Kastelle et at: Age validation of Microstomus pacificus by means of bomb radiocarbon 
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Figure 1 
Category-1 otolith (specimen number 82) from Dover sole ( Microstomus pacificus) treated by the break-and- 
burn method. The series of dots indicate the translucent zones that were counted to estimate a final age 
of 32 years. The “T” arrow points to the transition region from fast early growth to slower later growth. 
The sulcus region of the otolith is indicated as a reference point. 
1 Category-1 otoliths had clear growth zones that were 
easy to interpret, in that most of the translucent 
zones appeared with minimal or no splitting in the 
proximal growth axes in at least one region (dorsal 
or ventral) on the break-and-burn cross section (Fig. 
1). Splitting is defined as the branching of a single 
translucent zone into two or more translucent zones. 
Typically the translucent zones were spaced evenly, 
but with decreasing intervals, as the fish became 
older. Some samples in this category may have pre- 
sented interpretative options, and different reading 
axes in the cross section could be chosen, but typi- 
cally only small differences in age (of 1 or 2 years) 
would result. 
2 Category-2 otoliths had growth zones that were dif- 
ficult to interpret and that made these fish difficult 
to age. Many translucent zones had obvious splits 
and uneven spacing (Fig. 2). Widely different ages 
could be generated depending upon the interpretation 
chosen and which reading axis was used. 
A sample selection process for 14 C measurement 
occurred after re-examination of the ages, and this 
selection process relied on two factors. First, in category 
1 our intention was that the initial age and final age 
should agree within 3 years. For otoliths in category 2, 
which are more common for Dover sole than are category- 
1 otoliths, we did not use age agreement as a selection 
factor. Second, the estimated birth years, which were 
based on the final ages, had to be evenly distributed 
from about 1951 to 1977, to bracket the era of marine 
14 C increase. For several specimens in category 1, the 
first factor was relaxed to evenly populate the years of 
marine 14 C increase. This process provided 43 speci- 
mens for Z\ 14 C analysis: 38 otoliths in category 1 and 5 
in category 2 (Table 1). The range in catch years from 
1984 to 2005 generated a large range in Dover sole 
ages for potential validation. In the remainder of this 
article, unless specified differently, the ages referred to 
are these final ages. 
For the selected Dover sole specimens, the otolith 
core was extracted from the remaining whole eyed-side 
otolith for 14 C analysis. The core represented material 
deposited only in the first three years of life. Previous 
studies have often used a 1-year core (e.g., Campana, 
1997), but that was not possible with Dover sole because 
their otoliths are very small, therefore, the minimum 
mass required for 14 C analysis mandated a 3-year core. 
For the otolith coring procedure we used a Buehler® 
EcoMet® (Buehler Ltd., Lake Bluff, IL) grinder with 
320 grit wet or dry sandpaper to first remove otolith 
material on the proximal surface (the main growth axis 
in older otoliths). On some otoliths a small amount of 
material was also removed on the distal surface. Next, 
the grinder was used to remove material on the perim- 
eter, in the anterior-posterior and dorsal-ventral axes, 
beyond the third year. After the exterior layers were 
removed with this procedure, the location of the third 
year’s growth zone in each otolith became easier to see, 
and its location served as a primary guide in the coring 
