308 



Fishery Bulletin 88(2). 1990 



Alaska Peninsula 



Alaska Peninsula 



Figure 2 



Contours of observed ( ) and estimated ( — ) 



distributions of (a) 8-9 mm and (b) 9-10 mm walleye 

 pollock larvae during late May 1981. Source points of 

 larvae are indicated by ( + ) in each map. 



of larvae within the simulation box was compared with 

 the observed values, because the area used in the 

 simulation could be regarded as the survey area. In 

 general, the trends in size abundance curves, as well 

 as the absolute abundances, were very similar to one 

 another. The abundance of two major cohorts, both 

 observed and simulated, consisted of about 50% of the 

 total abundance. 



Discussion 



The application of a diffusion-advection model to ex- 

 amine the dispersal of larvae helps not only to explain 

 spatiotemporal distribution of abundance but also to 

 revise estimates of population parameters such as lar- 

 val mortality. Difficulties in determining parameter 

 values, however, often arise in this kind of study. In 

 describing plankton distribution, the physical proper- 

 ties (diffusion coefficients and advection rates) often 



