Trawling experiment in a circular water tank to assess the effects of towing speed, light intensity, and mesh shape on active escape of undersized fish

To assess the effect of towing speed and light intensity on the active escape of undersized fish through diamond and square mesh panels, a trawling experiment was simulated in a circular water tank. Juveniles of Japanese dace Tribolodon hakonensis (13-cm length class) were used as experimental fish. They were forced to swim inside a closed framed net with either diamond or square mesh (65-mm mesh size) that was moved using a speed-controllable motor. A submersible infrared CCD camera was used to observe and record the behavior of fish inside the net when it passed in front of the camera. Results indicated significant effects of towing speeds and light intensities (P < 0.05) on the escape of fish through the diamond and square meshes. Increase in light intensity enhanced the ability of fish to escape at lower towing speeds. At higher towing speeds, few fish could escape under light conditions. A strong negative correlation was found between towing speed and the frequency of fish escape (diamond mesh R2 = 0.99, square mesh R2 = 0.96). There was no significant difference between the numbers of fish escaping through the diamond and square meshes. These results suggest that the square-mesh panel may not be effective in the trawl cod end under dark or very low light intensity at high towing speed

Fishery Income Fluctuation with Changing Social Situation and Selecting Fishing Ground, in the Japanese Coastal Squid Jigging Fishery (1975-2008)

In recent years in Japan, falling fish prices and rising fuel costs have worsened the economic conditions for many fisheries-dependent households. Many fishermen select the fishing ground in which they anticipate they can maximize their total catch, even when such grounds are far from their home harbor. As a result, fishermen have the potential to select a fishing ground in which they do not maximize their income. Especially the Japanese coastal squid jigging fishermen need to develop energy-saving squid jigging fishery practices, because of the high fuel consumption in comparison to other fisheries. By using the Management Simulation Method, we show that income fluctuations are caused by various factors. We used social factors and fishing ground factors in this simulation. According to the simulation results, small changes in social and fishing ground situations can result in changes in selection of the optimal fishing grounds. We conclude that the selection of fishing grounds by fishermen based only on their own knowledge and/or intuition might not result in choices that maximize their income, and it is necessary to develop objective methods to choose the fishing ground in which they can maximize their income

The Strength and Composition of Some Tropical Wood of Siam

With the view of determining the strength and composition of some tropical woods of Siam which are now used in the Far East as a special wood for architecture, house furniture and decoration, we have made some experiments. The resnlts obtained are as follows. As will be seen from the above table, the strength of these woods is very big and especially ebony wood is found to be far stronger and heavier than oad woo