Nichol: Annual and between-sex variability of Pleuronectes asper 
559 
ner bays) totaled approximately 40,184 km 2 
(Fig. 1). In contrast, the two nearest shore strata 
within the AFSC survey area total 77,871 km 2 
(stratum 1) and 41,027 km 2 (stratum 2), respec- 
tively. The coastline areas, thus, offered yellow- 
fin sole a considerable refuge from the AFSC 
bottom trawl survey. According to past samples 
from Togiak Bay and Kuskokwim Bay areas 
(Table 2), yellowfin sole are more concentrated 
in the coastline areas than within the standard 
AFSC survey area (Fig. 4). Considering the vast 
unsampled areas near shore, as well as the large 
yellowfin sole concentrations that inhabit these 
areas, annual fluctuations in biomass within the 
standard AFSC area should be expected. 
Biomass estimates generated from standard 
AFSC eastern Bering Sea trawl surveys are 
considered a relative measure of population 
abundance. However, because nonsurveyed 
nearshore areas contain higher concentrations 
of yellowfin sole and because males outnumber 
females there, standard area biomass estimates 
underestimate male abundance. Distribution 
plots suggest a more extended northwesterly 
distribution of females compared with males. 
Within the northwest area (subareas 2, 4, and 
6) the average proportion of males from 1982 to 1996 
was 0.33 ± 0.016 (95% confidence) compared with 
0.50 ± 0.010 in the southeast area (subareas 1, 3, 
and 5). The lack of males in the northwest area may 
be an indication that a large percentage of males 
missed by the survey inhabit nearshore waters of 
Kuskokwim Bay and waters east of Nunivak Island 
(Fig. 1). 
Bottom temperature may be one factor that has 
influenced the availability of yellowfin sole to the 
standard AFSC survey. Except for the years 1982- 
84, when fish availability was affected more by popu- 
lation structure, biomass estimates were generally 
lower during colder years (Fig. 9). Midshelf bottom 
temperatures were chosen to represent annual tem- 
perature regimes because water exchange is mini- 
mal when compared with the inner shelf (< 50 m) 
and outer shelf (>100 m) waters (Coachman, 1986; 
Wilderbuer et al., 1992). Distribution patterns, as 
well as timing of the annual yellowfin sole cross-shelf 
migration, may in part be dependent upon the an- 
nual temperature regime. Fadeev (1965) indicated 
that spring yellowfin sole migrations occurred one 
month earlier than usual during years when warm 
water developed earlier on the eastern Bering Sea 
shelf. Pola et al. (1985) also demonstrated, using 
simulation models, that summer yellowfin and rock 
sole distributions could be established two months 
earlier in a warm year than in a cold year. If ice-edge 
Figure 9 
Increase in estimates of yellowfin sole ( Pleuronectes asper) 
biomass as related to mean midshelf (50-100 m) bottom 
temperatures for years 1985-1995. Line represents the lin- 
ear regression of biomass (dependent variable) against 
bottom temperature (independent variable); r 2 = 0.32, n = 
12, slope = 0.15 (two-tailed P=0. 054), intercept = 2.08. Note 
that 1982-84 data were excluded because the population 
structure was unique during those years. 
