208 
Observer-reported skate bycatch 
in the commercial groundfish fisheries of Alaska 
Kristy A. Lewis 
Email address for contact author: duane.stevenson@noaa.gov 
NMFS, Alaska Fisheries Science Center 
Fisheries Monitoring and Analysis Division 
7600 Sand Point Way NE 
Seattle, Washington 98115 
Abstract — We analyzed skate catch 
data collected by observers in the 
North Pacific Groundfish Observer 
Program (NPGOP) from 1998 through 
2008 to document recent changes in 
the identification of skates by observ- 
ers and to examine the species com- 
position of observed skate catch in 
Alaska’s groundfish fisheries as well 
as recent trends in skate retention 
by commercial fishermen. Histori- 
cally, almost all skate bycatch has 
been reported by NPGOP observers as 
“skate unidentified.” However, since 
2004 observers have been trained to 
identify skates to the genus and spe- 
cies level. In 2008 over 95% of all 
skates were identified at least to the 
genus level, and over 50% were iden- 
tified to species. The most common 
species of skates identified by observ- 
ers in groundfish fisheries are Bathy- 
raja parmifera (Alaska skate), Raja 
binoculata (big skate), and Bathyraja 
aleutica (Aleutian skate). Species com- 
position of reported skate catch gen- 
erally reflects recent survey-derived 
biomass estimates, with B. parmifera 
dominating the catches in the Bering 
Sea and, to a lesser extent, in the 
Aleutian Islands region, and species 
of the genus Raja dominating catches 
in the Gulf of Alaska. A relatively 
high percentage of the skate catch 
on longline vessels is still reported 
at the family or genus level because 
of difficulties in the identification 
of skates not brought onboard the 
vessel. For the larger skate species, 
the proportion retained for processing 
has increased in recent years as the 
market price for skate product has 
increased. Although observed skate 
catch does not give a complete account 
of skate bycatch in the fisheries of the 
region, observer data provide criti- 
cal information for the appropriate 
management of skate populations in 
Alaska. 
Manuscript submitted 28 September 2009. 
Manuscript accepted 19 January 2010. 
Fish. Bull. 108:208-217 (2010). 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Duane E. Stevenson (contact author) 
Skates are large, long lived fishes with 
relatively slow growth rates and low 
reproductive potential (Ebert, 2005; 
Ebert et al., 2008). These aspects of 
their life history, combined with their 
relatively low mobility and benthic 
habitat, make skates particularly 
vulnerable to fishing pressure and 
slow their recovery from population 
declines; yet few countries have man- 
agement plans for skates or other 
chondrichthyan species (Stevens et ah, 
2000). In cases where skates are tar- 
geted by fisheries, population declines 
can be rapid (Agnew et ah, 2000). 
Moreover, because discard mortality 
can be high (Stobutzki et al., 2002; 
Laptikhovsky, 2004), skate popula- 
tions may be dramatically affected 
by fishing activity even if they are 
not targeted directly (Brander, 1981; 
Casey and Myers, 1998; Dulvy et ah, 
2000; Stevens et al., 2000). In addition 
to population declines, fishing pres- 
sure may lead to significant shifts in 
community structure because declines 
in some species of a skate assemblage 
may be masked by increases in other, 
more resilient species (Agnew et al., 
2000; Dulvy et al., 2000; Stevens et 
al., 2000). Therefore, effective man- 
agement of skate populations requires 
species-specific data on abundance 
trends and exploitation rates. 
Skates are regularly caught in 
nearly all of the commercial ground- 
fish fisheries currently prosecuted in 
Alaska waters, including fisheries 
targeting Pacific cod ( Gadus mac- 
rocephalus), walleye pollock ( Ther - 
agra chalcogramma), yellowfin sole 
(Limanda aspera), and other species 
(Ormseth et al., 2009). In addition to 
their ubiquitous presence as bycatch 
species, skates have been targeted in 
Alaska waters on a short-term region- 
al basis. An unregulated fishery tar- 
geting Raja binoculata (big skate), R. 
rhina (longnose skate), and assorted 
species of Bathyraja (including Alaska 
skates) developed in the central Gulf 
of Alaska (GOA) in February 2003. 
Shifting economic conditions and fish- 
ing seasons soon made other target 
species more valuable, but this short- 
lived fishery revealed that skates can 
quickly become an attractive alterna- 
tive target when other fisheries are 
closed (Matta, 2006). More recently, 
the Alaska Department of Fish and 
Game (ADF&G) approved a pilot fish- 
ery for big and longnose skates in 
the state-managed waters of Prince 
William Sound (ADF&G Emergency 
Order #2-G-E-04-09) in 2009. Else- 
where in Alaska skates are still man- 
aged as part of a large nontarget spe- 
cies complex, although beginning in 
2011 skates in the Bering Sea and 
Aleutian Islands will be managed as 
a separate unit. 
Recent advances in the taxonomy 
of the skates of the North Pacific and 
Bering Sea (Ishiyama and Ishihara, 
1977; Ishihara and Ishiyama, 1985, 
1986; Stevenson et al., 2004, 2007, 
2008) have facilitated increasingly 
detailed identification of skates by 
observers in the commercial fisher- 
ies of Alaska. The resulting wealth 
of detailed catch data now permits 
an examination of skate bycatch on 
a level that was not previously pos- 
sible. The objectives of this study are 
1) to document recent changes for the 
identification of skates in the NPGOP, 
and 2) to provide an overview of po- 
tential management concerns by ex- 
