228 



Abstract— Longitudinal surveys of ang- 

 lers or boat owners are widely used 

 in recreational fishery management to 

 estimate total catch over a fishing 

 season. Survey designs with repeated 

 measures of the same random sample 

 over time are effective if the goal is 

 to show statistically significant differ- 

 ences among point estimates for succes- 

 sive time intervals. However, estimators 

 for total catch over the season that are 

 based on longitudinal sampling will be 

 less precise than stratified estimators 

 based on successive independent sam- 

 ples. Conventional stratified variance 

 estimators would be negatively biased 

 if applied to such data because the 

 samples for different time strata are 

 not independent. We formulated new 

 general estimators for catch rate, total 

 catch, and respective variances that 

 sum across time strata but also account 

 for correlation stratum samples. A case 

 study of the Japanese recreational 

 fishery for avu tPlecoglossus altivelis) 

 showed that the conventional stratified 

 variance estimate of total catch was 

 about 10^:i of the variance estimated by 

 our new method. Combining the catch 

 data for each angler or boat owners 

 throughout the season reduced the vari- 

 ance of the total catch estimate by 

 about 75%. For successive independent 

 surveys based on random independent 

 samples, catch, and variance estima- 

 tors derived from combined data would 

 be the same as conventional stratified 

 estimators when sample allocation is 

 proportional to strata size. We are the 

 first to report annual catch estimates 

 for ayu in a Japanese river by formu- 

 lating modified estimators for day-per- 

 mit anglers. 



Longitudinal logbook survey designs for 

 estimating recreational fishery catch, with 

 application to ayu iPlecoglossus altivelis) 



Shuichi Kitada 



Tokyo University of Fisheries 



4-5-7 Konan, Minato 



Tokyo 108-8477, Japan 



Email address kiladaia'tokyo-u-fish.ac ip 



Kiyoshi Tezuka 



Nakagawa Branch 



Tochigi Prefectural Fishenes Expenmental Station 



Ogawa, Nasu 



Tochigi 324-0501, Japan 



Manuscript accepted 14 September 2001 

 Fish. Bull. 100:228-243 (2002). 



Angler surveys are widely used in fish- 

 ery management to estimate recreation- 

 al catch, and there is an extensive body 

 of literature on this subject (see Guthrie 

 et al., 1991). Pollock et al. (1994) pub- 

 hshed a manual on angler sui-vey meth- 

 ods and their applications in fishery 

 management. The first purpose of our 

 study is to make two very important 

 points for the designers of recreational 

 fishery surveys: 1 ) longitudinal surveys 

 taking repeated measures on the same 

 random sample of anglers or boats over 

 time are better than successive indepen- 

 dent surveys if the goal is to determine 

 significant trends in catch and fishing 

 effort, and 2) stratified surveys, or suc- 

 cessive independent surveys based on 

 random independent samples of ang- 

 lers or boats, are better than longitu- 

 dinal surveys if the goal is to obtain pre- 

 cise estimates of annual total catch and 

 fishing effort. If longitudinal fisheries 

 data sets are used to estimate annual 

 catches, then correlations between 

 monthly sample observations must be 

 taken into account when evaluating 

 the precision of catch estimates. This 

 problem is not addressed in the litera- 

 ture, and the variance estimation pro- 

 cedures for this situation are unclear. 

 The second purpose of our study is to 

 estimate the annual catch of ayu iPleco- 

 glossus altivelis) in a river because no 

 estimates have been reported in Japan. 

 In our study, we formulated a new 

 method for accurate variance estima- 

 tion with longitudinal fishery data, ex- 



emplified by a case study of the rec- 

 reational fishery for ayu in Nakagawa 

 River in Tochigi Prefecture, Japan (Fig. 

 1). Annual catch estimates based on 

 sums of monthly estimates were com- 

 pared with those based on combined 

 data for each angler or boat through- 

 out the fishing season. We demonstrate 

 how use of a design with repeated mea- 

 sures facilitates determination of sig- 

 nificant seasonal trends in catches, and 

 show the usefulness of combined (non- 

 stratified) data analysis. We also esti- 

 mate the total annual catch of the ayu 

 fishery by formulating modified esti- 

 mators for day-permit anglers (anglers 

 who are granted permits to take fish 

 for one day). 



Materials and methods 



Case study of ayu 



We used longitudinal data collected for 

 the Japanese ayu fishery to compare 

 estimators of effort and catch and their 

 associated variance estimators. Ayu is 

 the most popular target species of rec- 

 reational anglers in rivers in Japan. 

 In the Nakagawa River (Fig. 1), the 

 upstream run of wild juvenile ayu from 

 the coast begins in late March to early 

 April, and is completed by early July 

 Ayu mature and spawn from September 

 to November, and then die after spawn- 

 ing. Cooperatives release both hatch- 

 ery-produced and wild juveniles caught 



