547 
Abstract .—Annual and between- 
sex variations in yellowfin sole, Pleuro- 
nectes asper, distributions in the east- 
ern Bering Sea during spring and sum- 
mer were examined by analyzing re- 
search survey data, including a stan- 
dard 15-year time series from 1982 to 
1996, as well as exploratory nearshore 
samples. Yellowfin sole were most con- 
centrated nearshore; abundance gradu- 
ally decreased with increasing bottom 
depth to trace numbers beyond 100 m. 
Male yellowfin sole were distributed 
nearer to shore than females in all 
years.. Proportions of males (no. males/ 
no. both sexes), therefore, increased 
nearshore with decreasing bottom 
depth. Males outnumbered females by 
two to one in waters less than 30 m 
deep. Yellowfin sole during 1982-84 
were distributed in deeper waters than 
during 1985-96. The shallower distri- 
butions after 1984 were attributed to 
greater percentages of mature fish that 
reside in nearshore spawning areas (< 
30 m) during spring-summer. High 
biomass estimates (>3 million metric 
tons) during 1982-84 were attributed 
in part to increased availability of yel- 
lowfin sole within the standard survey 
area. 
Manuscript accepted 10 December 1997. 
Fishery Bulletin 96:547-561 (1998). 
Annual and between-sex variability of 
yellowfin sole, Pleuronectes asper, 
spring-summer distributions 
in the eastern Bering Sea 
Daniel G. Nichoi 
Resource Assessment and Conservation Engineering Division 
Alaska Fisheries Science Center 
National Marine Fisheries Service, NOAA 
7600 Sand Point Way NE, BIN C I 5700 
Seattle, Washington 981 I 5-0070 
Yellowfin sol e, Pleuronectes asper, of 
North America has a Pacific coast 
distribution from British Columbia 
(49°N) north to the Chukchi Sea 
(70°N) and a distribution along the 
Asian coast that ranges from the 
Sea of Japan (35°N) north to the 
Gulf of Anadyr (Fadeev, 1970; Hart, 
1973; Bakkala, 1981; Wilderbuer et 
al., 1992). The eastern Bering Sea 
shelf has supported the largest con- 
centration of yellowfin sole (Bak- 
kala, 1993), with survey biomass 
estimates exceeding 2 million met- 
ric tons (t) since the early 1980s 
(Wilderbuer et al., 1992). 
Spring-summer (June-August) 
distributions of yellowfin sole in the 
eastern Bering Sea are dependent 
upon the timing of their annual cross- 
shelf migration from overwintering 
grounds near the shelf-slope break 
(about 200 m bottom depth) to near- 
shore waters (<50 m bottom depth) 
of Bristol Bay north to Nunivak Is- 
land (Bakkala, 1981; Wakabayashi, 
1989). This migration is thought to 
follow the ice edge as it recedes dur- 
ing spring (Bakkala, 1981). Many ju- 
venile yellowfin sole are likely nonmi- 
gratory and remain nearshore under 
ice-cover during winter (Fadeev, 
1970). Juvenile and adult distribu- 
tions, therefore, overlap during 
spring-summer when adults enter 
nearshore waters to spawn (Nichoi, 
1995, 1997). 
Past yellowfin sole abundance in 
the eastern Bering Sea has varied 
with the magnitude of fishery exploi- 
tation. A predominantly foreign-led 
commercial trawl effort (Japan and 
U.S.S.R.) accounted for annual land- 
ings in excess of 400,000 t from 1959 
to 1962. This trawl effort led to a de- 
cline of the stock and to significantly 
lower annual catches (<100,000 t) 
through the 1970s (Wilderbuer et al., 
1992). Lower exploitation rates dur- 
ing the late 1970s coincided with a 
major increase in stock abundance 
that appeared to peak in the early 
1980s. Considering the high abun- 
dance, annual yellowfin sole catches 
have been moderate since 1982, av- 
eraging 147,433 1 (Table 1). Commer- 
cial trawl catches of yellowfin in re- 
cent years have been limited by fish- 
ery management time and area clo- 
sures owing to by catch of species such 
as Pacific halibut ( Hippoglossus 
stenolepis). Pacific herring ( Clupea 
pallasi ), Tanner crab ( Chionoecetes 
bairdi), and red king crab ( Para - 
lithodes camtschaticus ) (Witherell, 
1995). Despite moderate exploitation, 
annual survey biomass estimates 
have fluctuated widely since the early 
1980s (Wilderbuer 1 ). These fluctua- 
1 Wilderbuer, T. K. 1996. Yellowfin sole. 
Chapter 3 in Plan team for groundfish fish- 
eries of the Bering Sea/Aleutian Islands (ed.), 
Stock assessment and fishery evaluation 
continued on next page 
