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



421 



50 



40 

 30 

 20 

 10 

 



0.50 55 60 65 70 75 0.80 0.85 0.90 0.95 1.00 



Maturity stage 3 - Fertilized 



Age 8 



Collected February 1996 



-[ — ' — i — ' — i 1 1 — — ' — — i — — 



50 55 60 0.65 0.70 75 80 85 90 95 100 



Oocyte or egg diameter (mm) 



Figure 2 



Prefertilization- and fertilized-egg-diameter frequency distributions show- 

 ing a single mode of developing oocytes at both developmental stages. 



black rockfish, either during development (stage 2) or 

 after fertilization (stage 3) (Fig. 2). Analysis of covari- 

 ance (ANCOVA) was used to test for annual effects in 

 the relationship between prefertilization fecundity and 

 age and a maturity-stage effect (prefertilization vs. 

 fertilized-egg development stages) on both absolute and 

 relative fecundity at age. We also used ANCOVA to test 

 for a maturity stage effect in the relationship between 

 absolute fecundity and fork length. All ANCOVA analy- 

 ses were conducted by using multiple linear regression 

 with the function lm in S-PLUS 2000 (MathSoft. Inc.. 

 Seattle, WA). 



To predict the probability of a female black rockfish 

 being mature based on its fork length, we fitted our 

 maturity-at-length data to a logistic regression. Dur- 

 ing those months without reproductive activity, late 

 spring through early fall, it was difficult to distinguish 

 between immature and mature-resting ovaries. Conse- 

 quently, only those females collected during the peak 

 months of reproductive development and from sampling 

 events where all fish, mature and immature, were col- 

 lected were included in our analysis. Binary maturity 

 observations (0=immature, l=mature) and fork length 

 were fitted to a logistic model by using the function 

 glm, family = binomial of S-PLUS (S-PLUS 2000). The 

 model used was 



S0+/Jl«. 



mFL)=P(Y = \\FL)-- 



\ + e 



00+010.  



where P(Y=1\FL) 



probability of female black rockfish 

 being mature at size FL; and 



/3 and P { = regression coefficients for the inter- 

 cept and fork length, respectively. 



For functional purposes, the response variable was 

 interpreted as the percentage of female black rockfish 

 mature at length. Assuming this relationship of fork 

 length to maturity had not changed over time, we ap- 

 plied our logistic model to fork-length data from random 

 sampling conducted by ODFW during the summers of 

 1992-2000 to calculate the percentage of female black 

 rockfish caught by the recreational fishery off Newport 

 that were mature in each year. 



Fork length-at-age data for female black rockfish were 

 fitted with the von Bertalanffy growth function (VB- 

 GF) by using the nonlinear function nisi ) in S-PLUS 

 2000. Age at 50% maturity was calculated by using 

 our estimate of length at 509i maturity and a VBGF 

 rearranged to the form 



^U', '() ~*~ ' 



where t 



L 



|9 j = age at 50% maturity; 

 ,, = = asymptotic length; 

 k = Brody growth parameter; 

 t = age at zero length; and 

 ._ = length at 50% maturity. 



Timing of parturition was estimated by microscopi- 

 cally determining embryo development stages for all 

 females with fertilized eggs following Yamada and 



