Tasae Kawakami

Race Separation of Deep Sea Smelt of Japan Sea

The spawning season of the deep sea smelt of Japan Sea was found to be very long, extending to several months. Hence it is believed that two or more races could be spawning one after the other. On the basis of otolith patterns this fish population could be separated into two major groups. The developmental pattern of the otolith of the deep sea smelt has been shown in a model else where. Linear discriminant function analysis of seven meristic characters showed a distinct variation between the groups. Tests showed that the yearly variation of the meristic characters were not significant.

ON A SIMPLE ESTIMATION OF WORKING DEPTH OF MID-WATER TRAWL

For successful mid-water trawling, it is necessary to estimate the working depth of the gear within a certain range of accuracy, because the mid-water trawl net have to be swept at the depth of fish school, otherwise nothing will be gained. As the fish schools are detected at various depths by the echo sounder, the net have to be operated at the recorded depth in the course of trawling. The operation of the gear is not so difficult but we can hardly regulate its working depth at an arbitrarily appointed layer. Recently, the depth measuring devices such as the net-sonde and the net depth telemeter are employed practically in the field, but the handling of the gear to which these apparatus are attached is quite troublesome on deck and moreover they are expensive. The authors desired to facililate the estimation of the working depth of the gear by means of a chart which was prepared by a computation based on the supposition that the configuration of the warp in action takes a part of circular arc.

STUDIES ON THE CONFIGURATION OF DANISH SEINE

Considering that the various curves of a fishing net assumed in working condition can be approximated by circular arcs of different curvatures, the authors get theoretically 18 equilibrium equations in regard to the distributing tensions and the shape of the net. From these equations, following relations between the horizontal spread of the wing and the height of the net-mouth were obtained: 1) Increasing of the horizontal spread of the wing and increasing of the stream velocity cause the lowering of the height of the net-mouth. 2) The change of the height of the net-mouth due to the change of the horizontal spread of the wing is diminished by the increase of the stream velocity. Experiments were carried out in a water tank of circulation type with a model net designed by a box-type. Comparing the experimental and the theoretical results, a satisfactory consequence is obtained qualitively.

On the Hygroscopicity of Fishmeal. II

After completely dried in an oven, several kinds of fishmeal (Table 1) were exposed into five humidors at several constant humidities and at an constant temperature (20°C.), and wetted to saturation. The increment of weight was measured. Thus, the hygroscopicity was calculated (Table 2), with the results as follows:- (1) Over the range of 1-0•49 of relative humidity R (in ordinal fraction) the relation between the moisture absorbed per unit mass of the dry matter WR and R is empirically formulated as (W1-WR)n=k(1-R), where n and k are constants (Fig. 1, Table 2). (2) The value of WR has a negative correlation with the fat content of the material, and as the humidity decreases the correlation becomes less close. Seeing that the transfer of moisture in the pile of fish meal obeys the ordinary law of diffusion, the author determined the coefficient of diffusivity K by measuring the distribution of moisture in the fishmeal, which was filled in a glass tube with an open end and kept in a constant humidity, R=0•9, for 1-3 days. The results obtained are summarized in Table 3 from which we can see that the value of K has a negative correlation with the apparent density of the material. This fact leads to the conclusion that the migration of moisture takes place in the space among the particles of fishmeal.