Method and device for counting fish

Abstract

To accurately count the number of fishes passing by with a simple configuration.SOLUTION: A method for measuring the number of fishes includes: forming a plurality of measurement areas by a plurality of wave sending units for sending a plurality of ultrasonic waves to an underwater passage frame and by a plurality of wave reception units for receiving an echo from the wave sending units; forming a non-measurement area next to the measurement areas in the passage frame; determining the number of fishes passing by the measurement areas; and predicting the number of fishes passing by a whole area including the non-measurement area from the determined number of fishes passing by the measurement areas.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a fish counting method and a fish counting device for counting the number of fish moving between, for example, aquaculture cages. [Background technology]

[0002] Measuring the number of fish in a cage is important for adjusting the amount of feed and production / shipment. In aquaculture, as fish grow, they may be split from one cage to two. When splitting, it is necessary to count the number of fish that pass between the cages.

[0003] Known conventional methods for counting fish numbers are described in Patent Documents 1 and 2. The method described in Patent Document 1 uses a camera. The method of using an underwater camera to count the number of fish within the underwater visible range makes counting difficult when the image is unclear due to low light or turbidity. Furthermore, conventional fish counting systems require adjustments such as camera calibration for each measurement.

[0004] A known example of an ultrasonic fish counting device is one that uses a fan-shaped beam that spreads across the width of an opening connected to a first cage, as described in Patent Document 2. Also, as described in Patent Document 3, it has been proposed to install an acoustic curtain in a tuna cage that is perpendicular to the swimming direction of the tuna, and to count the number of fish that pass through the acoustic curtain. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-81871 [Patent Document 2] Patent No. 6714261 [Patent Document 3] Patent Publication No. 2021-45102 Summary of the Invention [Problem to be solved by the invention]

[0006] However, all of the above-mentioned conventional configurations require the provision of a large number of ultrasonic transducers to form an acoustic curtain, which has the problem of being expensive.

[0007] The present invention aims to realize a fish counting method and fish counting device that can measure the number of fish with high accuracy using a low-cost configuration. [Means for solving the problem]

[0008] The present invention is an underwater passage frame. is an opening of a sector or a similar shape, and the central angle of the sector or similar shape is divided into N directions. A plurality of measurement areas are formed by a transmitter that transmits ultrasonic waves and a plurality of receivers that receive the echoes of the transmitters, In the passing frame, a non-measurement area is adjacent to a measurement area, Calculate the number of fish passing through the measurement area. This is a method for counting fish numbers, which predicts the number of fish passing through the entire area, including non-measurement areas, from the number of fish passing through the measurement area that has been determined. [Effects of the Invention]

[0009] According to the present invention, since measurement areas exist intermittently, costs can be reduced with a simple configuration. Also, the accuracy of counting fish can be improved. Note that the effects described here are not necessarily limited to those described herein, and any of the effects described in this specification may be used. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a fish counting system according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating an example of a passing frame and the relationship between the passing frame and the measurement area. [Figure 3] FIG. 3 is a schematic diagram for explaining the relationship between another example of the passing frame and the measurement area. [Figure 4]FIG. 4 is a schematic diagram for explaining the relationship between yet another example of the passing frame and the measurement area. [Figure 5] FIG. 5 is a block diagram showing a system configuration according to an embodiment of the present invention. [Figure 6] FIG. 6 is a block diagram illustrating an example of the configuration of the received signal processing unit. [Figure 7] FIG. 7 is a flowchart showing an outline of the processing flow of one embodiment of the present invention. [Figure 8] FIG. 8 is a flowchart showing the flow of processing according to one embodiment of the present invention. [Figure 9] FIG. 9 is a graph showing an example of the echo intensity of one channel. [Figure 10] FIG. 10 is a schematic diagram for explaining the process of connecting echo peaks. [Figure 11] FIG. 11 is an echogram corresponding to FIG. [Figure 12] 12A and 12B are schematic diagrams for explaining the angle of incidence of an ultrasonic beam on a fish. [Figure 13] 13A and 13B are schematic diagrams showing the relationship between the swimming direction and the angle of incidence. [Figure 14] FIG. 14 is a graph showing the relationship between the incident angle and the echo intensity. [Figure 15] 15A and 15B are graphs used to explain the change in echo intensity over time in one embodiment of the present invention. [Figure 16] 16A and 16B are graphs used to explain the change over time in echo intensity when the wave transmitting direction of the transducer is vertical from top to bottom. [Figure 17] FIG. 17 is a graph showing an example of the directivity angle according to the distance. [Figure 18] FIG. 18 is a graph showing an example of the relationship between the number of counted tails and the predicted number of tails. [Figure 19] 19A and 19B are graphs showing an example of measurement of an echogram and fish detection results for a certain channel. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described. Note that the embodiments described below are preferred specific examples of the present invention, and various technically preferable limitations are attached, but the scope of the present invention is not limited to these embodiments unless otherwise stated in the following description to the effect that the present invention is limited.

[0012] Figure 1 is a cross-sectional view showing the schematic configuration of a fish counting system according to one embodiment of the present invention. A first net cage 1 and a second net cage 2 are used for fish farming. The first net cage 1 comprises a net cage frame 11, a net 12 fixed to the net cage frame 11, and a float (not shown) attached to the net cage frame 11. The net 12 divides the underwater space into breeding spaces. The second net cage 2, like the first net cage 1, comprises a net cage frame 21, a net 22, and a float (not shown), and the net 22 divides the underwater space into breeding spaces.

[0013] A relatively narrow path 3 is formed between the first cage 1 and the second cage 2 by a net 13. Fish pass through the path 3 to be transferred from the first cage 1 to the second cage 2. A frame 14 is provided at the connection between the second cage 2 and the path 3, and fish can enter and exit through an opening (appropriately referred to as a passage frame) 15 formed by the frame 14. For example, the cross section of the path 3 is circular or rectangular, and the passage frame 15, which is located at the boundary between the second cage 2 and the path 3 and serves as the entrance to the second cage 2, is fan-shaped or similar in shape to a fan, or rectangular.

[0014] In one embodiment, in order to count the number of fish passing through the path 3 and moving from the first cage 1 to the second cage 2, a transducer 31 is provided that transmits an ultrasonic beam from the bottom to the top of the passage frame 15. The transducer 31 has, for example, five transducers. The transmission and reception path of each transducer is represented as a ch (channel). The transducer 31 may be provided above the passage frame 15 so that the transducer 31 transmits the ultrasonic beam from the top to the bottom. Furthermore, the transducer 31 may transmit the ultrasonic beam horizontally relative to the passage frame 15.

[0015] The ultrasonic beam used is, for example, a conical beam that spreads in a cone shape with a beam angle of 5 degrees. The conical shape is used when the shape of the transducer of the transducer 31 is circular, and when the shape of the transducer is square, it becomes a square pyramid. Furthermore, a fan beam may also be used. For example, the frequency of the ultrasonic waves is set to about 240 kHz.

[0016] In measurements, it is important to detect each individual fish. Because fish pass by in an instant, the ultrasonic waves are transmitted at least 10 times per second, for example 20 times. As a result, the echoes of individual fish can be separated and received even if they are swimming fast.

[0017] The transmitting directions of the ultrasonic beams of each transmitter of the transmitter / receiver 31 are different by a predetermined angle on the same plane, and the overall shape of the measurement areas (ch1 to ch5) and non-measurement areas formed by the multiple ultrasonic beams is a fan shape that approximately matches the passing frame 15, as shown in Fig. 2. For example, the transmitting directions of the ultrasonic beams are spaced apart by 15 degrees.

[0018] In one embodiment, instead of a state in which the measurement area completely covers the passing frame 15, the measurement area is configured to cover an area in which the passing frame 15 is thinned out to, for example, half. In Figure 2, measurement areas indicated by dark shading and non-measurement areas alternate. Therefore, compared to a configuration in which the measurement area covers the entire passing frame 15, the number of transducers included in the transducer 31 can be reduced, thereby reducing the cost of the fish counting device. The passing frame may be an elliptical passing frame 16 similar to a sector, as shown in Figure 3. Furthermore, it may be rectangular, as shown in Figure 4. In the case of a rectangular passing frame 17, a transducer 31' in which the transducers are aligned horizontally or vertically is used.

[0019] Furthermore, as shown in Figure 1, the transmitting direction of the transducer 31 is not parallel to the cross section of the passage frame 15, but is arranged at an angle relative to the passage frame 15. For example, it is arranged so as to be inclined forward in the direction of fish movement. As will be described later, this inclined arrangement makes it easier to determine the movement direction of fish passing through the passage frame 15. In one embodiment, the purpose is to count the number of fish moving from the first cage 1 to the second cage 2, and for highly accurate measurements, it is necessary to exclude the number of fish moving in the opposite direction.

[0020] Ultrasonic waves (properly referred to as echoes) emitted from each transmitter of the transducer 31 and reflected by fish passing through the passage frame 15 are received by each receiver to generate a received signal. Note that in Figures 2, 3 and 4, the directivity angle of the ultrasonic beam is shown as a constant value at any depth, but as will be described later, in one embodiment, the directivity angle changes according to the distance from each transducer of the transducer 31. In other words, the non-measurement area changes with distance.

[0021] The ratio of the transmission strength of the ultrasonic waves transmitted from the transducer 31 to the strength of the echo reflected by the fish (TS (Target Strength): echo strength 1 m from the transducer) is roughly expressed by the following formula: W is the body length of the fish, and A is a coefficient determined by the signal frequency and the fish species. TS=20logW+20logA

[0022] 5 shows the system configuration of one embodiment of the present invention. The transducer 3 has, for example, five transducers 32a to 32e. Transmit / receive switchers 33a to 33e are connected to the transducers 32a to 32e. A transmission signal is supplied from a transmitting unit 34 to each of the transmitters of the transducers 32a to 32e. A reception signal corresponding to the echo signal is generated from each of the receivers of the transducers 32a to 32e, and the reception signal is supplied to a receiving unit 35.

[0023] A received signal processing unit 36 ​​is connected to the receiving unit 35. The received signal processing unit 36 ​​is realized by a data processing device that processes digital data and associated software. The software is provided via a medium, communication, etc. The received signal processing unit 36 ​​counts the number of fish that have moved from the first cage 1 to the second cage 2 through the passage frame 15 based on the ratio TS between the transmission strength of the ultrasonic waves transmitted from the transducer 31 and the strength of the echo reflected back by the fish. The number of fish that have passed calculated by the received signal processing unit 36 ​​is displayed on the display unit 37. The number of fish may also be presented audibly along with the display. In addition to the number of fish that have passed, the received signal processing unit 36 ​​also measures the body length and height of the fish.

[0024] Instead of using the received signal as is, it is also possible to use a signal in which noise has been removed from the received signal using a band-pass filter, etc. Furthermore, it is also possible to use a correlation value obtained by analyzing the correlation between the transmitted signal and the received signal.

[0025] FIG. 6 shows an example of the received signal processing unit 36. The received signal (echo) of channel 1 is supplied to the detection unit 41a. The detection unit 41a determines the number of passing fish per predetermined time in predetermined distance units for each channel based on the received signal. When determining the number of passing fish, a process is performed to subtract the number of fish returning from the second cage 2 to the first cage 1. The number of fish determined by the detection unit 41a is supplied to the prediction unit 42a. The prediction unit 42a predicts the number of passing fish in the non-measurement area. The number of passing fish in the measurement area and the number of passing fish predicted by the prediction unit 42a are added by the adder 43a to determine the number of passing fish in channel 1. The output of the adder 43a is supplied to the addition circuit 44.

[0026] Detectors 41b to 41e, predictors 42b to 42e, and adders 43b to 43e are provided in association with the other channels 2 to 5, respectively, and the outputs of the adders 43b to 43e are supplied to an addition circuit 44. The output of the addition circuit 44 provides data on the total number of fish passing through the passage window 15.

[0027] FIG. 7 is a flowchart showing an outline of the processing of the received signal processing unit 36. The process starts from step S1. Step S2: The detection units 41a to 41e count the number of fish tails that pass through the passage window 15 in, for example, one second. Step S3: The prediction units 42a to 42e predict the number of passing tails in the non-measurement area, and the total number of passing tails per second is predicted. Step S4: The number of passing tails is displayed on the screen of the display unit 37. The number of passing tails is presented by voice with or without display. Step S5: End the process.

[0028] Furthermore, an example of the process of detecting fish passing through the passage window 15 (step S2) and the process of predicting the total number of passing fish (step S3) will be described with reference to the flowchart of FIG.

[0029] Step S11: The process starts. Step S12: A transmission signal is generated at a predetermined time interval, echoes are received, and peaks are detected from the echoes measured by each channel (receiver). Figure 9 shows an example of the echo intensity of one channel (relative values ​​are shown on the vertical axis of the graph; the same applies below). In the example of Figure 9, the echo intensity is at its maximum when the distance m (horizontal axis of the graph) is approximately 0.8 m. The dotted line indicates the threshold for peak detection, and echo intensities above the threshold are detected as peaks. The threshold is set to an absolute value or a constant multiple of the overall average value. Furthermore, the distance at which the peak exists is determined.

[0030] Step S13: Echo continuity evaluation is performed. If a peak exists at approximately the same depth in the previous transmission signal, the peaks are linked as shown in FIG. 10. In the graph in FIG. 10, the vertical axis represents pings and the horizontal axis represents distance (m). Pings are transmitted at transmission timing, for example, at intervals of 1 / 20 (seconds). If the estimated distance and the distance of the peak for the previous transmission are greater than a threshold, linking is terminated.

[0031] Figure 11 shows the echogram corresponding to the graph in Figure 10. The vertical axis represents pings, and the horizontal axis represents distance (m). The ping interval is 0.05 seconds. In Figure 11, the echo intensity is displayed as a monochrome image, with darker colors indicating stronger echo intensity. Furthermore, white dots represent connected peaks, and as with Figure 10, this is an example where the number of connections (number of consecutive transmissions) is 10.

[0032] Step S14: When the connection is complete, it is determined whether the detection criteria are met. That is, if the number of consecutive transmissions detected as a peak in the processing of step S12 is within a certain range (for example, 5 to 20 times) and the TS calculated at the maximum echo intensity is within a certain range, the fish is detected. If the detection criteria are not met, the processing returns to step S12. This processing can remove noise. That is, in the case of echoes from fish, echoes are measured continuously, but in the case of noise, there is a high possibility that only one echo is present.

[0033] Step S15: The swimming direction is detected from the change in echo intensity. Step S16: It is determined whether the detected swimming direction is correct. In one embodiment, as described above, the number of fish moving from the first cage 1 to the second cage 2 is counted, so that fish moving in the opposite direction are not counted to improve accuracy. The direction in which fish move from the first cage 1 to the second cage 2 is referred to as the forward direction, and the direction in which fish move in the opposite direction is referred to as the reverse direction.

[0034] Step S17: If it is determined in step S16 that the detected swimming direction is correct, the fish is counted as a passing fish in the correct direction. Step S18: If the detected swimming direction is determined to be the opposite direction in step S16, the fish is counted as a passing fish in the opposite direction. Step S19: The number of passing fish is counted by subtracting the number of passing fish in the opposite direction.

[0035] A typical fish finder transmits and receives ultrasonic waves directly downward from above the sea. Here, the incident angle is expressed as the angle between the incident direction of the ultrasonic waves and the dorsal direction, which is perpendicular to the fish's long axis. As shown in Figures 12A and 12B, an incident angle of 0 degrees means that ultrasonic waves are incident from the dorsal direction, and the positive direction is when the head is raised. Because the swim bladder, which is the main reflector of a fish, is tilted relative to the body axis, the echo intensity is greatest at a negative incident angle.

[0036] In one embodiment, as shown in Figures 13A and 13B, ultrasonic waves are transmitted and received from directly below toward the sea surface. Similarly, the incident angle is the angle between the incident direction of the ultrasonic waves and the ventral direction, which is perpendicular to the fish's long axis. The incident angle is positive when the angle is tilted toward the head. When incident from the ventral side, the normalized TS (reflection intensity) is maximized at a positive incident angle, as shown in Figure 14. Figures 13A and 13B show the positional relationship when TS is strongest. In both cases, the angle at which the head is tilted relative to the acoustic axis (dotted line) is positive. Figures 13A and 13B show schematic diagrams when TS is maximized. As stated in the sonar equation, directional characteristics are also factored in. When moving in the "positive direction," the echo intensity decreases because the fish is off the acoustic axis. Conversely, when moving in the "opposite direction," the angle of incidence is negative on the acoustic axis, resulting in increased echo intensity. The difference between the "positive direction" and the "opposite direction" arises from the TS's dependence on the incident angle and the difference in directional characteristics. Here, echo intensity refers to the echo level received by the receiver, and TS (reflection intensity) refers to the echo intensity when there is a target 1 m directly in front of the transmitter / receiver, and varies depending on the incident angle of the target.

[0037] Since the echo intensity changes differently in the forward and reverse directions, the change in echo intensity is evaluated and the swimming direction is determined. Figures 15A and 15B show simulation results showing the change in echo intensity per ping (time change) in one embodiment. As shown in Figure 15A, the normalized echo intensity in the forward direction is lower than the echo intensity in the reverse direction. Furthermore, when the time change in normalized echo intensity, i.e., the difference between successive values, is calculated, the depth change in echo intensity in the forward direction is lower than the depth change in echo intensity in the reverse direction, as shown in Figure 15B.

[0038] 16A and 16B show similar simulation results for the case where the transducer transmits ultrasonic waves from top to bottom (when the transmission direction is parallel to the cross section of the passage frame 15), unlike the first embodiment. As can be seen from these simulation results, when the transmission direction is not tilted, there is no significant difference in either the normalized echo intensity or the normalized echo intensity differential value depending on the swimming direction. Therefore, by placing the transducer 31 at a slight angle, the difference between the forward and reverse directions can be made more clear. Note that the effect is achieved regardless of the angle of the transducer 31.

[0039] Returning to the flowchart of Figure 8, in step S19 the number of passing fish on a certain channel at a certain time is counted. In one embodiment, since measurement areas exist intermittently, in order to determine the total number of passing fish, it is necessary to estimate the number of fish in the entire area from the number counted in the measurement areas. A simple estimation method is to use a volume ratio. The volume of a cone calculated from the directivity angle of the transducer is calculated as (base area S1 x depth D x (1 / 3)). The base area is calculated using the radius determined by the directivity angle. For example, if the measurement area and non-measurement area have the same volume, the total number of passing fish is calculated as twice the number of fish detected in the measurement area.

[0040] A method that does not take into account the fact that the echo level decreases due to propagation loss in the ocean (distance-dependent attenuation) and noise level will result in low accuracy. In one embodiment, the directivity angle is calculated by calculating the value of the directional characteristic at each depth at which a fish can be detected based on the TS of the fish at that distance, propagation loss in the ocean, noise level, and fish detection threshold.

[0041] The echo intensity EL is expressed by the following sonar equation: EL=SL-2TL+TS When the detection threshold is DT, the noise level is NL, and the directional characteristics are DI, detection is possible when the following formula is satisfied. DT≦SL-2TL+TS-(NL-DI) EL: Echo level DT: Detection threshold SL: Transmission level TL: Propagation loss in the ocean (distance-dependent attenuation) TS: Target Strength DI:Directional characteristics → Approximated by Bessel function in the case of circular NL: Noise level The minimum echo intensity EL0 at which a fish can be detected is calculated using the following formula: EL0=NL-DI+DT

[0042] From the above formula, if the echo intensity EL (= SL - 2TL + TS) is greater than the minimum echo intensity EL0 at which a fish can be detected, it can be detected as a fish. However, if the distance is long, and the echo level EL is less than EL0 due to the propagation loss TL, directional characteristic DI, and noise level NL, it cannot be detected. Therefore, based on the fish's TS at that distance, the propagation loss in the sea TL, the noise level NL, and the detection threshold DT, the value of the directional characteristic DI at each distance at which a fish can be detected is calculated, and the directivity angle is then calculated.

[0043] In step S20, the detectable directivity angle is calculated for a given distance, for example, in 10-cm increments, with a body width of 1 cm and a fish detection threshold set. The directivity angle in 10-cm increments is shown in Figure 17. The volume ratio in 10-cm increments is calculated based on the directivity angle, and the number of passing fish is predicted from the number of detected fish in each channel at that depth. This method has less variance than estimation based on a constant directivity angle, enabling more accurate measurements.

[0044] Step S21: The number of fish passing by is counted in steps of distance, for example, 10 cm, from the transducer. Step S22: The number of passing tails in the non-measurement area is predicted based on the number of passing tails per distance and the directivity angle calculated in step S20. In other words, the volume ratio of the measurement area to the non-measurement area is calculated, and the number of passing tails is predicted from the number of detection units for each channel at that distance. For example, if the transducers are spaced 15 degrees apart and the directivity angle is 8 degrees, it is necessary to predict for 7 degrees. The predicted number of tails is 7 / 8 times the number of passing tails.

[0045] Step S23: The total number of passing tails for each distance is integrated to predict the total number of passing tails. This method of predicting the number of passing tails in the non-measurement area from the number of passing tails and the pointing angle for each distance from the transducer, and predicting the total number of passing tails for each distance, has less variance than estimating with a constant pointing angle, and allows for more accurate measurements. Step S24: The process ends. The display unit 37 displays the number of fish that have passed. The fish length may be measured by calculating TS from the echo intensity when the fish passed. Furthermore, the body height may be calculated from the duration of the echo when the fish passed.

[0046] FIG. 18 is a graph showing an example of the number of tails (shown by the solid line) predicted as described above from the number of tails counted at distances of every 10 cm (shown by the dashed line).

[0047] Furthermore, Figures 19A and 19B are graphs showing measurement examples of the echogram and fish detection results for a certain channel. The horizontal axis represents the distance from the transducer, and the vertical axis represents the elapsed time. Figure 19A displays the measured echo level as a monochrome image, with darker colors indicating greater echo intensity. It can be seen that fish pass by in a short period of time. Figure 19B displays only the echoes of detected fish. It can be seen that the passing fish was successfully detected.

[0048] The experimental results are shown in Table 1 below.

[0049] [Table 1]

[0050] Table 1 shows the average and variance of the number of passing tails counted across all channels over multiple measurements. It also shows the average and variance of the total number of passing tails predicted with a constant beam angle and with a variable beam angle, as in the embodiment described above. As can be seen from Table 1, the variance of predictions made with beam angles at each distance, as in the embodiment described above, is smaller than that made with a constant beam angle, resulting in higher prediction accuracy.

[0051] Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical concept of the present invention are possible. For example, the present invention is not limited to counting the number of fish passing between fish pens, but may also count the number of fish passing through a fishway installed in a river. The configurations, methods, processes, shapes, materials, and values ​​described in the above-described embodiments are merely examples, and different configurations, methods, processes, shapes, materials, and values ​​may be used as necessary. [Explanation of symbols]

[0052] REFERENCE SIGNS LIST 1 First fish cage, 2 Second fish cage, 3 Route, 15, 16 Passage frame, 33a to 33e Wave transmission / reception switch, 36 Received signal processing unit

Claims

1. The underwater passage frame is an opening having a fan shape or a shape similar to a fan shape, and a plurality of measurement areas are formed by a wave transmitter that transmits ultrasonic waves in directions obtained by dividing the central angle of the fan shape or a shape similar to a fan shape into N, and a plurality of wave receivers that receive the echoes of the wave transmitters, In the passing frame, a non-measurement area is adjacent to the measurement area, Calculate the number of tails passing through the measurement area, This method for counting fish numbers predicts the number of fish passing through the entire area including the non-measurement area from the number of fish passing through the measurement area that has been determined.

2. 2. The method for counting fish numbers according to claim 1, wherein the direction in which the ultrasonic waves are transmitted from the transmitter is inclined with respect to the cross section of the passage frame.

3. A fish counting method as described in claim 1, in which, when determining the number of fish passing through the measurement area, the echo of each fish is continuously evaluated, the direction of fish movement is determined from the change in the echo amplitude, and the number of fish moving in the opposite direction is subtracted from the determined number of fish.

4. A tail counting method as described in claim 1, in which the number of tails passing through the non-measurement area is predicted based on the ratio of the directional angle of the measurement area to the directional angle of the non-measurement area, and the total number of tails is calculated by adding the number of tails calculated in the measurement area and the predicted number of tails.

5. Set measurement areas according to the distance from the transducer, The directivity angle is calculated for each distance from the transducer in accordance with the body width and detection threshold. A method for counting tails as described in claim 1, in which the number of tails in the non-measurement area is predicted based on the directional angle calculated for each distance, and the total number of tails is calculated by adding the number of tails calculated in the measurement area and the predicted number of tails.

6. The underwater passage frame is an opening having a fan shape or a shape similar to a fan shape, and a plurality of measurement areas are formed by a wave transmitter that transmits ultrasonic waves in directions obtained by dividing the central angle of the fan shape or a shape similar to a fan shape into N, and a plurality of wave receivers that receive the echoes of the wave transmitters, In the passing frame, a non-measurement area is adjacent to the measurement area, a reception signal processing unit for processing the reception signal of the receiver; The receiving signal processing unit of this tail counting device predicts the number of tails passing through the non-measurement area, and calculates the total number of tails by adding the number of tails calculated in the measurement area and the predicted number of tails.

7. The fish counting device according to claim 6, wherein the direction in which the ultrasonic waves are transmitted from the wave transmitter is inclined with respect to the cross section of the passage frame.

8. A fish counting device as described in claim 6, wherein when determining the number of fish passing through the measurement area, the echo of each fish is continuously evaluated, the direction of fish movement is determined from the change in the echo amplitude, and the number of fish moving in the opposite direction is subtracted from the determined number of fish.

9. A tail counting device as described in claim 6, which predicts the number of tails passing through the non-measurement area based on the ratio of the directional angle of the measurement area to the directional angle of the non-measurement area, and calculates the total number of tails by adding the number of tails calculated in the measurement area and the predicted number of tails.

10. Set measurement areas according to the distance from the transducer, The directivity angle is calculated for each distance from the transducer in accordance with the body width and detection threshold. A tail counting device as described in claim 6, which predicts the number of tails in the non-measurement area based on the directional angle calculated for each distance, and calculates the total number of tails by adding the number of tails calculated in the measurement area and the predicted number of tails.

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