FISHERY BULLETIN: VOL. 87, NO. 3, 1989 



A uniform random number generator was used to assign each tow to a 

 month and region, to determine whether the tow was positive or not, and 

 thus to produce n{i,j). 



Assignment of the Time of Tow 



Table 3 hsts parameters for Gamma distributions fitted to the actual time 

 between positive tows minus the minimum time between any two positive 

 tows (i.e., plankton tows which caught at least one anchovy larva) in each 

 region because the Gamma distribution takes all values to be greater than 

 zero. Each distribution is shifted to the right by the constant hsted (the 

 minimum time between any two positive tows). Actual times greater than 

 150 hours were assumed to be periods of transit to and from port and were 

 thus excluded when fitting the distributions. 



The time of the first tow of a simulated survey was chosen randomly and 

 incremented by time intervals selected from the distributions described in 

 Table 3. If the selected time interval was gi-eater than 4 hours, tows with 

 zero catch were inserted. The number of zero tows inserted was the time 

 interval between two positive stations divided by the average travel time 

 between stations (2 hours). 



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