Dell'Apa et al.; Modeling the distribution of Squalus acanthias, by sex 
95 
B 
40° N 
35° N 
80° W 70' W 
Figure 2 
Map of the median of the posterior estimates of the probability of the 
catch per unit of effort of the mature (A) female and (B) male spiny 
dogfish (Squalus acanthias) caught during fishery-independent sur- 
veys conducted between New England and North Carolina in 2007- 
2013. Values of CPUE, which ranged from 16 to 0 for females and 
from 6 to 0 for males, were used as a proxy for relative abundance. 
Morning was the period of the day during a sur- 
vey with the highest estimated probability of CPUE 
of adult females (posterior mean: 0.88; CrI: 0.32 to 
1.43) with respect to the reference level (afternoon). 
Conversely, hauls conducted at night had the lowest 
estimated CPUE (posterior mean: -0.65; CrI: -1.24 to 
- 0 . 12 ). 
Finally, higher estimated values of CPUE for adult 
females were found for waters off the southern area 
of the Cape Cod peninsula and off Georges Bank than 
for CPUE estimates for other areas sampled (Fig. 2A). 
Males 
For adult males, a positive relationship between ba- 
thymetry and CPUE (posterior mean: 1.85; CrI: 1.44 to 
2.36) was observed, as well as for salinity and CPUE 
(posterior mean: 0.65; CrI: 0.23 to 1.43). Predicted val- 
ues from the model indicated a negative relationship 
for adult males between expected CPUE and SST (pos- 
terior mean: -1.02; CrI: -2.33 to -1.51) and between ex- 
pected CPUE and chl-a concentration (posterior mean: 
-0.15; CrI: -1.56 to -0.02). We interpret this result as 
indicating a higher probability of catching adult males 
as depth and salinity increase and water temperature 
and chl-a concentration decrease. 
The estimated probability of CPUE for adult males 
indicated a seasonal effect, with lower values in spring 
(posterior mean: -0.37; CrI: -2.24 to -0.02) than in fall, 
the season of the reference level. 
Surveys conducted in the morning had the lowest 
estimated CPUE of adult males (posterior mean: -0.43; 
