
TY  - JOUR
A1  - Fletcher, WJ 
A1  - Blight, SJ 
T1  - Validity of using translucent zones of otoliths to age the pilchard <I>Sardinops sagax neopilchardus</I> from Albany, Western Australia
JF  - Marine and Freshwater Research
JO  - Mar. Freshwater Res.
Y1  - 1996
VL  - 47
IS  - 4
SP  - 617
EP  - 624
KW  - ageing, annuli, validation, growth, otolith weight
UR  - https://doi.org/10.1071/MF9960617 
N2  - Otoliths (sagittae) of the pilchard (Sardinops sagax neopilchardus) from the Albany region of Western Australia were examined on a monthly basis during 1989 to 1991. When read consecutively, with the month of capture known, a clear annual cycle of an increase in marginal increments to October followed by a decline was recorded. This pattern was, however, severely distorted when samples were re-examined after having been jumbled and the month of capture concealed. Younger age groups (&#8804;3) showed evidence of multiple rings being formed annually, but not in all years or individuals, and this was not evident in older individuals (&#8805;4). Agreement between readings was low (43-53%), especially between different readers. Resultant growth curves showed that males grow to a smaller size (L&#8734; =164, K = 0.805, &#934; = 1.03) than females (L&#8734; = 174, K = 0.584, &#934;= 0.95). Agreement between counts of annuli and ages estimated by using otolith weight and length was only 54% for all individuals, but increased to 76% for individuals assigned the same age by different readers. Given the poorer predictions of future catch rates from the relative number of 2-year-olds in the commercial catch using annuli (implying lower accuracy) and increased complexity in preparation, otolith weights will be the method adopted for future ageing. 
ER  -

