Analysis of Echo Counting Data: A 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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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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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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Hydroacoustic Target Strength Distributions of Alewives in a Net-Cage Compared with Field Surveys: Deciphering Target Strength Distributions and Effect on Density Estimates

Transactions of the American Fisheries Society ◽

10.1577/t07-215.1 ◽

2009 ◽

Vol 138 (3) ◽

pp. 471-486 ◽

Cited By ~ 7

Author(s):

Thomas E. Brooking ◽

Lars G. Rudstam

Keyword(s):

Target Strength ◽

Density Estimates ◽

Field Surveys ◽

Net Cage ◽

Strength Distributions

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Quantifying acoustic survey uncertainty using Bayesian hierarchical modeling with an application to assessing Mysis relicta population densities in Lake Ontario

ICES Journal of Marine Science ◽

10.1093/icesjms/fsw080 ◽

2016 ◽

Vol 73 (8) ◽

pp. 2104-2111 ◽

Cited By ~ 3

Author(s):

Patrick J. Sullivan ◽

Lars G. Rudstam

Keyword(s):

Hierarchical Modeling ◽

Survey Design ◽

Lake Ontario ◽

Sensitivity Analyses ◽

Target Strength ◽

Parameter Estimates ◽

Data Set ◽

Density Estimates ◽

Mysis Relicta ◽

Bayesian Hierarchical

Abstract A Bayesian hierarchical model was applied to acoustic backscattering data collected on Mysis relicta (opossum shrimp) populations in Lake Ontario in 2005 to estimate the combined uncertainty in mean density estimates as well as the individual contributions to that uncertainty from the various information sources involved in the calculation including calibration, target strength determination, threshold specification and survey sampling design. Traditional estimation approaches often only take into account the variability associated with the survey design, while assuming that all other intermediate parameter estimates used in the calculations are fixed and known. Unfortunately, unaccounted for variation in the steps leading up to the global density estimate may make significant contributions to the uncertainty of density estimates. While other studies have used sensitivity analyses to demonstrate the degree to which uncertainty in the various input parameters can influence estimates, including the uncertainty directly as demonstrated here using a Bayesian hierarchical approach allows for a more transparent representation of the true uncertainty and the mechanisms needed for its reduction. A Bayesian analysis of the mysid data examined here indicates that increasing the sample size of biological collections used in the target strength regression prove to be a more direct and practical way of reducing the overall variation in mean density estimates than similar steps employed to increase the number of transects surveyed. A doubling of target strength net tow samples resulted in a 23% reduction in variance relative to an 11% reduction that resulted from doubling the number of survey transects. This is an important difference as doubling the number of survey transects would add 5 days to the survey whereas doubling the number of net tows would add only one day. Although these results are specific to this particular data set, the method described is general.

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Comparing Fish Density and Echo Strength Distribution Recorded by Two Generations of Single Beam Echo Sounders

Applied Sciences ◽

10.3390/app9102041 ◽

2019 ◽

Vol 9 (10) ◽

pp. 2041 ◽

Cited By ~ 2

Author(s):

Arne N. Linløkken ◽

Frode Næstad ◽

Kjell Langdal ◽

Kjartan Østbye

Keyword(s):

Salvelinus Alpinus ◽

Arctic Charr ◽

Strength Distribution ◽

Target Strength ◽

Fish Density ◽

Fish Stock ◽

Coregonus Lavaretus ◽

Total Density ◽

Single Beam ◽

Two Generations

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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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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