To discuss the problem of estimating age composition from length-frequency data in a finite normal mixture distribution, I introduce a hybrid method for estimating the number of components in the full model without limitation and a structured model with relationship among unknown parameters. The computational procedure was expressed in four steps and statistical interpretation/significance of the hybrid method suggested by Eguchi and Yoshioka in 2001. The hybrid method was applied to the well-known length-frequency data for yellow sea bream, Dentex hypselosomus. The computer simulation experiment estimated the number of components in the finite normal mixture model whose probability density function resembles a log-normal distribution. Results showed that the selection performance of the hybrid method for choosing the true model was superior to traditional methods such as Akaike’s information criterion (AIC) and/or Baysian information criterion (BIC).

The relationship between catch and the speed at which the drift fishery gear used to capture the giant pacific octopus, Enteroctopus dofleini, was examined in the Soya/La Pérouse Strait. Latitude, longitude, time and catch data from 15 fishing boats were collected from April to December 2007 to calculate the number of dirft fsihery grounds visited, time spent for drifting, area covered, drift speed of the equipment, and the catch in each fishing ground. Catch was influenced by time spent for drifting and not by drift speed. The catch was greatest when time spent for drifting was over 2.03 h and drift speed was between 5 and 50 cm・s^-1. It is likely that the fishermen practically choose the time when the current speed is appropriate to operate the drift fishery gear in the Soya/La Pérouse Strait, where the current speed varies between 0 and ca. 100 cm・s^-1.

Around the eastern coast of Noto Peninsula, events of sudden strong currents (Kyucho) often cause serious damages to set-net fisheries. Previous studies have suggested that the Kyucho around Noto Peninsula are induced by meteorological disturbances. Here we statistically examined the features of such disturbances in order to understand the mechanisms of the events and to foresee the occurrence, aiming to establish effective measures to prevent the disasters. As the result, we revealed that Kyucho damages often occurred after strong southwesterly exceeding 20 m・s^-1 at Hegurajima Island due to typhoon with central pressure <990 hPa passing south of 41°N at 137°E. The maximum current velocity (v_max) at the eastern coast of the Noto Peninsula was positively correlated with the maximum of the southwest component of wind at Hegurajima (w_max). Conversely, v_max was negatively correlated with the delay of the appearance of v_max after the time of the appearance of w_max. Using these relationships, we propose simple methods to predict the occurrence time and v_max of Kyucho from the forecast information of the magnitude and passage of a typhoon.