Koob et al.: Age validation of the northern stock of Centropristis striata in the Atlantic Ocean 271 
age-1 fish and the first annulus measured on all samples 
used in MIA were similar, indicating that it was identified 
correctly in the MIA. 
The age-0 and age-1 samples in this study were con- 
firmed to be YOY by comparing their modal length fre- 
quencies to the length frequencies of the smallest black 
sea bass caught in the fall during the resource assess- 
ment survey and in the summer during the ventless trap 
survey (Fig. 8). The similarities between the length fre- 
quencies are clear, and the designation of the samples in 
this study as YOY was appropriate. It should be noted 
that the samples measured for first annulus validation 
in this study were all from waters of Massachusetts. The 
similarity in first annulus measurement between these 
samples and all the samples used in MIA, as well as 
the previously mentioned similarity in mean first annulus 
measurements between regions, north and south of the 
Hudson Canyon, indicates that the first annulus valida- 
tion completed in this study is applicable to the whole 
northern stock. 
Age-bin separation 
Results of this study confirm that separating samples 
into age bins was necessary for accurate age validation 
for this species. As a fish ages, somatic growth slows and 
otolith growth bands become closer together (Beamish 
and McFarlane, 1983). Otolith growth in a fish’s first 
year is expected to be greater than growth in its second 
year, which will be greater than growth in its third year, 
and so on until, at a certain size or age, growth becomes 
more consistent. Differences in mean MIR between age 
bins throughout the year indicate that otolith deposition 
varies with age. For example, otoliths from fish in AB1 
had a lower mean MIR than those from the other 2 age 
bins throughout most of the year. Additionally, the peak 
MIR for this age bin was less than 0.5. Marginal incre- 
ment ratios that approach 1.0 would indicate that the 
completed edge growth on an otolith equals the growth 
of the penultimate annulus. The low peak MIR for AB1 
signifies that there was rapid growth in the penultimate 
annulus followed by a decline in growth in the following 
year, as expected for this age group. 
Conversely, AB3 had the highest MIRs throughout the 
year and came closer to approaching 1.0 at the time of annu- 
lus completion (mean MIR: 0.76, in May—June). Otoliths in 
this age bin have a higher proportion of edge growth com- 
pared with that of the penultimate annulus because growth 
has slowed, and annuli measurements were more consis- 
tent. This pattern is supported by the observed somatic 
growth of black sea bass with age, where the rapid growth 
experienced by younger fish slows considerably by ages 5-6 
(NEFSC, 2017; McMahan et al., 2020). As expected, MIRs 
for AB2 fall between the values for AB1 and AB3 through- 
out most of the year. The effect of the interaction between 
Age Bin and Month Bin in the first model did not affect 
annulus validation, but it does further indicate the varied 
growth patterns throughout the year for otoliths from black 
sea bass in these age bins. 
Regional differences within the northern stock 
The documented variability of otolith growth for black 
sea bass by location (Dery and Mayo, 1988), as well as the 
recent separation of the northern stock into 2 subunits, 
motivated an analysis of possible differences in otolith 
growth between the regions north and south of the Hudson 
Canyon. The interaction between Age Bin and Season 
corroborated findings from the model with the predictor 
Month Bin discussed previously. No interaction between 
Age Bin and Region indicates that there was no regional 
difference in otolith edge growth within each age bin. The 
interaction between Season and Region, however, indicates 
that there was variability in otolith edge growth between 
regions throughout the year. 
Higher MIRs were observed for otoliths from fish 
caught in the region south of the Hudson Canyon in the 
winter, spring, and fall, but there was no difference in 
MIRs between regions in summer. The similarity of MIRs 
in summer is not surprising because the absolute amount 
of growth following annulus deposition is small (Mercer 
1978; Robillard et al.”). Differences throughout the rest 
of the year indicate that fish from south of the Hudson 
Canyon completed a higher proportion of the previous 
year’s growth at these times than fish from the north, 
indicating that overall annual otolith growth may be 
lower for fish from the region south of the Hudson Canyon. 
Additionally, fish from the south had an 81% increase in 
edge growth from summer to fall, compared with a 23% 
increase achieved by fish from the north in the same 
period. Instead, fish from north of the Hudson Canyon had 
a 60% increase in growth from fall to winter; whereas, the 
increase in growth for the region south was 14%. 
These findings are in line with those of previous research, 
but additional work is needed. In several studies, black sea 
bass were larger and had faster growth rates throughout 
the year at higher latitudes (Alexander, 1981; Dery and 
Mayo, 1988; Kolek*; Caruso, 1995; McMahan et al., 2020). 
McMahan et al. (2020) postulated that black sea bass from 
northern regions (e.g., north of Cape Cod) may either have 
adapted to grow in lower temperatures or have countergra- 
dient variation, with more growth achieved in the shorter 
growing season (i.e., winter). The differences in migration 
patterns between the 2 populations (i.e., east-west for fish 
south of the Hudson Canyon and north-south for fish in 
the north region) likely result in exposure to different tem- 
peratures throughout the year. This temperature variabil- 
ity could explain the differences in otolith growth between 
the 2 groups of fish in this study; however, a closer look at 
growth is needed to address this topic and should be consid- 
ered for future research. 
Although there were differences in otolith deposition 
between fish from the 2 regions, the otolith aging method 
4 Kolek, D. 1990. Homing of black sea bass, Centropristis striata, 
in Nantucket Sound, with comments on seasonal distribution, 
growth rates, and fisheries of the species. MADMF Black Sea 
Bass Investig. Intern. Rep., 9 p. [Available from Mass. Div. Mar. 
Fish., 251 Causeway St., Boston, MA 02114.] 
