FISHERY BULLETIN: VOL. 77, NO. 2 



become available, we expect to find increased var- 

 iation in growth rate. 



Correlations between the spatial-temperature 

 pattern of variation in growth rate and environ- 

 mental parameters may provide clues to the 

 events which control larval survival. This analy- 

 sis will require that the measured growth rates 

 reflect the larvae's response to the environmental 

 factors measured at the time the sample was col- 

 lected. We estimated the growth rate of larvae in a 

 sample by determining the relationship between 

 size (L) and age [T). This technique is susceptible 

 to several biases discussed above and is not sensi- 

 tive to changes in growth conditions occurring a 

 few days before the sample is taken. If the instan- 

 taneous growth rate of each individual could be 

 measured, then the same growth rate parameters 

 could be estimated from the relationship between 

 ilLldT and L. This alternative method would 

 reflect growth conditions at the time of sampling 

 and would be independent of changes in growth 

 conditions during the lifetime of the older larvae 

 in the sample. Ottaway and Simkiss (1977) de- 

 veloped a relative measure of the instantaneous 

 growth rate of adult fish using the in vitro rate of 

 incorporation of '•'C labelled glycine into scales, 

 but this technique may not be adaptable to larval 

 fish. Another approach is to correlate the width of 

 a daily growth increment with the growth of the 

 fish on that day. A measurement of the width of 

 the outer increments could provide an absolute 

 measure of growth rate during the few days before 

 capture. 



In addition, the radius of each increment in an 

 individual's otoliths could be used to back calcu- 

 late its growth history (Ricker 1969). The differ- 

 ence between the back calculated growth histories 

 of older individuals, the survivors captured with 

 nonselective gear, and the distribution of size at 

 age of all younger individuals supplies informa- 

 tion on differential mortality and size dependent 

 net avoidance by the larvae. Ultimately, analysis 

 of daily growth increments in the otoliths of larval 

 fish may provide a means of determining whether 

 larval survival is limited primarily by predation 

 or food and how these two factors interact. 



ACKNOWLEDGMENTS 



David Kramer passed away in December 1977 

 during the early stages of this paper's preparation. 

 The personnel at the Southwest Fisheries Center 

 are indebted to him for his contributions to the 



CalCOFI program, in particular for his early work 

 on the taxonomy and rearing of larval fish and for 

 his devotion to this project on the aging of larval 

 fish. We will miss him. He was a friend and a 

 model to many of us. 



I want to thank Ken Plummer for his assistance 

 in the preparation of many of the otoliths used in 

 this study. Special thanks are due John Hunter for 

 his helpful comments on early versions of this 

 manuscript. 



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