Stevenson et al.: Patterns of species richness, diversity, population density, and distribution in the skates of Alaska 
35 
Figure 6 
Distribution of (A) Bathyraja maculata (whiteblotched skate), (B) B. taranetzi (mud skate), (C) B. lindbergi 
(Commander skate), and (D) B. minispinosa (whitebrow skate) based on data from bottom-trawl surveys con- 
ducted in the eastern Bering Sea, Aleutian Islands, and Gulf of Alaska from 1999 through 2004. Black circles 
indicate the presence of the species in one or more survey hauls. Depth contour = 200 m. 
appear at depths of 300-400 m and are more common 
in deeper waters. Thus, there is a degree of assemblage 
separation; one suite of species is found on the lower 
slope and another suite is found on the upper slope but 
overall species richness remains relatively consistent 
throughout the depth range of the survey. A similar 
skate fauna has been reported from the northern Kuril 
Islands and southern Kamchatka (Orlov, 2005; Orlov et 
al., 2007), although trends in species richness in that 
region are unclear. Two additional species, A. badia and 
B. abyssicola, have been only rarely encountered in the 
deep waters of the eastern Bering Sea slope, although 
these species are widely distributed and have been re- 
corded from both sides of the North Pacific Ocean (Zorzi 
and Anderson, 1990; Stevenson and Orr, 2005). Spe- 
cies richness and density both show a clear geographic 
pattern in this region; subregions 2, 4, and 6 exhibit 
higher species richness and density than the other three 
subregions, although this effect is less pronounced in 
the diversity indices. These areas of high species rich- 
ness and density are generally associated with canyon 
features on the Bering Sea slope; this association may 
indicate that skates aggregate near these features. 
Alternatively, it may simply indicate that the skates in 
these areas cluster in the same habitats that are most 
suitable for bottom trawling. 
In the eastern Bering Sea, skate density increased 
with depth from shallow areas to the shelf break, and 
remained relatively uniform on the upper continental 
slope. A similar density pattern has also been observed 
along the Oregon coast (Pearcy et al., 1982) and in 
northwestern Australia (Williams et al., 2001). In the 
subregion encompassing Pribilof Canyon the pattern 
was slightly different; skate density was highest at 
greater depths on the lower slope, in the same general 
deeper depth range (700+ m) as noted by Gordon and 
Duncan (1985) and Merrett et al. (1991) in the north- 
east Atlantic. Although several distributional studies 
published for the western Pacific region have included 
basic distribution, depth range, and relative abundance 
information for some of the same species of skates re- 
ported here (Dudnik and Dolganov, 1992; Nakaya and 
Shirai, 1992; Dolganov, 1998, 1999; Orlov, 1998, 2003; 
Orlov et al., 2007), none of these studies have provided 
