Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, Bunkyo, Nagasaki 852-8521, Japan
An empirical formula expressing the relationship between catch amount and number of pixels of the fish echo displayed in the scanning sonar prior to net shooting was obtained in the coastal purse seine fishery with fishing lights that targets Japanese anchovy Engraulis japonicus. By using this formula, we compared the expected catch amounts of fish abandoned at the end of the luring process with the expected catch amounts of fish at which the fishing master decided to shoot the net. The fishing master always decided to capture a school when the expected amount from the sonar display exceeded 1.5 tons. The probability of net shooting was expressed by a logistic function of expected catch amount. The net was shot at 50% probability when a catch of more than 1.3 tons was expected. The number of luring processes that satisfied the expected amount of over 1.5 tons accounted for only 24% of the total number of luring processes. Thus, the present style of fishing depends on many attempts to lure fish by 3 lighting boats. Cost-saving measures such as energy- and labor-saving technology should be considered to allow for fluctuations in the abundance of E. japonicus, steady increase of fuel prices, and shortage of labor that are expected in the future.