In situ side-aspect target strength of Japanese anchovy (Engraulis japonicus) in northwestern Pacific Ocean

(anchovy)

(Shelton et al., 1993).

In situ side-aspect target strength of Japanese anchovy (Engraulis japonicus) in northwestern Pacific Ocean

Hyungbeen L

and Donhyug K

*

Marine Living Resources Research Department, KORDI, Ansan 425-600, Korea

Acoustic side-aspect target strength (TS) of living Japanese anchovy (Engraulis japonicus) was measured at 120kHz during in situ experiments. The data were collected by lowering and horizontally projecting the split- beam transducer into the anchovy school. For analysis and interpretation of the side-aspect TS data, acoustic theoretical model, based on the fish morphology, and dorsal-aspect TS data were used. Total length of the anchovy ranged from 6.6 to 12.8cm (mean length 9.3cm). The side-aspect TS distributed between 40 and 55dB, has an obvious length dependency. The mean side-aspect TS of the anchovy was 47.8dB, and the TS was about 2dB higher than mean TS generated from dorsal-aspect measurements. With reference to maximum TS, the results of the side-aspect TS were distributed within the range of the theoretical and dorsal-aspect TS. Apparently these tendency indicates that side-aspect TS measured from the study is useful data. These in situ measurements of side-aspect TS can be applied to improve acoustic detection and estimates of the anchovy, and is necessary to measure with a various frequency and length for making enhance data.

Keywords: Acoustic model, Anchovy (Engraulis japonicus), In situ measurement, Side-aspect Target strength

*

.

1990 2006 143

(Peruvian anchovy) ,

1992 2007

81 (Japanese anchovy,

Engraulis japonicus)

(FAO, 2010).

1992 2007 22

,

(Statistics Korea, 2010).

.

,

(Hampton, 1996; Kim and Lo, 2001).

.

.

,

(MacLennan and Simmonds, 1992).

.

(Berger et al., 2009).

(target strength, TS)

(Zhao et al., 2008).

TS (in situ) (ex situ)

(Kang et al., 2009).

(side- aspect TS, TS)

.

TS .

,

TS

(dorsal-aspect TS) .

TS 2008 9 3 5

(

MRC) .

.

2007 MRC

.

(Japanese anchovy)

2008 9 .

6 3 4 m

(Fig. 1).

, .

.

TS

.

(total length) 9.3cm

(6.6 12.8cm) , 5.78g

(1.32 18.24g) .

TS TS

120

kHz .

SIMRAD

(spilt- beam) (Simrad, 1997).

, (Fig. 1).

24.6 , 29.7 psu .

13cm ( τ) 0.3ms (c τ/2 22.9cm,

c

1527m/s) ,

1 .

3dB , two-way angle, gain

7.1 , 20.6dB, 26.5dB .

Table 1 .

.

.

TS

(volume backscat- tering strength, SV) ping

. TS serial

Fig. 1. Experimental scheme for in situ side-aspect target strength measurement of Japanese anchovy.

Table 1. System parameters for side-aspect target strength measurement of Japanese anchovy

System parameter Value Comment

Frequency 120kHz

Beam type split beam

Pulse length 0.3ms

3 dB beam width 7.1deg

Ping rate 1 ping/s

2-way beam angle 20.6dB

Hardware parameter Transducer gain 26.5dB

TS detection parameter

Min. threshold 55dB Min. echo length 0.8 Max. echo length 1.8 Max. gain Comp. 6.0dB

Absorption coefficient 0.0412dB/m Temperature: 24.6 Sound speed 1527m/s Salinity: 29.7psu image data

acoustic data 120 kHz split-beam

transducer

underwater camera

Japanese anchovy

timesync acoustic

system

2.0

3.0

4.0

(unit: meter) net

. TS SV

SonarData Echolog

(SonarData, 2000).

TS ping time (hh:mm:ss), (meter), TS (dB),

(degree) .

TS

.

.

30 ,

2008 9 4 17:04

20:18 3 14 .

TS

.

2.0 3.5m

3dB ,

TS

3,892 .

, TS (threshold

level) TS

. Kang et al. (2009) 120 kHz TS

( 6.56cm)

TS 51.7dB .

55dB .

TS

TS Kirchhoff ray mode (KRM)

. KRM

.

, fluid-filled ,

gas-filled (Clay and Horne, 1994).

,

X-ray .

X-ray (lateral aspect)

(ventral aspect) ,

2mm .

KRM

.

(axis) X , (width) Y , (height) Z .

, KRM

. X ,

Y Z

(Clay and Horne, 1994; Cho et al., 2006).

0 , ,

. , ,

, 1518, 1570, 345

(Japanese anchovy)

Fig. 2. 3-D coordinate to calculate side-aspect (yaw angle) target strength from theoretical acoustic model of Japanese anchovy.

Tail 2

1 0 -1 -2 0

Y (cm)

X (cm)

Body Swimbladder

1 2 3 4 5 6 7 -2 -1 0 1 2

Head

+90 90

Incident wave

(Medwin and Clay, 1994).

KRM

7.4, 8.9, 10.6cm , ,

.

TS,

TS ,

Coherent

TS .

TS

(Fig. 3).

TS

.

TS

Fig. 4 2.5 3.5m

4 TS

.

TS 55 TS 41

dB, 54dB , 48

dB .

9.3cm

(6.6 12.8cm) ,

TS 54

40dB 98% .

Fig. 3. Example of free swimming anchovy at day and night in the large cage.

Fig. 4. Example of in situ side-aspect target strength of Japanese anchovy at 120 kHz.

(a) day

(b) night

-30 -32 -34 -36 -38 -40 -42 -45 -47 -49 -51 -53 -55 17:56

17:54 17:52 17:50 17:48 18 15 12 9 6 3 0

1m 2m 3m 4m 5m

-59 -57 -55 -53 -51 -49 -47 -45 -43 -41 -39 -37 Side TS (dB)

TimeFrequency (%)

Distance from transducer

(Japanese anchovy)

.

TS 18.5 % 52dB ,

TS 47.8dB (Fig. 5).

TS

TS 49.8dB (Kang et al., 2009)

2dB .

TS 41 40dB

1.4% .

TS

90 ( 0 )

.

TS .

Bay anchovy (Anchoa mitchilli)

TS (Boswell and Wilson, 2008).

6.6 12.8cm ,

Bay anchovy 4.5 7.1cm

. 420kHz

Bay anchovy TS 42dB

, 55dB

TS TS

.

, 420kHz Bay anchovy

TS 5.8cm 0

43.5dB ,

50.5dB . TS

TS

.

Bay anchovy TS

TS .

TS 120kHz

TS 0

10.6cm 42.2dB, 8.9cm 44.7

dB, 7.4cm 45.6dB .

TS TS

Fig. 5. Frequency distribution of in situ side-aspect target strength of Japanese anchovy at 120 kHz.

Fig. 6. Theoretical side-aspect target strength of Japanese with yaw angle at 120 kHz.

20

16 12

8 4

0

-56 -54 -52 -50 -48 -46 -44 -42 -40 Side-aspect target strength (dB)

n=3,892

Frequency (%)

-40 -45

-50 -55

-60

-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 Side-aspect angle (deg)

Side-aspect TS (dB)

TL=8.9cm

TL=10.6cm

TL=7.4cm

TS 55dB

10.6cm 70 70 , 8.9cm

67 66 , 7.4cm 62 61

.

TS 0

Parabolic (Kubecka and

Duncan, 1998).

9.3cm 8.9cm TS Parabolic

.

TS θ (dB) 0.0042 θ

0.104 θ 44.7 ( 80 θ 0 )

TS

. TS

, TS

.

TS TS

. (dorsal-aspect) TS

TS .

TS TS

0 TS

(Simmonds and MacLennan, 2005).

Kang et al. (2009) 35

( 4.83 12.22cm) TS

.

3 120kHz

TS (Fig. 7).

Fig. 7 3 TS

7.4, 8.2, 10.5cm . , KRM

TS 0

7.4, 8.9, 10.6cm .

TS 10.5cm

Fig. 7. Comparison dorsal-aspect TS with side-aspect maximum TS of Japanese anchovy at 120 kHz. Gray color indicates maximum TS with respect to side aspect.

Theoretical side TS at 0 Theoretical side TS at 0

Theoretical side TS at 0 -40

-45

-50

-55

0 1000 2000 0 1000 2000 0 1000 2000

Ping number

(a) TL : 7.1cm (b) TL : 8.2cm (c) TL : 10.5cm

Dorsal TS (dB)

2dB TS

. TS

TS

TS .

TS .

9.3cm TS TS

47.8dB TS 2dB

, TS

TS

.

,

3 TS

.

TS 3 TS

,

.

120kHz

(side-aspect TS) .

TS

TS

, TS

. 9.3cm (6.6 12.8cm)

TS 55 40dB

.

TS 47.8dB TS

2dB

.

TS

TS .

,

, TS

.

/

(PE98474) MRC (

)

(PK07780) .

MRC

, ,

.

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