Nichol: Effects of geography and bathymetry on growth and maturity of Pteuronectes asper 
499 
stocks (Grant et al., 1983), the persistence of area- 
based differences suggests that mixing of adults be- 
tween northwest and southeast complexes may be 
minimal. 
Growth-rate differences may be associated with 
geographic differences in yellowfin sole density or 
bottom temperature (or both). Yellowfin sole mean 
density (1982-94; author, unpubl. data), measured 
in catch per unit of effort (kg/hectare) during spring- 
summer, has been consistently higher in the south- 
east area (88.9 kg/ha) than in the northwest area 
(27.8 kg/ha). Spring-summer bottom temperatures 
have also been consistently higher in the southeast 
area than in the northwest area (Fig. 6). The higher 
yellowfin sole growth rate in the northwest areas is 
consistent with density-dependent hypotheses 
(Beverton and Holt, 1957; Cushing, 1975; Rijnsdorp, 
1994) that suggest a negative correlation between 
fish growth and fish density. 
Reasons why fish growth ap- 
pears faster in cooler northwest 
waters are less clear. 
Age-composition data used in 
stock assessments for yellowfin 
sole in the eastern Bering Sea 
(Wakabayashi et al., 1985) have 
been based upon age-length 
keys generated from annual 
age-length collections (Armi- 
stead and Nichol, 1993). Al- 
though independent age (oto- 
lith) collections have been made 
for the southeast and northwest 
areas, age-length keys are cur- 
rently pooled across areas. The 
resulting estimates of growth 
are considered accurate because 
Alaska Fisheries Science Center 
age-structure collections have 
been spread fairly evenly be- 
tween areas. However, given the 
spatial patterns described here, 
separate northwest-southeast 
age-length keys might improve 
the precision of these estimates. 
Implications of depth- 
related sampling biases 
Immature yellowfin sole, like 
many other fish species ( Hunter 
et al., 1990; Macpherson and 
Duarte, 1991; Jacobson and 
Hunter, 1993), undergo an on- 
togenetic migration, distribut- 
ing themselves along a size- 
depth continuum where smaller 
individuals inhabit shallow wa- 
ters and larger individuals in- 
habit deeper waters. A single 
cohort can also distribute itself 
along this size-depth continu- 
um. In doing so, faster-growing 
individuals can be found at 
Males 
Females 
40 
35 
30 
25 
20 
15 
10 
5 
0 
NW 
y«0 
r 
°o # 
V 
>50 
m 
• 
30- 
49 m 
o 
<30 
m 
1 1 1 1 1 1 1 1 ■ ■ ■ i ■ ■ ■ 1 1 1 1 1 1 1 1 1 1 1 1 
5 10 15 20 25 30 
40 — i 
35 
30 - 
25 - 
20 
15 
10 
5 
0 
NW 
•o 
v >50 m 
• 30-49 m 
o <30 m 
0 
5 10 15 20 25 30 
40 
35 
30 
25 
20 
15 - 
10 - 
5 
0 
SE 
qO O a 
Q • 
«• * • 
v >50 m 
• 30-49 m 
O <30 m 
0 
1 I 1 1 1 1 I 1 ' ‘ 1 i 1 ’ 1 1 i * 1 1 1 i 1 1 1 1 i 
5 10 15 20 25 30 
7 
6 
5 
4 
3 
2 
1 
0 
-1 
-2 
-3 
-4 
NW-SE 
• o * 
V w 
° 5 v V qO 
1 ~T t 1 1 1 | 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 
5 10 15 20 25 30 
7 
6 
5 
4 
3 4 
2 
1 - 
0 - 
-1 - 
-2 - 
-3 - 
-4 
NW-SE 
■ . .. v;! S3”* * “ 
«• v* -• 
CO O 
V 
0 
1 1 1 1 1 1 1 1 1 1 1 i 11 1 1 i 1 1 1 1 1 1 1 1 1 i 
5 10 15 20 25 30 
Age (yr) 
Figure 3 
Factorial length at age model results comparing length at age of male and female 
yellowfin sole across bottom depths (m) in both northwest (NW) and southeast (SE) 
areas of the eastern Bering Sea. Age x Area x Depth interactions are included with 
data pooled across 1982-94 age-length collections. 
