Yukio Nose

銚子産ホシザメの年齢,成長,繁殖および食性について

Over 400 specimens of Mustelus manazo were collected from Choshi to study its age, growth, reproduction, and food habits. Annuli were estimated to occur on vertebral centra yearly from analysis of monthly marginal growth ratios. Linear relations were obtained between radius of centrum and total body length. Von Bertalanffy growth equations are described as follows; male: lt=l043[l-exp{-0.19 (t+2.00)}]: female: lt=277l[l-exp{-0.032(t+4.77)}]. Both males and females reached their first maturity at 621-640mm and all the specimens over 700mm attained their maturity. However, age determination suggests that females reached maturity at a little older age than males. Monthly gonad indices of males show that copulation occurred between June and July. Gestation period is estimated to be approximately 10 months. Litter size ranged from 1 to 22 with an average of 4.9, although litter size increased with the length of the parent. Stomach content analysis shows that Crustacea were the most important prey animals with 85% occurrence. Among others, percentage occurrence of crabs exceeded 50%. Fishes composed chiefly of sardine were also important food items as well as Polychaeta and Spinculoidea.

Mechanical properties of a rectangular purse seine in ideal conditions

Abstract The mechanical properties of a rectangular purse seine during the pursing stage were studied applying Miyoshis formula. The formula was made under the following assumptions of ideal conditions: (1) the meshes open in a square shape; (2) the setting of the net is done uniformly in a circle; (3) the sinker line moves uniformly; (4) forces are kept in equilibrium. Using the necessary factor determined by the constants obtained in previous studies, the formulae were solved by numerical analysis. The mechanical property curves were made based on the numerical solutions obtained. These curves were applied to a Peruvian small purse seine which is a prototype of a rectangular purse seine. The calculated value of the rigged net depth was verified by the sinker line depth curve obtained from the experiments, and was found to agree with the experimental result. Thus, the graphical method based on Miyoshis formula is useful to determine approximate mechanical properties of a rectangular purse seine during the pursing stage.

Determination of mechanical properties of a Peruvian purse winch

The study was undertaken utilizing only an engine tachometer and an oil pressure gauge of a prototype Peruvian small purse seiner. The empirical relationships between a velocity of a winch (Vw; m/s) and an enging revolution (Ne; rpm), and between an effective force of a winch (Fw; kgw) and an effective output pressure of an oil pump (P-Po; kgw/cm2) were determined based on the equations obtained by the previous study. Assuming the loaded pressure (P; kgw/cm2) and the non-loaded pressure (Po; kgw/cm2) of the pump, since Po=19.7kg/cm2, then Vw=0.000415Ne and Fw=24.5 (P-19.7) Moreover, in standard fishing operations of Peruvian small purse seiners, Vw=0.52m/s and Fw=367kgw could be practically determined. These values could be used to examine the mechanical properties of a fishing gear during fishing operation.

Size of Peruvian small purse seines.

The size of Peruvian small purse seines was examined applying the size of anchovy purse seine. Also, a comparison between Peruvian and Japanese purse seines was undertaken. The size adopted was the overall length (Loa; ft) and gross tonnage (GT; t) of the fishing boat, and float line length (Lf; fm), net height (He; fm) and net area (A; fm2) for the fishing net, where the units were fathoms. Analysis was based on the data for 1967, when it was considered that the fishing net in relation to fishing boat had reached a maximum size. The results were expressed for the size of fishing boat as, Lf/Loa=3.24, He/Loa=0.484, A/Loa2=1.57, or Lf/GT1/3=49.2, He/GT1/3=7.35, A/GT2/3=362.The Lf of Peruvian fishing net was designed shorter than the Japanese one for the same GT.

Comparisons of the equations to estimate the weight in air of nylon netting

We compared the results obtained in our previous studies (one strip of netting and a single mesh) with the results of other authors on the same subjects. We dealt with English knot nylon netting. The comparisons were made with the work of litaka for one strip of netting and with the works of Tauchi, Miyoshi and Iitaka for a single mesh. For the weight of one strip of netting (100 fathoms long and 100 meshes deep), our results fitted very well with the Netting Weight Table values, but Iitakas equation yielded values generally higher. For the weight of a single mesh (ω: two legs and one knot) ω=(π/2)D2 •L •{A+B(D/L)} •ρ, the constants A and B were obtained 1, 4 in Tauchi, 1, 6 in Miyoshi, 0.65, 6.5 in Iitaka, and 0.50, 4.5 in the authors respectively, where D is the diameter of twine, L is the length of one leg, and ρ is the density of twine. The assump-tions for leg and knot length are included in both the works of Tauchi and Miyoshi. litakas equation was derived from the weight of netting in water. Our results were obtained from the measurements of netting based on the theoretical relationships of the weight in air.

The consideration of coastal fishing by the small boats - II. Classification of coastal fishing boats in Iwawada district by the species caught with linear discriminant function.

A total of 275 fishing boats smaller than 5 tons, in the Iwawada Fisheries Cooperative of Chiba Prefecture, was classified by the species gaining the highest income, and further by the stepwise linear discriminant analysis for examining the income of the other species caught in each boat. As the results of the analysis, five groups are discriminated as follows: The number of boats was counted to 112 in G1 group which mainly caught yellowtails, 48 in G2 for flounders, 43 in G3 for miscellaneous species, 39 in G4 for skepjack and tunas, and 33 in G5 for squids. Among these five groups, the average income of catch were the highest in G4 and G5, in which most of the boats were bigger than 4 tons. The G2 and G3 groups were ranked as the lowest in average catch income, while the G1 as the middle, the boats of these three groups consisted mainly of fishing boats under 4 tons.

ON THE TAGGED RATIO METHOD FOR ESTIMATING THE NAURAL MORTALITY COEFFICIENT

When two-release tagging design, such that the first tagged fish (X1) are released some time (τ unit intervals) before fishing starts and the second release (X2) is done just before fishing starts, is used, the natural mortality coefficient (M) may be estimated by the tagged ratio method as follows. M=(A2-A5)+ln(X2/X1)/τ-TWhere A1 and A2 are Y-intercepts of linear regression lines of logarithmic value of sample tagged ratios on time respectively, and T is the tag diminution coefficient which is supposed to be constant and is also estimated simultaneously. An example for calculation by this method is also shown.

AN ANALYSIS OF THE PETERSEN-TYPE FISH POPULATION ESTIMATE

Assuming that the diminution of tags which involves the extra natural mortality of the tagged fish and the loss of tags, occurs at a constant rate throughout the period of experimentation, the extent of overestimation in the PETERSEN-type estimate, caused by the above factors was analysed. The calculation showed that the bias of estimate increases as time passes and tends to approach the maximum limit which is determined by the ratio of the tag diminution coefficient to the total mortality coefficient (Eqns. 4, Table 1 and Fig. 1). In order to eliminate this bias, a method based on the series of sample tag ratios obtained for regular intervals after liberation, was deduced (Eqns. 7 and 14). The validity of this method was ascertained by the bead drawing experiment and comparing the results obtained by this method with those of simple PETERSEN method and the BEVERTON method, the advantages and disadvantages were discussed. It was also shown that the size of natural mortality coefficient may roughly be estimated by using the Authors method and the BEVERTON method together (Table 4).