558 
Fishery Bulletin 96(3), 1 998 
1985-96 
Figure 7 
Length composition of yellowfin sole (Pleuronectes asper ) in terms of bottom depth and bio- 
mass (metric tons) for years 1982-84 combined and 1985-96 combined. Shaded areas indi- 
cate 22-27 cm length groupings for males, and 25-32 cm length groupings for females. Each 
depth label represents a 10-m range (i.e. 40=40-49 m). 
sampled during the standard AFSC surveys likely 
contained more males than females. Hence, a shift 
of the population to deeper waters possibly exposed 
a higher proportion of males to the survey gear than 
during subsequent years. 
Effects of distribution on survey biomass 
Given that the standard AFSC survey area does not 
encompass the entire yellowfin sole distribution, 
annual distributional shifts between surveyed and 
nonsurveyed areas may explain the annual biomass 
fluctuations observed within the standard AFSC sur- 
vey area. Yellowfin sole biomass estimates within the 
standard AFSC survey area have fluctuated from a 
high of 3.5 million t in 1983 down to 1.9 million t in 
1986 (Table 1). These fluctuations are not possible 
according to yellowfin sole life history and the rela- 
tively light fishing exploitation of this species since 
the late 1970s (Wilderbuer et al., 1992). Stock syn- 
thesis models based on catch-at-age data (Methot, 
1990) predict much more stable changes in yellow- 
fin sole biomass (Fig. 8). Even though these models 
incorporate survey biomass estimates as auxiliary 
information (Wilderbuer 1 ), predicted biomass esti- 
mates from 1982 to 1984 were much lower than what 
survey estimates indicated. I propose that the deeper 
overall spring-summer distributions from 1982 to 
1984 contributed to an inflation of survey biomass 
estimates in contrast with subsequent years, owing 
to increased availability of yellowfin sole to the AFSC 
survey. Strong year classes that were present in the 
survey area during 1982-84 may have become less 
accessible to the survey gear during later years ow- 
ing to their sexual maturation and subsequent mi- 
gration into shallower nearshore spawning waters. 
Nearshore areas from the standard survey bound- 
ary to the coastline (excluding river systems and in- 
