Miller et al.: Relation between otolith size and larval size at hatching for Gadus morhua 



299 



Figure 3 



Scatter plots of individual measures of otolith diameter (mm) at hatching for newly 

 hatched cod larvae collected on the Scotian Shelf Correlation coefficients (r) and sig- 

 nificance for each relationship are given in each panel. 



cise to detect anything other than substantial differ- 

 ences in hatching size among the survivors and the 

 initial cohort. 



Meekan and Fortier ( 1996) reported evidence that 

 surviving cod larvae on the Scotian Shelf in 1992-93 

 were significantly different from the cohort from 

 which they originated. In contrast, survivors did not 

 differ from the cohort at large in 1991-92. Meekan 

 and Fortier (1996) suggested that the change in ra- 

 dius at hatching that they observed in 1992-93 was 

 evidence of selection for faster growing larvae in that 

 cohort. Meekan and Fortier's suggestion, as it relates 

 to the relative sizes of otoliths in the survivors and 

 the initial cohort, is indisputable. Our findings that 

 the size of a larva and its otoliths are weakly corre- 

 lated do not allow us to reject the notion that survi- 

 vors may have differed in size at hatching from the 

 overall cohort. Our results suggest an additional ex- 

 planation. We report here a significant relationship 

 between otolith size and the residual from the pre- 



dicted relationship between egg and larval sizes. 

 Larvae that hatch from relatively larger eggs, which 

 have relatively larger yolks, have larger otoliths. 

 Hence, we agree with the Meekan and Fortier's 

 ( 1996) suggestion, but we would further hypothesize 

 that the difference observed may have been caused 

 by variation in egg size rather than by variation in 

 larval size at hatching directly. If correct, we suggest 

 that the greater amount of yolk in larger eggs enhanced 

 initial larval growth and survival. An understanding 

 of the actual mechanism responsible for these faster 

 growing larvae will require additional analyses. 



Our results suggest that attempts to backcalculate 

 size of cod larvae will be most successful if they are 

 based on measurements from the lapillus. Although 

 larval SL at hatching was significantly related to all 

 measures of otolith size, relationships involving the 

 lapillus explained more variation than correspond- 

 ing relationships involving the sagitta. Moreover, 

 regressions involving the projected area of the lapil- 



