NOAA Protocols for Fisheries Acoustics Surveys and Related ...

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A schedule for calibration and maintenance of net mensuration equipment should follow the manufacturer’s recommendations. If possible, spare parts or complete backup systems should be available for all critical net mensuration instruments. Underwater video. Underwater video and still-camera systems provide visual identification of species and has the potential to document behavior. Limitations of underwater video include small detection ranges and volumes (order of meters) and potential disruption of behavior. Because of the limited light penetration in water, cameras must be positioned near the targets of interest and often, artificial lighting must be used. These two factors complicate acquisition of visual data for species identification and potentially alter the behavior of the organisms. Additional sensors, such as altimeters or depth sensors and towbody orientation sensors (tilt, roll, and pitch) are also required to quantify the data for behavioral measurements. Bottom Tracking Echo sounders and post-processing software use algorithms to detect the seabed. Performance of these algorithms depends on bottom type and topography. On hard, flat substrate, the algorithms perform well. On soft substrate, or rugged topography, the ability to accurately detect the water-seabed interface is reduced. The echo return from the seabed is typically orders of magnitude greater than that from organisms, so it is critical to eliminate seabed echoes from the water column data. Improper bottom detections are found and corrected manually through inspection of the echograms. Bottom detection parameters used during data collection and in post-processing should be documented. Error Uncertainty in classifying and separating acoustic backscatter by target species from nontarget species is a potential source of error in acoustic estimates of density and abundance. Possible errors include misclassification (either incorporating volume backscatter by non-target species or eliminating volume backscatter by target species), scaling acoustic data with trawl catch data that are not representative of species composition or length- and age-frequency distributions, incorporating seabed echoes in water column data, use of an inappropriate attenuation coefficient, and improper calibration of echo sounder systems and temperature and salinity sensors. Considerations Remediation Determining whether trawl catch data are representative of species composition and lengthand age-frequency distributions is complex. Comparison of data from different gear types used from the same vessel as close in time and space as possible could be useful in evaluating potential errors and designing corrections to be applied. Improvements Improvements in bottom tracking algorithms will greatly increase the efficiency of postprocessing acoustic data and improve accuracy of the estimates. A bottom tracking algorithm failure in real-time might be corrected with a post-processing algorithm (such as that available in 24
Echoview) or by comparison with or substitution by bottom detect data from a second echo sounder or frequency. Introduction of new opening-closing nets with multiple cod ends attached to the end of a standard trawl will allow more discrete sampling. Trawls currently in use sample mid-water layers and schools of fish continuously throughout a deployment. Thus, samples of deeper layers contain fish caught in shallow layers, because the net is open on descent and ascent. Use of opening-closing gear will result in better characterization of targeted schools and layers, and will result more accurate length-frequency distributions. Multiple frequency data include multiple narrow-band (single frequency) echo sounders and broadband sonars. Currently, broadband systems are not routinely used for surveys. Both broadband and multiple frequency systems are undergoing intensive development and testing, and may be introduced soon, at least on an experimental basis. Although some success has been achieved, especially for zooplankton (e.g., Martin et al. 1996), problems such as differences in the insonified volume between frequencies, short ranges associated with high frequencies, and change in noise levels with frequency must be overcome (see Reid (2000) for a brief review and bibliography). Such methods seem promising, and although multi-frequency studies of fish are still in their infancy, they are likely to be part of routine surveys in the future. Protocols for their use will be developed along with the systems themselves. Underwater video and low ambient light level still-camera systems provide visual identification of species and have the potential to document behavior. Limitations of underwater video include small detection ranges and volumes (order of meters) and potential disruption of behavior. Because of the limited light penetration in water, cameras must be positioned near the targets of interest and often, artificial lighting must be used. These two factors complicate acquisition of visual data for species identification and potentially alter the behavior of the organisms. Additional sensors, such as altimeters or depth sensors and towed body orientation sensors (tilt, roll, and pitch) are also needed to quantify the data for behavioral measurements. Underwater video methods and techniques are currently under development. If these methods and techniques become routine part of a survey, protocols should be developed for video maintenance, data collection and archiving, and data analysis. Performance Degradation Definition & Importance Performance degradation is the reduction in echo sounder performance due to mechanical, biological, or electrical processes. Degradation in echo sounder performance can be caused by acoustical, vessel, and electrical noise, bio-fouling of the transducer face, excessive transducer motion, and bubble attenuation. Performance degradation differs from system performance in that the causes of performance degradation are external to the echo sounder, where as ‘system performance’ concerns the echo sounder electronics. Routine monitoring of data by scientific personnel during data collection is necessary to ensure a high standard of data quality. 25
Page 1: NOAA Protocols for Fisheries Acoust
Page 4 and 5: Echo Sounder Parameters ...........
Page 6 and 7: Trawls ............................
Page 9: Introduction In response to Vice Ad
Page 12 and 13: Advanced Survey Technologies Progra
Page 14 and 15: Techniques Before conducting a cali
Page 16 and 17: Considerations Remediation Echo sou
Page 18 and 19: transmission loss. To correct for s
Page 20 and 21: unavoidably discarded, just as some
Page 22 and 23: factors such as orientation are not
Page 26 and 27: Techniques Noise Acoustical A commo
Page 28 and 29: ⎛ I ⎞ r TS ≡ 10 log10 ⎜ ⎟
Page 30 and 31: Considerations Remediation If a TS-
Page 32 and 33: Techniques Beam Pattern Transducers
Page 34 and 35: during vertical migration, will cau
Page 36 and 37: A schedule for calibration and main
Page 38 and 39: degradation are external to the ech
Page 40 and 41: permanently archived for each surve
Page 42 and 43: Numerical Density to Biomass Densit
Page 44 and 45: An electronic ‘event log’ can b
Page 46 and 47: References Demer, D.A., M.A. Soule,
Page 48 and 49: Regional Protocols Because of the d
Page 51 and 52: Table of Contents Introduction.....
Page 53: Electrical ........................
Page 56 and 57: Center Background NEFSC The Northea
Page 58 and 59: S v Calibrations The NEFSC acoustic
Page 60 and 61: Operation Menu/Transmit Power Norma
Page 62 and 63: Software The echo sounder firmware
Page 64 and 65: ii. Minimum Sv for good pick: -50.0
Page 66 and 67: Net mensuration sensors are attache
Page 68 and 69: We remove backscattering by surface
Page 70 and 71: GPS The primary Global Positioning
Page 72 and 73: Electrical Electrical noise protoco
Page 74 and 75:
Scientific Computer System (SCS) Fi
Page 77:
Appendix 2 March 11, 2005 NOAA Prot
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Techniques ........................
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Center Background AFSC The Alaska F
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On-axis sensitivity and S v calibra
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Volume Backscattering Measurements
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Mid-water juvenile pollock (max sa=
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Biological Sampling Mid-water and n
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Bubble Attenuation Vessel speed is
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Data Collection Since 1990 to the p
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sampling resolution of scattering l
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A decision must be made as to wheth
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design. If fish abundance in this a
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Simrad. 2001. Simrad EK60 scientifi
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104
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Acoustic Data......................
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ackscattering cross-section (σ i )
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o For the 38 kHz transducer operati
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• Two-way integrated beam pattern
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Classification Techniques Single Fr
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Performance Degradation Definition
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Biological Data Data from catch pro
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elation also assumes that backscatt
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finer than the 13.5-18.9 nmi (25-35
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Improvements - The annual hake migr
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Techniques The primary source of th
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Hamano, A., Sasakura, T., Kieser, R
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