Remotely Operated Vehicles (ROVs) equipped with underwater video cameras are often used to conduct
Visual investigations such as observing fish behavior. It is, however, Very difficult to guide an ROV to its target
Without the aid of an accuracy positioning system. Therefore, We have developed an ROV positioning system
using an ultrasonic pinger, Which presents a highly accuracy real time track pIot.
A pinger is an underwater ultrasonic tag, Whose bearing can be determined from the directivity of a directional
transducer, and the distance from the transducer to the pinger is inferred from the amplitude of the
received pulse. The positioning accuracy in such cases however, is unreliable. In this study, the distance from
the transducer to the pinger is calculated by using an original method in which the receiver and the pinger are
Synchronised to measure the time difference between transmitting and receiving a pulse. A synchronising drift
error which accumulates with time was corrected by using the time average of the distance which was calculated
from the transmission loss. In this way we obtained more accurate measurement of distance. Using the distances
calculated by the synchronising method, We fixed the ROV position using the range-range (p-p) positioning method.
Compared with the hyperbolic positioning method, the positioning accuracy in this study is clearly improved.
A combination method of TV camera census and fishing-gear sampling was devised to estimate demersal fish
abundance on artificial reefs. Capturing area (A') of a fishing gear for a fish species was defined as the area
Where all individuals of the species could be captured by the gear, i.e. catchability q=1. When A'was determined,
density (D) and biomass (B) can be estimated by the fishing gear, calculated from the number captured
(C) and their weight (W) using the equations, D =C/A'and B= W/A'. we evaluated A' for a bottom trammel
net and a bottom long line by sampling where fish densities were measured by a TV camera census. The density
and biomass of the dominant fishes on Okama artificial reef situated at a depth of about 130 m off Kamaishi, Japan,
Were estimated by using these two fishing gears.
To clarify the characteristics of NOx emission and optimum speed for environment on a small fishing boat,
concentration of NOx and O2, Ship's speed and fuel oil consumption were examined by using 12 GT size fishing
boat equipped with 265kW/2200 rpm 4-CyCle marine diesel engine. Two comparative examinations, Sailing and
trawling conditions, were carried out in order to study the relationship between the ship's speed and NOxemission.
The results obtained from the examinations are as follows : (1)At the sailing condition of a sIow speed,
NOx emission [kg/h] increased proportionally to the approximate square of the ship's speed, but the condition of
a high speed, the NOx emission practically keeps constant value ; (2) Both conditions of sailing and trawling,
NOx emission [kg/h] correlates with fuel oil consumption ; (3) Total NOx emission [kg] per unit sailing distance
increased with the ship's speed unti1 13 knot, then decreased gradually ; (4) To sail at the high speed that actual
fuel oil consumption become smaller than theoretical fuel oil consumption based on propeller low is effective for
reduction of NOx emission and improvement of fisherboat’s function.
An accelerated motion of conical net is associated with a reduction of water velocity inside the net. Water
mass retained inside the net will move with the towed net. This water mass is defined as the added mass. In order
to evaluate the added mass of the conical net, ten models of different mesh factors and attack angles were tested
in a large scale towing tank at the National Research Institute of Fisheries Engineering. The measured added
mass is then converted into dimensionless added mass coefficient using the volume of the conical net and the
mesh factor. The added mass coefficients of conical nets can thus be compared by type of models and evaluated.
In this paper, an experimental system was constructed by a vacuum pump, a suction room, two sets of ball
valve and sieve of longitudinal. In the system, the fry was sucked from head. In order to hold invariable suction
velocity, the suction pressure of the system was adjusted by tank of pressure control. By using two sets of laser
sensor set up outside wall of a measuring pipe (or U-shaped ditch), the body length of the fry inside the pipe (or
U-shaped ditch) was measured when the fry drained from the system. The ability of the laser wave to pass
through pectoral fins, the effects of the existence of water, diameter of the measurmg pipe and the fry velocity
on the accuracy of measuring fry body length were discussed. Measuring error caused by laser wave diffusion
was also analyzed. The results were as follows.
1. When fry body width (13 -18mm) was nearly equal to the imer diameter (20mm) of a measuring pipe,
the measurement of fry body length was most accurate as the laser wave could pass through the pectoral fin.
2. Whether the velocity of the fry inside a pipe flowing water rose or not, measuring accuracy didn't drop.
When measuring fry body length, it was necessary to adjust the velocity of the fry inside the U-shaped ditch to
below 2m/s, because measuring accuracy dropped if the velocity rose to 2m/s.
3. As this system had only a minimal measuring error (0.0959mm) caused by laser wave diffusion, it could
be considered an effective method for measuring fry body length.
Local scour plays an important role on sinking phenomena of artificial fish reefs placed on sand bed in shallow
seas. If artificial fish reefs sink into sea bottom, they lose their ability to gather fishes. In order to clarify
this sinking mechanism and to overcome this problem, an experimental study on local scour around an artificial
fish reef was initiated. This paper presents the results of experiments on scour around cylindrical artificial fish
reef models in one way currents in an open channel. The local scour around artificial fish reefs is substantially
different from that of bridge pier which have been investigated by many researchers because the artificial fish
reef inclines and slides into the scour hole developed in scouring process. In addition to actual scour tests, a flow
visualization study was carried out to understand the flow pattems around cylindrical shape models. The important
parameter for estimation of the equilibrium local scour depths around the artificial fish reefs was found to
be the ratio of the sediment number (Ns) to the critical sediment number (N*sc ), when the model width to
water depth ratio was constant.
Water temperature, salinity, dissolved oxygen, nutrient salts, transparenoy and benthos were observed
throughout a year in Uranouchi Bay, Kouchi Prefecture.
In a stratified season, the benthos died, the concentration of nutrients increased and the environments of bay
were becoming worse rapidly due to the oxygen deficincy occurred at the sea bottom.