Dorsal Aspect Target Strength Research Articles

Ex situandin situtarget strength measurements of European anchovy in the Bay of Biscay

AbstractThis study measures the dorsal aspect target strength (TS; dB re 1 m2) and TS–length (standard length, SL; cm) relationships for European anchovy, attained both ex situ and in situ in two different seasons across 7 years in the Bay of Biscay. The measurements were made at three frequently used acoustic frequencies (38, 120, and 200 kHz). A backscattering model for physostome fish was utilized to help interpret the results. The obtained experimental mean TS for anchovies with an SL of 3.5–19.5 cm was −44.6 (±2.3), −46.9 (±3), and −48.4 (±2.7) dB at 38, 120, and 200 kHz, respectively, yielding b20 values of −66.4, −68.7, and −70.4 dB, respectively. The results were consistent across seasons and between in situ and ex situ conditions, presenting TS–length relationships with statistically significant slopes (p-values <0.05) for all frequencies. This research represents part of a series of efforts planned to obtain a comprehensive TS vs. length and depth relationship to update the acoustic assessment methodology of European anchovy in the Bay of Biscay.

Estimating individual fish school biomass using digital omnidirectional sonars, applied to mackerel and herring

Abstract Economic profitability and responsible fisheries are objectives of fishermen and fisheries managers. In purse seine fisheries, an accurate biomass estimate of the targeted school is crucial to accomplish this. For this study, omnidirectional fisheries sonar was used to estimate individual school biomass of Norwegian spring spawning herring (Clupea harengus) and Atlantic mackerel (Scomber scombrus). A sonar sampling design based on professional skipper’s experience provided detailed information on school dimensions and acoustic backscattering. Using calibrated digital sonar data, school volume and fish densities were obtained, and school biomass computed. A positive linear relation was found between the estimated sonar school biomass and purse seine catches for both species (r2 = 0.92; residual standard error, RSE = 4.7 t). Large variability in volume backscattering coefficient and uncertainty in side-aspect target strength (TS) are the main sources of discrepancy between the estimates and the catch. Using a 4 dB (39%) weaker mean TS for mean side-aspect TS than the normal mean dorsal aspect TS was needed for optimizing the 1:1 relationship between sonar biomass estimate and catch. Accurate estimation of single school biomass can reduce the catch of unexpectedly large schools, leading to improvements in economic efficiency and reduced release of dead or dying fish.

Observations of in situ Atlantic bluefin tuna (Thunnus thynnus) with 500-kHz multibeam sonar

Abstract Field studies to investigate the survey capability of a 500-kHz multibeam sonar to monitor and quantify Atlantic bluefin tuna were undertaken at several fishing locations (commercial and recreational) off Prince Edward Island and at a grow-out pen in Nova Scotia. The results demonstrate that individual bluefin can be detected, enumerated, and tracked acoustically within the swathe of the sonar. Bluefin were observed individually, and in groups ranging from 2 to 16 fish. Schooling tuna, assumed to be foraging, were observed moving in a soldier formation. Estimates of in situ swimming speeds (0.5–11.0 m s−1) were made by tracking individual fish within the swathe. The mean interspatial distance between fish when swimming in a group of two or more tuna was estimated to be 8.94 m with a range of 2.68–22.63 m. Groups of up to 48 bluefin were observed aggregating around active herring gillnet vessels. Dorsal aspect target strength estimates of bluefin, obtained from an accompanying 120-kHz echosounder (Simrad EK60), ranged from −33 to −14 dB for fish from 220 to 313 cm (size estimated from commercial catches). Sonar detection ranges were dependent upon sea state and water depth. In rough seas, the surface layer became too turbulent, and air bubble attenuation too high, to consistently separate reverberation from fish-like targets. In shallow water (20–30 m), a range setting of >50 m could not be utilized due to seabed reflections. In water depths >50–60 m, a tilt angle of 7.5o below the horizontal allowed the sonar's range of up to 150 m to be utilized with minimal reverberation from the surface and seabed. The results indicate there is potential for using a 500-kHz multibeam sonar in fishery-independent surveys to monitor and to quantify bluefin in shallow water (<100 m).

Measurement of Diurnal Body Tilt Angle Distributions of Threeline Grunt Parapristipoma trilineatum Using Micro-Acceleration Data Loggers

The body tilt angle of a fish has a large effect on the acoustic target strength. For an accurate estimation of fish abundance using acoustic methods, it is necessary to measure body tilt angles in free-ranging fish. We measured diurnal body tilt angle distributions of threeline grunt (Parapristipoma trilineatum) while swimming in schools in a fish cage. Micro-acceleration data loggers were used to record (for 3 days) swaying and surging accelerations (at 16 Hz intervals) of 10 individuals among 20 forming a school in a fish cage. Time series analysis of 1-h mean body tilt angles revealed significant differences in body tilt angles between day (−7.9 ± 3.28°) and night (0.8 ± 5.89°), which must be taken into account when conducting acoustic surveys. These results will be useful for calculating the average dorsal aspect target strength (TS) of threeline grunt for accurate estimations of fish abundance.

북서 태평양 멸치(Japanese anchovy)에 대한 측면 음향 반사강도 특성

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 splitbeam 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.

Lateral-aspect, target-strength measurements of in situ herring (Clupea harengus)

Abstract Pedersen, G., Handegard, N. O., and Ona, E. 2009. Lateral-aspect, target-strength measurements of in situ herring (Clupea harengus). – ICES Journal of Marine Science, 66: 1191–1196. Surveys of schooling herring with the new multibeam sonar (Simrad MS70) pose new challenges when converting the echo energy to estimates of biomass. Because the sonar projects horizontally, data and models of lateral-aspect, herring target strength (TS) are needed. In this study, the TS of herring is measured with a horizontally projecting, split-beam echosounder (Simrad EK60). Target-tracking methods are used to estimate swimming angles relative to the horizontal (θ) of individual herring within schools and layers and to evaluate how θ and TS change with depth (z). Measurements of θ and TS are used as inputs for a model describing TS as a function of θ and z. The results indicate that the mean lateral-aspect TS of in situ herring depends on z. Moreover, the mean lateral-aspect TS is more sensitive to z than the mean dorsal-aspect TS predicted by a published model. At z = 50 m, the mean lateral-aspect TS is nearly 2.5 dB higher than the mean dorsal-aspect TS. Conversely, at z = 350 m, the lateral-aspect TS is 5 dB lower. These results suggest that herring swimbladders do not compress uniformly with increasing pressure, but compress dorsoventrally more than laterally.

Modelling the target strength of Trachurus symmetricus murphyi based on high-resolution swimbladder morphometry using an MRI scanner

Abstract Peña, H., and Foote, K. G. 2008. Modelling the target strength of Trachurus symmetricus murphyi based on high-resolution swimbladder morphometry using an MRI scanner. – ICES Journal of Marine Science, 65: 1751–1761. The acoustic target strength (TS) of Chilean jack mackerel (Trachurus symmetricus murphyi) was computed from three-dimensional reconstructions of the swimbladder form. The primary morphometric data were derived from high-resolution images made with a clinical whole-body 3-tesla magnetic resonance imaging (MRI) scanner. The fish were obtained from a commercial purse-seiner operating off Chile during 2003. Transverse MRI sequences of 18 fish were performed with a volumetric pixel 0.5 × 0.5 mm in cross section and 0.7 mm in the axial direction. From each transverse section, the swimbladder contour was traced manually using a digital pen tablet and smoothed using an automatic interpolation routine. The digital contours were used to build a triangular mesh spanning the swimbladder surface. The high-resolution swimbladder models revealed details such as undulations in the dorsal surface of the swimbladder caused by the backbone, and holes where the haemal spines penetrate the posterior end of the swimbladder. The Kirchhoff approximation was used to compute TS as a function of fish orientation at 38 kHz. The mean dorsal-aspect TS was computed for several orientation patterns and regressed on the logarithm of total fish length to derive operationally simple formulae.

A Target Strength and Length Relationship for Striped Bass and White Perch

AbstractFor hydroacoustic studies in which estimation of fish size and absolute abundance is desirable, researchers must either develop a relationship between target strength and fish length or borrow one from the literature. The purpose of this study was to provide a relationship between target strength and total length for two economically and ecologically important sympatric species: striped bass Morone saxatilis and white perch M. americana. We measured the dorsal aspect target strength of 12 white perch and 22 striped bass with a 120‐kHz split‐beam hydroacoustic system. The calculated target strength (TS (decibels)) to length (Lcm (cm)) relationships were as follows: white perch TS = 26.48 log10Lcm − 69.45 (r2 = 0.81, P < 0.001); striped bass TS = 15.37 log10Lcm − 56.26 (r2 = 0.80, P < 0.001); and a combined model TS = 15.613 log10Lcm − 56.47 (r2 = 0.82, P < 0.001). Each of these models differs substantially from the equations of Love (1971) and Foote (1987), which are commonly used in acoustic studies when the actualrelationships are lacking.

Acoustic backscattering by Hawaiian lutjanid snappers. 1. Target strength and swimbladder characteristics.

The target strengths and swimbladder morphology of six snapper species were investigated using broadband sonar, x rays, and swimbladder casts. Backscatter data were obtained using a frequency-modulated sweep (60-200 kHz) and a broadband, dolphinlike click (peak frequency 120 kHz) from live fish, mounted and rotated around each of their three axes. X rays revealed species-specific differences in the shape, size, and orientation of the swimbladders. The angle between the fish's dorsal aspect and the major axis of its swimbladder ranged from 3 degrees to 12 degrees and was consistent between individuals within a species. This angle had a one-to-one relationship with the angle at which the maximum dorsal aspect target strength was measured (r2 = 0.93), regardless of species. Maximum dorsal aspect target strength was correlated with length within species. However, the swimbladder modeled as an air-filled prolate spheroid with axes measured from the x rays of the swimbladder predicted maximum target strength significantly better than models based on fish length or swimbladder volume. For both the dorsal and lateral aspects, the prolate spheroid model's predictions were not significantly different from the measured target strengths (observed power >0.75) and were within 3 dB of the measured values. This model predicts the target strengths of all species equally well, unlike those based on length.

조피볼락과 참돔의 표적 강도에 관한 연구

우리 나라 연안에서 주로 서식하고 있는 조피볼락(Schlegel's Black Rockfish, Sebastes schlegeli)과 참돔(Red Seabream, Pagrus major) 의 자원량을 추정할 때 보다 더 정확히 추정할 수 있는 기초 자료를 얻기 위하여 in situ TS 측정법과 유사한 환경 속에서 망과 3개의 주파수를 이용하여 어체의 크기와 자세별 및 주파수 특성에 따른 TS 에 대하여 조사하여 얻어진 결과를 요약하면 다음과 같다. 1. 전장(L, cm)에 따른 최대 TS 값을 이용한 조피볼락의 변환 계수(A) 값은 38kHz에서 -63.7dB, 120kHz에서 -64.4dB, 200kHz에서 -62.4 dB로 나타났으며, 참돔은 38kHz에서 -62.6dB, 120kHz에서 -65.4dB, 200kHz에서 -65..dB이었다. 또한, 평균 TS 값을 이용한 조피볼락의 변환 계수 값은 38kHz에서 -68.4dB, 120kHz에서 73.4dB, 200kHz에서 -70.8dB로 나타났으며, 참돔은 38kHz에서 -67.9dB, 120kHz에서 -72.7 dB, 200kHz에서 -73.4dB로 각각 나타났다. 2. 어체 1g당 최대 TS 값을 이용한 조피볼락의 변환 계수( B) 값은 38kHz에서 -52.0dB, 120 kHz에서 -52.7dB, 200kHz에서 -50.7dB로 나타났으며, 참돔은 38kHz에서 -50.9dB, 120kHz 에서 -53.7dB, 200kHz에서 -53.3dB이었다. 또한 평균 TS 값을 이용한 조피볼락의 변환 계수 값은 38kHz에서 -56.7dB, 120kHz에서 -61.7 dB, 200kHz에서 -59.IdB로 나타났으며, 참돔은 38kHz에서 -56.2dB, 120kHz에서 -61.0dB, 200 kHz에서 -61.6dB로 각각 나타났다. 3. 참돔 2마리를 대상으로 한 자세각 분포는 -26<TEX>$^{\circ}$</TEX>~25<TEX>$^{\circ}$</TEX>로 나타났으며, 그 때의 주파수에 따른 자세별 표적 강도는 38kHz에서 변화 폭이 비교적 적었으며, 120kHz에서는 Head down 되었을때 보다 Head up 되었을 때 3~6dB 정도 높게 나타났다. This study investigates dorsal aspect target strength with fish size, tilt angle and frequency characteristics for the schlegel's black rockfish(Sebastes achlegeli) and the red seabream (Pagrus major). This study was carried out on free swimming fish in a cage in order to obtain acoustic data of the biomass estimation using the scientific echo sounder. The results obtained from this study are summarized as follows; 1 The coefficients of the schlegel's black rockfish and the red seabream using maximum TS with fish length were expressed -63.7dB and -62.6dB at a frequency of 38kHz, -64.4dB and -65.4dB at 120kHz, and -62.4dB and -65.0dB at 200kHz, respectively. 2. The coefficients of the schlegel\`s black rockfish and the red seabream using averaged TS with fish length were expressed -68.4dB and -67.9dB at a frequency of 38kHz, -73.4dB and -72.7dB at 120kHz, and -70.BdE and -73.4dB at 2001Hs, respectively. 3. The coefficients of the schlegel's black rockfish and the red seabream using maximum TS with body weight were expressed -52.0dB and -50.9dB at a frequency of 38kHz, -52.7dB and -53.7dB at 120kHz, and -50.7dB and -53.3dB at 200kHz, respectively. 4. The coefficients of the schlegel's black rockfish and the red seabream using averaged TS with body weight were expressed -56.7dB and -56.2dB at a frequency of 38kHz, -61.7dB and -61.0dB at 120kHz, and -59.ldE and -61.6dB at 200kHz, respectively. 5. Varying the tiIt angle of the two red seabream from -26<TEX>$^{\circ}$</TEX>to +25<TEX>$^{\circ}$</TEX>, the variation width of target strength expressed smaller at a frequency of 38kHz than at 120kHz and expressed about 3~6dB higher head up than head down at 120kHz.

Target strength measurements of Hawaiian mesopelagic boundary community animals

A 200-kHz echosounder modified to digitize the envelope of the received echoes directly into a computer was used to measure the ex situ target strength (TS) of live animals from the Hawaiian mesopelagic boundary community as a function of animal size, tilt and roll angle, and biological classification. Dorsal aspect TS (in dB//1 m) at 200 kHz was related to the animal’s length: myctophid fish TS=20 log (standard length in cm)−58.8, r2=0.91, squid TS=18.8 log (mantle length in cm)−61.7, r2=0.81, shrimp TS=19.4 log (length in cm)−74.1, r2=0.83. Tilting the fish 5° and 10° changed the measured TS by up to 3.0 dB, decreasing TS as the fish was tilted forward and increasing TS as the fish was tilted backwards. In shrimp, forward tilt increased TS while backward tilt decreased TS by up to 3.3 dB. No consistent trend in squid TS change was observed with tilt angle. Roll angles of 5° and 10° increased the TS of all groups by up to 3.0 dB. Myctophid lateral aspect TS was consistently about 6 dB higher than the dorsal TS. Physiological analysis of the fishes’ swimbladders revealed that the swimbladder is not the dominant scattering mechanism in the myctophid fishes studied.

Experimental verification of the deformed cylinder scattering model and its application for the calculation of backscattering from fish

The dorsal aspect target strength pattern of straight cylinders made of polystyrene (EPS) are measured and compared with the deformed cylinder scattering model (DCM) proposed by Ye [Zhen Ye, J. Acoust. Soc. Am. 102, 877–884 (1997)] in the range of the tilt angle from −50° to 50°. Both experiments and the theory agreed very well for the wide range of tilt angle. The deformed cylinder model is also applied to predict the target strength pattern of Ayu (Plecoglossus altivelis) which is a river fish with an open swimbladder. The dorsal target strength of Ayu is measured by keeping it in alive condition. Then its swimbladder’s shape is observed using a soft x-ray system and digitized. Digitized data is used for the calculation on the basis of the deformed cylinder model and also the shape of the swimbladder is reproduced carving a rectangular solid of EPS by hand. The measured TS pattern of alive Ayu, the physical EPS model of swimbladder, and the DCM calculation agreed very well. Expanded polystyrene is a useful material to verify the scattering theory of the gas model and can become an artificial fish model with a swimbladder. Scattering from a complicated shape as a fish is predictable using DCM.

A re-evaluation of relationships between fish size, acoustic frequency, and target strength

There are many measurements of dorsal aspect target strength of fish, but relatively few studies compare estimation methods or attempt to combine data from different studies into general relations between fish size, acoustic frequency and target strength (or acoustic cross-section). We edited and updated earlier summary regressions relating fish size, acoustic frequency and acoustic cross-section. Experimental measurements on marine fish were separated into swimbladder and non-swimbladder species, model results compared with experimental data, target strengths of marine, and freshwater fish were contrasted, and previous and new target strengths of commercial New Zealand fish species were placed in the context of the new regressions. Analysis of variance was used to show significant effects of species, freshwater vs. marine, swimbladder vs. non-swimbladder fish, model vs. experimental, and dead vs. alive fish on the relationship between maximum dorsal aspect target strength and fish length. For experimental results on gadoids we found significant species and live vs. dead (or stunned) fish effects on the target strength to length relationship. The quadratic dependence of target strength on fish length was also tested and found to be the exception rather than the rule. Existing pitch tilt angle data was compiled and a normal distribution with standard deviation of at least 15° was required to describe most distributions.

Depth dependence of target strength of live kokanee salmon in accordance with Boyle's law

The target strength (TS) offish varies with a number of factors, especially the presence or absence of a swimbladder. This study investigated the eVect of the swimbladder on the TS of live kokanee (Oncorhynchus nerka) in relation to depth. Experiments were conducted at Lake Kuttara, Hokkaido, Japan, which is abundant with kokanee. Fish samples were caught with a fishing net. The live fish were suspended on the sound beam axis, and tilted from 50) (head-down aspect) to +50) (head-up aspect). The dorsal aspect TS functions were measured at 50 kHz. Measurements were performed when the fish were forced to change depth rapidly. The TS values were measured as a function of tilt angle and depth, and the maximum dorsal aspect TS (TSmax) values and the averaged dorsal aspect TS (TSavg) values were calculated and compared. TSavg values were calculated with respect tofish tilt-angle distribution, which was assumed to have a mean value of 5) and a standard deviation of 15). Both TSmax and TSavg decreased with depth in accordance with Boyle’s law, i.e. a reduction rate of 6.7 dB per 10 atm was observed. ? 1996 International Council for the Exploration of the Sea

Lateral target strength of Antarctic krill

An area of high krill (Euphausia superba Dana) density was continuously monitored with down-looking and side-looking sonars over a period of 24 h. Measurements of volume backscattering strength were used to describe the density of krill with depth and the vertical movement of krill over time. In situ measurements were made of dorsal aspect target strength (TS) and, as krill moved into the near-surface layer (0-15 m), in situ measurements were made of lateral-aspect TS. The probability density function (PDF) of TS measurements made with the down-looking transducer had a mode at approximately −73 dB. The PDF of TS measurements made with the side-looking transducer was broader with a mode at approximately −67 dB. Sampled krill had a bi-modal length distribution with a major mode at 44 mm and a minor mode at approximately 30 mm.

東シナ海で漁獲された魚の背方向ターゲットストレングスとうきぶくろとの関係

The target strength (TS) of fish varies with acoustic frequency, fish size, fish activity, orientation, swimbladder and so on. Among these, the swimbladder is recognized as having the most important effect on TS. The dorsal aspect TS as a function of tilt angle of fish caught by bottom trawling in the East China Sea was measured at two frequencies (25 and 100 kHz). The swimbladder sizes (length and height) and inclination angle of the swimbladder to the lateral line of the fish were measured by X-ray photographs. TS and swimbladder data were then compared and analyzed, and the following results were obtained: (1) The eight species of fish, except the silver pomfret, have swimbladders, but the angle and size of the swimbladder varies. (2) For bladder fish, the angle of the maximum dorsal aspect TS agrees with the broadside direction of the swimbladder. (3) The dorsal aspect TS of the silver pomfret is clearly lower than that of bladder fish at the two frequencies. (4) The maximum and averaged dorsal aspect TS values of the silver pomfret, were lower by about 7-8 dB, 8-10 dB at 25 kHz, and by 8-10 dB, 9-11 dB at 100 kHz than two other bladder fish (yellow sea bream and whitefin crevalle).

東シナ海で漁獲された活ガザミの背方向ターゲットストレングスの測定

The dorsal aspect target strength (TS) of four live swimming crab Portunus trituberculatus were measured at 25kHz and 100kHz in Cheju port (Korea). Probability density functions (PDF), i.e., Rayleigh PDF and Rice PDF, were fitted to the distribution of backscattering amplitude from the live swimming crab. The following results were obtained: (1) TS was more dispersed at 100kHz than at 25kHz. (2) The PDFs of the backscattering amplitude agree approximately with Rice PDF at 25kHz and with Rayleigh PDF at 100kHz. (3) The Rice parameter γ tends to decrease with increasing carapace length, carapace width and acoustic frequency. (4) The averaged TS , estimated from PDFs, is about 2dB higher at 25kHz than at 100kHz. (5) Mean values of averaged target strength B, which is normalized with respect to body weight, are -52.5dB at 25kHz, -54.9dB at 100kHz. These values agree approximately with those of bladder fish.

Dorsal-aspect target strength of yellowtail and mackerel measured by frequency sweeping method.

Dorsal-aspect target strength of yellowtail and mackerel measured by frequency sweeping method.

東シナ海で漁獲された主要１０魚種のターゲットストレングスの測定

The dorsal aspect target strength functions of ten species of fish collected by bottom trawl were measured at two frequencies. The average TS were calculated with respect to fish tilt angle distribution, which is assumed to have a mean value of -5 degrees and a standard deviation of 15 degrees. Both maximum TS and average TS were normalized with the fish length (L[cm]) squared and the 2/3 power of body weight (W[g]), namely, TS=20logL+A, TS=20/3log W+B.The results obtained were as follows:(1) The target strength is generally higher at low frequency (25kHz) than at high frequency (100kHz). But for two species (Chub mackerel and Kandari), neither maximum nor average TS differ between low and high frequencies.(2) The target strength of Silver pomfret, a bladderless fish, is clearly lower than that of bladder fish at two frequencies.(3) The normalized TS (A or B) were calculated for the maximum TS (Amax or Bmax) and average TS (Aavg or Bavg). The results are: Amax = -63 - -59 dB, Aavg = -68 - -64 dB at low frequency; Amax = -65 - -59 dB, Aavg = -72 - -65 dB at high frequency, and Bmax = -52 - -45 dB, Bavg = -57 - -50 dB at low frequency; Bmax = -54 - -45 dB, Bavg = -60 - -52 dB at high frequency.

An Analytical Model of Acoustic Fish Reflection for Estimation of Maximum Dorsal Aspect Target Strength

We develop a simple analytical model of the acoustic reflectivity offish targets based on empirical observations in field and laboratory settings. It enables unbiased estimation of maximum dorsal aspect target strength in cases where individual fish are observed a minimum of three times in successive pings of a survey transect. The model results are consistent with observations of example fish targets of two demersal species. It promises improved estimates of target strength from field measurements.