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Fishery Bulletin 111(3) 
Figure 2 
Image of the operculum of a 9-year-old male (142.9 mm shell length) channeled whelk 
( Busycotypus canaliculatus). Readers counted annuli to determine the age of whelk col- 
lected for our study in August 2010 and July 2011 in Buzzards Bay, Massachusetts. 
Dots are placed on each annulus for reference. The interior margin is at the top of 
this opercula, and the exterior margin is at the bottom. For the first annulus of each 
operculum examined in our study, there generally was a 6-mm linear distance from the 
interior to the exterior margin. 
cess, and shrinkage was not a concern because counting 
of annuli did not depend on accurate measurement of 
widths of annuli. 
Each operculum was read by 3 readers to estimate 
age (Kraeuter et al., 1989). Each reader recorded their 
confidence for each operculum, a technique similar to 
the one used by Herbst and Marsden (2011) to age oto- 
liths for Lake Whitefish ( Coregonus clupeaformis). Con- 
fidence levels for aging channeled whelk opercula were 
defined as 1) not confident — the initial year’s growth 
was at least partially missing and annuli were difficult 
to distinguish because of opaque or dark zones on the 
operculum; 2) somewhat confident — the initial year’s 
growth was partially missing but the shape was rea- 
sonably approximated; annuli were partially obscured 
by washed out or dark zones but were reasonably ap- 
proximated; 3) confident — operculum showed initial 
year’s growth and annuli were easily readable; or 4) 
very confident — operculum exhibited strongly promi- 
nent annuli that were easy to read. 
We analyzed operculum only from whelk with an av- 
erage confidence rating >2. If 2 of the 3 readers record- 
ed the same age for an operculum, that age was used. 
If all 3 readers recorded 
different ages, the mean 
value (rounded to the 
nearest year) was used if 
variance was <1 (equiva- 
lent to a confidence bound 
of ±2 years); whelk with 
greater variance were de- 
termined to be unaccept- 
able. Only 227 whelk (115 
females and 112 males) of 
292 total dissected whelk 
(155 females and 137 
males) were used for oper- 
culum analysis (Table 1). 
Histology and gonad 
staging 
A histological examina- 
tion of gonads from 112 
males and 115 females 
was undertaken to deter- 
mine gonad development 
stage. Not all dissected 
whelks (155 females and 
137 males) were used for 
analysis because some 
opercula were not de- 
termined acceptable for 
operculum analysis and, 
therefore, could not be 
used for the comparison of 
age with gonad develop- 
ment. Two tissue samples 
were processed from each whelk gonad with a Tissue- 
Tek VIP-E150 (Sakura Fineteck USA, Inc., Torrence, 
CA) automated tissue processor that contained a de- 
hydration series of 70% EtOH, 95% EtOH, and various 
concentrations of 100% EtOH and clearing agent and 
melted paraffin. Tissue samples were taken from a one- 
third portion and a two-thirds portion (approximately 
5 mm apart) of the gonad sample to address synchrony 
within the gonad. The processed tissues were embed- 
ded in paraffin and sectioned to 10 pm (male) or 14 
pm (females). Each tissue sample produced 4 repli- 
cates, which were mounted on slides and dried on a 
slide warmer. The best 2 slides from each tissue sample 
(4 slides per gonad) were stained with a haematoxylin 
and eosin stain; coverslips were then mounted with a 
resin mounting medium. 
Four slides from each whelk gonad were examined 
to determine sex and gonad stage. The dominant stage 
was defined as the stage that represented at least 50% 
of the section (llano et al., 2003). If both tissue samples 
from a whelk’s gonad had different dominant stages, 
then the most advanced stage was recorded. The clas- 
sifications for each stage followed descriptions of Buc- 
