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Fishery Bulletin 102(3) 



Kusakari's (1991) stages of embryonic development for 

 kurosoi (Sebastes schlegeli) modified to reflect the gesta- 

 tion period of 37 days for black rockfish (Boehlert and 

 Yoklavich, 1984). Gestation period is likely to vary with 

 water temperature. In determining gestation period, 

 Boehlert and Yoklavich (1984) held black rockfish in 

 the laboratory at 9-11 :, C. Mean water temperatures 

 in our study area during the period of egg and larval 

 development (December-April) were 10.9°, 10.1°, and 

 11.4°C in 1995-96, 1996-97, and 1997-98, respectively 

 (http://co-ops.nos.noaa.gov/data). Even in the strong El 

 Nino year of 1997-98, nearshore water temperature 

 during the winter larval development period was only 

 slightly outside this range. Therefore, we assumed a 

 37-day gestation period for all years of our study. Us- 

 ing the Boehlert and Yoklavich (1984) equation; (stage 

 duration = 0.0452 xstage 1 090 ) we solved for duration at 

 each stage by adding 5 days to account for the time 

 between hatching (stage 32) and parturition (also from 

 Boehlert and Yoklavich, 1984). To calculate the time 

 until parturition for each stage, we subtracted the pre- 

 vious stage durations from the total gestation period of 

 37. For example, at stage 1, parturition would occur in 

 37 days. At stage 2, parturition would take place in 37 

 days - stage-1 duration (-2 days) = 35 days. 



For each year of our study, estimated parturition 

 dates for all females in our sample were grouped into 

 one-week time intervals and further subdivided into 

 age categories: 6-8: 9-11; 12-14; and >15. These num- 

 bers were then multiplied by the appropriate value for 

 age-class-specific fecundity based on fertilized eggs 

 (Table 3) to estimate relative spawning output by week 

 for each age class. 



Results 



Ovarian development 



Black rockfish off Oregon exhibited group-synchronous 

 oocyte development; and females extruded only one 

 brood of larvae per year (Fig. 2). Based on our observa- 

 tions of ovarian development from all three years of 

 this study, parturition took place from mid-January 

 through mid-March and peaked in February. Following 

 parturition, unextruded larvae were quickly resorbed 

 and the ovary lost much of its vascularization. From 

 April through early August ovaries were in a resting 

 state and contained oogonial nests and slightly larger 

 oocytes with a basophilic cytoplasm and a maximum 

 diameter of 50 jjl. Also present at this time were develop- 

 ing oocytes ranging from 50 to 150 n in diameter with 

 small lipid vacuoles surrounding the nuclear membrane. 

 Yolk deposition (vitellogenesis) began in late August 

 and was observed through the third week of February. 

 In the final stages of vitellogenesis. the largest oocytes 

 were approximately 700 n in diameter and had numer- 

 ous oil vacuoles and yolk globules throughout the cyto- 

 plasm. The first female with fertilized eggs (stage 3) was 

 observed during the second week of January, and stage-3 



Table 3 



Age group-specific absolute fecundity (based on fertilized 

 eggs l and age distribution of mature females as a percent- 

 age of all mature females, used to estimate larval pro- 

 duction. Calculated from data pooled from 1996 through 

 1998. 



' Absolute fecundity for each age group is the estimated fecundity 

 (based on fertilized eggs) for ages 7. 10, 13, and 16. respectively. 



females were observed until the third week of February. 

 Recently fertilized eggs were approximately 850 ,u in 

 diameter. The period of parturition as indicated by the 

 occurrence of ovaries containing eyed larvae extended 

 from the second week in January through the second 

 week of March. Spent females were first collected during 

 the last week of January and were most frequently col- 

 lected in late February and early March. 



Sexual maturity 



Parameter values for the length-maturity logistic model 

 were ft, = -26.73 and ^ = 0.068. The smallest mature 

 female black rockfish we observed was 345 mm; all 

 individuals were mature by 450 mm. Fifty percent of 

 females were estimated to be mature at 394 mm fork 

 length (Fig. 3). As reflected in our length-maturity logis- 

 tic model, there was a decreasing trend in the percent 

 maturity for female black rockfish in recreational land- 

 ings from ODFW collections from 1992 through 2000 

 (Fig. 4). The von Bertalanffy parameter estimates for 

 female black rockfish were L re = 442 mm, k = 0.33, t = 

 0.75 (Fig. 5). Using these estimates, along with the fork 

 length at 509c maturity, we estimated the age at 50% 

 maturity for female black rockfish to be 7.5 years. The 

 median age of mature females decreased in each col- 

 lection year from 10 years in 1996 to 9 in 1997 and to 

 7 years in 1998. In addition, we observed a significant 

 decrease in the proportion of mature fish age 10 or older 

 over the three years of our study (Pearson's ^ 2 = 52.4, 

 df=2, P<0.001). The proportions decreased from 0.511 

 in 1996, to 0.318 in 1997, and 0.145 in 1998. 



Fecundity 



Absolute fecundity for prefertilization female black 

 rockfish ranged from 482,528 oocytes for a 5-year-old 

 female to 998,050 oocytes for a 19-year-old female. 

 The results of ANCOVA (Table 4) over a common age 



