Natanson et a!.: Gestation period and pupping seasonality of Squaius acanthias off southern New England 
479 
♦ 80-84 cm STL 
® 85-89 cm STL 
A 90-94 cm STL 
x 95-99 cm STL 
—-Female SSB 
2005 
Year 
I- 0 
2015 
Figure 3 
Mean fecundity of females by maternal size class, defined in 
5-cm increments of stretched total length (STL), and female 
spawning stock biomass (SSB), estimated by using a 3-point 
moving average (Rago and Sosebee 3 ), for catch of spiny dogfish 
(Squaius acanthias) from the NOAA Northeast Fisheries Science 
Center spring bottom trawl survey, plotted over time. Fecundity 
data from 1998 to 2002 were obtained from Sosebee (2005), an 
average from 2006 to 2009 was obtained from Bubley (2010), 
and an average from 2013 to 2015 was obtained from this study. 
ses with the use of relative abundance estimates also 
showed negative correlations between abundance and 
fecundity for each size class. Significant correlations 
with the use of relative abundance were found only for 
the 90-95 cm STL size class during the 2000s (Fig. 4). 
Reproductive seasonality 
The shift from a predominance of large full-term em¬ 
bryos, to empty uteri, and then candled embryos in the 
uteri took place between January and April. The first 
females with flaccid, empty uteri were caught in Janu¬ 
ary of both 2014 and 2015, and the first females with 
candled embryos were caught in February of 2014 and 
January of 2015. The occurrence of both these stages 
and the observation of full-term pups proceeded through 
at least April of both years, after which all females were 
either in the first or second year of gestation. These 
data suggest that protracted pupping and subsequent 
mating take place between January and April, possibly 
extending from late December to early May, although 
embryo development among individuals is synchronous 
during the rest of the year. No mating scars were ob¬ 
served at any time of the year to corroborate or refute 
mating periodicity. On the basis of these data, we plot¬ 
ted growth of the embryos starting in January (month 
1) as the first month of possible fertilization. We used 
data gathered for newly mated females from February 
through June of 2014 (months 2-6) plotted in front of 
the data collected in July 2013 (month 7) with 
candled embryos, to illustrate the entire 2-year 
growth cycle during gestation, with the result 
showing growth from fertilization (month 1) 
through birth (month 23; Fig. 5A). Moreover, 
the decrease in external yolk size is plotted to 
show the use of the yolk during growth. Assum¬ 
ing that those oocytes that are fertilized first 
are pupped first, one can calculate the gesta¬ 
tion period as 23 months: mating first occurs 
in January and parturition possibly as early as 
December, 23 months later. 
Data plotted by using the mean weight of 
the ovaries during the growth period of these 
same fish show a concurrent increase in ovary 
size during gestation (Fig. 5B). The data from 
January 2014 were limited (n= 4) but indicated 
a drastic decrease in ovary size followed by an 
increase that is most likely an artifact of the 
small sample size. Together, these data suggest 
a 2-year synchronous growth cycle such that 
once the embryos are pupped, the female is 
ready to mate again. This is further supported 
by the observation of a short period where fe¬ 
males had flaccid empty uteri followed imme¬ 
diately by females with candled embryos. The 
lack of any significant number of mature non- 
gravid females at any other time of the year 
also supports this conclusion. 
Size of full-term embryos 
The lack of an external yolk sac was not a decisive in¬ 
dicator of the terminal stage of embryonic development 
because litters were observed with no external yolks. 
Additionally, embryos were found with no internal yolk 
and they had healing or healed umbilical scars, indi¬ 
cating that term embryos would have no internal or 
external yolks. Full-term embryos (no internal yolk) 
ranged in size from 22.0 to 30.8 cm STL. The small¬ 
est mean litter size with no external yolks and healed 
umbilical scars was 20.2 cm STL (from a 77.6-cm-FL 
female); the average weight of the internal yolks was 
1.3 g and this litter was caught at the end of Octo¬ 
ber. The largest mean size of pups in a litter was 30.5 
cm STL (78.4 cm FL). These embryos were observed 
at the beginning of April, had no external or internal 
yolks, and they had healing umbilical scars. The data 
indicate that a full-term embryo has a mostly healed 
umbilical scar and no internal or external yolk. 
Discussion 
With this study, we confirm that spiny dogfish have a 
2-year reproductive period in the region off SNE be¬ 
tween Massachusetts and Rhode Island. Our data indi¬ 
cate that these spiny dogfish have at least a 23-month 
gestation period, which we determined by following the 
development of a group of embryos from candled em- 
