Stevenson et at: Patterns of species richness, diversity, population density, and distribution in the skates of Alaska 
33 
Table 6 
Depth range (m) for skate species encountered in bottom-trawl survey hauls performed in the eastern Bering Sea (shelf and 
slope), Aleutian Islands, and Gulf of Alaska from 1999 through 2004. * = not collected in this region. 
Species 
Bering Sea shelf 
Bering Sea slope 
Aleutian Islands 
Gulf of Alaska 
Overall 
Bathyraja parmifera 
19-190 
202-392 
47-283 
62-375 
19-392 
B. aleutica 
77-173 
202-1200 
47-535 
29-882 
29-1200 
B. maculata 
174 
206-1200 
91-488 
185-208 
91-1200 
B. interrupta 
53-190 
202-1017 
64-369 
37-566 
37-1017 
B. taranetzi 
77-153 
202-1063 
82-488 
64 
64-1054 
B. lindbergi 
* 
342-1200 
342-458 
917 
342-1200 
B. minispinosa 
* 
206-1200 
223-368 
666 
206-1200 
B. trachura 
* 
221-1200 
369-407 
345-946 
221-1200 
B. mariposa 
* 
* 
95-457 
* 
95-457 
B. abyssicola 
* 
951-1400 
* 
* 
951-1400 
Raja rhina 
70-139 
* 
87-133 
24-601 
24-601 
R. binoculata 
37-135 
* 
26-192 
16-376 
16-376 
Amblyraja badia 
* 
1508-1556 
* 
* 
1508-1556 
relationship was not significant (P=0.117). Subregions 
4 and 5 seemed to contradict this trend, with consider- 
ably higher mean density values in the shallow stratum, 
but the standard errors of these means indicated that 
catches in these subregions were highly variable. Like 
species richness, mean density was higher in the central 
subregions and lower in the western and southeastern 
subregions. The two Alaskan species of the genus Raja 
( R . binoculata and R. rhina) were the most common 
skates in this region (Table 5). The only two species of 
Bathyraja that were relatively common in the Gulf of 
Alaska were B. interrupta and B. aleutica. A total of ten 
skate species were encountered in this region, but four 
of these were recorded in five or fewer hauls. 
Species distributions 
Of the 14 species of skates currently known from Alaska, 
13 were encountered on the surveys included in this 
study, and 5 of these species were found in all four 
regions. Two species ( B . abyssicola and Amblyraja badia) 
were encountered only on the Bering Sea slope, and one 
{B. mariposa) was encountered only in the Aleutian 
Islands. Bathyraja violacea, although known from Alas- 
kan waters, was not encountered in these surveys. 
Some species of the genus Bathyraja were commonly 
and widely encountered in all survey regions (Table 6). 
Bathyraja parmifera, the most common species of skate 
in Alaskan waters, was found throughout all the survey 
regions (Fig. 5A). Bathyraja aleutica (Fig. 5B) and B. 
interrupta (Fig. 5C) were also widespread, both geo- 
graphically and bathymetrically. Although much more 
rarely encountered than the aforementioned species, B. 
trachura (Fig. 5D) was also found throughout all survey 
regions in deep hauls. 
Other species were common in some survey regions, 
but rarely (if ever) encountered in others. Bathyraja 
maculata (Fig. 6A) and B. taranetzi (Fig. 6B) were com- 
monly encountered on the Bering Sea slope and in the 
Aleutian Islands at broad depth ranges (Table 6), but 
B. maculata was recorded only a few times in the Gulf 
of Alaska, and B. taranetzi was not recorded east of 
Unimak Pass. Bathyraja lindbergi (Fig. 6C) and B. 
minispinosa (Fig. 6D) were common only on the Bering 
Sea slope, but rarely encountered elsewhere. Raja bin- 
oculata (Fig. 7A) and R. rhina (Fig. 7B) were common 
only in the Gulf of Alaska, although R. binoculata was 
also encountered several times in the Bering Sea and 
eastern Aleutian Islands. 
Three skate species were encountered in only a few 
hauls throughout the 1999-2004 survey period (Fig. 8). 
Bathyraja abyssicola and A. badia were encountered 
only in a few deep hauls on the Bering Sea slope at 
depths greater than 950 m, and Bathyraja mariposa 
was encountered only in the central Aleutian Islands. 
Discussion 
Recent NMFS bottom-trawl surveys provide a wealth 
of reliable species-specific data on the geographic and 
bathymetric distributions of the skates of Alaska, as well 
as insight into relative population densities and regional 
species assemblages. Although most of the skate spe- 
cies of Alaska have relatively widespread distributions, 
each geographic and bathymetric region of Alaska has 
its own characteristic skate fauna and demographic 
characteristics. 
The eastern Bering Sea shelf supports large popu- 
lations of fishes and invertebrates and serves as an 
important commercial fishing area. Among skates, 
B. parmifera is by far the most common species, ac- 
counting for over 90% of the skate catch of this region. 
Therefore, even though skates are encountered in the 
