Pearson and Shaw: Age determination errors for Anoplopoma fimbria 



133 



ably determined in four otoliths (2A c /c) because the marks 

 were between a hyaline and opaque zone. Of the .36 otoliths 

 with the mark in an opaque zone, the mark occurred just 

 after a hyaline zone in four otoliths. In 24 of the 36 otoliths 

 with the mark in an opaque zone, the mark was on the 

 edge where it can be difficult to determine whether it is 

 opaque or hyaline. In no case did the reader indicate that 

 the mark was in a hyaline zone at the edge and thus the 

 edge appeared to be opaque in most cases. 



The OTC mark occurred on the otolith edge in 30 of the 

 otoliths recaptured prior to 1993 (up to 16 months after 

 injection). Examination of the monthly distribution of oto- 

 liths with marks on the edge ( Table 1 ) indicated that some 

 fish exhibited little or no otolith growth for substantial 

 lengths of time. 



Otoliths from fish recaptured in 1992 with marks on the 

 edge (i.e. showing little growth) were examined and classi- 

 fied by morphological type (Table 2). This examination indi- 

 cated that the thick type is more likely to have little growth 



because 32"* of the otoliths with marks on the edge were the 

 thick type, yet they made up only Y1 C A of the otoliths in the 

 study. Conversely, only 18% of the otoliths with the mark on 

 the edge were of the wide type; however, they made up 33^ 

 of the otoliths in the study. This trend was not statistically 

 significant, however, because the P-value was 0.106. 



Number of visible hyaline zones 



The number of prominent hyaline zones after the OTC 

 mark for fish recaptured in 1992 at three-month intervals 

 is shown in Table 3. This distribution shows the otoliths 

 that had no detectable growth but also shows that a hya- 

 line zone forms in many fish during the winter. It also 

 shows that in some fish, a summer hyaline zone is formed; 

 however, the sample size for October-December was small 

 and this is a period when a summer hyaline zone would be 

 expected to be fully visible. 



The number of visible and prominent hyaline zones after 

 the OTC mark for fish recaptured after 1992 (Table 4), com- 

 pared with the number of zones which should have been 

 counted, showed that if a reader had counted each of the 

 prominent hyaline zones as an annulus, the count would 

 have overestimated the age of the fish. An example of an 

 otolith with a larger number of prominent hyaline zones 

 than expected is shown in Figure 5. It should be noted that 

 a reader would not necessarily have counted each of the 



