375 
Abstract — -We used bomb radiocarbon 
( 14 C) in this age validation study of 
Dover sole ( Microstomus pacificus). 
The otoliths of Dover sole, a com- 
mercially important fish in the North 
Pacific, are difficult to age and ages 
derived from the current break-and- 
burn method were not previously 
validated. The otoliths used in this 
study were chosen on the basis of esti- 
mated birth year and for the ease of 
interpreting growth zone patterns. 
Otolith cores, material representing 
years 0 through 3, were isolated and 
analyzed for 14 C. Additionally, a small 
number of otoliths with difficult-to- 
interpret growth patterns were ana- 
lyzed for 14 C to help determine age 
interpretation. The measured Dover 
sole 14 C values in easier-to-inter- 
pret otoliths were compared with a 
14 C reference chronology for Pacific 
halibut (. Hippoglossus stenolepis) in 
the North Pacific. We used an objec- 
tive statistical analysis where sums 
of squared residuals between otolith 
14 C values of Dover sole and the refer- 
ence chronology were examined. Our 
statistical analysis also included a 
procedure where the Dover sole 14 C 
values were standardized to the ref- 
erence chronology. These procedures 
allowed an evaluation of aging error. 
The 14 C results indicated that the 
Dover sole age estimates from the 
easier-to-interpret otoliths with the 
break-and-burn method are accurate. 
This study validated Dover sole ages 
from 8 to 47 years. 
Manuscript submitted 24 March 2008. 
Manuscript accepted 13 June 2008. 
Fish. Bull. 108:375-385 (2008). 
The views and opinions expressed 
or implied in this article are those of 
the author and do not necessarily reflect 
the position of the National Marine 
Fisheries Service, NOAA. 
Age validation of Dover sole 
( Microstomus pacificus ) 
by means of bomb radiocarbon 
Craig R. Kastelie (contact author) 
Defsa M. Ancierl 
Daniel K. Kimura 
Chris G. Johnston 
Email address for C. R. Kastelie: Craig.Kastelle@noaa.gov 
National Oceanic and Atmospheric Administration 
National Marine Fisheries Service 
Alaska Fisheries Science Center 
7600 Sand Point Way NE. 
Seattle, Washington 98115-6349 
The otoliths of Dover sole ( Micros- 
tomus pacificus), a commercially 
important fish in the North Pacific, 
are difficult to interpret. Ages derived 
with the current otolith break-and- 
burn method have not been previously 
validated. The age data are important 
for population modeling and setting 
the total allowable catch (Stockhau- 
sen et ah, 2005). The necessity of age 
validation studies is widely recog- 
nized (Beamish and McFarlane, 1983; 
Campana, 2001) and age validation 
has become the focus in an expand- 
ing number of studies at the Alaska 
Fisheries Science Center (AFSC) (e.g., 
Kastelie and Kimura, 2006; Kimura 
et al., 2006; Hutchinson et ah, 2007; 
Kastelie et al., 2008). 
Two methods of Dover sole otolith 
preparation are used by various agen- 
cies. At the AFSC; the Groundfish 
Program of the Pacific Biological Sta- 
tion, Nanaimo, B.C.; and the North- 
west Fisheries Science Center, Dover 
sole are aged by the break-and-burn 
method (Chilton and Beamish, 1982) 
and are estimated to have a maxi- 
mum age of 54 years. An alternative 
aging method employed at the South- 
west Fisheries Science Center uses 
transverse thin sections of otoliths 
(Hunter et ah, 1990). The maximum 
age estimated with thin sections is 
58 years (Hunter et ah, 1990). The 
two methods appear to produce simi- 
lar results but any similarity has not 
been tested quantitatively, and nei- 
ther method has been validated. 
Workshops on the interlaboratory 
calibration of methods and on otolith 
interpretation for determining the age 
of Dover sole have been held periodi- 
cally among agencies responsible for 
the management of this species. How- 
ever, age validation has not been a 
focus of these workshops. Because the 
otoliths of this fish species are small 
and the species has a relatively long 
life expectancy, the precision of mul- 
tiple readings on a sample of otoliths 
can be poor. The precision measured 
by percentage coefficient of variation 
(CV) between two age readers is re- 
ported to be 9.64% which is higher 
than that for most species aged at the 
AFSC (Kimura and Anderl, 2005). 
For many North Pacific Pleuronecti- 
formes the CV is under 4% (Kimura 
and Anderl, 2005). The poor precision 
(high CV) is an indication of the dif- 
ficulty in reading otoliths from Dover 
sole, and indicates that validating the 
accuracy of the ages is necessary. 
The goal of this study was to use 
bomb-produced radiocarbon ( 14 C) to 
validate the ages of Gulf of Alaska 
(GOA) Dover sole determined by 
the otolith break-and-burn method. 
Otoliths were selected on the basis 
of estimated birth year and two de- 
scriptive categories: 1) otoliths with 
uniform growth zones that were easy 
to enumerate, and 2) otoliths with 
growth zones that were difficult to 
enumerate. The first category was 
used to validate general aging crite- 
ria and the second was used to help 
