738 



Fishery Bulletin 91(4), 1993 



T: 



I 

 O 



z 



UJ 



_J 



o 

 a. 

 < 



Q 



Z 

 < 



80 



120 



160 200 



JUUAN DATE 



240 



280 



Figure 4 



Relationship between standard length and calendar date of 

 Dover sole. Microstomas pacificus, held in an ambient flow- 

 through seawater tank, 21 March-30 September 1991 (Julian 

 dates 80-272). Smaller fish were not marked initially; dotted 

 lines indicate uncertainty regarding growth trajectories. 



however, the power of this test was also too weak 

 to conclude that increments were deposited daily 

 (1-13=0.05). 



Error in the preceding regressions was due, in part, 

 to poor resolution of laboratory-formed increments 

 (Fig. 3; Campana and Neilson, 1985) and may there- 

 fore be greater than the error associated with ageing 

 wild-captured fish. However, several resolution prob- 

 lems appeared common to otoliths of wild-captured and 

 laboratory-reared fish: difficulty interpreting incre- 

 ments at the otolith margin, difficulty resolving in- 

 crements around stress checks (Campana and Neilson, 

 1985) in certain regions of the otolith because of com- 

 pression (and sometimes fusion) of increments, and 

 occasional difficulty distinguishing daily and subdaily 

 increments. For these reasons, use of both slope and 

 intercept estimates was considered reasonable when 

 back-calculating days from increments in otoliths of 

 wild-captured fish. The same relationships were ap- 

 plied to increment counts outside the range of obser- 

 vations, which may introduce an unavoidable source 

 of additional error. 



P=0.899) or when the model with separate intercepts 

 and one slope was compared with a model containing 

 one slope and one intercept (P=1.14, df=5,22, P=0.369), 

 so all experimental groups were initially combined into 

 one regression. However, inspection of residuals from 

 that regression suggested that a greater error was as- 

 sociated with counts from Stage-5 juveniles than with 

 counts from Stage-3 and Stage-4 larvae, regardless of 

 experimental group. Mean ratios of observed:expected 

 counts for fish <80mm (0.924) than for fish >80mm 

 (0.718) U-test, df=26, P=0.012). Therefore, each size 

 group was treated separately in the final regression 

 models. 



The relationship for Dover sole <80 mm was 



Days since marking = 3.81 + 10.962 * observed increments), 



where n=21, r 2 = 0.85, SE INTERCEPT = 2.90, and SE SL0PE = 

 0.091 (Fig. 5A). The calculated slope was not signifi- 

 cantly different from 1.0 (/ =0.419, df=26, P=0.34); how- 

 ever, the power of this test (Peterman, 1990) was too 

 weak to conclude that increments were deposited daily 

 (1-13=0.06; Rice, 1987, Neter et al., 1989). 

 The relationship for Dover sole >80 mm was 



Days since marking = 6.32 + (1.026 * observed increments i 



where n=l, r 2 = 0.93, SE INTERCEPT = 2.81, and SE SL0PE = 

 0.122 (Fig. 5B). The calculated slope was not sig- 

 nificantly different from 1.0 (**=0.211, df=6, P=0.42); 



o 



UJ 



o 



z 



CO 

 CO 



> 

 < 



a 



10 20 



30 40 50 



10 20 30 40 50 



OBSERVED INCREMENTS 



Figure 5 



Relationship between days since OTC injection and number 

 of growth increments in Dover sole, Microstomus pacificus, 

 otoliths. Inner dashed lines are 95^ confidence limits for 

 mean response; outer dashed lines are 95% prediction limits. 

 (Ai Relationship for Stages 3 and 4 <80mm SL. Formula: 

 days since injection = 3.81 + (0.96 * observed increments); 

 n=21; r 2 =0.85. <Bi Relationship for Stage-5 Dover sole >80mm 

 SL. Formula: days since injection = 6.32 + (1.03 * observed 

 increments I; n=l: r'=0.93. 



