24 
Abstract — Six years of bottom- 
trawl survey data, including over 
6000 trawls covering over 200 km 2 
of bottom area throughout Alaska’s 
subarctic marine waters, were ana- 
lyzed for patterns in species richness, 
diversity, density, and distribution of 
skates. The Bering Sea continental 
shelf and slope, Aleutian Islands, and 
Gulf of Alaska regions were stratified 
by geographic subregion and depth. 
Species richness and relative density 
of skates increased with depth to the 
shelf break in all regions. The Bering 
Sea shelf was dominated by the 
Alaska skate ( Bathyraja parmifera), 
but species richness and diversity 
were low. On the Bering Sea slope, 
richness and diversity were higher 
in the shallow stratum, and relative 
density appeared higher in subre- 
gions dominated by canyons. In the 
Aleutian Islands and Gulf of Alaska, 
species richness and relative density 
were generally highest in the deepest 
depth strata. The data and distribu- 
tion maps presented here are based on 
species-level data collected throughout 
the marine waters of Alaska, and this 
article represents the most compre- 
hensive summary of the skate fauna 
of the region published to date. 
Manuscript submitted 16 May 2007. 
Manuscipt accepted 1 August 2007. 
Fish. Bull. 106:24-39(2008). 
The views and opinions expressed or 
implied in this article are those of the 
author and do not necessarily reflect 
the position of the National Marine 
Fisheries Service, NOAA. 
Emerging patterns of species richness, diversity, 
population density, and distribution in 
the skates (Rajidae) of Alaska 
Duane E. Stevenson (contact author ) 1 
James W. Orr 1 
Gerald R. Hoff 1 
John D. McEachran 2 
E-mail address for D. E. Stevenson: duane.stevenson@noaa.gov 
1 National Oceanic and Atmospheric Administration 
National Marine Fisheries Service, Alaska Fisheries Science Center 
Resource Assessment and Conservation Engineering Division 
7600 Sand Point Way NE 
Seattle, Washington 98115 
2 Department of Wildlife and Fisheries Sciences 
Texas A&M University 
College Station, Texas 77843 
Patterns of species richness, diversity, 
density, and distribution for the spe- 
cies of skates inhabiting the North 
Pacific Ocean and Bering Sea are 
still largely unknown. Earlier stud- 
ies have been limited because of prob- 
lems with identification of skates in 
the field and, to some degree, in the 
laboratory. Summarizing trawl survey 
data for commonly encountered spe- 
cies, Allen and Smith (1988) reported 
serious problems in the fisheries and 
survey data reported for even the most 
common skates throughout Alaska 
and the eastern North Pacific Ocean 
because of widespread problems with 
field identification of skates. Simi- 
larly, in the only previously published 
analyses of skate abundance and dis- 
tribution data for Alaska, Teshima 
and Wilderbuer (1990) and Raschi et 
al. (1994) treated their data in the 
aggregate at the family level because 
of difficulty with identification of spe- 
cies. In contrast, Japanese and Rus- 
sian authors have published several 
studies including general species-level 
information on the skate fauna of the 
western North Pacific Ocean and Sea 
of Okhotsk (Dudnik and Dolganov, 
1992; Nakaya and Shirai, 1992; Dol- 
ganov, 1999, 2001). 
Skates present difficulties for iden- 
tification because they are a mor- 
phologically conservative group of 
fishes, and although they represent 
a large proportion of the diversity of 
elasmobranchs worldwide, external 
morphological differences among spe- 
cies (or even genera) are often subtle. 
Moreover, the extent of morphologi- 
cal variation in many species is poor- 
ly known despite earlier taxonomic 
work (Ishiyama and Ishihara, 1977; 
Ishihara and Ishiyama, 1985, 1986), 
and although molecular methods have 
shown promise for species identifica- 
tion in the laboratory (Tinti et al., 
2003; Bremer et al., 2005; Spies et 
al., 2006), skates are often difficult 
to identify in the field. In Alaska wa- 
ters, namely the eastern Bering Sea, 
Aleutian Islands, and Gulf of Alas- 
ka, this has been particularly true 
as Allen and Smith (1988), Teshima 
and Wilderbuer (1990), and Raschi et 
al. (1994) have noted. More recently, 
Mecklenburg et al. (2002) stated that 
the poorly understood taxonomic rela- 
tionships of the skates in this region 
complicate the determination of spe- 
cies distributions. These challenges 
are compounded by the fact that 
skates are generally large fishes and 
are, thus, difficult to collect, preserve, 
and curate. Therefore, they are poorly 
represented in museum collections and 
difficult to study in the laboratory. 
Because of identification difficulties 
and a relative lack of commercial im- 
