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Fishery Bulletin 115(1) 
CrI: -1.52 to -0.04) compared with surveys conducted 
in the afternoon (the reference level), which was the 
period of time with the highest CPUE. Night-time sur- 
veys also had lower values of CPUE (posterior mean = 
-0.25; CrI: -1.09 to -0.02) compared with the values 
from afternoon surveys. 
Higher estimated values of CPUE for adult males 
occurred at higher latitudes, above 40°N, and off 
Georges Bank, than estimated values of CPUE from 
other sampled areas (Fig. 2B). 
Model performance 
For model validation, reasonably high values for Pear- 
son’s r were obtained for both sexes. In particular, from 
the model for adult females, an r value of -0.65 was 
obtained in the cross-validation with the original data 
set, and an r value of -0.71 was obtained in the cross- 
validation with half of the data set. For adult males, 
the r value was -0.68 in the cross-validation with the 
original data set and was -0.74 in the cross-validation 
with half of the data set. 
Low values of RMSE and avg. error were achieved 
for adult females, with an RMSE of 0.98 and an avg. 
error of 0.045 in the cross-validation with the original 
data set and with an RMSE of 1.14 and an avg. er- 
ror of -0.023 in the cross-validation with half of the 
data set (Table 3). For adult males, low values were 
also observed, with an RMSE of 1.15 and an avg. error 
of 0.032 in cross-validation with the original data set 
and an RMSE of 1.11 and an avg. error of -0.018 in 
the cross-validation with half of the data set (Table 3). 
These validation results indicate a good performance 
of the 2 models. 
Discussion 
This study provides predictive information on the habi- 
tat distribution of spiny dogfish in US. Atlantic coastal 
waters, by modeling the CPUE in the NEAMAP survey 
as a proxy for the abundance of this species. The re- 
sults of this study offer insight into the key environ- 
mental and temporal variables that influence the habi- 
tat selection for each of the sexes of this species. For 
our modeling approach, we assumed CPUE is a proxy 
for species abundance and that CPUE should be the 
same for both female and male spiny dogfish, although 
CPUE is not always a viable proxy for species abun- 
dance and is not always the same for each sex because 
of inherent variability in the catchability coefficient 
(see Hilborn and Walters, 1992; Walters, 2003; Maun- 
der and Punt, 2004; Maunder et al., 2006). However, 
the lack of linearity between CPUE and fish abundance 
is largely reduced when data from standardized fish- 
ery-independent surveys are used (Maunder and Punt, 
2004), as was done in our study. 
Another confounding issue in our analysis was that 
in the NEAMAP survey, female spiny dogfish mark- 
edly outnumbered males, by a ratio of 20:1. Ideally, the 
Table 3 
Statistics used in the hierarchical Bayesian spatiotem- 
poral model to estimate abundance of spiny dogfish 
iSqualus acanthias), by sex. The statistics include root 
mean square error (RMSE) with the original data set, 
average error (avg. error) with the original data set, 
root mean square error (RMSE-cross) with half of the 
data set, and average error (avg. error-cross) with half 
of the data set. 
RMSE- avg. error 
Sex RMSE avg. error cross -cross 
Eemales 0.98 0.045 1.14 -0.023 
Males 1.15 0.032 1.11 -0.018 
analysis of data from a simultaneous offshore survey 
would have been more suitable for determining wheth- 
er patterns inshore and offshore are the same, but such 
data were not available. This lack of information points 
to a need for concurrent offshore sampling to support 
the extrapolation of our conclusions to the offshore 
component of and for the generalization of our predic- 
tions for the entire US. Atlantic stock of spiny dogfish. 
Our results related to sex-based segregation and 
distribution are in line with those reported in other 
studies. As expected, a higher number of adult females 
were caught in shallower, inshore, and warmer waters 
in comparison with adult males, which are more com- 
monly reported in deeper, offshore, and colder waters 
(Shepherd et al., 2002; Methratta and Link, 2007; 
Sagarese et al., 2014a). 
On the basis of the results of the hierarchical Bayes- 
ian spatiotemporal model, abundance of adult female 
spiny dogfish is predicted to decrease with depth, but 
abundance of adult males is predicted to increase with 
depth. In addition, CPUE of adult females is predicted 
to be higher in warmer, less saline waters and in wa- 
ters with higher concentrations of chl-a, but CPUE of 
adult males is predicted to be higher in colder, more sa- 
line waters, and in waters with lower concentrations of 
chl-a. Nevertheless, adult females occasionally move to 
deeper waters, mainly in the spring. More studies are 
needed to understand the drivers for these movements 
into deeper waters. However, considering that partu- 
rition in spiny dogfish is likely to occur in offshore, 
deeper areas off the edge of the continental shelf and 
in deep basins (Jensen, 1966; Nammack et al., 1985; 
Hanchet, 1988; Campana et al., 2009) and that the 
time of parturition is commonly reported to be between 
November and January in the northwest Atlantic popu- | 
lation (Nammack et al., 1985), despite the observation 
in a recent study of neonate in more inshore waters off 
Rhode Island in February (Sulikowski et al., 2013), it is 
likely that these offshore movements of adult females 
in the spring are not related to parturition events but 
might be the result of a strategy to avoid males and 
