Gunderson: Spatial patterns in the dynamics of slope rockfish stocks 
223 
arrowtooth 
POP 
Figure 2 
Species composition of the catch (kg) during the 1992 survey of north- 
ern Washington index sites. Arrowtooth = arrowtooth flounder; Do- 
ver = Dover sole; rex = rex sole; and POP = Pacific Ocean perch. 
sablefish 
dogfish 
other 
Dover 
hake 
halibut 
other rockfish 
Table 4 
Mean catch rates (kg/h) and their standard error (SE) for surveys of the northern Washington index sites, 1968-92. 
1968 
1969 
1970 
1992 
kg/h 
SE 
kg/h 
SE 
kg/h 
SE 
kg/h 
SE 
S. alutus 
205.3 
56.8 
211.6 
32.6 
230.0 
34.8 
186.9 
25.4 
S. aleutianus 
9.5 
6.6 
32.8 
11.1 
9.0 
1.6 
28.9 
10.1 
S. diploproa 
19.9 
5.9 
15.7 
4.6 
9.8 
2.0 
16.6 
6.7 
S. cramer i 
4.8 
0.9 
12.6 
2.7 
13.3 
3.2 
6.7 
1.6 
Total Sebastes 
247.0 
59.7 
348.5 
65.2 
276.7 
37.0 
257.5 
35.6 
S. alascanus 
4.0 
0.5 
6.6 
1.7 
8.1 
1.1 
14.4 
1.4 
Total catch 
592.5 
68.0 
Pacific ocean perch in Moresby Gully, Leaman ( 1991) 
found that the 1952 year class still dominated sur- 
vey catches as 30-year-olds in 1982 (Fig. 6). A com- 
parison of the 1992 age composition in the northern 
Washington index area with that of lightly (Moresby 
Gully) and heavily (Langara Spit) exploited stocks 
off British Columbia (Fig. 6) suggests that Pacific 
ocean perch stocks in the index areas still showed 
signs of heavy exploitiation. Although the catch curve 
for the index area does not show the truncation at 
age 40 that characterized the heavily exploited 
Langara Spit stock, stocks in this area can hardly be 
classified as lightly exploited. The size composition 
of stocks at the index sites (Fig. 7) reflects little of 
the rather substantial interannual changes in age 
composition seen in Figure 5. This is due to the un- 
informative nature of the length data in relation to 
age composition, characteristic of slow-growing fish 
in general. 
Mean length at age declined with depth (Fig. 8), a 
phenomenon previously reported in a number of stud- 
ies (Westrheim, 1973; Gunderson, 1974). The results 
are summarized in terms of predicted length at age 15 
with the Bertalanffy growth model, following 
Gunderson (1974). Age 15 was taken as the refer- 
ence age because this was generally the oldest age 
group for which age-length data were available from 
all sampling depths and reflects the accumulated 
