34 



Fishery Bulletin 98(1) 



B 



Element wt % 



40 



^'^^- 



i — i- 



=5 Calcium 



-Cal 

 -Sr% 



k lirtl ^-^ I — ^ 



-i Strontium 



\_y Distance from leading edge of Sr band (microns) 



Figure 6 



Details of the strontium mark on polished LS of specimen OB 96. Backscattered 

 SEM images showing overall location of mark (A) and detail of region analyzed for Sr 

 and Ca levels (B). Dashed line indicates transect followed for x-ray microanalysis (C): 

 Measured variation in Sr and Ca levels along transect shown in B; points A-D indicate 

 representative positions along the transect to enable comparison of sections B and C. 



the backscattered imaging which band, if any, is a 

 strontium mark. 



Reliabilrty of marking through injection of strontium 



Of the 67 otoliths from which an age was estimated, 

 strontiimi marks were detected with the Robinson detector 



in 19 of the 20 sectioned otoliths (95% detection rate) and 

 with EDS in 40 out of 47 whole otoliths (85% detection 

 rate). Strontium marks were as visible in the obhque 

 longitudinal section (postrostral axis) as in the transverse 

 section (Fig. 3). However, as increments are more widely 

 spaced along the postrostral axis, we generally used the 

 postrostral axis on the whole otolith for measuring the 



