Ko Matuda

Selectivity and gear efficiency of trammel nets for kuruma prawn (Penaeus japonicus)

Abstract To study the effect of gear selectivity on kuruma prawn ( Penaeus japonicus ) fishing experiments using trammel nets with different mesh sizes were conducted in Ohmi Bay, Yamaguchi Prefecture, Japan. To provide comparative data the same nets were used on kuruma prawn of known size composition under controlled conditions in a water tank at the Yamaguchi Prefectural Naikai Fisheries Experimental Station. The experiments clarified the gear efficiency of trammel nets for kuruma prawn and confirmed the optimal mesh size for resource conservation. Mesh selectivity by a trammel net used for kuruma prawn shows a peaked curved, with the efficiency at the peak of mesh selectivity increasing in proportion to the mesh size. From the resulting catching efficiency data, an optimum mesh size of 42.8 mm was determined for kuruma prawn of 110–140 mm body length. This paper includes a method for estimating the efficiency of gillnets, which is an extension of Kitaharas method.

A method of determining selectivity curve of separator grid

This paper describes a theory and method for determining a grid selectivity curve from the data of a fishing experiment using a grid separator with several bar spacings. Grid selectivity is defined as the probability that a fish does not pass through a grid given that it has encountered the grid. Assuming that grid selectivity is regarded as a sieve process, grid selectivity, sg, can be expressed as a function of the ratio of cross-sectional diameter to bar spacing as follows: sg(d,L) = Sg(R), where L and d are the cross-sectional diameter of the fish body and bar spacing of the grid, respectively, and R = Ld. Application of the model is demonstrated by a fishing experiment using three grids with bar spacings of 8, 10 and 15 mm, carried out in a shrimp beam trawl in the Inland Sea of Japan. Grid selectivity was plotted against length by bar spacing, of two shrimp species (southern rough shrimp Trachypenaeus curvirostris and mantis shrimp Oratosquilla oratoria), two crab species (charybdid crab Charybdis bimaculata and portunid crab Portunus hastatoides), and frog flounder Pleuronichthys cornutus. The selectivity analysis in terms of the non-dimensional parameter R revealed that, for each species, a single selectivity curve describes accurately data of each of the grids as a master curve of grid selectivity. The master curve of grid selectivity allows estimation of the selectivity curve of grids other than those tested in this experiment.

A mathematical model of fish behavior in a water tank

A mathematical model is proposed to describe the behavior of fish in a water tank. The motion of the fish is expressed by a set of nonlinear state equations which consider external forces representing the interactions with other fish in a school and the effect of environmental fields. The parameters to be included are estimated by using observed data.

Catching efficiency and selectivity of entangling nets

Abstract Fishing experiments for entangling nets (semi-trammel and trammel nets) of different mesh sizes and vertical slacks were conducted simultaneously in Tokyo Bay from 1986 to 1989. The purpose of the experiment was to compare the catch and to study the effect on the catching efficiency and selectivity of variations in the construction of the nets. From the overall catch, it was found out that the semi-trammel net was more efficient than the trammel net. However, based on the type of fish caught, the efficiency of the net is species selective. For gizzard shad ( Konosirus punctatus ), which is the most abundant species caught, the following observations were made; (1) the semi-trammel net caught more fish than the trammel net for any vertical slack; (2) the selection range of 3.6 cm mesh size for both nets was wider compared to larger mesh sizes owing to several large individuals caught by entangling; (3) the master selectivity curve showed a similar pattern for both nets (skewed to the right) with the same modal value. However, the points on the right tail of the trammel net were more scattered.

Estimating the entangling effect of trammel and semi-trammel net selectivity on rainbow trout (Oncorhynchus mykiss)

Abstract The selectivity of gillnets and entangling nets (trammel and semi-trammel nets) was estimated directly by setting nets in outdoor tanks containing a known population of rainbow trout ( Oncorhynchus mykiss ). From the directly estimated selectivity, the entangling effect of the trammel and semitrammel nets was estimated using the gillnet as the standard of comparison. The study assumed that the selectivity curve of gillnets was a slightly skewed unimodal curve while that for entangling nets was bimodal. The bimodal curve was dissected into two unimodal components by presuming that the first component has a selective nature similar to a gillnet while the second component was attributed to additional entangling — a method of capture peculiar to entangling nets. The selectivity of gillnet and the components of the selectivity of entangling nets were fitted using a logarithmic normal distribution. The components of the selectivity curve of the semi-trammel net had higher amplitudes but narrower ranges than the trammel net. The trammel net appeared to entangle a wider range of size and inclined towards smaller individuals. The selectivity of the semi-trammel net attributed to entangling was more severe than the trammel net but had a higher amplitude. The selection range of the selectivity curves of the entangling nets was wider than that of the gillnets. It was suggested that the selectivity of the entangling net could be estimated by comparing it with that of a gillnet of the same mesh size.

Outdoor tank experiments on the influence of soaking time on the catch efficiency of gillnets and entangling nets

Abstract An outdoor tank experiment was conducted to study the influence of soaking time on the catch efficiency of gillnets and entangling nets (trammel and semi-trammel nets). The catch efficiency of the nets was also compared with detecting the difference between entangling nets and gillnets in relation to soaking time. Nets of the same mesh sizes were set simultaneously in separate outdoor tanks containing 200 rainbow trout ( Oncorhynchus mykiss ) whose composition size was known. The experiment was carried out at night using four soaking times; 0.5, 1, 3 and 5 h. The variations of the catch efficiency of all nets had a U-shaped trend, showing that the efficiency increased at the shortest time (0.5 h), decreased at the intermediate time (1 h), and increased again at the longest soaking time. The average catch efficiency of the semi-trammel net appeared to be slightly higher than that of the gillnet.

Headline height of bottom gill nets set across a water flow

Abstract An approximate formula for the headline height of a bottom gill net set across a water flow was derived analytically from estimates of a cross-sectional shape, calculated numerically from differential equations describing the forces of the net. It was assumed that the headline was set perpendicular to a uniform current and with the headline free. This approximate formula is h/l=(2B−wl)/√(2b+kl) 2 U 4 +(2B−wl) 2 where h is the headline height, l the depth of the bottom gill net, B the buoyancy of the headline, w the weight of the net webbing in water, b the drag coefficient of the headline, k the drag coefficient of the net webbing, and U the mean speed of the water flow within the net height. This formula was compared with data obtained separately in a flume experiment, close agreement being obtained.

A simulation study on self-organization in the behavior of a heterogeneous fish school

Abstract A fish school is considered as a typical example of autonomous decentralized system (ADS) or a self-organizing system existing in nature, because it often shows a high degree of coordinative behavior in the absence of a leader. A mathematical model was proposed in our earlier paper to describe the behavior of a homogeneous fish school which consists of individuals with almost the same character. In this paper, another model is proposed to describe the behavior of a heterogeneous fish school, in which there exist individuals with different characters. Since the behavior of a fish school varies with environmental variations, simulations are carried out by setting a box-shaped trap in a behavior space as an obstacle. The self-organization of the school and the variations of moving pattern with changing the quantity of information exchange among individuals are discussed.

A Methodology for Mathematical Modeling of Fish Behavior in a Water Tank

Abstract This paper deals with a method for investigating the behavior of fish in a water tank. The motion of fish is described mathematically by nonlinear state equations, in which the main causes for the motion are expressed as the components of the external force. A water tank experiment is carried out for obtaining the observation records of fish behavior. The time series data of the position for each fish is calculated from the image data recorded by a video tape. The parameter included in the model are estimated by using the least squares algorithm. As case studies, results are shown for two experiments in which bitter ling and rainbow trout are used respectively

Modeling of Fish Behavior in Relation to Fishing

Abstract The purpose of this paper is to develop a method of modeling and simulation in the fishing techniques and tactics. The motion of fish is described by the nonlinear state equations, which contain the fundamental elements of fish behavior. The model parameters are estimated by using the observation data on a water tank experiment with small fish. The moving patterns of the school obtained by the computer simulation are examined in a good agreement with the experimental results. It is confirmed that the proposed model is available for investigating the fish behavior related to the fishing gears.