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Fishery Bulletin 106(1 ) 
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Bering Sea 
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Figure 4 
Relationship between overall skate density (no. of indi- 
viduals/km 2 ) and depth for bottom-trawl survey hauls 
completed in the Bering Sea, Aleutian Islands, and Gulf 
of Alaska from 1999 through 2004. Solid lines represent 
linear regressions of estimated skate density values, 
dashed line in upper panel divides Bering Sea shelf 
records (open circles) from Bering Sea slope records 
(closed circles). 
throughout the survey area, but in only 51% (718 of 1409) 
of the hauls conducted in this region. Species richness 
was similar among the four subregions of the Aleutian 
Islands (Table 2) and increased with depth in all but 
subregion 1, the westernmost subregion. For all subre- 
gions combined, species richness increased significantly 
(P<0.0001) with increasing depth (Fig. 3). Maximum 
species richness was encountered in the deepest strata 
of subregions 2, 3, and 4 and the intermediate depth 
of subregion 1, whereas the minimum species richness 
was encountered in the shallow stratum of subregion 4. 
More species of skates were encountered in the Aleutian 
Islands (11) than in any of the other regions (vs. 10 in the 
Gulf of Alaska, 9 on the Bering Sea slope, and 7 on the 
Bering Sea shelf). Diversity indices were lowest in the 
shallow strata in all but subregion 4, where the shallow 
stratum exhibited the highest diversity and the deepest 
stratum exhibited the lowest (Table 3). 
Skate population densities were variable in the Aleu- 
tian Islands. Aggregate skate density ranged from 0 
to 4609 individuals/km 2 , and had an overall mean of 
109.38 ±7.96. The spatial pattern of mean density was 
similar to that of mean species richness and diversity, 
increasing with depth in all but one subregion (Table 4), 
although in this case it was the easternmost subregion 
(subregion 1) that contrasted with the other subregions. 
The minimum mean density was encountered in the 
shallow stratum of subregion 4. The maximum mean 
density was encountered in the middle depth stratum 
of subregion 1 and in the deep stratum of subregion 3, 
and mean density was not as uniform as mean species 
richness across the four subregions. Subregions 1 and 3 
yielded overall mean density values considerably higher 
than those of subregions 2 and 4. For all subregions 
combined, density increased significantly (P<0.0001) 
with increasing depth (Fig. 4). The three most common 
skate species in the Aleutian Islands were B. maculata, 
B. taranetzi, and B. parmifera (Table 5). Bathyraja aleu- 
tica was also moderately common. 
Gulf of Alaska 
The Gulf of Alaska received moderate trawling effort, 
which was concentrated in the western and central 
subregions, and skates were comparatively rare in this 
region. Effort was similar for the shallow and middle 
depth strata, but the deep stratum was not as heavily 
sampled (Table 1), and central subregion 3 received the 
most effort whereas southeastern subregion 5 received by 
far the least. Although skates were encountered through- 
out the survey area, they occurred in less than 40% (828 
of 2094) of the hauls conducted in the region. Mean spe- 
cies richness was generally higher in the central Gulf of 
Alaska (subregions 2, 3, and 4) than in either the western 
(subregion 1) or southeastern subregions (subregion 5) 
(Table 2). Although the overall trend in this region was 
for species richness to be higher at deeper depth strata, 
and the relationship between richness and depth for all 
subregions combined was significant (P=0.0047) (Fig. 
3), this pattern was clearly evident only in subregion 2. 
Maximum species richness was encountered in the deep 
stratum of subregion 2, whereas the minimum species 
richness was encountered across all strata of subregion 
1 and the two shallow strata of subregion 5. Diversity 
indices were not as clearly related to subregion, and only 
subregion 5 showed a strong trend toward increasing 
diversity with increasing depth (Table 3). 
Skate densities were generally low in the Gulf of 
Alaska. Aggregate skate density ranged from 0 to 986 
individuals/km 2 , and had an overall mean of 36.65 
±1.64. The highest mean density was encountered in the 
shallow depth stratum of subregion 5, but the variabil- 
ity associated with this mean was extremely high. The 
lowest mean density was encountered in the shallow 
stratum of subregion 1 (Table 4). Overall mean density 
generally increased with depth (Fig. 4), although the 
