28 
Fishery Bulletin 106(1 ) 
Table t 
Total number of hauls (n) and bottom area swept (km 2 ) by subregion and depth range for bottom-trawl surveys conducted 
in the eastern Bering Sea (shelf and slope), Aleutian Islands, and Gulf of Alaska from 1999 through 2004 (see text for subregion 
boundaries). 
Subregion 
1 2 3 4 5 6 Total 
Depth range (m) 
72 
km 2 
n 
km 2 
n 
km 2 
n 
km 2 
n 
km 2 
n 
km 2 
n 
km 2 
Bering Sea shelf 
<50 
182 
7.68 
245 
10.90 
18 
0.81 
445 
19.39 
51-100 
386 
17.86 
361 
17.18 
302 
15.03 
1049 
50.07 
101-200 
141 
7.33 
147 
7.11 
328 
16.51 
616 
30.95 
Total 
709 
32.87 
753 
35.19 
648 
32.35 
2110 
100.40 
Bering Sea slope 
201-600 
112 
4.38 
31 
1.09 
32 
1.10 
32 
1.08 
15 
0.55 
53 
1.94 
275 
10.14 
601+ 
57 
2.30 
32 
1.12 
33 
1.23 
30 
1.12 
23 
0.87 
33 
1.15 
208 
7.78 
Total 
169 
6.68 
63 
2.21 
65 
2.33 
62 
2.20 
38 
1.42 
86 
3.09 
483 
17.92 
Aleutian Islands 
<100 
34 
0.78 
83 
1.83 
67 
1.54 
171 
3.90 
355 
8.05 
101-200 
103 
2.37 
154 
3.37 
164 
3.73 
103 
2.37 
524 
11.84 
201+ 
70 
1.63 
134 
3.05 
170 
3.99 
156 
3.72 
530 
12.38 
Total 
207 
4.78 
371 
8.25 
401 
9.26 
430 
9.99 
1409 
32.27 
Gulf of Alaska 
<100 
247 
5.74 
174 
4.02 
280 
6.60 
50 
1.19 
15 
0.33 
766 
17.87 
101-200 
121 
2.87 
188 
4.52 
365 
8.90 
104 
2.51 
58 
1.33 
836 
20.12 
201 + 
30 
0.72 
128 
3.17 
138 
3.64 
119 
3.68 
77 
1.79 
492 
13.00 
Total 
398 
9.33 
490 
11.71 
783 
19.14 
273 
7.38 
150 
3.45 
2094 
50.99 
individual skates captured in a single haul ranged from 0 
to 833, yielding aggregate density (all species combined) 
estimates for individual survey hauls ranging from 0 to 
22,005 individuals per km 2 (mean = 160.55 ±5.39). For 
individual species, maximum density figures ranged over 
several orders of magnitude, from 26.42 individuals/km 2 
for the rare and deepwater B. abyssicola to over 19,759 
individuals/km 2 for an extraordinarily large haul of B. 
parmifera on the northern Bering Sea slope. 
Bering Sea shelf 
The Bering Sea shelf received as much trawling effort 
as the other three regions combined and skates were 
common, but skate species richness and diversity were 
low. Approximately half of the effort was expended in 
the 51-100 m depth range, and the other half of the 
effort was almost equally distributed between the other 
two depth strata (Table 1). The southern, central, and 
northern subregions were sampled approximately evenly, 
and the depth distribution of the effort was similar in 
subregions 1 and 2. However, the depth distribution 
of the effort was significantly different in subregion 
3, where the deepest depth stratum (100-200 m) was 
most heavily sampled, and very little sampling was con- 
ducted in the shallow stratum. Skates were encountered 
throughout the entire geographic and bathymetric range 
of the survey area in over 87% (1830 of 2110) of the hauls 
conducted in this region. Skate species richness was 
highest in subregion 3 and lowest in subregion 1 (1.21 
vs. 0.94), increasing with depth in all three subregions 
(Table 2). In all three subregions, species richness was 
highest in the deepest strata, and the lowest species 
richness was encountered in the shallow stratum of sub- 
region 1. For all subregions combined, species richness 
increased significantly (PcO.0001) with depth (Fig. 3). 
Diversity indices were near zero in all three subregions 
in the shallow and middle depth strata, but were slightly 
higher in the deepest depth zone (Table 3). 
Skates were often encountered at moderate to high 
densities on the Bering Sea shelf. Aggregate skate den- 
sity on the eastern Bering Sea shelf ranged from 0 to 
5103 individuals/km 2 , and an overall mean of 229.49 
±5.97. The largest mean density values were encoun- 
tered in the middle depth stratum (51-100 m) of sub- 
region 2 and the shallow and deep strata of subregion 
3, although the variability associated with the mean 
in the shallow stratum of subregion 3 was extremely 
high. The smallest mean density was encountered in the 
shallow stratum of subregion 1 (Table 4). Overall mean 
density for the entire region was considerably lower in 
the shallow depth stratum than in either of the two 
