Kiiada and Tezuka: Survey designs for estimating recreational fishery catch 



229 



Figure 1 



Location of the angler survey. Bold lines in the lower figure indicate 

 the area of the Nakagawa River where the sui"vey was conducted. 



in Biwako Lake, Shiga Prefecture (Fig. 1) from early April 

 to the end of May. Thus, recreational anglers catch both 

 naturally recruited wild juveniles and transplanted wild 

 juveniles from Biwako Lake and hatchery-produced ayu 

 released by the cooperatives. Both hatchery and wild stocks 

 consist of a single year class that recruits in the spring. The 

 river fishing season for ayu begins on June 1st and closes 

 at the end of October To estimate the annual ayu catch by 

 recreational anglers in the Nakagawa River, we conducted 

 a longitudinal log book survey in 1993. 



Sampling procedure 



There are four cooperatives that set fishing rights on the 

 Nakagawa River in Tochigi Prefecture. Fishing permits 

 for ayu are sold at the cooperatives and fishing tackle 

 shops, and these permits are valid over the entire Nak- 

 agawa River in the prefecture. The cooperatives record 

 the total number of season- and day-permits sold, and a 

 complete list of season-permit anglers is available. An a 



priori sample size of 120 anglers (an expected sampling 

 fraction of about 0.5% of the total number of season-per- 

 mit anglers) was allocated to the four cooperatives in pro- 

 portion to the number of season-permits sold (Table 1). 

 Anglers who possess a permit (season or day! can fish for 

 ayu over the whole Nakagawa area, regardless of where 

 the permit was purchased. Hence, we treated the samples 

 as if they were drawn from the population by simple 

 random sampling, even though they were drawn by strati- 

 fied random sampling of cooperatives. 



We asked the cooperatives to select samples randomly, 

 but the samples were drawn arbitrarily. The selection, 

 however, was not a purposive sampling; therefore we treat- 

 ed them as random samples. The sampled season-permit 

 anglers were asked to record catch data throughout the 

 fishing season, including each fishing date, the number 

 of ayu caught, and the fishing site, on a printed form, 

 which was returned after the fishing season was over. To 

 estimate the total catch in weight, we also surveyed the 

 body weights of ayu in recreational catches by month. The 



