Teisuke Miura

Spawning behavior and interspecific breeding in three japanese greenlings (hexagrammidae)

The spawing behavior ofHexagrammos otakii. H. octogrammus andH. agrammus was observed in two different regions of northern Japan using underwater video cameras placed near nests guarded by males. The spawning behavior of the three species consisted of similar patterns, although body size and nuptial coloration and nest location of territorial maleH. otakii differed from those of the other twoHexagrammos species. The courtship display of territorial males in each species involved rushing, butting and undulation of the trunk. When a female entered the nest, the male leaned his head on the future spawning bed in the nest and spasmodically undulated his trunk. The female that responded to the courtship laid her eggs within the seaweed bed. The territorial male then passed over the eggs, touching his genital pore to the egg mass, and released sperm. Sneaking by other males was frequently observed following the sperm emission. In both regions, females ofH. octogrammus andH. agrammus commonly responded to courtship of maleH. otakii and mated with them, but not vice versa. Possble reasons for the natural occurrence of such unidirectional hybridization are discussed.

Effect of towing speed and net mouth size on catch efficiency in framed midwater trawls

To investigate fish density using rigid-mouth, towed net gear, such as a tramed midwater trawl (FMT), it is necessary to know the catch efficiency. The catch efficiency with an FMT is described as the rate of fish entering the net (entering rate) versus the rate of fish retention, i. e. the mesh selectivity. This study investigated the change in the catch efficiency under several towing conditions using three types of FMT of different net mouth areas (4.0, 12.3, and 16.0 m2) with the same mesh size. The catch efficeency of the FMT was evaluated by comparing catch per unit effort obtained from each towing condition. The catch efficiency of FMT varied with towing speed and net mouth area. Particularly, the effect of net mouth area on the catch efficiency was greater than that of towing speed. Additionally, under the same towing condition, the catch efficiency for large length fish was lower than that for small length fish.

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.

Total utilization of squids: its zero emissions approach

Abstract Zero emission was advocated as ZERI (Zero Emission Research Initiative) by Gunter Pauli in United Nations University in 1994. Afterwards, this concept has been rapidly generalized. In the fishery, this idea is also beginning to spread for solution of problems. A large amount of raw squid material is used in our country, and, as a result, the squids- processing industry has generated a large amount of wastes. Thinking of this point, we have begun the research on utilization of squid wastes. One is the development of the dyestuff extracted from squid ink. Another is the artificial bait made from squid liver. The former is a trial of clarifying the industrial character in region by the reason why squids are used not only for food but also for culture and art. The latter was developed for the tuna long line fishery. This fishery is currently done in the sea all over the world. Because the nitrogen included in the bait is carried out to the sea area in foreign countries, it would contribute to the world circulation of nitrogen. In this respect, it is thought that the artificial bait needs some incentives in price competition. Moreover, it should be recognized as an ecological commodity in the future.

A simulation study of stationary nets by the use of a compartmend model

Computer simulations using compartment models were performed to examine the characteristics of stationary nets. Simulations showed that the front funnel affected the fish catching speed and the rear funnel primarily affected the number of fish retained in the front bag net.It was found that the fish density of a three compartment model and a two compartment model could increase by 2.64 times and 1.74 times the standard density of fish, respectively.In addition to these facts, Synergism was found between the functions of funnels (front and rear).