Shi et al.: Growth and survival of Pieuronectes vetulus 
169 
Figure 5 
Population sizes (millions) plotted against time (number of days from 1 July) for O' English sole 
off Washington during July through September, 1985-88. All lines represent the predicted tra- 
jectories with the month-specific, density independent mortality model (model 3); solid symbols 
represent the observed data. 
ing line out to bottom depth used in our survey (10- 
15 in shallow waters) was greater than that in 
Kuipers’ experiment (4-8), resulting in better bot- 
tom contact and reduced vessel avoidance. 
During a series of 15 pairs of day-night compara- 
tive tows, for which gear and operating procedures 
were the same as those described in this paper, 
Gunderson and Ellis (1986) failed to detect any sig- 
nificant net avoidance by either butter sole ( Pieuro- 
nectes isolepis) over the length range from 40 to 280 
mm, or Pacific tomcod ( Microgadus proximus) over 
the length range from 60 to 220 mm. In the present 
study, the data for English sole did not show any 
decline in estimated growth with size (Fig. 4). We 
conclude that the efficiency of the gear used in this 
study does not decrease with fish size over the length 
range from 20 to 150 mm and has little influence on 
estimates of growth or mortality. 
Growth 
It has been shown that English sole juvenile migra- 
tion in and out of estuaries is size dependent 
(Gunderson et al., 1990; Shi et al., 1995), and our 
approach to the length modal progression method 
(LMP), namely pooling length data from coastal and 
estuarine areas to estimate growth, accounts for the 
effect of such migrations. Our nearshore survey area 
covered the outer limit of 0 + English sole bathymet- 
ric distribution; less than 1% of the total population 
was found in the deepest nearshore stratum (Shi et 
al., 1995). To minimize the effects of inter-area mi- 
gration, we pooled data from all three areas surveyed 
(Fig. 1), which cover a major portion of waters avail- 
able to English sole juveniles along the Washington 
coast. The resulting estimates fall between faster 
growth rates estimated from previous LMP analy- 
ses (Westrheim, 1955; Smith and Nitsos, 1969; 
Krygier and Pearcy, 1986) and slower growth rates 
estimated from fortnightly ring counts by Rosenberg 
(1982) (Table 4). Gunderson et al. (1990) and Shi et 
al. (1995) suggested that the population of English 
sole juveniles in this study may not be closed, how- 
ever, and that some migrations, especially during 
May and June each year, involve areas outside the 
study area shown in Figure 1. Continuous recruit- 
ment of young juveniles from outside the study area 
would result in an underestimation of growth rates, 
as could emigration of larger juveniles. Our data do 
not show any decline in growth at either the begin- 
ning or end of the survey season (Fig. 4); thus the 
influence of continuous recruitment of small fish or 
emigration of larger fish on growth estimation ap- 
peared to be minimal. 
