768 



Fishery Bulletin 94(4). 1996 



tions were located across the shelf at 1 km ( 15 m 

 water depth), 3 km (30 m water depth), 7 km (60 m 

 water depth), 13 km ( 100 m water depth), and 19 km 

 (180-713 m water depth) from shore. During 1991- 

 92, samples were collected at approximately two- 

 week intervals from early December to April; less 

 frequent sampling extended through June because 

 of the absence of expected upwelling events during 

 spring. Sampling between January and April 1993 

 was limited to monthly intervals by frequent storms 

 and rough seas. 



Larvae were sampled with two 70-cm (mouth di- 

 ameter) open nets of 0.505-mm mesh, black Nitex 

 fitted onto a bongo frame. Volume of water filtered 

 (30-465 m 3 per net) was estimated from calibrated 

 mechanical flowmeters positioned in the mouth of 

 each net. Tows were made parallel to bathymetry at 

 1-3 k for 2-20 min (depending on depth) obliquely 

 from near the bottom to the surface at nearshore sta- 

 tions and from 200 m to the surface at the offshore 

 station. Three replicate tows were conducted at most 

 stations (Table 1). Oceanographic data were collected 



from near bottom to the surface at each station with 

 a calibrated CTD (conductivity, temperature, and 

 depth) profiler (model SBE 19 SEACAT, Sea-Bird 

 Electronics). Daily wind speed and direction during 

 the survey period in each year were calculated from 

 daily averages of east and north wind components 

 measured at the National Data Buoy Center moored 

 buoy 46042 (Fig. 1). 



Plankton samples were preserved at sea, one 

 sample from each bongo pair in 5% buffered forma- 

 lin and the other in 80% buffered ethanol. Rockfish 

 larvae were sorted under a dissecting microscope 

 from each paired sample for all replicates per sta- 

 tion. Formalin-preserved rockfish from all replicates 

 were enumerated for abundance estimates. Only one 

 ethanol-preserved replicate per station was processed 

 for species identification. Standard length (or noto- 

 chord length for preflexion larvae) was measured to 

 the nearest 0.1 mm for shortbelly rockfish, Sebastes 

 jordani, and blue rockfish, S. mystinus, preserved in 

 ethanol. Otoliths were removed for age determina- 

 tion from a subsample of these two dominant spe- 

 cies; larval ageing methods (i.e. counting daily growth 

 increments in otoliths) followed Yoklavich and Bailey 

 (1990). Within the otolith microstructure of larval 

 shortbelly rockfish, a well-defined increment is 

 formed at parturition, which has been adequately 

 resolved with optical microscopy at 1250x magnifi- 

 cation (Ralston et al., 1996). Daily formation of in- 

 crements in otoliths has been demonstrated in juve- 

 nile black rockfish (S. melanops; Yoklavich and 

 Boehlert, 1987) and in shortbelly and brown rock- 

 fish (S. auriculatus; Laidig et al., 1991). 



Birthdates of larval shortbelly and blue rockfishes 

 were calculated by using a linear growth model (e.g. 

 fitted from the aged subsample) to estimate age from 

 length and by subtracting age from date of capture. 

 Birthdate distribution estimated from larvae was 

 compared with that estimated from older pelagic 

 young-of-the-year shortbelly rockfishes collected from 

 May to July, 1992 and 1993, near Monterey Bay (see 

 Loeb et al. 1 for details of surveys). Ages of these pe- 

 lagic juveniles were estimated from length by using 

 linear growth models developed for this species and 

 size range collected from central California during 

 May and June 1992 and 1993 (Woodbury 2 ). Birthdate 

 distributions were corrected for age-specific mortal- 

 ity across all daily cohorts with rates modified from 



1 Loeb, V. J., M. M. Yoklavich, and G. M. Cailliet. 1994. The 

 importance of transport processes in recruitment of rockfishes 

 (Genus Sebastes) to nearshore areas of Monterey Bay, Califor- 

 nia. Final Report, NOAA, California Sea Grant College, Project 

 R/F-142, 25 p. 



2 Woodbury, D. 1996. Natl. Mar. Fish. Serv., NOAA, 3150 Para- 

 dise Dr., Tiburon, CA 94920. Unpubl. data. 



