39 



Abstract — We estimated annual 

 abundance of juvenile blue (Sebastes 

 mystinus), yellowtail (S. flavidus), 

 and black (S. melanops) rockfish off 

 northern California over 21 years and 

 evaluated the relationship of abun- 

 dance to oceanographic variables (sea 

 level anomaly, nearshore tempera- 

 ture, and offshore Ekman transport). 

 Although mean annual abundance 

 was highly variable (0.01-181 fish/ 

 minute), trends were similar for the 

 three species. Sea level anomaly and 

 nearshore temperature had the stron- 

 gest relationship with interannual 

 variation in rockfish abundance, and 

 offshore Ekman transport did not cor- 

 relate with abundance. Oceanographic 

 events occurring in February and 

 March (i.e., during the larval stage) 

 had the strongest relationship with 

 juvenile abundance, which indicates 

 that year-class strength is determined 

 during the larval stage. Also of note, 

 the annual abundance of juvenile yel- 

 lowtail rockfish was positively cor- 

 related with year-class strength of 

 adult yellowtail rockfish; this find- 

 ing would indicate the importance of 

 studying juvenile abundance surveys 

 for management purposes. 



Relationship between abundance 

 of juvenile rockfishes iSebastes spp.) and 

 environmental variables documented off 

 northern California and potential mechanisms 

 for the covariation 



Thomas E. Laidig (contact author) 

 James R. Chess 

 Daniel F. Howard 



Email address for T, E. Laidig: torn. laidig(g)noaa. gov 



National Marine Fisheries Service 



Southwest Fisheries Science Center 



Fisheries Ecology Division 



110 Shaffer Road 



Santa Cruz, California 95060 



Manuscript submitted 1 December 2005 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 15 March 2006 by the Scientific Editor. 



Fish. Bull. 105:39-48 (2007). 



Success of annual recruitment of juve- 

 nile rockfishes {Sebastes spp.) from 

 the pelagic to a demersal phase is 

 highly variable and leads to large fluc- 

 tuations in year-class strength in the 

 fisheries (Ralston and Howard, 1995). 

 With the abundance of many rockfish 

 stocks at historic low levels, assess- 

 ment of recruitment is paramount for 

 fishery managers to improve plans 

 for sustainable harvests. Fisheries 

 models (such as the stock synthesis 

 model) often include recruitment data 

 (PFMC). In recent years, larval and 

 juvenile rockfish abundance data have 

 been included in stock assessments for 

 bocaccio (S. paucispinis) and cowcod 

 (S. levis) (MacCall^, Butler et al., 

 2003). If the larval or juvenile abun- 

 dance data do not accurately reflect 

 the numbers of adults, the models can 

 either over- or underestimate the bio- 

 mass available to the fishery. 



Rockfishes are viviparous, giving 

 birth to larvae that reside in open 

 water for several months before re- 

 cruiting from the plankton to a more 

 benthic life (Love et al., 2002). The 

 habitat where rockfish initially re- 

 cruit varies among species and in- 

 cludes floating drift algae (e.g., split- 

 nose rockfish, S. diploproa [Shaffer et 

 al., 1995]), soft sediments (e.g., strip- 

 etail rockfish, S. saxicola [Johnson 

 et al., 20G1J), and deeper rocky areas 

 with crevices (e.g., rosy rockfish, S. 

 rosaceus [Love et al., 2002]). A major 

 area of recruitment is the nearshore 



environment, where numerous species 

 of rockfish recruit in the kelp canopy, 

 sand channels, on rocky outcrops, and 

 in midwater among the kelp stipes 

 (Anderson, 1983). 



The factors that influence the mag- 

 nitude of juvenile recruitment of rock- 

 flshes are not well known. VenTresca 

 et al.3 suggested that upwelling was 

 the major factor contributing to the 

 annual variability of juvenile rockfish 

 abundance off Monterey, California. 

 Ralston and Howard (1995) found 

 that the highest survival of blue (S. 

 mystinus), and yellowtail rockfish (S. 

 flavidus), occurred when sea surface 

 temperature and upwelling were at 

 intermediate levels. Ainley et al. 



1 PFMC (Pacific Fisheries Management 

 Council). 2002. Status of the Pacific 

 Coast groundfish fishery through 2001 

 and acceptable biological catch for 

 2002, 26 p. PFMC, 7700 NE Ambas- 

 sador Place, Suite 200, Portland, Oregon 

 97220. 



- MacCall, A. D. 2002. Status of bocac- 

 cio off California in 2002. In Appendix 

 to the status of the Pacific coast ground- 

 fish fishery through 2001 and acceptable 

 biological catches for 2002, 58 p. Pacific 

 Fisheries Management Council, 7700 NE 

 Ambassador Place, Suite 200, Portland, 

 Oregon 97220. 



3 VenTresca, D. A., J. L. Houk, M. J. Pad- 

 dack, M. L. Gingras, N. L. Crane, and S. 

 D. Short. 1996. Early life-history stud- 

 ies of nearshore rockfishes and lingcod 

 off central California, 1987-92. Cal. 

 Fish Game. Resources Division. Admin. 

 Rep. 96-4, 77 p. 



