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



425 



All female black rockfish. except the 

 smallest immature females, followed a sea- 

 sonal cycle in which their ovaries developed 

 an orange coloring during the months of 

 reproductive activity — a pattern observed 

 in olive rockfish (Love and Westphal, 1981). 

 Similarly, Nichol and Pikitch (1994) ob- 

 served darkblotched rockfish undergoing 

 an "immature cycling" and even assigned 

 these fish a maturity stage. After the re- 

 productive season, the ovaries of immature 

 black rockfish once again became pale pink 

 in color. Because these fish were function- 

 ally immature and there was no way to 

 project when they would become sexually 

 mature, they were combined with those 

 small, young females undergoing no sea- 

 sonal ovarian development and were staged 

 as immature. 



Our estimate of fork length at 50% ma- 

 turity for female black rockfish off Oregon 

 was similar to the 400 mm estimate re- 

 ported for north-central California females 

 (Wyllie Echeverria, 1987), but lower than 

 the estimate of 422 mm from Washington 

 (Wallace and Tagart, 1994). Our estimated 

 age at 50% maturity of 7.5 years was simi- 

 lar to the estimates of 7.9 and 7 years from 

 Washington and north-central California, 

 respectively. McClure (1982) reported that 

 over 50% of examined female black rockfish 

 collected off Depoe Bay, Oregon, were ma- 

 ture by age six. The difference between our 

 estimate and McClure's was most likely due 

 to using whole otoliths to age fish, which 

 resulted in underestimates of age, and 

 to assigning maturity stages only during 

 summer months, which we have already de- 

 scribed as problematic. Both absolute and 

 relative fecundity increased with age for 

 female black rockfish in Oregon waters, 

 although there was a great deal of varia- 

 tion not accounted for by age. The low r 2 

 values for absolute fecundity regressions 

 for pre- and postfertilization females (0.25 

 and 0.45 respectively) are due largely to 

 the relatively poor correspondence between 

 age and size (Fig. 5). Black rockfish, like 

 many slow growing, long-lived fish grow 

 slowly after sexual maturity. The rate of 

 growth during their first few years can be 

 quite variable depending on oceanographic 

 conditions and food availability. As a re- 

 sult, young fish can be as large or larger 

 than much older fish (Fig. 5). Length is a 

 better predictor of fecundity than age as judged by the 

 goodness-of-fit of the multiple linear regression model 

 (Fig. 10; /- 2 =0.70). 



An increase in absolute fecundity with age was ob- 

 served in both prefertilization and postfertilization 



females, but they occurred at different rates. As il- 

 lustrated in Figure 8, the absolute fecundity for a post- 

 fertilization 6-year-old black rockfish was only 58% 

 of the estimated absolute fecundity for a prefertiliza- 

 tion fish of the same age. By age 15 absolute fecundity 



