Natanson et ai.: Gestation period and pupping seasonality of Squalus acanthias off southern New England 
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Figure 5 
Growth of embryos and (A) external yolk and (B) ovary weight 
through the 2-year gestation period of spiny dogfish (Squalus acan¬ 
thias) sampled off southern New England and New Jersey in 2013- 
2015. Month 1 corresponds to January of the first year of the cycle. 
For months 2-6, data are from just fertilized embryos from February 
to June 2014 and are included to exemplify the typical first 6 months 
of growth. Months 7-23 correspond to monthly samples collected 
from July 2013 to April 2015. Error bars indicate 95% confidence 
intervals (CIs). 
only free-living embryos, was similar although the 
estimates based on oocytes were higher than those 
based on embryo counts. Jensen (1985) noted prema¬ 
ture delivery of near-term pups directly after collec¬ 
tion aboard fishing vessels and speculated that this 
phenomenon is widespread, but is not often reported. 
He stated that the premature pupping was never ex¬ 
cessive and therefore reported estimates 
of fecundity are still appropriate (Jensen, 
1965). The fecundity estimate based on oo¬ 
cytes (5.3) is the highest of the 3 estimates 
and suggests that not all oocytes are suc¬ 
cessfully fertilized. Nammack et al. (1985) 
also found higher numbers of oocytes than 
embryos and found evidence of ovulation 
failure. The estimate of fecundity per fe¬ 
male from the number of free-living em¬ 
bryos only (4.3) is slightly lower than the 
estimate from the number of total embryos 
(4.5) suggesting the potential influence of 
premature pupping on the estimate of free- 
living embryos. Because the total estimate 
eliminates some of the decrease caused by 
premature pupping, this is the more accu¬ 
rate estimate of fecundity of spiny dogfish. 
The estimate of free-living embryos from 
this study falls within the range of other 
studies in the WNA (Templeman, 1944 
[mean: 3.7]; Nammack et ah, 1985 [mean: 
6.6]; Sosebee, 2005 [mean: 4.4]; Campana 
et ah, 2009 [mean: 4.7]). 
Nammack et al. (1985) suggested a pos¬ 
sible compensatory increase in the number 
of pups (overall and by size class) was due 
to a reduction in stock biomass but noted 
that the increase could simply be due to 
differences in sampling locations. Silva 
(1993) found a negative correlation be¬ 
tween spiny dogfish fecundity by size class 
and abundance estimates from the WNA 
through 1991 (including data from Temple- 
man [1944] and Nammack et al. [1985]). 
Additionally, significant correlations for 
the 80-84, 85-89, and 90-94 cm STL size 
classes suggest that spiny dogfish fecun¬ 
dity is density dependent (Silva, 1993). 
Sosebee (2005) reported that the reduction 
in overall mean fecundity in her study in 
comparison with results from the Nam¬ 
mack et al. (1985) study is likely due to a 
truncation of the population size structure 
resulting from the size selective nature of 
the fishery. There was also no evidence of 
density-dependent changes in mean fecun¬ 
dity by maternal size class in the study by 
Sosebee (2005). At that time, reproductive 
spiny dogfish were no longer declining in 
abundance, which may have negated any 
changes that would result from density 
dependence (Sosebee, 2005). Our overall 
mean fecundity based on free-living embryos is simi¬ 
lar to that of Sosebee (2005), but data by size class in 
all length groups showed a decrease in mean fecun¬ 
dity from Sosebee (2005) and more notable drops in the 
larger size classes. Because status updates (Rago and 
Sosebee 2 ’ 3 ) indicate that female spawning stock bio¬ 
mass has been rebuilding since the time of the study 
