Yoklavich et al.: Larval rockfishes and their physical environment off central California 



773 



was computed for pooled age-length data because of 

 the narrow age range (i.e. Length=4.63 + 0.20 [Age]; 

 ^=0.83; rc=288). As an aside, the larval length at time 

 of extrusion estimated by this model was 4.63 mm, 

 which closely approximates the mean size of full-term 



10.0 



-10.0- 



B 



29 12 07 06 



Average temperature (°C) 







40 



80- 



120 

 160 



200 



29 12 07 



January February March 



Average salinity (•/„) 



06 

 April 



Figure 5 



Wind, temperature, and salinity profiles for offshore Dav- 

 enport, California. (A) Daily averaged wind vectors mea- 

 sured at buoy 46042 in Monterey Bay (arrows point in di- 

 rection to which wind was blowing [north is toward top of 

 page]); (B) temperature (°C); and (C) salinity Cfc) in upper 

 200 m at the most offshore station ( 19 km) during ichthyo- 

 plankton surveys 29 January-6 April 1993. CTD sampling 

 dates are indicated with dashes. 



shortbelly rockfish larvae collected from females off 

 central California (4.7 mm SL; Laidig et al., 1991). 



Birthdate distributions were compared between 

 shortbelly rockfish larvae collected early in the sea- 

 son and pelagic juveniles collected from May to July. 

 According to larval ages and collection dates, 

 birthdates of shortbelly rockfishes extended from 

 December to early May (median=5 February) 1992, 

 and January to early April (median=12 February) 

 1993 (Fig. 7). Birthdates estimated from juvenile 

 shortbelly rockfishes occurred much later in both 

 years (Fig. 7). The relatively few pelagic juveniles 

 (2.3 fish/trawl, n=56 midwater trawls; see Loeb et 

 al. 1 for survey results) collected in May-July 1992 

 had an extremely narrow range of birthdates from 8 

 April to 2 May (median=21 April). Greater numbers 

 of surviving juvenile shortbelly rockfishes during 

 May-July 1993 (75.1 fish/trawl, rc=64 midwater 

 trawls; see Loeb et al. 1 for survey results) had a 

 broader range of birthdates from 24 January to 7 

 June (median=15 March). 



Larval blue rockfish, the second most abundant of 

 the identified species, had a much narrower range of 

 lengths (2.8-6.9 mm SL) and, unlike shortbelly rock- 

 fish, were abundant only from late January to early 

 February in both years (Table 3). Size of larval blue 

 rockfishes, collected on the same days in 1992, var- 

 ied significantly among the 7, 13, and 19 km sta- 

 tions (ANOVA, P<0.001), with larger larvae occur- 

 ring at the innermost station (mean size=5.0 mm SL, 

 SE=0.1; Table 3). As with shortbelly rockfish larvae, 

 size composition of blue rockfishes was not signifi- 

 cantly different between the two offshore stations 

 (overall mean=4.5 mm SL, SE=0.1). Although 1993 

 collections were limited and comparisons not statis- 

 tically significant, there was a continued trend of 

 smaller blue rockfish larvae farther offshore. 



Ages of 96 larval blue rockfish collected in Janu- 

 ary-February of 1992 and 1993 ranged from 2 to 21 d 

 (Table 4); only 7 of these specimens were from 1993 

 because of problems with preservation. Because 

 growth rates estimated over similar age ranges were 

 not significantly different in January and February 

 1992 (ANCOVA, P>0.78), age-length'data were com- 

 bined and a least-squares linear model was calcu- 

 lated (i.e. Length=3.98 + 0.14 [Age]; r*= 0.63; n=96). 

 Birthdates were estimated for all blue rockfish lar- 

 vae collected in 1992 and 1993 by using fish length 

 and this growth model. Birthdate distribution was 

 narrow in both years, ranging from 31 December 

 1991 to 21 February 1992 and from 12 January to 12 

 February 1993; the median birthdate was 27 Janu- 

 ary in both years. Birthdates could not be compared 

 with those of pelagic juvenile blue rockfishes because 

 no juveniles were collected in 56 midwater trawl 



