Potential acoustic discrimination within boreal fish assemblages
TL;DR: Frequency differencing successfully discriminated between fish species but the choice of frequency to maximize target strength differences was not consistent among species pairs, and were dependent on fish size and body orientation.
Abstract: Differences in the acoustic characteristics of forage fish species in the Gulf of Alaska and the Bering Sea were examined using Kirchhoff ray-mode (KRM) backscatter models. Our goal was to identify species-specific characteristics and metrics that facilitate the discrimination of species using acoustic techniques. Five fish species were analyzed: capelin (Mallotus villosus), Pacific herring (Clupea pallasii), walleye pollock (Theragra chalcogramma), Atka mackerel (Pleurogrammus monopterygius), and eulachon (Thaleichthys pacificus). Backscatter amplitude differences exist among these species, especially between swimbladdered and non-swimbladdered fish. Echo intensities were variable within and among species. The effect of morphological variability was indexed using the ratio of the Reducedscattering length (RSL) standard deviation over its mean. Morphological variability was low only at fish length to acoustic wavelength ratios less than eight. Target strength differences between pairs of carrier frequencies (ranging from 12 kHz to 200 kHz) differed among species, and were dependent on fish size and body orientation. Frequency differencing successfully discriminated between fish species but the choice of frequency to maximize target strength differences was not consistent among species pairs. Frequencydependent, backscatter model predictions facilitate comparison of target strength differences prior to acoustic data collection.
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TL;DR: In this paper, the feasibility of identifying major acoustic scatters in North Pacific ecosystems based on empirical measurements of relative frequency response was evaluated, and the authors concluded that the acoustic measurements in areas where...
Abstract: We evaluated the feasibility of identifying major acoustic scatters in North Pacific ecosystems based on empirical measurements of relative frequency response. Acoustic measurements in areas where ...
135 citations
TL;DR: A classification-tree system using the multifrequency information from the ground-truthed echotraces that can be translated into a processing tool for objective species allocation is compared with the traditional method of expert-based scrutiny.
Abstract: Fernandes, P. G. 2009. Classification trees for species identification of fish-school echotraces. - ICES Journal of Marine Science, 66: 1073-1080.Acoustic surveys provide valuable information on the abundance and distribution of many fish species, but are particularly effective for schooling pelagic fish of commercial importance. However, despite recent advances in multifrequency processing, the technique still requires some subjective judgement when allocating the acoustic data, fish-school echotraces, to particular species—the so-called “scrutiny process”. This is assisted by “ground truth” trawling and operator experience of relating trawl data to echotraces of particular fish schools. In this paper, a method to identify species based on “classification trees” is applied to data from a component of the International North Sea Herring Acoustic Survey. Classification trees may be considered as a variant of decision trees, and have properties that are intuitive to biologists, because they are similar to the keys used for the biological identification of species. The method described here incorporates a multifrequency fish-school filter, image analysis to isolate fish-school echotraces, and finally, a classification-tree system using the multifrequency information from the ground-truthed echotraces that can be translated into a processing tool for objective species allocation. The classification-tree system is compared with the traditional method of expert-based scrutiny. Unlike the latter, however, a measure of uncertainty is attributed to the classification-tree approach and this could be propagated through the acoustic-survey estimation procedure as a component of the total uncertainty in the abundance estimate.
69 citations
Cites background from "Potential acoustic discrimination w..."
...As a result of such developments, the work on fish-species identification using multifrequency data has expanded (e.g. Kang et al., 2002; Brierley et al., 2004; Gauthier and Horne, 2004; Korneliussen and Ona, 2004)....
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TL;DR: Hydroacoustic records from 2006 to 2012 were analysed to test the hypothesis that age-0 polar cod segregate vertically from larger congeners, and found low biomass in the mesopelagic layer from February to September likely resulted from large polar cod settling on the seafloor to avoid diving marine mammals.
Abstract: The offshore marine ecosystem of the Canadian Beaufort Sea faces the double pressure of climate change and industrialization. Polar cod (Boreogadus saida) is a pivotal forage species in this ecosystem, accounting for 95 % of the pelagic fish assemblage. Its vertical distribution over the annual cycle remains poorly documented. Hydroacoustic records from 2006 to 2012 were analysed to test the hypothesis that age-0 polar cod segregate vertically from larger congeners. Trawls and ichthyoplankton nets validated the acoustic signal. Fish length, weight, and biomass were estimated from new regressions of target strength and weight on standard length. Polar cod were vertically segregated by size in all months, with small age-0 juveniles in the epipelagic (<100 m) layer and larger age-1+ deeper in the water column. From December to March, the biomass of age-1+ peaked in a mesopelagic layer between 200 and 400 m. With increasing irradiance from April to July, the mesopelagic layer deepened and extended to 600 m. Starting in July, age-0 polar cod formed an epipelagic scattering layer that persisted until November. From September onward, age-0 left the epipelagic layer to join small age-1+ in the upper mesopelagic layer. Low biomass in the mesopelagic layer from February to September likely resulted from large polar cod settling on the seafloor to avoid diving marine mammals. Longer ice-free seasons, warmer sea-surface temperatures, or an oil spill at the surface would likely impact epipelagic age-0, while mesopelagic age-1+ would be vulnerable to an eventual oil plume spreading over and above the seafloor.
65 citations
Cites background from "Potential acoustic discrimination w..."
...curve, with TS-SL points falling either well above or well below the regression, may reflect some bimodal orientation of the fish (head/tail on versus top/side on) in the acoustic beam (Gauthier and Horne 2004)....
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...The bimodal distribution of variance around the regression curve, with TS-SL points falling either well above or well below the regression, may reflect some bimodal orientation of the fish (head/tail on versus top/side on) in the acoustic beam (Gauthier and Horne 2004)....
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TL;DR: A strong correlation among increased prey density and ocean vertical structure relative to increased click densities and increased prey scattering layers is found within the Atlantic Undersea Test and Evaluation Center acoustic sensor system.
Abstract: Beaked whales, specifically Blainville's (Mesoplodon densirostris) and Cuvier's (Ziphius cavirostris), are known to feed in the Tongue of the Ocean, Bahamas. These whales can be reliably detected and often localized within the Atlantic Undersea Test and Evaluation Center (AUTEC) acoustic sensor system. The AUTEC range is a regularly spaced bottom mounted hydrophone array covering >350 nm2 providing a valuable network to record anthropogenic noise and marine mammal vocalizations. Assessments of the potential risks of noise exposure to beaked whales have historically occurred in the absence of information about the physical and biological environments in which these animals are distributed. In the fall of 2008, we used a downward looking 38 kHz SIMRAD EK60 echosounder to measure prey scattering layers concurrent with fine scale turbulence measurements from an autonomous turbulence profiler. Using an 8 km, 4-leaf clover sampling pattern, we completed a total of 7.5 repeat surveys with concurrently measured physical and biological oceanographic parameters, so as to examine the spatiotemporal scales and relationships among turbulence levels, biological scattering layers, and beaked whale foraging activity. We found a strong correlation among increased prey density and ocean vertical structure relative to increased click densities. Understanding the habitats of these whales and their utilization patterns will improve future models of beaked whale habitat as well as allowing more comprehensive assessments of exposure risk to anthropogenic sound.
55 citations
Cites background from "Potential acoustic discrimination w..."
...[56]) or additional sampling gear necessary to tease apart the composition of the deep scattering layer....
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TL;DR: The distinctive acoustic signature of Chaoborus demonstrates the usefulness of multi-frequency acoustics for species identification and discrimination, and can represent a major error in acoustic estimates of fish densities obtained at higher echosounder frequencies, but not at lower frequencies.
53 citations
References
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Book•
30 Oct 1997
TL;DR: The fundamental principles of underwater sound propagation are described in this paper, which is an authoritative reference for specialists in acoustics, oceanography, marine biology, and related fields, and also encourages a new generation of scientists, engineers and entrepreneurs to apply the modern methods of acoustical physics to probe the unknown sea.
Abstract: Fundamentals of Acoustical Oceanography an important reference for specialists in acoustics, oceanography, marine biology, and related fields. This book also encourages a new generation of scientists, engineers, and entrepreneurs to apply the modern methods of acoustical physics to probe the unknown sea. The book is an authoritative, modern text with examples and exercises. It contains techniques to solve the direct problems, solutions of inverse problems, and an extensive bibliography from the earliest use of sound in the sea to present references. The book provides background to measure ocean parameters and processes, find life and objects in the sea, communicate underwater, and survey the boundaries of the sea. Fundamentals of Acoustical Oceanography explains principles of underwater sound propagation, and describes how both actively probing sonars and passively listening hydrophones can reveal what the eye cannot see over vast ranges of the turbid ocean. This book demonstrates how to use acoustical remote sensing, variations in sound transmission, in situ acoustical measurements, and computer and laboratory models to identify the physical and biological parameters and processes in the sea.
660 citations
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
"Potential acoustic discrimination w..." refers background in this paper
...This is not surprising, since the swimbladder contributes to at least 90% of the sound scattered by a fish (Foote, 1980b)....
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...Additional backscatter from other structures are not expected to be large, since the difference in acoustic impedance between cartilaginous bone and soft tissues is much less than that between gas in the swimbladder and flesh or bone (cf. Foote, 1980b)....
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...(Foote, 1980a; McQuinn and Winger, 2003; Stanton et al., 2003)....
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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.
257 citations
"Potential acoustic discrimination w..." refers background in this paper
...Variation in body and swimbladder width, depth, and shape affect the amount of energy that is backscattered by a fish (Ona, 1990; Ona et al., 2001)....
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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
"Potential acoustic discrimination w..." refers background in this paper
...acoustics is species identification (Rose and Leggett, 1988; Horne, 2000; Petitgas et al., 2003)....
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...Introduction One of the main challenges and limitations in fisheries acoustics is species identification (Rose and Leggett, 1988; Horne, 2000; Petitgas et al., 2003)....
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01 Jan 1977
198 citations
"Potential acoustic discrimination w..." refers background in this paper
...Target strength is more sensitive to incident angle as frequency increases (Nakken and Olsen, 1977; Miyanohana et al., 1990)....
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