Sagarese et a!.: Spatiotemporal overlap of Squalus acanthias and commercial fisheries within the northeast U.S. marine system 
11 
100 
A 
80 - 
60 - 
20 - 
0 
M 100 -i 
ro 
Q. 
CO 
80 - 
60 - 
Q. 
TO 
5> 
> 
o 
Autumn 
— - Spring 
1990 1995 2000 2005 2010 
B 
0 J 
1990 1995 2000 2005 2010 
Year 
Figure 3 
Spatial overlap (.SOe). measured as a percentage, of spiny dogfish 
(Squalus acanthias) distribution (derived from the Northeast Fisher- 
ies Science Center bottom trawl survey) with commercial fishery effort 
in the northeast U.S. shelf large marine ecosystem between 1989 and 
2009 during autumn (solid line) and spring (dashed line) for the (A) 
sink gillnet fishery and (B) otter trawl fishery. SOe was calculated as 
the number of grid cells contained both survey catch and commercial 
fishery effort divided by the number of survey grid cells representing 
areas that were fished. Higher overlap indicates increased availability 
of spiny dogfish to the fishery. 
were also relatively weak, some exceptions were noted. 
Interpolated values resulted in moderate to high cor- 
relations (r sp : autumn: -0.02 to 0.75; spring: -0.54 to 
0.33) for the SGN fishery during both seasons. The OT 
fishery also displayed moderate correlations (r sp <0.66) 
during each season. 
Discussion 
Spatial overlap analyses indicate that changes in 
availability of spiny dogfish to commercial fisheries 
may have been manifested as apparent increases in 
local abundance on commercial fishing grounds. In- 
creased co-occurrence of spiny dogfish with commer- 
cial fisheries was further indicated by availability 
analyses that assessed the annual percentage of the 
spiny dogfish stock that was located on SGN and OT 
fishing grounds between 1989 and 2009. A proxy for 
spawning stock biomass, abundance of mature female 
spiny dogfish was significantly related to availability 
for each commercial fishery, although the pattern was 
not consistent among fisheries. Spatial overlap anal- 
yses revealed recent increases for both the SGN and 
OT fisheries but not consistently across seasons. Anal- 
ysis of fishery-dependent data revealed differences in 
fishery behavior between the SGN and OT fisheries: a 
high spiny dogfish bycatch in the OT fishery and high 
retained catch in the SGN fishery indicative of target- 
ing. Seasonal examination of centers of spiny dogfish 
abundance revealed differences between inshore and 
offshore areas, with trends in data from the bottom 
