Physiological factors causing natural variations in acoustic target strength of fish
01 Feb 1990-Journal of the Marine Biological Association of the United Kingdom (Cambridge University Press)-Vol. 70, Iss: 1, pp 107-127
TL;DR: Evidence for both periodic variations, as from uncompensated vertical migrations, and seasonal variations, caused by the fat cycle and gonad development, are presented.
Abstract: The swimbladder is recognized as responsible for a major part of the acoustic backscattering from fish. In most fishes it has the function of a buoyancy regulator but in others its main function is rather unclear. Based on methods for exact mapping of the swimbladder shape, observations of deviations from normal appearance and shape are discussed in relation to possible effects on target strength. Evidence for both periodic variations, as from uncompensated vertical migrations, and seasonal variations, caused by the fat cycle and gonad development, are presented.
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01 Jan 1999
TL;DR: Pelagic fisheries Habitat selection and migration Schooling behaviour Avoidance Attraction and association Learning Effects of behavior on fisheries and stock assessment by population dynamic models Effects of behaviour on stock assess by acoustic surveys Other methods of stock assessment and fish behaviour.
Abstract: Pelagic fisheries Habitat selection and migration Schooling behaviour Avoidance Attraction and association Learning Effects of behaviour on fisheries and stock assessment by population dynamic models Effects of behaviour on stock assessment by acoustic surveys Other methods of stock assessment and fish behaviour.
384 citations
Cites background from "Physiological factors causing natur..."
...This can affect acoustic stock assessment, both through a horizontal dilution of fish density in the path of the acoustic beam and by a lower target strength than predicted, both because the fish is tilted downwards (Nakken & Olsen, 1977) and due to a compression of the swimbladder during fast diving (Ona, 1990)....
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...Such swimming behaviour may result in a horizontal dilution of fish density in front of the vessel, and a reduction in target strength both due to compression of the swimbladder if rapid diving occurs, and because of an increase in the tilt angle (Ona, 1990)....
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TL;DR: Exclusive use of acoustics to identify aquatic organisms reliably will require a set of statistical metrics that discriminate among a wide range of similar body types at any packing density, and incorporation of these algorithms in routine data processing.
Abstract: Noninvasive species identification remains a longterm goal of fishers, researchers, and resource managers who use sound to locate, map, and count aquatic organisms. Since the first biological applications of underwater acoustics, four approaches have been used singly or in combination to survey marine and freshwater environments: passive sonar; prior knowledge and direct sampling; echo statistics from high-frequency measures; and matching models to low-frequency measures. Echo amplitudes or targets measured using any sonar equipment are variable signals. Variability in reflected sound is influenced by physical factors associated with the transmission of sound through a compressible fluid, and by biological factors associated with the location, reflective properties, and behaviour of a target. The current trend in acoustic target identification is to increase the amount of information collected through increases in frequency bandwidth or in the number of acoustic beams. Exclusive use of acoustics to identify aquatic organisms reliably will require a set of statistical metrics that discriminate among a wide range of similar body types at any packing density, and incorporation of these algorithms in routine data processing.
238 citations
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...…(Olsen et al., 1983; Misund and Aglen, 1992; Soria et al., 1996) are fairly well documented, but other factors such as abdominal cavity contents (Ona, 1990), degree of aggregation (Stanton, 1985b; Misund, 1993), animal orientation (Clay and Horne, 1995; Medwin and Clay, 1997), and the material…...
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TL;DR: Underwater acoustics enables the detection and precise location of fish and is therefore a prerequisite for effective fishing methods such as pelagic trawling and purse seining, and the application of acoustic instruments to detect fish and monitor gear performance in modern commercial fisheries is outlined.
Abstract: Underwater acoustics enables the detection and precise location of fish and is therefore a prerequisite for effective fishing methods such as pelagic trawling and purse seining. The application of acoustic instruments to detect fish and monitor gear performance in modern commercial fisheries is outlined. The latest developments in obtaining information such as bottom roughness and determining such characteristics of fish detected as size and species are presented.
160 citations
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...Ona (1990) found that the swimbladder volume of herring followed a depth relation according to Boyle’s law, and Halldorsson and Reynisson (1983) and Olsen and Ahlquist (1989) found a certain reduction in backscattering cross section of herring with increasing depth....
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TL;DR: In this article, the authors used split-beam tracking methods and still-frame photography to study the herring behaviour inside the dense wintering schools of Norwegian spring-spawning herring.
Abstract: When plankton production in the feeding areas decreases in the fall, adult Norwegian spring-spawning herring migrate into two fjords in northern Norway In these wintering areas the herring occupy deeper water Lacking the ability to refill the swimbladder they are constantly negatively buoyant This leads to different adaptive behaviour during the day and at night, behaviour which is reflected in swimming angle Split-beam tracking methods and still-frame photography have been used to study the herring behaviour inside the dense wintering schools Negative buoyancy seems to be controlled through constant swimming at speeds between 025-042 ms −1 because these are sufficiently high to generate lift when the pectoral fins are used as spoilers During the day, when the layers aggregate, the average swimming angle is close to horizontal while positive average swimming angles of up to 40° were recorded at night A bimodal distribution of tilt angles, with one positive and one negative component, indicating a “rise and glide” swimming strategy was also observed at night Vertically undulating split beam tracks confirmed this particular type of swimming behaviour As adult herring are directional targets at the echo-sounder frequency used for acoustic assessment of the stock, the possible impact of the observed tilt angles on average acoustic target strength is discussed
151 citations
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...Ona (1990) found that herring with a fat content of 16.8% all sank when being anaesthetized in situ at a depth of 30 m. Brawn (1969) calculated a sinking factor for herring as the ratio of herring body density, including the swimbladder, to sea-water density multiplied by 1000....
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TL;DR: The mean TS of herring was found to be significantly dependent on the depth (pressure) and the gonadosomatic index, which are the additional parameters included in the new TS relationship.
Abstract: Target-strength (TS) experiments on captive, adult herring have been conducted at intervals over several years to investigate the acoustic effect of pressure and seasonal changes on fish physiology. Experiments in a large, net pen (4500 m 3 ) were done at 18, 38, and 120 kHz frequencies with calibrated, split-beam echosounders. The main ex situ results at 38 kHz, including a vertical-excursion experiment, were combined with in situ TS data collected at 38 kHz with a probing, split-beam transducer lowered into the dense herring layers, recorded during two surveys in the wintering area of the Norwegian spring-spawning stock. Multiple-linear regression analysis was used to investigate the functional relationship between TS and the measured parameters. The mean TS of herring was found to be significantly dependent on the depth (pressure) and the gonadosomatic index. These are the additional parameters included in the new TS relationship.
145 citations
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...Unlike many other fishes, the ability of the herring (Clupea harengus L.) to use the swimbladder as an efficient buoyancy regulator has been questioned (Brawn, 1962; Blaxter and Batty, 1984; Ona, 1990 )....
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References
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TL;DR: In this article, the relative swimbladder contribution to both maximum and averaged dorsal aspect backscattering cross sections is shown to be approximately 90% to 95%, which is higher than most other estimates.
Abstract: Previous determinations of the swimbladder contribution to the fish backscattering cross section have been hindered by ignorance of the acoustic boundary conditions at the swimbladder wall. The present study circumvents this problem by direct comparison of target strengths of three gadoid species and mackerel — anatomically comparable fusiform fish which respectively possess and lack a swimbladder. The relative swimbladder contribution to both maximum and averaged dorsal aspect backscattering cross sections is shown to be approximately 90% to 95%, which is higher than most other estimates. The new results were established for fish of 29‐ to 42‐cm length and acoustic frequencies of 38 and 120 kHz.
333 citations
TL;DR: In this article, a new model was proposed to describe acoustic scattering by swimbladdered fish of lengths from at least 8 to 36 wavelengths, which represented a fish by an ideal pressure-release surface having the exact size and shape as the swimbladder.
Abstract: A new model describes acoustic scattering by swimbladdered fish of lengths from at least 8 to 36 wavelengths. It represents a fish by an ideal pressure‐release surface having the exact size and shape as the swimbladder. The backscattering cross section, or target strength, is computed by means of the Kirchhoff approximation. To test the model, predictions of target strengths based on swimbladder morphometries of 15 gadoids of lengths from 31.5 to 44.5 cm are compared with conventional target strength measurements on the same, surface‐adapted fish, anesthetized before acoustic measurement, and shock‐frozen immediately afterwards. Details are given of the swimbladder morphometry. In essence, this consists of slicing the frozen fish with a microtome, photographing the exposed swimbladder cross sections, digitizing the contours, and triangulating the surface between pairs of contours on adjacent, parallel planes. Theory and experiment are compared through the dorsal and ventral aspect target strength functions, their averages, and simulated probability density functions.
144 citations
TL;DR: In this paper, the mean in situ target strengths for cod, saithe, Norway pout, herring, redfish, and greater silver smelt were derived using a split-beam echo sounder.
Abstract: Data derived with a 38‐kHz split‐beam echo sounder have been analyzed to yield target strengths suitable for use with echo integrators. This has required compensation for both thresholding and saturation, since these operations can significantly bias data intended for use with systems, such as echo integrators, whose dynamic ranges are much larger. A nonparametric statistical method is introduced for this purpose. Pure‐species acoustic data are extracted in several two‐species cases by a method for separating superimposed frequency distributions. Mean in situ target strengths are presented for cod, saithe, Norway pout, herring, redfish, and greater silver smelt. For com‐ parison with other data, these are expressed through the standard equation ∼(TS) =20 log l +b, where ∼(TS) is the mean target strength in decibels, and l is the fish length in centimeters. For gadoids of lengths from 10 to over 105 cm, b=−67.5 dB. For herring of lengths from 24 to 34 cm, b=−72.1 dB. The often‐ignored problem of obtaining ...
122 citations
TL;DR: In this article, a general model for averaging the acoustic target strength functions of fish is stated in calculable form, which accounts for the influences of the distribution of generally coupled spatial and orientation states of fish, geometric perspective, and beam patterns on observations of target strength.
Abstract: A general model for averaging the acoustic target strength functions of fish is stated in calculable form. It accounts for the influences of the distribution of generally coupled spatial and orientation states of fish, geometric perspective, and beam patterns on observations of target strength. The model is developed and applied to observation of fish by directional, downward‐looking sonars. A particular example is considered in which the sonar is represented by an ideal circular piston, the spatial distribution of fish is homogeneous, and the orientation distribution is spatially homogeneous and characterized by a uniformily distributed azimuthal variable and an independent, essentially normally distributed tilt angle variable. Averaged and averaged‐squared backscattering cross sections are computed from high quality gadoid target strength functions measured at two ultrasonic frequencies. Results for a sonar half‐beamwidth of 2.5 deg for three different realizations of the tilt angle distribution are expressed in the logarithmic domain and regressed linearly on fish length. The significance of species, frequency, and orientation distribution differences among the regressions is noted. Estimates of the mean ratio of averaged‐squared backscattering cross section and squared‐averaged backscattering cross section are presented.
109 citations