Love and Johnson: Life history of Sebastes rastrelliger and 5. aunculatus 



101 



rockfish may be found in small aggregations. The 

 young are often found in nearshore bays, often 

 around piers or over rubble. Older fish tend to move 

 out of shallow waters and live over both high and 

 low relief, often near the sand-rock interface 

 (Matthews, 1990; Adams, 1992). Brown rockfish feed 

 on crustaceans and fishes (Quast, 1968; Washington 

 et al.'^). In Puget Sound, spawning occurs during 

 June, whereas off central California larvae are re- 

 leased in December-January and May-June (Wyllie 

 Echeverria, 1987; Washington et al.^). There has been 

 no published information on growth rates. In addi- 

 tion, despite their importance, little work on this 

 species has been conducted in southern California. 

 Knowledge of the life history of a species is an es- 

 sential prerequisite for effective fisheries manage- 

 ment. Our goal was to fill gaps in knowledge of the 

 basic life history of these two species in southern 

 California waters. 



Methods 



We collected 162 grass rockfish during 1984 and 1996 

 and 367 brown rockfish between 1977 and 1995. All 

 were collected from southern California waters by 

 spear or hook and line. Data collected included total 

 length (cm), weight (g), sex, capture location, and 

 collection date. In the laboratory, we weighed the 

 gonads, assessed reproductive state, and removed 

 sagittal otoliths. 



Age determination 



Otoliths were placed on wood blocks and embedded 

 in clear epoxy Each block with its otoliths was placed 

 on a Buehler Isomet low-speed saw, and an 0.05-cm 

 wafer (transverse section) was cut from it with two 

 diamond-edge blades separated by a stainless steel 

 shim. Before reading, the wafers were burned slightly 

 over an alcohol lamp. The wafers were then placed 

 in a water-filled, black-bottomed watch glass and 

 examined under a dissecting microscope. 



Ages were assigned by direct observation of otolith 

 annuli. We aged a total of 149 grass rockfish, includ- 

 ing 78 males (16.6-47.5 cm) and 71 females (14.4- 

 50.5 cm), as well as 269 brown rockfish, including 

 120 males ranging in length from 15.0 to 49.8 cm 

 and 149 females ranging from 17.2 to 53.2 cm. Growth 

 was assumed to be described by the von Bertalanffy 

 growth curve model (von Bertalanffy, 1938); 



/,=L(l-e-*''-'»'), 



where /, = length at time t\ 



/^ - theoretical maximum length; 



k - constant expressing the rate of approach 



to /^; and 

 <Q = theoretical age at which /, = 0. 



Growth equation constants for the von Bertalanffy 

 growth model were calculated from length-at-age 

 data for each species by using the least-squares, non- 

 linear regression (SYSTAT, 1992). 



Maturation and reproduction 



We estimated length and age at first maturity by clas- 

 sifying gonads as immature or mature on the basis 

 of criteria given in Westrheim (1975), Gunderson 

 ( 1977 ), and Love and Westphal ( 1981 ). As with other 

 rockfishes, it was difficult to distinguish between 

 immature and mature resting-stage females during the 

 nonreproductive season. Thus, we did not use females 

 captured during the nonreproductive season for either 

 the length-maturity or age-maturity analyses. 



The relationships between length and maturity 

 and age and maturity were established by using a 

 natural log transformation of the equation 



1 



ax + b 



l + e 



(Gunderson et al., 1980) to yield 



In ^— = ax + b, 



P 



where p^ - the proportion mature at length or age 

 x; and 

 a and b = fitted parameters. 



We then plotted ;c against 



In 



1-P. 



^ Washington, P. M., R. Gowan, and D. H. Ito. 1978. A biologi- 

 cal report on eight species of rockfish Sebastes spp. from Puget 

 Sound, Washington. Northeast Alaska Fisheries Center. Pro- 

 cessed Rep., 50 p. 



using simple linear regression to estimate values for 

 a and b. Fifty-percent maturity was calculated by 

 using fitted values of a and 6, and by using p^ - 0.50 

 to solve for x. 



Agonadosomatic index [(gonad weight )/( total body 

 weight) X 100] was computed to quantify changes in 

 gonad size with season. Gonad condition (immature, 

 resting, vitellogenesis, eyed, spawned [Wyllie Eche- 

 verria, 1987] ) was determined for each female. 



We determined egg production in grass rockfish, 

 counting subsamples of unfertilized eggs. Eggs were 



