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crease in LW and the subsequent increase in volume 
of female shells, the lack of any observed difference in 
the relationship of Wt and SL could have occurred be- 
cause the nidamental gland has a lower density than 
the density of muscle tissue. 
During dissections of channeled whelk in our study, 
there were no signs of hermaphroditism; all whelk had 
either a penis or a nidamental gland. No whelk were 
found to contain both male and female gonads in his- 
tological sections. Male penis length increased with SL, 
a finding that also indicates channeled whelk may not 
be protandric hermaphrodites. In knobbed whelk, the 
penis of males that changed sex to females shrank to 
a round protuberance (Castagna and Kraeuter, 1994). 
The results of Castagna and Kraeuter ( 1994) indicate 
knobbed whelk can be protandric hermaphrodites, al- 
though sex is determined at birth and there is a 1:1 
sex ratio at hatching (Avise et ah, 2004). 
We found an equal sex ratio for male and female 
channeled whelk at early ages, but later, males domi- 
nated at ages of 7-9 years and females dominated at 
ages of 10-14 years (Table 2). Males did not live as 
long as females (Table 2), and there was a greater pro- 
portion of males at the size range of 120-160 mm SL 
(Table 1). Both factors could explain why there were 
more males than females at the ages of 7-9 years. It 
also is possible that the fishery has inflated the pro- 
portion of males at smaller sizes. Males have a lower 
maximum size and mature at smaller sizes than fe- 
males. We define large whelk as those individuals >160 
mm SL because this size is slightly above the female 
SM, 5 o and is equivalent to the 97.5 percentile of male 
SL (on the basis of a sample of 9460 whelk; B. Stevens, 
unpubl. data). Because the fishery is directed at catch 
of large whelk, which are mostly females, fishermen do 
not actively target males and males may accumulate 
at smaller sizes. 
However, it is possible that knobbed whelk may ex- 
hibit protandric behavior in extreme conditions; Cast- 
agna and Kraeuter (1994) held only male knobbed 
whelk in the laboratory. Whelks generally grow slowly 
and move slowly, and, at low population levels, inter- 
action between sexes may be minimal. Protandry in 
knobbed whelk may be opportunistic, and not every 
individual may be capable of it. In addition, unknown 
pollutants potentially could cause the sex change seen 
in knobbed whelk by Castagna and Kraeuter (1994). 
Whether or not protandry occurs in channeled whelk, 
the fishery will remain in peril if mature females are 
not protected. 
There is a lack of evidence to support the hypothesis 
that protandry may occur in channeled whelk. Further, 
no channeled whelk with evidence of imposex were 
found in our study. In gastropods, tributyltin (TBT) 
causes higher testosterone, which in turn can cause the 
penis in male bruised nassa ( Nassarius vibex) to devel- 
op earlier and males to mature earlier (Demaintenon, 
2001). Female bruised nassa with imposex developed a 
penis, and that development caused sterility in some 
cases because the penis blocked the oviduct (Demain- 
tenon, 2001). Females with imposex can be confused 
with sequential hermaphrodites in sex transition be- 
cause individuals may have both male and female sex 
organs. Castagna and Kraeuter (1994) indicated that 
knobbed whelk could be sequential hermaphrodites be- 
cause some male knobbed whelk switched sex to female 
in the laboratory, and some of the newly formed female 
knobbed whelk laid viable egg strings. However, it is 
possible that their knobbed whelk were originally fe- 
males with imposex, or that sex change was the result 
of social and physiological effects of confinement in a 
laboratory setting. 
Gonad histology of the “male” channeled whelk that 
was abnormally large (more than 20 mm longer than 
the second-largest male) revealed that its gonad was 
nonfunctional. The gonad was empty of any male or fe- 
male gonadal precursors and contained only connective 
tissue. The sizes of the penis and gonads were much 
smaller in this abnormally large male than in fully ma- 
ture male channeled whelk in the size range of 150- 
160 mm SL. Because the testis and penis were very 
small, this whelk may never have been reproductively 
viable or was too old to reproduce. However, it is still 
possible that this large male was exhibiting protandric 
or even imposex conditions. 
The gonads of only 3 of 115 female channeled whelk 
contained different dominant stages in the replicate 
slides; males did not have different dominant stages 
(n=112). This finding indicates that gonadal develop- 
ment was mostly synchronous. Mann et al. (2006) re- 
ported asynchrony for 2 of 3 male specimens of Rapana 
venosa but not for female specimens collected in June 
from the Chesapeake Bay. The gonad developmental 
stages determined for channeled whelk in this study 
are point-in-time estimates and do not provide a sea- 
sonal evaluation. Gonad samples from our study were 
collected in July and August, most likely at the be- 
ginning of the spawning season for channeled whelk 
(Betzer and Pilson, 1974). The I and ED stages were 
differentiated to determine when spermatozoa (males) 
and nuclei (females) were first produced. 
Male maturity was determined mostly by the pres- 
ence and amount of spermatozoa. We believed that a 
male was capable of spawning effectively if it contained 
spermatozoa in at least 50% of its tubules, and we la- 
beled such whelk in our study as mature. A LD-stage 
male that contained spermatozoa in 25-50% of its tu- 
bules could potentially spawn, but it may not contrib- 
ute enough spermatozoa to be considered effective. 
There is no paternity information on egg strings of 
channeled whelk, but this species could follow a similar 
reproductive strategy to that of knobbed whelk. Walker 
et al. (2005) reported sex-linked markers in knobbed 
whelk that can be used to determine the biological par- 
ents of embryos. A knobbed whelk egg string contained 
7 different fathers, indicating that the female knobbed 
whelk most likely used a “well-blended sperm pool” 
for fertilization (Walker et al., 2007). Female knobbed 
