Toole et al.: Otolith microstructure, microchemistry. and early life history of Microstomus paaficus 



743 



B 



Figure 10 



Frontal sections of left and right Dover sole, Microstomus paaficus, otoliths 

 showing differences in orientation of the clear central growth area; ante- 

 rior to right, lateral surface to top. (A) Left otolith from 58.0-mm Stage-3 

 larva collected on 16 March 1990. Central area tilts towards the lateral 

 surface posteriorly and towards the medial surface anteriorly. (Bl Right 

 otolith from 64.9-mm Stage-3 larva collected on 17 March 1990. Central 

 area is oriented in the same direction as surrounding peripheral growth. 



Stage-5 juveniles; and the third, of only 

 Stage-5 juveniles. 



Microchemical patterns 



Ratios of Sr/Ca exhibited similar patterns 

 along transects through the otoliths of all lar- 

 vae and juveniles examined (Figs. 20, A-B, 

 page 747, and 21, page 748). An initial Sr/Ca 

 spike (0.007-0.010) occurred approximately 

 48 urn from the central primordium, inside the 

 clear central area. Following the spike, Sr/Ca 

 levels within the clear central area fluctuated 

 at intermediate levels (0.004-0.006). Sr/Ca 

 ratios began a second, more gradual, decline 

 beginning near the clear-to-opaque transition 

 in the central area of the otolith, which also 

 corresponded to the area in which the ante- 

 rior AP was forming. This decline began in 

 late summer or fall of the calendar year prior 

 to settlement. 



Sr/Ca ratios often reached minimum levels 

 following formation of accessory primordia. In 

 a 65.7-mm Stage-4 larval otolith (Fig. 20A), 

 Sr/Ca ratios reached a minimum (0.002) at 

 about the end of January. This minimum point 

 was approximately 10 days beyond enclosure 

 of growth from the central primordium and 31 

 days beyond the most recently formed acces- 

 sory primordium. In a second Stage-4 larva, a 

 minimum (0.003) was first reached in mid-De- 



ver sole collected in January and 

 March, otolith weight in Stage-5 

 juveniles was nearly double that 

 of Stage-4 larvae (Fig. 18, page 

 746). A discontinuity in the rela- 

 tionship between Stage 3-5 right 

 otolith length and fish length dur- 

 ing the first winter following 

 settlement was also apparent (Fig. 

 19, page 746). This relationship 

 was best described by a three- 

 stanza segmented linear model 

 (Bacon and Watts, 1971; Laidig et 

 al., 1991). Parameter estimates in 

 Table 5 (page 746) resulted in a 

 good fit (r-=0.955) and no 

 discernable pattern in residuals. 

 The first segment consisted of 

 Stage-3 and Stage-4 larvae; the 

 second, of Stage-4 larvae and 



¥ 



Figure 1 1 



Posterior accessory primordium on right otolith of 58.0-mm Stage-3 Dover sole, 

 Microstomus paaficus, larva collected on 16 March. Narrow dark band in the opaque 

 central area is associated with origin of the accessory primordium. Magnification =400> 



