,-~. / 



306 



Fishery Bulletin 88(2), 1990 



di and dp = observed larval densities during 

 late April and late May surveys, 

 respectively, and 

 / = out-fraction. 



Note that the first term of the right side means the 

 daily mortality rate for the closed population, which 

 was used in Kim and Gunderson (1989), and that the 

 second term is the correction factor due to dispersion. 

 Once the new mortality rate was determined, it was 

 used for the second simulation to obtain a revised 

 estimate of larval abundance in late May 1981. 



Parameter estimation 



Some parameters for the model were available from 

 other studies. Kim and Gunderson (1989) found two 

 dominant larval cohorts during April and May surveys, 

 and assumed that 4-5 mm larvae in late April had 

 grown to 8-9 mm, and regarded this group as cohort 

 1. Also, the 5-6 mm size class in late April and the 9-10 

 mm size class in late May were treated as cohort 2. By 

 comparing the larval abundances of these two cohorts, 

 they estimated an instantaneous daily larval mortality 

 of 0.086 and a daily growth rate of 0.17 mm. 



Daily larval production was derived from daily egg 

 production and time-specific egg mortality during 

 development (Kim and Gunderson 1989). A rapid in- 

 crease in daily larval production occurred in mid-April, 

 and most larvae were produced during late April (Table 

 1). Toward the end of the spawning season, larval pro- 

 duction decreased but tended to be prolonged due to 

 decreased egg mortality late in the spawning season. 



Advective velocities and turbulent diffusivities were 

 derived by examining changes in the distributional cen- 

 troids and variances of several larval size groups. We 

 treated the distribution of a certain size of larvae at 

 a specific time as a single dispersing system in Shelikof 



Strait. The change in the centroids in along- and cross- 

 strait coordinates for three size groups (4-5, 5-6, and 

 6-7 mm) from each survey was used to estimate advec- 

 tion, assumming that larvae were hatched in the same 

 area and that these larvae were not flushed out of 



