Stevenson and Lewis: Skate bycatch in the commercial groundfish fisheries of Alaska 
211 
Table 1 
Species composition (% by weight) of observed skate catch by year reported in Alaska’s groundfish fisheries for 1998- 
less than 0.1%. 
-2008. * = 
Taxon 
1998 
1999 
2000 
2001 
2002 
2003 
2004 
2005 
2006 
2007 
2008 2004-2008 
Skate unidentified 
99.7 
99.6 
99.5 
98.6 
98.6 
88.7 
61.3 
25.2 
21.4 
7.1 
2.4 
23.2 
Bathyraja sp. 
* 
* 
0.1 
1.1 
0.2 
0.4 
0.5 
39.3 
34.2 
42.6 
47.4 
33.1 
Bathyraja parmifera 
(Alaska skate) 
* 
* 
0.1 
0.2 
0.7 
7.9 
30.2 
27.2 
36.6 
40.0 
40.1 
34.8 
Bathyraja aleutica 
(Aleutian skate) 
* 
* 
* 
* 
0.1 
0.7 
2.2 
2.6 
1.9 
2.5 
2.7 
2.4 
Bathyraja interrupta 
(Bering skate) 
* 
* 
* 
* 
* 
0.3 
1.6 
1.5 
1.1 
1.3 
2.7 
1.7 
Bathyraja maculata 
(whiteblotched skate) 
* 
* 
* 
* 
* 
0.1 
1.1 
0.4 
0.7 
0.5 
1.0 
0.7 
Bathyraja lindbergi 
(Commander skate) 
* 
* 
* 
* 
* 
* 
0.1 
0.2 
0.1 
0.2 
0.2 
0.2 
Bathyraja taranetzi 
(mud skate) 
* 
* 
* 
* 
* 
* 
0.2 
0.1 
* 
0.1 
0.3 
0.2 
Bathyraja trachura 
(roughtail skate) 
* 
* 
* 
* 
* 
* 
0.1 
* 
0.1 
0.1 
* 
0.1 
Bathryaja minispinosa 
(whitebrow skate) 
* 
* 
* 
* 
* 
* 
* 
* 
* 
* 
* 
* 
Raja sp. 
* 
* 
* 
* 
* 
* 
* 
0.1 
0.5 
* 
0.1 
0.1 
Raja binoculata 
(big skate) 
0.3 
0.4 
0.3 
* 
0.2 
1.7 
2.3 
2.3 
2.4 
3.7 
2.1 
2.5 
Raja rhina 
(longnose skate) 
* 
* 
* 
* 
* 
0.2 
0.5 
1.0 
1.0 
1.9 
1.0 
1.1 
52% was identified to species (i.e., Bathyraja parmifera 
and other species). 
The portion of the OSC that was identified to the spe- 
cies level was dominated by Bathyraja parmifera, Raja 
binoculata, and Bathyraja aleutica (Aleutian skate), 
which accounted for 40.1%, 2.1%, and 2.7%, respectively, 
of OSC in 2008 (Table 1). These proportions have re- 
mained relatively stable since observers began identi- 
fying skates in 2004, with B. parmifera, R. binoculata, 
and B. aleutica averaging 34.8%, 2.5%, and 2.4%, re- 
spectively, of the annual OSC from 2004 through 2008. 
Seven other species of skates, including R. rhina and 
six species of Bathyraja ( B . interrupta, B. maculata, B. 
lindbergi, B. taranetzi, B. trachura, B. minispinosa ), 
have been regularly reported in smaller proportions 
by observers since 2004. Although unidentified skates 
now constitute less than 5% of OSC, a large propor- 
tion of skates are still identified only to the genus level 
(“ Bathyraja sp.” and “ Raja sp.”). 
The species composition of OSC varied by region and 
by gear type within each region. During the 2004-08 
period, Bathyraja parmifera was the most commonly 
observed species in both the Bering Sea and Aleutian 
Islands region (Table 2). In the Bering Sea, no other 
single species made up more than 1.7% of OSC, and a 
large percentage of skates were identified only to the 
genus level. Species composition profiles were similar 
for both types of trawl, but for fisheries using longline 
gear a much higher percentage of skates were not iden- 
tified to the species level. 
In the Aleutian Islands, B. parmifera again accounted 
for a higher proportion of OSC than any other species 
(Table 2). However, notable proportions of B. maculata 
and B. aleutica were reported in this region as well. 
As in the Bering Sea, a large proportion of the skates 
were not identified to the species level, and most of 
the unidentified skates and skates identified to genus 
were encountered in fisheries using longline gear. The 
species composition profile for pelagic trawl gear in the 
Aleutian Islands, with only two species reported and B. 
interrupta accounting for over 80% of OSC, was mark- 
edly different from any of the other region-gear combi- 
nations reported in our study. However, that profile was 
based on only two species composition samples in which 
skates were reported. 
The species composition of OSC was quite different 
in the Gulf of Alaska, where the two species of Raja (R. 
binoculata and R. rhina) are more common, accounting 
for over half of OSC in the region (Table 2). Among 
species of Bathyraja, B. aleutica accounted for the high- 
est proportion in the Gulf of Alaska. The proportion of 
skates not identified to the species level was consider- 
ably lower in the Gulf of Alaska than in either the Ber- 
ing Sea or Aleutian Islands, and the species composition 
