Peemoeller and Stevens: Age, size, and sexual maturity of Busycotypus canaliculatus in Buzzards Bay, Massachusetts 
275 
Table 6 
Estimates of size at 50% maturity (SM50) by shell length (SL), lip 
width (LW), and age for male and female channeled whelk ( Busyco- 
typus canaliculatus ) collected for our study in Buzzards Bay, Massa- 
chusetts, in August 2010 and July 2011. We resampled each data set 
with replacement 1000 times with a bootstrap routine to calculate 
the resampled SM50 estimate and the bias and standard error (SE) 
of the original SM50 estimate. Bias is the difference of the original 
SM50 estimate from the resampled SM50 estimate. Standard error 
(SE) is ±1 SE around the original SM50 estimate. 
Sex 
Sample 
size (n) 
Subject 
SM 50 
estimate 
Bias 
SE 
Female 
115 
Age 
8.6 years 
0.0014 
0.3 
SL 
155.3 mm 
0.24 
3.0 
LW 
80.6 mm 
0.11 
1.9 
Male 
112 
Age 
6.9 years 
-0.0027 
0.2 
SL 
115.5 mm 
0.12 
2.2 
LW 
61.3 mm 
0.04 
0.9 
terns. From the von Bertalanffy growth 
model, estimates of SL for 10-year-old male 
and female channeled whelk were 145.7 
mm and 174.8 mm, respectively (Fig. 4C; 
Table 5). Kraeuter et al. (1989) reported 
knobbed whelk in the seaside lagoons of 
Virginia with SL of 176 mm after 10 years 
(average for ages 9-11). Bruce et al. 3 re- 
ported 10-year-old knobbed whelk in Del- 
aware Bay with average SL of 112.8 mm 
and 127.6 mm for males and females, re- 
spectively. The Delaware Bay population of 
knobbed whelk appears stunted (possibly 
because of heavy fishing pressure from the 
whelk dredge fishery) when compared with 
the Virginia population. Error in aging 
opercula also could attribute to shorter SL 
at age in Delaware Bay. Channeled whelk 
and knobbed whelk share sexual dimor- 
phism in maximum size. The largest male 
knobbed whelk in Delaware Bay reached an 
SL of 161 mm; whereas the largest female 
reached an SL of 197 mm (Bruce et al. 3 ). In 
Buzzards Bay, Massachusetts, the second-largest male 
had an SL of 175 mm, but the largest female reached 
an SL of 214.2 mm. The largest male found in Buz- 
zards Bay was deemed reproductively unviable and 
subsequently discarded from our analysis. 
Females had a slightly larger LW at larger SL when 
compared with males. This finding could be due to the 
presence of the nidamental gland, which takes up a 
large portion of shell volume in mature females. Fe- 
male waved whelk invest more energy in reproduction 
than do males of that species: 3.84 kj-m -2 -yr _1 versus 
0.26 kj-in~ 2 -yr _1 , respectively (Kideys et ah, 1993). The 
nidamental gland is essential for forming egg cases 
and may require channeled whelk females to spend 
more energy on reproduction than do males. Channeled 
whelk males only need to form a penis and testis, which 
may explain why males have a lower maximum size. 
Males and females had a similar relationship of Wt 
to SL, although females 
grew to larger sizes. 
We expected that the 
weights of males and 
females would differ be- 
cause females form ova- 
ries and a nidamental 
gland, which would alter 
the relationship between 
Wt and SL at larger SL. 
Castagna and Kraeu- 
ter (1994) reported the 
seasonal gonad index of 
nidamental gland per 
meat weight (N/MW) at 
a range of 9.5-18.3% for 
female knobbed whelk. 
N/MW was lowest in the 
spring and in October; 
there has been no field 
observations report- 
ed for knobbed whelk 
spawning in the spring, 
although observed egg 
laying peaked in October 
(Castagna and Kraeuter, 
1994). Despite the in- 
A B 
Figure 6 
Size at 50% maturity (SM50), on the basis of (A) shell length (SL) or (B) lip width (LW), 
for male (M) and female (F) channeled whelk (Busycotypus canaliculatus) collected in 
August 2010 and July 2011 in Buzzards Bay, Massachusetts. Lines indicate predictions 
from a generalized linear model (GLM); points represent the average proportion within 
each size interval of 10 mm SL or 5 mm LW. Vertical lines indicate SM50. For age and 
gonad analysis, we used 115 females and 112 males. 
