494 
Abstract-Length at age, length at 
maturity, and age at maturity of yel- 
lowfin sole, Pleuronectes asper, in the 
eastern Bering Sea, are influenced by 
area of sampling and bottom depth. 
Yellowfin sole sampled during spring 
and summer bottom trawl surveys 
(1982-94) grew faster in the northwest 
area compared with the southeast area. 
Mean lengths at age were generally 
more than 2 cm greater than those for 
southeast fish at ages greater than 10 
years. Length at 50% maturity in fe- 
males during 1993 and 1994 was re- 
spectively 2.3 cm and 0.94 cm larger in 
the northwest area than in the south- 
east area. In contrast, there was no 
apparent difference in age at 50% ma- 
turity between areas. 
Spring-summer patterns in bathy- 
metric habitation of yellowfin sole dif- 
fer for immature and mature individu- 
als and cause a potential bias in esti- 
mates of growth and maturity. There 
is a clear relation between length and 
depth for immature fish, with older, 
immature fish inhabiting deeper water. 
In contrast, mature fish distribute simi- 
larly by size across a wide range of bot- 
tom depths. As a result, estimates of 
length and age at 50% maturity (L 50 , 
A 50 ) tended to increase with increasing 
bottom depth. Because current resource 
assessment surveys do not sample the 
shallowest areas of the summer distri- 
bution of yellowfin sole, estimates of L 50 
and A 50 are inherently biased high. 
Manuscript accepted 27 February 1997 
Fishery Bulletin 95:494-503 (1997). 
Effects of geography and bathymetry 
on growth and maturity of 
yellowfin sole, Pleuronectes asper, 
in the eastern Bering Sea 
Daniel G. Nichol 
Resource Assessment and Conservation Engineering Division 
Alaska Fisheries Science Center 
National Marine Fisheries Service, NOAA 
7600 Sand Point Way NE 
Seattle, Washington 981 15-0070 
E-mail address: Dan.Nichol@noaa.gov 
Yellowfin sole, Pleuronectes asper, 
inhabit the nearshore shelf areas of 
the eastern Bering Sea, from Bristol 
Bay to north of Nunivak Island 
(60°N lat.XFig. 1), during spring 
and summer months. Adult indi- 
viduals overwinter near the shelf- 
slope break at approximately 200 m. 
Two main eastern Bering Sea over- 
wintering groups, composed mainly 
of sexually mature adults (Krivobok 
and Tarkovskaya, 1964) have been 
identified: a southern complex near 
Unimak Island and a central com- 
plex located west of the Pribilof Is- 
lands (Fadeev, 1970; Bakkala, 1981; 
Wakabayashi, 1989). During spring, 
as the edge of the shelf ice recedes 
toward the coast, yellowfin sole mi- 
grate across the shelf to nearshore 
spawning areas in Bristol Bay and 
off Nunivak Island (Bakkala, 1981). 
Yellowfin sole generally spawn at 
bottom depths less than 50 m (Wil- 
derbuer et al., 1992); most spawn- 
ing activity, however, occurs at 
depths less than 30 m, May through 
August (Nichol, 1995). Juvenile yel- 
lowfin sole probably do not undergo 
the long cross-shelf migration. At 
least some juveniles (<6 years) are 
known to overwinter nearshore 
(Fadeev, 1970; Wilderbuer et al., 
1992), whereas relatively few juve- 
niles overwinter offshore (Krivobok 
and Tarkovskaya, 1964; Fadeev, 
1970). 
Bottom trawl surveys for ground- 
fish resource assessment are con- 
ducted annually in the eastern 
Bering Sea to obtain abundance es- 
timates of commercially important 
fish and invertebrate species. Dif- 
ferences in fish distributions and 
oceanographic factors have prompted 
scientists who analyze survey results 
to stratify the eastern Bering Sea 
into discrete northwest and south- 
east areas, and three different depth 
regimes (Walters and McPhail, 1982; 
Walters, 1983; Wakabayashi, 1989; 
Bakkala, 1993). Thus, both geo- 
graphic and bathymetric factors af- 
fect fish distribution and abundance 
in the eastern Bering Sea. In this 
paper I describe regional differences 
in growth of yellowfin sole (P. asper ) 
from the eastern Bering Sea and 
effects of geographic area and bot- 
tom depth on estimates of length 
and age at maturity. 
Commercial catch records (Norris 
et al. 1 ) indicate that yellowfin sole 
occur in substantial numbers in 
waters shallower than 30 m, where 
1 Norris, J. G., J. D. Berger, and K. T. 
Black. 1991. Fisherman’s guide to catch 
per unit effort and bycatch data from the 
National Marine Fisheries Service Ob- 
server Program: Bering Sea/Aleutian Is- 
land yellowfin sole trawl fishery. AFSC Proc. 
Rep. NOAA-NMFS 91-07, 200 p. Alaska 
Fisheries Science Center, Natl. Mar. Fish. 
Serv., NOAA, 7600 Sand Point Way NE, 
Seattle, WA 98115-0070. 
