532 



Fishery Bulletin 89(3). 1991 



this effect. In this sense, the histograms presented in 

 Figure 9 represent the birthdate distributions of the 

 fish that survived to the time of sampling. 



The distributions are also influenced by other factors. 

 For example, there are differences among the species 

 in duration of the pelagic phase. This is especially true 

 for widow and yellowtail rockfish, which tend to settle 

 at a relatively young age. Results may also be biased 

 if parturition occurs unusually late in the year. In this 

 case the larvae/juveniles might not be large enough to 

 be captured by the gear we used. However, our sam- 

 pling occurred annually at similar times, and marked 

 differences in the distributions were still noted. The 

 early birthdate distributions characterizing bocaccio, 

 chilipepper, and shortbelly rockfish in 1988 were due 

 to the prevalence of relatively old fish, whereas fish 

 sampled in 1986 were relatively young. Although these 

 shifts may be influenced by settlement and gear selec- 

 tivity, they nonetheless provide a conservative repre- 

 sentation of interannual differences. 



Two possible hypotheses accounting for interannual 

 variation in the means of back-calculated birthdate 

 distributions are (1) annual variation in the seasonal 

 timing of parturition, and (2) year-specific seasonal 

 variation in the expression of mortality rates within fix- 

 ed parturition seasons. Although at present we have 

 no basis to distinguish between these two alternatives, 

 this topic is currently under detailed investigation. 



Oceanographic conditions 



It is well known that temperature has a major influence 

 on larval growth at sea. There is evidence that sea- 

 surface temperature (SST) affects the growth perfor- 

 mance of pelagic juvenile rockfish off central Califor- 

 nia Oat. 36-39°). In this area mean January SST from 

 1983-87 (Cole and McLain 1989) was positively asso- 

 ciated with growth performance. For example, in 1984 

 shortbelly rockfish were estimated to be 37.7 mm SL 

 at a standard age of 70 days. This represented this 

 species' best growth during the 1983-88 period, and 

 in this year mean January SST was a very warm 

 13.12°C. In contrast, in 1985, when mean January SST 

 was at its lowest value in the time series (12.05°C), 

 estimated length at age was lowest also (31.3 mm SL). 

 Similar to growth, there is evidence that sea-surface 

 temperature has a strong influence on interannual 

 shifting of back-calculated birthdate distributions. Cold 

 years were associated with early successful parturition. 

 Our results show that for shortbelly rockfish the an- 

 nual mean of the birthdate distribution was at its 

 minimum in 1985 (8 February) when mean January 

 SST was only 12.05°C. By comparison, in 1983 (an El 

 Nino year) the birthdate mean was at its maximum 

 value (21 April) in association with warm January SST 



(13.16°C). These findings are intriguing and form the 

 basis of ongoing investigations into the establishment 

 of year-class strength in Sebastes spp. 



Acknowledgments 



We would like to thank Richard Methot, John Butler, 

 and Susan Longinotti of the SWFC La Jolla Labora- 

 tory for their assistance in automating data collection 

 and for sharing their expertise in preparing otolith 

 samples. Don Pearson wrote the two computer pro- 

 grams to accept and summarize the daily increment 

 data, and Tom Laidig completed much of the technical 

 work presented in this paper. We would also like to 

 thank Jim Bence, Tom Laidig, Bill Lenarz, George 

 Boehlert, and Richard Methot for reviewing early 

 drafts of this paper. 



Citations 



Bailey, K.M., and E.D. Houde 



1989 Predation on eggs and larvae of marine fishes and the 

 recruitment problem. Adv. Mar. Biol. 25:1-82. 

 Boehlert, G.W. 



1981 The effects of photoperiod and temperature on laboratory 

 growth of juvenile Sebastes diploproa and a comparison with 

 growth in the field. Fish. Bull., U.S. 79:789-794. 

 Bolz, G.R., and R.G. Lough 



1983 Growth of larval Atlantic cod, Gadus morhua, and had- 

 dock, Melanogrammus aeglefinus, on Georges Bank, spring 

 1981. Fish. Bull., U.S. 81:827-836. 

 Brett, J.R. 



1979 Environmental factors and growth. In Hoar, W.S., D.J. 

 Randall, and J.R. Brett (eds.), Fish physiology, Vol. VIII: 

 Bioenergetics and growth, p. 599-675. Academic Press, NY. 

 Brothers, E.B., C.P. Mathews, and R. Lasker 



1976 Daily growth increments in otoliths from larval and adult 

 fishes. Fish. Bull., U.S. 74:1-8. 

 Brothers, E.B., E.D. Prince, and D.W. Lee 



1983 Age and growth of young-of-the-year bluefin tuna, Thun- 

 nus thynnus, from otolith microstructure. In Prince, E.D., 

 and L.M. Pulos (eds.), Proceedings, International workshop 

 on age determination of oceanic pelagic fishes: Tunas, bill- 

 fishes, and sharks, p. 49-59. NOAA Tech. Rep. NMFS 8. 

 Campana, S.E., J.A. Gagne, and J. Munro 



1987 Otolith microstructure of larval herring (Clupea haren- 

 gus): Image or reality. Can. J. Fish. Aquat. Sci. 44: 

 1922-1929. 

 Cole, D.A., and D.R. McLain 



1989 Interannual variability of temperature in the upper layer 

 of the North Pacific eastern boundary region, 1971-1987. 

 Tech. Memo. NOAA-TM-NMFS-SWFC-125, Southwest Fish. 

 Sci. Cent., La Jolla, 10 p. 

 Deriso, R.B., T.J. Quinn II, and P.R. Neal 



1985 Catch-age analysis with auxiliary information. Can. J. 

 Fish. Aquat. Sci. 42:815-824. 

 Green, P.E. 



1978 Analyzing multivariate data. Dryden Press, Hinsdale, 

 IL, 519 p. 



