Dell'Apa et al.: Modeling the distribution of Squalus acanthias, by sex 
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energy-demanding copulation (Pratt and Carrier, 2001; 
Sims et al., 2001; Dell’Apa et al., 2014, 2015). More 
studies are needed to test this hypothesis. 
That the CPUE predicted in our analysis for adult 
females was higher in warmer waters than in less 
warm waters is in accordance with results of Sagarese 
et al. (2014a), a study in which adult females in the 
northeastern U.S. continental shelf large marine eco- 
system were observed to occupy significantly warmer 
waters than those occupied by adult males. In regard 
to adult male abundance, the results of the Bayesian 
model obtained from our study are also in agreement 
with results from Sagarese et al. (2014a): results from 
both studies indicate a higher occurrence of adult 
males than adult females in deeper, colder waters. In 
spiny dogfish, gestation lasts for almost 2 years, and 
it has been hypothesized that this species may have 
an evolutionary advantage in that adult, pregnant fe- 
males actively seek inshore, warmer waters because 
such habitats can maximize the growth rates of em- 
bryos (Sagarese et al., 2014a). 
Salinity was found to be a relevant environmental 
variable for predicting the habitat distribution of spiny 
dogfish for both sexes — a finding that is in agreement 
with Shepard et al. (2002) and Sagarese et al. (2014a), 
but we interpret this result and the results of other 
studies as a possible artifact of the association of salin- 
ity with other key environmental habitat characteris- 
tics, such as depth and temperature, that better define 
habitat selection of spiny dogfish. Generally, inshore 
waters are less saline than offshore environments be- 
cause of the increased contribution of freshwater runoff. 
On the basis of the Bayesian model, we predict that 
abundance of adult females should be higher in the 
spring than in the fall and higher in the morning than 
in the afternoon and night. Conversely, abundance of 
adult males is predicted to be higher in the fall than 
in the spring, as well as higher in the afternoon than 
at other times of day. For adult females, this predicted 
seasonal pattern of abundance is in agreement with re- 
sults from the NEFSC survey, which is conducted far- 
ther offshore than the NEAMAP survey (Sagarese et 
al., 2014b). This pattern also indicates that the habitat 
distribution of adult females in the spring is mainly 
driven by environmental factors (i.e., temperature and 
depth) and that habitat distribution in the fall is main- 
ly influenced by ecological factors (i.e., prey abundance) 
(Sagarese et al., 2014a, 2014b). 
For adult males, the results of this study contrast 
with those reported by Sagarese et al. (2014b), in that 
we predicted a greater abundance of males in the fall 
than in the spring. We acknowledge that our analysis 
is based on fewer males than females, but we are confi- 
dent that the level of uncertainty that may result from 
this limited number is included within the parameters 
analyzed by a Bayesian approach. In combination, how- 
ever, our results and those of Sagarese et al. (2014b), 
for inshore and offshore waters, respectively, indicate 
that abundance of adult males should be higher in the 
fall than in the spring in inshore coastal waters, al- 
though a greater chance for catching larger aggrega- 
tions of adult males may occur in offshore, deeper wa- 
ters in the spring. More studies are needed to support 
this hypothesis and to analyze specific seasonal differ- 
ences in habitat distribution and abundance of spiny 
dogfish, by sex, throughout its range. Unfortunately, it 
was not possible to run the hierarchical Bayesian spa- 
tiotemporal model and develop probability distribution 
maps for each sex, by season, as with the maps ob- 
tained for CPUE for each sex, because of the consistent 
presence in the survey of locations that were sampled 
multiple times. 
This study is the first one to provide a predictive 
model for the spatial distribution of each sex of spiny 
dogfish on the basis of time of day, which previously 
has been suggested to be an important aspect as- 
sociated with the sexual segregation of this species 
(Dell’Apa et al., 2014). Such information could be used 
to enhance fishery sustainability by developing fishery 
strategies based on the distribution and habitat associ- 
ation of each of the sexes. For example, targeting adult 
females inshore, in shallower waters, would result in 
greater pressure on the entire U.S. Atlantic stock of 
spiny dogfish. Fishery sustainability is measured in 
terms of fishing mortality and spawning stock biomass, 
and adult female biomass is used as a biological refer- 
ence point. Although the spiny dogfish is not currently 
considered overfished and overfishing is not occurring, 
low numbers of adult females are expected to be re- 
cruiting to the stock over the next few years (Rago and 
Sosebee^; Dell’Apa et al., 2015). 
Considering the concentration of chl-a as a valid 
proxy for primary production (de Leiva Moreno et 
al., 2000), adult females were predicted to associate 
with habitats characterized by higher productivity, but 
adult males were predicted to occur in less productive 
waters. As with our analysis of results for salinity, 
we interpreted this result for chl-a concentration as 
the direct association of primary productivity with the 
preferred habitat for females rather than as a driver 
per se. Because adult females are found most com- 
monly inshore, in shallower and warmer waters where 
primary production is usually highest, it is likely that 
chl-a concentration and primary production should 
not be considered as an important predictive variable 
for abundance of spiny dogfish. However, for coastal 
elasmobranch species, such as the Atlantic sharpnose 
shark {Rhizoprionodon terraenouae), chl-a concentra- 
tion has been found to be an important environmen- 
tal variable that affects the abundance and habitat 
association of that species (Drymon et al., 2013). Pa- 
pastamatiou et al. (2013) reported that for both sexes 
of tiger shark (Galeocerdo cuvier), immigration across 
the Hawaiian Archipelago was correlated with chl-a 
concentration — a result that they interpreted to be in- 
dicative of a foraging activity. It is, therefore, likely 
that for large pelagic shark species, such as the blue 
shark (Prionace glauca), primary production is an im- 
portant variable that influences species habitat distri- 
bution (Mitchell et al., 2014). 
