Laldig et al Relationship between abundance of luvenile Sebastes spp, and environmental variables 



47 



years of lowest abundance for juvenile rockfishes oc- 

 curred during El Nino events. 



The primary factors that lead to annual fluctuations 

 in abundance were similar for blue, yellowtail, and 

 black rockfish. These three species are found in similar 

 areas at the planktonic stage (Lenarz et al., 1991; Lar- 

 son et al., 1994). Therefore, it is expected that changes 

 in ocean conditions affect all three species similarly. 

 Nearshore temperature and sea level anomaly had high 

 negative correlations with abundance for all three spe- 

 cies, whereas offshore Ekman transport was not corre- 

 lated with abudance. This finding implies that poor re- 

 cruitment occurs during years of high temperature and 

 strong, positive sea level anomaly (poleward flow), and 

 vice versa. Our results indicate that recruitment is poor 

 during periods of strong, positive sea -level anomaly and 

 that recruitment is strong only during years of negative 

 sea level anomaly (equatorward flow). However, poor 

 recruitment also occurs in some years with negative 

 sea level anomaly. Therefore, other factors are prob- 

 ably involved in the process and can affect year-class 

 strength in rockfishes. Some of the other factors that 

 have been suggested to have at least some influence on 

 rockfish recruitment include adult spawning biomass 

 (Mason, 1998), increased predation by siphonophores 

 and chaetognaths on larval stages during years of high 

 sea temperature (Yoklavich et al., 1996), turbulence 

 (Ainley et al., 1993), and diet of juvenile rockfishes 

 (Reilly et al., 1992). 



Large-scale multiyear oceanographic events (e.g.. Pa- 

 cific Decadal Oscillation and the El Nino-Southern Os- 

 cillation indices) also appear to affect juvenile rockfish 

 abundance. Large changes in indices reflect regime 

 shifts in ocean conditions, such as those occurring in 

 1977, 1989. and 1998 (Hare and Mantua, 2000; Ben- 

 son and Trites, 2002). Although the mechanisms that 

 affect or cause changes in abundance are unclear, our 

 time series of juvenile rockfish abundance reflects these 

 large-scale shifts in ocean conditions by the generally 

 high recruitment prior to 1989, the much reduced re- 

 cruitment from 1989 to 1998, and the generally higher 

 recruitment after 1998. 



We have continued our juvenile rockfish surveys to 

 present, and have had the opportunity to determine 

 the usefulness of our abundance index as a predictor of 

 rockfish year-class strength. In 2005, average monthly 

 temperature was elevated from January to June (as 

 much as two degrees above average as measured by our 

 temperature monitors). Interestingly, the abundance 

 index of all three species of juvenile rockfishes from 

 our surveys in 2005 was very low. Black and yellowtail 

 rockfish abundances, in particular, were at the third 

 lowest level estimated during what is now a 23-year 

 time-series of recruitment. Therefore, our results dem- 

 onstrate our ability to predict annual levels of abun- 

 dance for these species of juvenile rockfishes. 



Juvenile yellowtail rockfish abundance in our study 

 reflected adult yellowtail rockfish abundance in the 

 fishery. Mearns et al. (1980) also reported a relation- 

 ship between juvenile abundance and subsequent adult 



biomass for stripetail and calico rockfishes by following 

 yearly cohorts from seasonal trawls in southern Califor- 

 nia over nine years. The high recruitment for bocaccio 

 in 1985 was manifested in the recreational fishery in 

 Monterey Bay, CA in subsequent years (Mason, 1998). 

 Similar trends were observed with large year-classes of 

 chilipepper, S. goodei, and yellowtail rockfish (Mason, 

 1998). Ralston and lanelli (1998) also found that the 

 abundance of juvenile bocaccio was an indicator of year- 

 class strength in the fishery. Accordingly, the study of 

 juvenile rockfish abundance can help predict good and 

 bad year classes entering a fishery. These data can then 

 be incorporated into fisheries models (see stock assess- 

 ments for widow rockfish, S. entomelas, [He et al.*"]) to 

 better manage the stocks. 



Acknowledgments 



We first thank Edmund (Ted) Hobson for his initial 

 conception of this project and his many years of data 

 collection and direction. We also thank all the divers 

 who helped with juvenile rockfish surveys, especially 

 Kelly Silberberg for his many years of dedication to this 

 project. We thank Peter Adams, Steve Ralston, Susan 

 Sogard, Ralph Larson, Mary Yoklavich, and four anony- 

 mous reviewers for helpful comments on drafts of this 

 manuscript. Lastly, we thank Craig Syms and Brian 

 Wells for their generous help with statistical matters. 



Literature cited 



Ainley, D. G., W. J. Sydeman, R. J. Parrish, and W. H. Lenarz. 

 1993. Oceanic factors influencing distribution of young 

 rockfish (Sebastes) in central California: A predator's 

 perspective. Calif. Coop. Oceanic Fish. Invest. Rep. 

 34:133-139. 



Ammann, A. 



2001. Evaluation of a standard monitoring unit for the 

 recruitment offish in central California. M.Sci. thesis, 

 92 p. Univ. California, Santa Cruz, CA. 



Anderson, T. W. 



1983. Identification and development of nearshore juve- 

 nile rockfishes (genus Sebastes) in central California 

 kelp forests. M.Sci. thesis, 216 p. California State 

 Univ., Fresno, CA. 



Benson, A. J., and A. W. Trites. 



2002. Ecological effects of regime shifts in the Bering 

 Sea and eastern North Pacific Ocean. Fish and Fish- 

 eries 3:95-113. 



Boehlert, G. W., and M. M. Yoklavich. 



1983. Effects of temperature, ration, and fish size on 

 growth of juvenile black rockfish, Sebastes melanops. En- 

 viron. Biol. Fish. 8:17-28. 



6 He, X., D. E. Pearson, E. J. Dick, J. C. Field, S. Ralston, 

 and A. D. MacCall. 2005. Status of the widow rockfish 

 resource in 2005, 119 p. Pacific Fisheries Management 

 Council, 7700 NE Ambassador Place, Suite 200, Portland, 

 Oregon 97220. 



