6 
Fishery Bulletin 106(1 ) 
Table 3 
The estimated mean weighted values and niche width (w) across each of the three resource gradients (position, depth, and tem- 
perature) for the species-subgroups examined in this analysis. Although the species were initially split into male, female, and 
juvenile components, they were recombined if overlaps within a species (i.e., between sexes or between juveniles and adults) were 
greater than 0.9 across all three environmental variables. 
Species 
Common name 
Group 
Position (km) 
mean w 
Depth (m) Temperature (°C) 
mean w mean w 
Sebastes variabilis 
Dusky rockfish 
All 
757 
780 
141.3 
57.0 
5.4 
0.9 
Sebastes variegatus 
Harlequin rockfish 
All 
200 
1124 
159.8 
50.3 
5.6 
0.7 
Sebastes polyspinis 
Northern rockfish 
Adults 
1265 
818 
134.1 
54.4 
5.0 
0.9 
Juveniles 
1819 
1180 
137.6 
56.0 
4.7 
1.0 
Sebastes alutus 
Pacific ocean perch 
Adults 
1205 
1176 
211.8 
75.9 
4.7 
0.9 
Juveniles 
857 
1231 
164.2 
47.9 
5.1 
0.9 
Sebastes babcocki 
Redbanded rockfish 
All 
-443 
1532 
232.5 
78.5 
5.4 
0.6 
Sebastes proriger 
Redstriped rockfish 
All 
-676 
1720 
193.8 
42.3 
5.6 
0.6 
Sebastes helvomaculatus 
Rosethorn rockfish 
All 
-779 
1760 
215.1 
54.7 
5.6 
0.6 
Sebastes aleutianus 
Rougheye rockfish 
Adults 
1112 
1043 
315.7 
164.6 
4.4 
1.0 
Juveniles 
685 
987 
244.3 
112.9 
5.0 
0.9 
Sebastes zacentrus 
Sharpchin rockfish 
All 
-430 
1482 
195.9 
45.9 
5.6 
0.6 
Sebastes borealis 
Shortraker rockfish 
All 
1325 
1124 
354.4 
194.5 
4.2 
1.1 
Sebastolobus alascanus 
Shortspine thornyhead 
All 
468 
1160 
318.4 
192.9 
4.7 
0.9 
Sebastes brevispinis 
Silvergray rockfish 
Adults 
-713 
1737 
202.4 
49.1 
5.7 
0.7 
Juveniles 
-186 
1319 
153.0 
54.2 
6.0 
1.0 
Sebastes ruberrimus 
Yelloweye rockfish 
All 
66 
1101 
143.8 
45.8 
5.7 
0.7 
assemblages that had similar distributions along the 
environmental gradients. The combined overlap indi- 
ces for each species pair were also compared to the 
frequency of co-occurrence for the species pair in trawl 
hauls by using linear regression to determine if the 
distribution of species across environmental variables 
was directly linked to their co-occurrence in trawl 
hauls. 
Results 
There was little difference in the distributions of the 
examined rockfish species among sexes. For all species, 
the overlap indices exceeded 0.9 across all three envi- 
ronmental gradients between males and females and, 
thus, the CPUE data were combined across sexes. Some 
differences between adults and juveniles were observed 
in their distributions across all three environmental 
variables (Table 3). Juvenile Pacific ocean perch (POP) 
( Sebastes alutus) and silvergray rockfish ( S . brevispinis) 
were distributed at shallower depths than were adults of 
the same species. There was also a distinct separation 
between juvenile and adult rougheye rockfish (S. aleu- 
tianus) along the temperature gradient; juveniles were 
found at slightly higher temperatures than were adults. 
Juvenile northern rockfish ( S . polyspinis) were found 
farther west (approximately 600 km) along the Alaska 
Peninsula than were adults. In total, these preliminary 
analyses indicated that there were four species where 
juveniles and adults were found to be separate and nine 
species that did not have different distributions between 
either sexes or life stages for any of the three environ- 
mental gradients. As a result, 17 species subgroups were 
analyzed (Table 3). 
The cluster analysis resulted in five assemblages of 
rockfish species subgroups (Fig. 3). There was a rel- 
atively shallow-water assemblage (Aleutian Islands- 
shelf) containing northern rockfish, juvenile POP, and 
dusky rockfish (S. variabilis). These species had mean 
weighted depths from 134 to 164 m and were widely 
distributed around the northern Gulf of Alaska and 
Aleutian Islands (mean weighted distances from 757 to 
1819 km). A similar assemblage (central Gulf of Alaska- 
shelf) had mean weighted depths from 144 to 160 m and 
was distributed from 200 to -186 km. This assemblage 
contained three species subgroups: yelloweye rockfish 
(S. ruberrimus), harlequin rockfish (S. variegatus), 
and juvenile silvergray rockfish. The third assemblage 
(southeastern Alaska-break) consisted of a group of spe- 
cies found predominantly in southeastern Alaska (mean 
weighted distance -430 to -779) at depths centered 
around 208 m. These species included adult silvergray 
rockfish, redbanded rockfish OS. babcocki ), rosethorn 
rockfish (S. helvomaculatus), sharpchin rockfish (S. 
zacentrus ), and redstripe rockfish (S. proriger). The 
