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Fishery Bulletin 106(1 ) 
deeper strata, yielding a significant trend (PcO.OOOl) of 
increasing density with increasing depth for combined 
subregions (Fig. 4). Subregions 2 and 3 exhibited a 
higher overall mean density than subregion 1. Bathyraja 
parmifera (Alaska skate) was by far the most common 
species in this region, appearing in over 86% of hauls 
and with a mean density an order of magnitude larger 
than the next most common species, B. interrupta (Ber- 
ing skate) (Table 5). A total of seven skate species were 
encountered in this region, two of which (B. maculata 
and R. rhina) were encountered in only one or two hauls 
over the entire six-year period. 
Bering Sea slope 
The Bering Sea slope received comparatively little trawl- 
ing effort, but skates were common and species rich- 
ness and diversity were high. Slightly more effort was 
expended on the upper slope (201-600 m depth) than 
on the lower slope (>601 m). Subregion 1, in the south- 
ern part of the eastern Bering Sea, received the most 
effort and the remaining five subregions were sampled 
approximately evenly (Table 1). Skates were encountered 
throughout the entire geographic and bathymetric range 
of the survey region, occurring in 95% (460 of 483) of 
hauls conducted. Species richness was approximately 
50% higher in subregions 2, 4, and 6 (canyons and 
northern gentle slope habitats) than in subregions 1, 
3, and 5 (intercanyons and southern gentle slope habi- 
tats). In four of the six subregions, mean species rich- 
ness was higher on the upper slope than on the lower 
slope (Table 2), and the overall trend was for richness 
to decrease significantly (PcO.OOOl) with increasing 
depth (Fig. 3). Mean species richness was highest on the 
upper slope in subregion 6 and lowest on the lower slope 
in subregion 5. Diversity indices for the three southern 
subregions were similar on the upper and lower slope, 
whereas in the three northern subregions the diversity 
index was notably higher on the upper slope (Table 3). 
Skates were encountered at high densities on the Ber- 
ing Sea slope. Aggregate skate density ranged from 0 
to 22,005 individuals/km 2 , and had an overall mean of 
545.81 ±53.48. These figures are heavily influenced by 
one particularly large haul of B. parmifera during the 
2002 survey. With this haul removed, the density range 
and overall mean became 0 to 5350 individuals/km 2 
and 501.29 ±29.69 individuals, respectively. The larg- 
est mean density was encountered on the upper slope 
in the northernmost subregion (subregion 6), although 
this mean was also influenced by the large haul of B. 
parmifera. With the aberrant haul removed from the 
data set, the largest mean was that of the lower slope 
in subregion 2 (Table 4). The smallest mean density was 
encountered on the lower slope in subregion 5. Subre- 
gions 2, 4, and 6 exhibited considerably higher overall 
mean density values than those of subregions 1, 3, and 
5 — a pattern similar to that of species richness in this 
region. Overall mean density was similar for the two 
depth ranges, but slightly higher on the lower slope and 
increasing nonsignificantly (P= 0.128) with increasing 
depth (Fig. 4). Although B. parmifera exhibited the 
highest maximum density, B. aleutica produced the 
highest mean density value in this region, followed by 
B. lindbergi and B. interrupta (Table 5). A total of ten 
skate species were encountered in this region, although 
two of these (A. badia and B. abyssicola ) were encoun- 
tered in only two hauls. 
Aleutian Islands 
The Aleutian Islands received moderate trawling effort, 
and skates were inconsistently encountered. Trawl- 
ing effort in this region was distributed approximately 
evenly between the two deeper depth strata, whereas the 
shallow stratum received slightly less effort (Table 1). 
The easternmost subregion (subregion 4) was most 
heavily sampled, but effort progressively decreased in 
the more western subregions. Skates were encountered 
