Lytton et al.: Age validation of Polyprion americanus based on bomb radiocarbon 0 4 C) 
85 
Age estimate (yr) 
Figure 6 
Comparison of growth curves from the fitted von Bertalanffy 
growth models for wreckfish (Polyprion americanus) from 
Peres and Haimovici (2004, dashed-and-dotted line), Vaughan 
for specimens caught in 1988-1992 (dashed line), Vaughan 
et al. (2001) for the specimens caught in 1995-1998 (dotted 
line), and the study described in this paper (solid line) 
At face value, such a phase shift indicates a system- 
atic underaging of wreckfish by 5-6 years, but Filer 
and Sedberry (2008) observed a similar phase shift in 
an age validation study performed on barrelfish (Hy- 
peroglyphe perciformis ) captured from the Charles- 
ton Bump. The authors hypothesized that the phase 
shift observed in barrelfish resulted from differences 
in oceanographic conditions experienced by barrelfish, 
compared with those experienced by haddock in the 
standard chronology for that species, variances 
caused by localized upwelling events or regional 
differences in onset of increases in 14 C in surface 
waters. Because the only known spawning loca- 
tion for adult wreckfish in the North Atlantic is 
the Charleston Bump, juvenile wreckfish may 
also have been exposed to lower levels of radio- 
carbon in a given year compared with the lev- 
els to which known-age haddock captured off the 
eastern coast of Canada were exposed. 
Researchers also have also documented a sim- 
ilar phase shift in bomb radiocarbon levels in 
the Pacific Ocean. A radiocarbon validation study 
performed on canary rockfish ( Sebastes pinniger ) 
revealed that differences in oceanographic condi- 
tions caused by upwelling caused a phase shift 
of 5-6 years between the radiocarbon chronolo- 
gies of canary rockfish and that of a reference 
chronology developed from Pacific halibut (Hip- 
poglossus stenolepis ) (Piner et al., 2004). 
Two additional sources of aging error that 
could explain the observed phase shift and ap- 
parent underaging in aging studies are 1) the 
misidentification of the first annulus and 2) the 
annulus overlay at older ages due to otolith sec- 
tion thickness. Misidentification of the first an- 
nulus could be directly related to our reliance 
on the aging protocol developed for the popula- 
tion of wreckfish in the South Atlantic by Peres 
and Haimovici (2004). On the basis of the dai- 
ly increment counts in their study, Peres and 
Haimovici proposed that there were 1-3 false 
rings before the first annual increment. Inclusion of 
the false rings as annuli in our age estimates would 
have potentially shifted the curve to a later date, 
leading to a better phase agreement with the stan- 
dard curve. Interestingly, such systematic underaging 
of wreckfish due to incorrect first annuli identifica- 
tion would shift the resulting growth curve along the 
x-axis and would provide a more realistic estimate 
of the t o parameter. Researchers have not performed 
Table 2 
Parameters from the von Bertalannfy growth model (VBGM), with associated standard errors (SE), from our study in which 
the converted total lengths (TLs) [see Methods and methods section] and from 2 previous studies on wreckfish ( Polyprion 
americanus) in Atlantic ocean waters. An asterisk (*) indicates that Vaughan et al. 2001 experienced problems with con- 
vergence when trying to freely estimate VBGM parameters with data collected in 1988-1992. To alleviate this issue, they 
fixed L„ to 1638 mm TL, constraining the values that the other VBGM parameters can take because of correlation among 
parameters. 
Source 
Population 
Period 
Sex 
n 
L 0 „ 
SE 
k 
SE 
to 
SE 
^max 
Our Study 
North 
2000-2011 
Combined 
554 
1071 
6.80 
0.124 
0.007 
-4.96 
0.553 
80 
Vaughan et al., 2001 
North 
1988-1992 
Combined 
738 
1638* 
0.028 
0.001 
-16.56 
0.590 
39 
1995-1998 
Combined 
117 
1638 
121.92 
0.032 
0.006 
-12.48 
1.760 
30 
Peres and Haimovici, 2004 
South 
1986-1997 
Combined 
337 
1210 
0.063 
-6.30 
76 
