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Otoliths at the Alaska Fisheries Science Center are typically prepared and
processed using the break and burn method. This method begins by placing
the whole otolith in a petri dish that is lined with a black, felt
background and enough water to completely submerge it. The surface of the
otolith is viewed under a dissecting microscope at about 10x
magnification. The core is then identified and marked with a pencil.
The whole otolith is placed in clay, which has been mounted on a chuck of
the low speed saw, then cut in half. Using forceps, one of the otolith
halves is held over the flame of an alcohol burner until it becomes carmel
colored. This process allows the protein called otolin to react with the
heat, and display the annuli.
The burnt otolith half is placed in a dish of clay, and examined under
microscope on 40x magnification. Annuli are counted and an age estimate is
recorded for the sample currently being examined.
All ages are entered in a database and a randomly select sample of 20% is
selected and independently examined, or "tested", by a second age reader.
Using a statistical program, ages assigned by the first age reader are
compared with the ages assigned by the second age reader. We record the
percent agreement between the two readers and compare these figures with
other tests on record for the same species. All differences or
discrepancies are resolved between the readers, and then ages are released
for use in stock assessment.
Click here for an explanation of precision statistics. |
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