Francis et al.; Age and growth estimates for Polypnon oxygeneios 



229 



165°E 170° 175° 

 — I 1 1 1 1 1 1 1 1 1 — 



180° 



35°S 



40' 



45° 



Three Kings Is 



n Otolith site 



 Tagging site 



Q Otolith and tagging sites 



Poor Knights Is 

 *a' iGreat Barrier Is 



Cook Strait 

 Kail<oura 



o ° 



35°S 



40° 



45° 



165°E 



170° 



175° 



180° 



Figure 2 



Hapuku otolith collection sites and tag-release sites. 



ings by reader 2) by using age-bias plots and plots of 

 the coefficient of variation (CV) against age, as rec- 

 ommended by Campana et al. ( 1995). These two plots 

 show the means (and their standard errors), and the 

 CVs, respectively, of the band counts made by reader 

 X for each "age" as determined by reader y. For ex- 

 ample, for all the hapuku that were judged by reader 

 y to have 10 bands, the mean, standard error, and 

 CV were calculated from the band counts made by 

 reader .v for the same fish, and plotted at age 10 on 

 the X-axis. Age estimates made by reader 2 on the 

 second reading (Rr,r,> were selected as a baseline 

 against which to compare other estimates because it 

 was anticipated that the experience gained during 

 the first reading would produce more reliable age 

 estimates during the second reading. 



Validation of the annual formation of otolith bands 

 was attempted by marginal increment analysis and 

 oxytetracycline injection. The marginal composition 

 of 76 otoliths from northern and central hapuku, aged 

 3-8 years, was graded as opaque, narrow hyaline, or 

 wide hyaline. The classification of hyaline zones as 

 narrow or wide was based on a comparison of the 

 marginal zone width with the width of the preceding 

 hyaline zone. A qualitative classification was used 

 because the presence of split opaque bands made it 

 difficult to measure the marginal increment. The 

 data were grouped into two-month intervals because 

 not all months were sampled and because sample 

 sizes were small. 



Thirty-nine hapuku were tagged (see "Tag-recap- 

 ture" section), injected intramuscularly with oxytet- 



