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Fishery Bulletin 113(2) 
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Figure 4 
Spatial overlap (SOq, SOj), measured as a percentage, of spiny dogfish ( Squalus acanthias) 
distribution (derived from the Northeast Fisheries Science Center trawl survey data) with com- 
mercial fishery catch in the northeast U.S. shelf large marine ecosystem between 1989 and 
2009 for the sink gillnet fishery in (A) autumn and (B) spring and the otter trawl fishery in 
(C) autumn and (D) spring. Solid lines indicate direct spatial overlap (SOq), and dashed lines 
indicate spatial overlap revealed through the use of interpolated values (SO\). Higher values 
indicate increased overlap between spiny dogfish distribution and fishery catches. 
trawl survey validating seasonal movements of spiny 
dogfish (Sagarese et al., 2014b). Trends in fishery-de- 
pendent data displayed interannual differences in lo- 
cations where spiny dogfish were encountered on com- 
mercial fishing grounds. 
Availability can be understood as a localized effect 
between CPUE and density of spiny dogfish (Wilberg et 
al., 2009). Changes in availability to commercial fisher- 
ies can have long-lasting impacts on marine resourc- 
es, especially on species, such as the spiny dogfish, 
which has a slow life history (Musick, 1999). During 
the 1990s, a southward shift in distribution of Atlantic 
cod increased the availability of this stock to fishing 
fleets and helped contribute to its collapse (Rose et al., 
1994; Rose and Kulka, 1999). For spiny dogfish, the 
observed increase in SOe throughout the time series 
for the SGN fishery during spring and for the OT fish- 
ery during autumn indicates a concomitant increase in 
the portion of the stock available to fisheries. Results 
from an availability analysis, in addition to quantified 
spatial overlap, support recent increases in availabil- 
ity of spiny dogfish and revealed changes in availabil- 
ity for individual life-history stages. Increased overlap 
may stem from technological advancements or social 
networking that can increase the efficiency of fishing 
crews in locating and capturing aggregations of either 
spiny dogfish directly or indirectly by targeting their 
prey (Hilborn and Walters, 1992). 
The trend toward increased availability, particu- 
larly for mature females either as targeted catch or 
as bycatch, elicits the need for caution regarding the 
sustainability of the stock of spiny dogfish in the NES 
