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Fishery Bulletin 95(2), 1997 
Table 3 
Number of Pacific ocean perch sampled for length, sex, and 
otoliths during surveys of the northern Washington index 
sites, 1968-92. 
Depth 
Length 
(m) 
and sex 
Otoliths 
1968 
219 
1,316 
486 
293 
868 
392 
366 
800 
241 
Total 
2,984 
1,119 
1969 
219 
592 
584 
293 
2,016 
1,518 
366 
1,837 
1,258 
Total 
4,445 
3,360 
1970 
219 
1,663 
1,120 
293 
1,761 
1,144 
366 
589 
564 
Total 
4,013 
2,828 
1992 
219 
1,432 
355 
293 
1,366 
412 
366 
453 
391 
Total 
3,251 
1,158 
l t =L„(l 
where l f = fork length (cm) at age t years; 
L oo = theoretical asymptotic length; 
K = constant expressing rate of approach to 
Lj, and 
t 0 = theoretical age at which l. = 0. 
A total of 453 Pacific ocean perch females were clas- 
sified as to state of maturity during the 1992 survey, 
following the criteria described in Gunderson ( 1977). 
Maturity observations were obtained from all index 
site-depth strata, and emphasis was placed on ob- 
taining as many observations as possible from fish 
less than 38 cm, the size at which the transition from 
juvenile to adult occurs. A maximum-likelihood al- 
gorithm (SYSTAT) was used to fit these data to the 
logistic model: 
p - _ , 
' l + e- ,a+/3/ ’ 
where P^, = proportion mature at length l (cm); 
a, (3 - constants; and 
—oc 
—— - l Q5 - length at which 50% of the females 
P are mature. 
The variance of -a/j3 was estimated with the delta 
method (Gunderson, 1977), and the variance esti- 
mates for a and [3 were provided by SYSTAT. 
Results 
Rockfish dominated the catches in the northern 
Washington index sites during the 1992 survey (Table 
4; Fig. 2), and Pacific ocean perch was the most abun- 
dant species present. In contrast to the sharp reduc- 
tions in rockfish abundance in the Canadian portion 
of the Vancouver area (Table 1 ), catch rates for rock- 
fish in the northern Washington index sites (Table 
4) indicated little change in abundance between 1968 
and 1992. Overlapping approximate 95% confidence 
intervals (± 2SE) indicated nonsignificant inter- 
annual differences in the catch rates for most spe- 
cies, including Pacific ocean perch and rougheye rock- 
fish, the two most abundant species of rockfish (Fig. 
3A). Both of these mature relatively late in life and 
are quite long-lived. The median age at maturity 
(t 0 50 ) for females is about 10 years for Pacific ocean 
perch (Gunderson, 1977) and about 20 years for 
rougheye rockfish (McDermott, 1994). Pacific ocean 
perch can live to be 90, rougheye rockfish to 140 years 
(Chilton and Beamish, 1982). As a result, reductions 
in abundance would be expected to be sharp and of 
long duration if stocks off northern Washington had 
experienced the same level of fishing as that observed 
off Canada (Table 1). One species, shortspine 
thornyhead, actually showed a statistically signifi- 
cant increase in abundance over the period covered 
by the surveys (Fig. 3B) despite the fact that this 
species appears to be long-lived (otolith counts indi- 
cate that some individuals live at least 100 years; 
Butler 2 ). 
Comparison of trends in abundance within the in- 
dex sites and within the U.S. Vancouver-Columbia 
area as a whole (as estimated by Stock Synthesis 
analysis, Ianelli et al., 3 ) are also possible in the case 
of Pacific ocean perch (Fig. 4). This comparison sug- 
gests that the abundance of Pacific ocean perch at 
the index sites remained at comparable levels be- 
tween 1968 and 1992, at a time when most stocks in 
the Vancouver-Columbia area continued to decline 
from 1962 levels. 
Nevertheless, stocks within the index area showed 
evidence of significant fishing during 1970-92 be- 
cause the strong 1961 year class present during 
1968-70 (Fig. 5) was no longer apparent (as 31-year- 
olds ) in 1992 (Fig. 6). In a lightly exploited stock of 
2 Butler, J. L. 1995. Southwest Fisheries Science Center, P.O. 
Box 271, La Jolla, CA 92038. Personal commun. 
3 Ianelli, J. N., D. H. Ito, and M. E. Wilkins. 1995. Status and 
future prospects for the Pacific ocean perch resource in waters 
off Washington and Oregon as assessed in 1995. App. B in 
Status of the Pacific coast groundfish fishery through 1995, and 
recommended acceptable biological catches for 1996. Pacific 
Manage. Council, Portland, OR, 39 p. 
