166 
Fishery Bulletin 95 ( 1 ), 1997 
Early and late settlement was defined by visual 
inspection of length frequency (Shi et al., 1995). A 
recruitment influx with mean modal length less than 
40 mm during the May survey was defined as late 
settlement, and that with mean modal length greater 
than 40 mm in May was defined as early settlement. 
A multiple-partial F-test was used here to test the 
significance of settlement time (/3 ; c), year (/1 .), den- 
sity (P 3 d t ), and temperature (p 4 Tp effects on growth. 
The computer program MGLH (SYSTAT [Wilkinson, 
1989]) was used to carry out all calculations. 
Mortality rates The significance of density and season 
effects on mortality was examined by using the restated 
Beverton-Holt equation (Beverton and lies, 1992): 
dP 
— = -^ 1+f i 2 ]nP) t (5) 
Pdt 
1) By integrating Equation 5 with fi 2 = 0, the den- 
sity-independent mortality model is 
P,,= P oi e ~’“‘‘- < 6 > 
2) Integrating Equation 5 over the time period from 
t = 0 to t = t i without any constraint on /li 1 or /u 2 , 
the full model is 
P t = e u 
"-I) ; 
(7) 
3) Integrating Equation 5 with = 0, and allowing 
to vary, the model becomes 
P ol e M t , =0 to 31 (July) 
< P 0; e- #i ' (32) e" /J " (ti “ 32) t t =32 to 62 (August) 
P e -^ e -^62-32) e -ru r e2) t > 62 (September) 
l “ 1 (8) 
where P is the population of juvenile English sole in 
our study area; /u 1 is the density independent coeffi- 
cient, as defined in Beverton and lies (1992), and |r 9 
is the density-dependent coefficient. 
Population estimates from the surveys were fitted 
to the following three competing models, by using 
nonlinear least-squares regression (Wilkinson, 1989): 
where t i = time, number of days elapsed since 1 July 
for surveys conducted in year i ( 1985-88); P t - the ob- 
served total population size (0 + group ) for all areas com- 
bined at time t i in year i; and P oi = initial total popula- 
tion size on 1 July in year i. P m was estimated as a 
parameter along with the coefficients q, and q 2 . n', 
ji", and fi'" are the density-independent mortality 
