Fish density and target strength distribution of single fish echoes in varying light conditions with single and split beam echosounding and trawling

Hydroacoustic acquisition was performed by means of two different single beam systems, the Simradmodel EK15 from 2015 and the Simrad model EY-M from the 1980s to explore potential differences of fish density and target strength (TS) distribution between EK15 and EY-M-based estimates. The oligotrophic Lake Storsjøen (48 km2) with steep shores, was chosen for the survey. The pelagic fish stock is dominated by whitefish (Coregonus lavaretus L.), and, recently, illegally stocked smelt (Osmerus eperlanus L.), and a low proportion of Arctic charr (Salvelinus alpinus L.). The total density was estimated at two depth layers (18–32 and 32–48 m), and was quite similar for TS ≥ −56 dB: 755 and 498 fish ha−1, respectively for the EK15-based estimates and similarly 766 and 490 fish ha−1 for the EY-M estimate. Target strength distributions were similar for TS > −48 dB. The proportion of single fish detected with EK15 was negatively affected by the long pulse duration. Six acquisitions from 1986 to 2016 showed a dramatic increase of density of TS = −46 to −44 dB echoes (>10 cm) between 2013 and 2016. This was due to the growth of the introduced smelt population.

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POLA SEBARAN IKAN PADA MUSIM BARAT DAN PERALIHAN DI PERAIRAN UTARA JAWA TENGAH

Jurnal Penelitian Perikanan Indonesia ◽

10.15578/jppi.14.1.2008.67-76 ◽

2017 ◽

Vol 14 (1) ◽

pp. 67

Author(s):

Asep Priatna ◽

Mohammad Natsir

Keyword(s):

Food Source ◽

Target Strength ◽

Fish Density ◽

Current Direction ◽

North West ◽

Pelagic Fishes ◽

Central Java ◽

The Difference ◽

West Monsoon ◽

Demersal Fishes

Penelitian ini bertujuan untuk mempelajari perbedaan pola sebaran ikan pada musim barat dan peralihan di perairan utara Semarang sampai dengan Brebes, berdasarkan pada pengambilan contoh akustik dan oseanografi pada bulan Desember 2005 dan Mei 2006. Hasil menunjukkan secara spasial, pada musim barat di perairan utara Semarang sampai dengan Brebes kepadatan ikan pelagis lebih besar di daerah yang lebih dangkal yaitu sebelah selatan pada kedalaman <40 m, semakin ke tengah kepadatan semakin berkurang. Dilihat dari nilai target strength yang terdeteksi yaitu antara -60 sampai dengan -50 dB bahkan didominasi oleh ikan -60 sampai dengan -55 dB, sasaran merupakan ikan pelagis kecil yang rata-rata mempunyai ukuran 4 sampai dengan 12,5 cm. Pada musim peralihan sebaran kepadatan ikan pelagis kecil cenderung lebih merata dengan jumlah yang lebih rendah daripada jumlah ikan pada musim barat. Faktor pergerakan arah arus dan keberadaan sumber makanan yang lebih besar pada musim barat diduga merupakan penyebab perbedaan tersebut. Ikan pelagis kecil pada musim peralihan berukuran lebih besar dibandingkan ketika musim barat, dengan nilai target strength yang terdeteksi antara -60 sampai dengan -45 dB atau sekitar 4 sampai dengan 22 cm dan didominasi oleh ikan yang berukuran -55 sampai dengan -50 dB atau sekitar 7 sampai dengan 12,5 cm. Sebaran kepadatan Ikan demersal hampir merata pada ke-2 musim tersebut, pada musim peralihan kepadatan lebih rendah daripada musim barat. Ikan demersal pada musim barat terdiri atas ikan berukuran kecil (-55 sampai dengan -50 dB) atau sekitar 7 sampai dengan 12,5 cm terutama di daerah pada kedalaman <40 m, semakin ke tengah ukuran semakin besar yaitu antara -50 sampai dengan -45 dB atau sekitar 12,5 sampai dengan 22 cm. Pada musim peralihan, ikan demersal dengan target strength -55 sampai dengan -50 dB terdapat di kedalaman <40 m. Ikan demersal dengan ukuran -50 sampai dengan -45 dB mendominasi periode ini. Pada kedalaman >45 m terdeteksi ikan -45 sampai dengan -35 dB yang berkisar 22 sampai dengan 70 cm. The aim of this study is to understood the difference of fish pattern distributions at North West and intermonsoon in North of Central Java waters, based on acoustic and oceanography sampling in December 2005 and May 2006. At North West monsoon, the density of pelagic fishes was more gathering in narrower areas <40 m, and low fish density was going to middle areas. Seen from target strength the value was detected about -60 to -50 dB and it was dominated by fishes -60 to -55 dB, the targets for small pelagic fishes are about 4 to 12,5 cm. At the intermonsoon, distribution of small pelagic fishes density tends to be flat, but fish density at this time was the lower than North West monsoon. The higly current direction and food source factor at North West monsoon may cause this difference. The size of small pelagic fishes at the intermonsoon was bigger than fishes at North West monsoon, which target strength value was detected about -60 to -45 dB or 4 to 22 cm and dominated by fishes -55 to -50 dB of about 7 to 12,5 cm. The density distribution of demersal fishes almost flat at both monsoon. How ever at intermonsoon, the demersal fishes density was lower than that at North and West season. Demersal fishes at North West monsoon consisted of small fishes (-55 to -50 dB) with size of about 7 to 12,5 cm especially in narrow areas <40 m, and fish sizes the larger (-50 to -45 dB or 12,5 to 22 cm) were going to the middle areas. At intermonsoon, there were demersal fishes with target strength -55 to -50 dB at <40 m. Demersal fishes with target strength -55 to -50 dB were dominant at this time. At areas >45 m it was detected fishes of -45 to -35 dB target strength of about 22 to 70 cm.

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DISTRIBUSI KEPADATAN IKAN PELAGIS DI PERAIRAN PANTAI UTARA JAWA BAGIAN TIMUR, PULAU-PULAU SUNDA, DAN LAUT FLORES

Jurnal Penelitian Perikanan Indonesia ◽

10.15578/jppi.13.3.2007.223-232 ◽

2017 ◽

Vol 13 (3) ◽

pp. 223

Author(s):

Asep Priatna ◽

Mohammad Natsir

Keyword(s):

Environmental Factor ◽

Pelagic Fish ◽

Target Strength ◽

Fish Density ◽

Small Pelagic Fish ◽

Pelagic Fishes ◽

East Region ◽

Marginal Areas ◽

Near Shore ◽

Distribution Of Fish

Penelitian ini bertujuan untuk mempelajari distribusi spasial kepadatan ikan pelagis serta hubungan dengan kondisi perairan pada musim peralihan di perairan pantai utara Jawa bagian timur dan Laut Flores, berdasarkan pada pengambilan contoh akustik dan 34 stasiun oseanografi pada bulan Oktober 2005. Data target strength menunjukkan bahwa rata-rata ukuran ikan pelagis yang terdeteksi di perairan pantai utara Jawa bagian timur adalah 10 sampai dengan 56 cm. Ukuran ikan di daerah lepas pantai lebih kecil dibanding daerah dekat pantai. Pada musim peralihan, kondisi suhu dan salinitas perairan relatif homogen. Sehingga faktor tersebut kurang signifikan terhadap distribusi keberadaan ikan. Diduga faktor lingkungan lain seperti faktor biologi dan kimia, berperan dalam pola penyebaran ikan pelagis kecil di perairan ini. Di Laut Flores dan sekitar Pulau-Pulau Sunda, densitas ikan tertinggi pada stratum 10 sampai dengan 50 m dengan ukuran 10 sampai dengan 20 cm terutama di beberapa lahan marginal seperti sekitar selat dan kepulauan. Selain merupakan lapisan tercampur di mana kondisi suhu dan salinitas relatif stabil pada kedalaman 10 sampai dengan 50 m, lahan marginal merupakan daerah subur tempat pertemuan 2 massa air yang berbeda yang membentuk front diharapkan merupakan tempat berkumpul ikan. Lapisan termoklin yang bersifat lemah berada di bawah 50 m, hal ini mempengaruhi densitas ikan yang semakin rendah pada kedalaman lebih dari 50 m. Ikan pelagis yang berada pada lapisan termoklin mempunyai ukuran yang lebih besar yaitu 14 sampai dengan 40 cm. Pada musim yang sama, rata-rata kepadatan dan ukuran ikan pelagis kecil di wilayah timur lebih rendah daripada sebelah barat. The aim of this research is to study the distribution of spasial density of pelagic fish with waters condition at intermonsoon in north of Java coast waters part of east and Flores Sea, based on acoustic sampling and 34 oceanography stations in October 2005. The target strength of fish indicated that pelagic fish measure in north of Java coast waters part of east is about 10 to 56 cm. Fish sizes in offshore is smaller than near shore. At intermonsoon, the waters condition of temperature and salinity was homogeneous relatively. Therefore, that are less to distribution of fish density. Anticipated, the others environmental factor like chemical and biological, was influenced to distribution of small pelagic fish in this area. In Flores Sea and Sunda Islands, the highest of fish density at 10 to 50 m and fish sizes about 10 to 20 cm especially in some marginal areas near archipelago and strait. At 10 to 50 m is mixed layer, where temperature and salinity was relative stabilize, the maginal areas is fertility waters which is passage of the shifting by two different water masses and front were formed . The weak termocline was formed below 50 m, maked fish density are progressively lower below 50 m. The pelagic fish residing in termocline layers have larger ones measure than stratum 10 to 50 m is about 14 to 40 cm. On same season, the fish measure and density of small pelagic fishes in east region is lower than at westside.

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Comparing two 38-kHz scientific echosounders

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2005.02.014 ◽

2005 ◽

Vol 62 (6) ◽

pp. 1168-1179 ◽

Cited By ~ 19

Author(s):

J. Michael Jech ◽

Kenneth G. Foote ◽

Dezhang Chu ◽

Lawrence C. Hufnagle

Keyword(s):

Standard Deviation ◽

Beam Width ◽

Scientific Work ◽

Strength Distribution ◽

Target Strength ◽

Absolute Difference ◽

Time Variability ◽

Full Potential ◽

Plane Normal ◽

Acoustic Axis

Abstract The EK500 has been the state-of-the-art scientific echosounder for surveying marine fish stocks for over a decade; the EK60 is its successor. Ensuring comparability in performance is vital during the transition from the EK500 to the EK60. To quantify the respective performances, each echosounder was calibrated in tandem by the standard-target method using the same 38-kHz, 12° beam width, split-beam transducer, with alternating pinging by means of an external triggering-and-switching system. The principal measurements comprised split-beam-determined angle and target strength, on-axis sensitivity, and directionality in the plane normal to the acoustic axis, as measured with a 60-mm-diameter copper sphere. Ambient noise, including volumetric reverberation, was also measured. Principal comparisons included those of the time-series and histograms of split-beam-determined target strength; respective alongship and athwartship angles as determined by the split-beam system; and as expected, difference in the split-beam-determined and experimental target-strength values in the plane normal to the acoustic axis. The mean absolute difference in off-axis angle values was also compared. While the performance of the two echosounders is generally similar, systematic differences exist. For the particular calibration measurements, the time variability in measurements of on-axis target strength was of the order of 1 dB for the EK500 and 2 dB for the EK60. The target-strength distribution for measurements made with the EK500 was normal, with standard deviation 0.2–0.3 dB, whereas for the EK60, the target-strength distribution was distinctly skewed and the standard deviation varied over 0.3–0.5 dB. Differences were found between the split-beam and physical-angle measurements. They were noticeably larger in the case of the EK60. Differences in performance between the two echosounders suggest refinements to the new system that will help realize its full potential in scientific work.

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Acoustical Assessment of Squid (Loligo opalescens) off the Central Oregon Coast

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f87-149 ◽

1987 ◽

Vol 44 (6) ◽

pp. 1261-1267 ◽

Cited By ~ 19

Author(s):

Katharine Jefferts ◽

Janusz Burczynski ◽

William G. Pearcy

Keyword(s):

Geographic Distribution ◽

Distribution Density ◽

Strength Distribution ◽

Target Strength ◽

Adjacent Area ◽

Density Estimates ◽

Oregon Coast ◽

Loligo Opalescens ◽

Dual Beam

Squid (Loligo opalescens) were surveyed acoustically in an area off the Oregon coast using dual-beam and echo integrator techniques. The method developed is shown to be feasible for in situ estimation of target strength, distribution, and abundance of midwater squids. Average target strength was estimated both while drifting with a squid school and cruising over one. The values derived, −58.6 to −58.7 dB, are much lower than previous estimates, but more realistic in relation to the target strength of fishes. Schools judged to be fish or squid showed little difference in depth or size, but varied significantly in geographic distribution. Density estimates ranged from 9.9 t/km2 in a known spawning area to 0.93 t/km2 in an adjacent area.

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Comparison of in situ, ex situ, and backscatter model estimates of Pacific hake (Merluccius productus) target strength

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f07-134 ◽

2007 ◽

Vol 64 (12) ◽

pp. 1781-1794 ◽

Cited By ~ 14

Author(s):

Mark J Henderson ◽

John K Horne

Keyword(s):

Acoustic Energy ◽

Common Method ◽

Ex Situ ◽

Target Strength ◽

Fish Density ◽

Fish Length ◽

Merluccius Productus

To convert acoustic energy into estimates of fish density, the target strength (TS) of a representative fish must be known. TS is a measure of the acoustic reflectivity of a fish, which is variable depending on the presence of a swimbladder, the size of the fish, its behavior, morphology, and physiology. The most common method used to estimate the TS of a fish is a TS-to-length empirical regression, with TS values increasing with fish length. This study uses in situ and ex situ TS measurements and a backscatter model to develop TS-to-length conversions for Pacific hake (Merluccius productus). Results from in situ and ex situ measurements had regression intercepts 4–6 dB lower than the previous Pacific hake TS-to-length regression. These differences suggest that an individual hake reflects 2.5–4 times less acoustic energy than was previously estimated.

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Analysis of Echo Counting Data: A Model

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f84-054 ◽

1984 ◽

Vol 41 (3) ◽

pp. 451-458 ◽

Cited By ~ 21

Author(s):

R. Kieser ◽

T. J. Mulligan

Keyword(s):

Strength Distribution ◽

Range Limits ◽

Target Strength ◽

Density Estimates ◽

Correct Model ◽

Counting Data ◽

Chart Recorder ◽

Standard Tool ◽

Echo Pulse ◽

Counting Model

Echo counting is a standard tool for the estimation of fish density and hence population. Density estimates are readily obtained using an uncalibrated, stable echo sounder with accurate time-varied gain. We extended a standard nonstochastic echo pulse counting model to include the analysis of single fish echo traces as they are obtained from the sounder chart recorder. The trace counting analysis depends strongly on the overlap in the insonified volumes between successive sounder transmissions. An equation for the nonoverlapping volume is given in terms of range, distance between transmissions, and effective beam angles. The near and far range limits of the model are given and the errors associated with the commonly used approximations to the correct model are shown. A generalization of the model considers the analysis of data from a tilted transducer. A sensitivity analysis gives a qualitative indication of the model's performance for echoes from fish with a realistic target strength distribution. Single fish echo returns are analyzed by the echo pulse and trace counting methods to illustrate the model.

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Diel patterns in pelagic fish behaviour and distribution observed from a stationary, bottom-mounted, and upward-facing transducer

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2004.07.006 ◽

2004 ◽

Vol 61 (7) ◽

pp. 1100-1104 ◽

Cited By ~ 43

Author(s):

Thomas Axenrot ◽

Tomas Didrikas ◽

Charlotte Danielsson ◽

Sture Hansson

Keyword(s):

Pelagic Fish ◽

Strength Distribution ◽

Fish Distribution ◽

Target Strength ◽

Diel Variation ◽

Fish Behaviour ◽

Additional Information ◽

Diel Patterns ◽

The Baltic ◽

Survey Planning

Abstract Diel variation in pelagic fish distribution influences hydroacoustic abundance estimates. To study and quantify diel patterns in behaviour and spatial distribution in pelagic fish without causing avoidance reactions or attraction to any floating equipment or vessel we used a bottom-mounted, upward-facing transducer. Light intensities were measured as skylight and underwater light (at 5-m depth). The study was performed in a coastal area in the Baltic Sea, late July to mid-August in 2001 and 2002. The results provided additional information on fish behaviour and distribution valuable for future survey planning and in the analyses of hydroacoustic data from regular surveys in this area. At night, the data on hydroacoustic backscattering (sA) were less variable, the vertical distribution of fish was more even, with fewer fish in the deepest layer, and the percentage of single-echo detections was higher. The tilt angle of fish seemed to differ day and night, but trawling and target-strength distribution results taken together also implied a partial diel change in the fish assemblage in the midwater layers. The processes of formation and disintegration of schools happened rapidly and coincided with day and night transition periods.

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