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Fishery Bulletin 1 13(3) 
Longitude 
Slope 
Figure 8 
From the best-fitting generalized additive model (GAM), predictions of conditional abundance (scaled, 
normalized CPUE where present) of adult Pacific ocean perch ( Sebastes alutus ) at trawl stations in the 
Aleutian Islands during 1997-2010 in relation to (A) longitude, (B) kriged bottom slope, and (C) the inter- 
action between depth and temperature. A change in number orientation indicates that either a maximum 
or a minimum was reached for the GAM effect. 
regions of high production, especially to the north of 
the passes (Ladd et ah, 2005). In addition, upwelling 
can occur around passes and may enhance local pro- 
duction (Swift and Aagaard, 1976; Coyle, 2005), lead- 
ing to potentially greater abundance of the zooplankton 
prey of Pacific ocean perch (Carlson and Haight, 1976; 
Brodeur, 1983; Boldt and Rooper, 2009). Southward cur- 
rents that flow through Aleutian passes typically flow 
down the western side of the pass, whereas northward 
flow occurs on the eastern side (Stabeno et ah, 2005). 
Because the dominant current along the south side of 
the Aleutian chain is to the west and the dominant 
current along the north side is to the east, larval re- 
tention zones could exist near passes (Stockhausen and 
Hermann, 2007). Genetic studies of Pacific ocean perch 
in other areas have indicated that stock structure on 
a small scale (70-400 km) may occur and could be the 
result of limited dispersal of early life stages (Seeb 
and Gunderson, 1988; Withler et al., 2001; Palof et ah, 
2011). The possibility for high productivity and larval 
retention around Aleutian passes, combined with the 
potential natural barriers to migration of Pacific ocean 
perch along the archipelago (e.g., predominant currents 
as well as deeper passes in the western Aleutian Is- 
lands), could further explain our results that indicate 
increases in presence and abundance near Aleutian 
passes. 
The structural heterogeneity created in trawlable 
habitats by the presence of sponges, corals, and bryo- 
zoans presumably provides refugia from predation and 
shelter from currents for juvenile Pacific ocean perch 
(Stoner, 1982; Ryer, 1988; Ryer et al., 2004) and re- 
cently has been shown to provide nursery habitat for 
redfish larvae ( Sebastes spp.) around sea pens (Baillon 
