2 
Fishery Bulletin 106(1 ) 
160°0'0"E 1 70°0'0"E 180“0'0"E 170°0'0"V\ / 160°0'0"W 150“0'0"W 140“0'0"W 130°0'0"W 120°0'0"W 
1 70°0'0"W 1 60°0'0"W 1 50 o 0'0"W 140°0'0"W 
Figure 1 
Map of Alaska showing the Gulf of Alaska and Aleutian Islands ecosystems (sepa- 
rated by a dashed line). The geographical position of each bottom trawl haul was 
calculated as the distance from Hinchinbrook Island (star). The distance of trawl 
hauls from Hinchinbrook Island along the southeastward arrow was coded as nega- 
tive, and the distance along the westward arrow was coded as positive. 
as documentation of the important differences among 
life-stage and species subgroups along environmental 
gradients. 
Materials and methods 
Study area 
The data used for these analyses were collected during 
bottom trawl surveys of the Gulf of Alaska and Aleutian 
Islands ecosystems (Britt and Martin, 2001; Zenger, 
2004). The Aleutian Islands are a chain of volcanic 
islands stretching from the Alaska Peninsula in south- 
west Alaska across the North Pacific Ocean and dividing 
the western Gulf of Alaska from the Bering Sea. The 
upper continental slope in the Aleutian Islands is narrow 
and steep. In the Gulf of Alaska, the continental shelf 
ranges in width from 20 km to greater than 200 km and 
the continental slope is steep and features periodic gul- 
lies and submarine canyons extending into the continen- 
tal shelf. These two ecosystems encompass a large area 
of the Alaska continental shelf, from Dixon Entrance 
(133°W) in the southeastern Gulf of Alaska to Stalemate 
Bank (170°E) at the far western end of the Aleutian 
Islands (Fig. 1). The Gulf of Alaska bottom trawl survey 
is conducted from the Islands of Four Mountains (170°W) 
to Dixon Entrance. The Aleutian Islands bottom trawl 
survey is conducted along the island chain from 165°W 
to Stalemate Bank on the Bering Sea side and from the 
Islands of Four Mountains (170°W) to Stalemate Bank 
on the Gulf of Alaska side. 
The Aleutian Islands and Gulf of Alaska ecosystems 
are connected by oceanic currents over the shelf. The 
Alaska Coastal Stream and Alaska Coastal Current 
flow westward (counter-clockwise) around the Gulf of 
Alaska from Dixon Entrance to the end of the Aleutian 
Island chain, whereas on the Bering Sea side of the 
Aleutian Islands the current flows eastward and pro- 
vides extensive transport through passes in the chain 
from the Gulf of Alaska to the Bering Sea (Stabeno et 
al., 1999, 2002). The Islands of Four Mountains area is 
thought to be an area of change in both oceanographic 
properties (a higher influence of marine waters to the 
west) and biological properties (Ladd et ah, 2005; Lo- 
gerwell et al., 2005). 
Trawl survey data 
The National Marine Fisheries Service (NMFS) Alaska 
Fisheries Science Center (AFSC) has conducted standard 
bottom trawl surveys in the Gulf of Alaska and the 
