Abstract
Water Pollution due to organic substances, called eutrophication, has gained growing social concern in a region with a closed water body. It is not only detrimental to withdrawal uses such as municipal water supply, but to in-stream uses such as commeircal fishing. A survey questionaire was undertaken in order to estimate eutrophication-caused damage on fish production on a monthly basis. This survey was carried out as part of the current Kasumigaura Project of N. I. E. S., which is a comprehensive research plan directed at inland waterbody planning.
The survey was executed from December 1978 to March 1979, where the survey period was four consecutive months, June to September, of 1978. All the fishery households were sampled for the self-reporting survey, who carried out the designated fishing gears of fixed netting, trawl net and carp culture. A total of 489 out of 976 households responded to the questionaire. The items included in the questionaire were: (1) the species composition of the catch and the damage with the specified symptoms such as fish died in net, infected fish, malformed fish, and stinking fish; (2) the fishing effort involved in obtaining the catch and in avoiding the damage.
The survey results show that fishery households operating either fixed netting or carp culture were affected in terms of the production loss by lake eutrophication more strongly than those engaged in trol netting. Second, the significant mean difference were detected for the average production loss per culture net between fishermen with automatic feeding devices and those feeding with their hands. Third, the regression analysis of the survey data along with the water quality data of Lake Kasumigaura revealed that the damage per catch were positively related to Chlorophyll a data and negatively related to Secchi depth data for fishermen who were actively and in large scale engaged in fixed netting operation.
