1 



Map of the Oregon coast showing the study area where black 

 rockfish (Sebastes melanops) were collected. 



through October 1996 were obtained from Newport 

 recreational charter boat landings. Females were ran- 

 domly selected from each maturity stage observed each 

 month and from as wide a range of ages as available 

 (Table 2). Ovaries were embedded in paraffin, sectioned 

 at 4-5 jjm, and stained with gill-3 haematoxylin and 

 eosin y solution. 



We determined stage-specific fecundity in black rock- 

 fish for females with unfertilized yolked oocytes (?i=184) 

 and fertilized eggs (n = 85). Postfertilization ovaries were 

 very fragile and tended to rupture easily and release 

 embryos under the slightest pressure. Consequently, 

 for estimating fecundity for these stages, we used only 

 fish collected by ourselves so that we were certain that 

 no eggs or larvae had been released during capture. 

 To ensure that no eggs were lost after capture, these 

 fish were immediately placed into plastic bags in order 

 to retain any eggs that might be extruded before the 

 ovary could be processed. Ovaries were processed fol- 

 lowing procedures modified from Lowerre-Barbieri and 

 Barbieri (1993) to separate eggs and embryos from 

 connective tissue. Briefly, fixed ovaries were manually 

 manipulated and rinsed with water through a 1-mm 

 square mesh sieve, which retained most of the con- 

 nective tissue, into another sieve with 0.75-mm mesh. 

 Ovary connective tissue was retained in the coarse 

 sieve, and freed eggs were collected in the fine-mesh 

 sieve. Freed eggs were patted dry, weighed (nearest 

 0.1 g), and three subsamples were collected, weighed 

 (nearest 0.001 g), and placed in 10% buffered formalin. 



