Hydroacoustic Methods Research Articles

Use of radars to monitor stream discharge by noncontact methods

Conventional measurements of river flows are costly, time‐consuming, and frequently dangerous. This report evaluates the use of a continuous wave microwave radar, a monostatic UHF Doppler radar, a pulsed Doppler microwave radar, and a ground‐penetrating radar to measure river flows continuously over long periods and without touching the water with any instruments. The experiments duplicate the flow records from conventional stream gauging stations on the San Joaquin River in California and the Cowlitz River in Washington. The purpose of the experiments was to directly measure the parameters necessary to compute flow: surface velocity (converted to mean velocity) and cross‐sectional area, thereby avoiding the uncertainty, complexity, and cost of maintaining rating curves. River channel cross sections were measured by ground‐penetrating radar suspended above the river. River surface water velocity was obtained by Bragg scattering of microwave and UHF Doppler radars, and the surface velocity data were converted to mean velocity on the basis of detailed velocity profiles measured by current meters and hydroacoustic instruments. Experiments using these radars to acquire a continuous record of flow were conducted for 4 weeks on the San Joaquin River and for 16 weeks on the Cowlitz River. At the San Joaquin River the radar noncontact measurements produced discharges more than 20% higher than the other independent measurements in the early part of the experiment. After the first 3 days, the noncontact radar discharge measurements were within 5% of the rating values. On the Cowlitz River at Castle Rock, correlation coefficients between the USGS stream gauging station rating curve discharge and discharge computed from three different Doppler radar systems and GPR data over the 16 week experiment were 0.883, 0.969, and 0.992. Noncontact radar results were within a few percent of discharge values obtained by gauging station, current meter, and hydroacoustic methods. Time series of surface velocity obtained by different radars in the Cowlitz River experiment also show small‐amplitude pulsations not found in stage records that reflect tidal energy at the gauging station. Noncontact discharge measurements made during a flood on 30 January 2004 agreed with the rated discharge to within 5%. Measurement at both field sites confirm that lognormal velocity profiles exist for a wide range of flows in these rivers, and mean velocity is approximately 0.85 times measured surface velocity. Noncontact methods of flow measurement appear to (1) be as accurate as conventional methods, (2) obtain data when standard contact methods are dangerous or cannot be obtained, and (3) provide insight into flow dynamics not available from detailed stage records alone.

Ontogenetic changes in the bathypelagic distribution of European perch fry Perca fluviatilis monitored by hydroacoustic methods

The behaviour of bathypelagic perch fry (BPF) was monitored during 21 May, 24 June, 8 August and 5 September 1996 along the longitudinal profile of Řimov reservoir (Czech Republic), using acoustic methods (SIMRAD EY 500 echosounder, elliptical split-beam transducer, Sonar5 postprocessing software). In May, the BPF layer comprised a mass of solitary perch larvae at an abundance of over 31,000 ind. ha−1. In contrast, in June, the BPF layer consisted almost exclusively of shoaling individuals. The abundance of BPF increased up to 166,000 ind. ha−1. Similary, in August, fish in shoals prevailed in the BPF layer but the abundance dropped to less than 3,000 ind. ha−1. In September, the BPF layer consisted of both individuals and small groups of fish. At this time the abundance of BPF slightly increased to almost 5,000 ind. ha−1. Individual parameters describing the BPF layer, depth of the main layer, abundance of BPF in the main layer and thickness of the whole layer, differed significantly among months. The negligible abundance of potential predators below the thermocline, both in June and in August (exclusively adult perch), suggests that the BPF shoals were more likely to be created as a result of a social need rather than as a defense against predators. During similar surveys carried out prior to (25 April, 5 May, 7 May, 12 May, 15 May) and after this period (3 October, 7 November, 2 December), the BPF layer was not recorded.

Prediction of hydroacoustic target strength of vendace ( Coregonus albula) from concurrent trawl catches

Despite frequent applications of hydroacoustic methods to estimate freshwater fish densities and behaviour, species-specific regressions to predict fish total length (TL) from target strength (TS) and vice versa are surprisingly rare in literature. Here, night trawl catches and trace track analyses of concurrent hydroacoustic surveys of a vendace stock in a deep lake during three sampling occasions over 2 years were combined. Frequency distributions of TL and TS revealed three modal lengths on each occasion and were used to calculate a linear regression (TS (dB) = 25.5 × log 10 TL (cm) − 70.9) which predicted higher TS values than the standard formula by [Love, R.H., 1971. Dorsal aspect of an individual fish. J. Acoust. Soc. Am. 49, 816–823] for vendace smaller than about 12 cm TL, but lower TS values for larger fish. In an alternative approach, an iterative estimate of the intercept of the TS–TL equation based on the main mode per frequency distribution was conducted and this also substantially differed from the general formula of Love. By correlating the cumulative TS distributions from the echo tracking and those calculated from the equations based on either three or one mode per sampling and the species-unspecific formula of Love, the three modes approach and the Love formula performed comparably well, whereas the one-mode approach did not reliably predict the TS distribution of the tracks. A re-calculation of a previous hydroacoustic survey from the same lake revealed that the newly derived vendace-specific formula predicted a lake-wide vendace biomass about 13.8% lower than one based on the formula of Love.

어군탐지기를 이용한 인공어초 주변의 어군량 추정

The hydro-acoustic method is widely used for estimating biomass and distribution of fisheries resources along the coast and in the ocean. High costs and time are necessary to construct systems for this method and to initially educate specialists. It has been used in fisheries of advanced nations like Japan and Norway, because it is more efficient than other methods. In order to research the behavior of fish around an artificial reef using an echo sounder, volume backscattering strength (SV) and fish per cubic meter (FPCM) of darkbanded rockfish around the model artificial reef in a water tank were measured. Moreover, behavior of fish was observed in an adjacent artificial reef, which was constructed at Tongyeong marine ranching area. Following that, an acoustics survey was conducted at Mirukdo around the Tongyeong marine ranching area, in order to understand the spatial distribution and strength of fisheries resources. Very high patches of fish were found in a wide area around the artificial reef. It is thought that an approaching fish school around the artificial reef can be measured accurately by using an echo sounder of high resolution. Moreover, use of other monitoring methods like of diving or ROV simultaneous with an echo sounder is required in order to grasp the species and ecology of fish inhabiting the area around the artificial reef.

Hydroacoustic experiments to establish a method for the determination of methane bubble fluxes at cold seeps

Hydroacoustic methods are particularly suitable for investigations of the occurrence, cyclicity and amount of bubbles released at cold seeps without disturbing them. Experiments with a horizontally looking single beam transducer (40 and 300 kHz) directed towards artificially produced bubbles show that the backscattering strength of the bubbles increases with the gas flux rate independently of the bubble radii distribution. It is demonstrated that an acoustic system can be calibrated in such a way that gas flux rates of bubble-size spectra, as observed at natural seeps, can be directly related to the echo level of a known, acoustically insonified volume. No system-specific parameters have to be known except the beam width.

Spatio-temporal variability of fish assemblages in the Gambia Estuary (West Africa) observed by two vertical hydroacoustic methods: Moored and mobile sampling

The Gambia Estuary is one of the last estuaries in West Africa not to have been affected by strong environmental changes and adverse human disturbances. In order to describe the spatio-temporal change in fish biomass in this estuary, and the seasonal changes in fish size classes, five research surveys have been conducted at characteristic periods in the river's water regime and meteorological seasons. The fish assemblages were sampled by two vertical echosounding protocols: mobile surveys (zigzag transects) in the estuary and moored stations. The two sampling methods produced a similar image of the fish assemblages in terms of the distribution of total biomass and target strength distributions. Large fish aggregations were detected in the most marine area at the end of the wet season, and fish biomass increased through the dry season in the upstream zone. Fish were smaller at the beginning of the wet season and they were always larger in downstream areas.

Comparison of Teleseismically and Hydroacoustically Derived Earthquake Locations along the North-central Mid-Atlantic Ridge and Equatorial East Pacific Rise

This letter examines earthquake locations derived using independent teleseismic and hydroacoustic data sets for events along the north-central (15°-35°N) Mid-Atlantic Ridge (MAR) and equatorial (10°S-10°N) East Pacific Rise (EPR). It represents the first large-scale comparison of such data, providing ground-truth information for the teleseismic locations and insight into the process of T -wave generation. An assessment of location accuracy and catalog completeness in these remote ocean settings is critical for explosion monitoring efforts associated with the Comprehensive Test-Ban Treaty (CTBT), as well as seismotectonic studies at mid-ocean ridges (MOR's). During the last decade, the value of hydroacoustic studies in monitoring MOR seismicity has been demonstrated through work using the U.S. Navy's SOund SUrveillance System (SOSUS) ( e.g., Fox et al., 1994) and arrays of moored autonomous underwater hydrophones (AUH's) ( e.g., Fox et al., 2001; Smith et al., 2002). These studies utilize seismically generated tertiary (7) waves that propagate within the ocean's SOund Fixing And Ranging (SOFAR) channel (Tolstoy and Ewing, 1950). In locating submarine earthquakes, the main advantages of the hydroacoustic method stem from the efficiency of this low-velocity wave guide, which allows for the detection of much smaller events at longer ranges relative to that possible with waves that travel through the solid earth, as well as from the existence of a well defined ocean sound-speed model ( e.g., Teague et al., 1990). Although T waves may be produced within regions of shallow sloping bathymetry near oceanic islands, continental shelves, and subduction zones ( e.g., Shurbet and Ewing, 1957; Johnson and Norris, 1968; Talandier and Okal, 1998), here we examine their generation in association with shallow hypocenter events within a deeper-ocean or abyssal environment ( e.g., Johnson, et al., 1968; Fox et al., 1994). In this setting, the scattering of energy from a rough seafloor has emerged as the …

New applications of hydroacoustic methods for monitoring shallow water aquatic ecosystems: the case of mussel culture grounds

The development of acoustics tools and methods for monitoring anthropized ecosystems represents a new field for the application of acoustics. Monitoring such an environment was not possible with single vertical echo sounders, due to the fact that the artificial structures and the natural targets were not distinguishable. Monitoring data were collected along the French Mediterranean coastline, during five short surveys of mussel culture longline areas. Both the Reson Seabat 6012 multibeam sonar (455 kHz) and the Simrad SR 240 omnidirectional sonar (23.75 kHz) were used for target detection. The former tools allow accurate allocation of the different types of echoes to artefacts, fish schools and scattered fish. The school characteristics collected included morphological, geographical (GPS, school location), and behavioural (connections with the longlines). An acoustic survey undertaken with the same hardware near the study area allowed the comparison of fish schools and the TS distribution of individual fish in the open sea and in the mussel area. These data permitted us to evaluate the ecological impact of a mussel culture on the ecosystem, in a context of predation behaviour of fish on these longlines. Finally, the acoustic data revealed the configuration of each concession and the level of charge of each line. We discuss the applicability of this technology for in situ real time monitoring for joint management of such ecosystems. The information can allow littoral cooperative management or incorporating it into an ecosystem approach.

Evidence of harmonic tremor from a submarine volcano detected across the Pacific Ocean basin

Since the 1950s seismic activity associated with submarine volcanic eruptions has been detected throughout the Pacific Ocean basin using hydroacoustic methods. However, narrowband harmonic tremor with multiple overtones typically associated with subaerial volcanic eruptions has not commonly been observed. This paper presents a series of recently recorded hydroacoustic signals that originated in the Volcano Islands arc south of Japan, a region that frequently experiences submarine eruptions. The signals are characterized by a narrowband, long‐duration, high‐amplitude fundamental centered at 10 Hz with three harmonics at 20, 30, and 40 Hz and are consistent with harmonic tremor signals observed using traditional seismic methods at active subaerial volcanoes throughout the world. These hydroacoustic signals were detected 21 different times over the period from April 1998 through December 1999, typically lasting from several days to several weeks. After a 6‐month hiatus, the signals were detected 26 more times from June 2000 through August 2001. The signals are qualitatively interpreted as a result of resonance of a magma‐gas mixture within a large chamber/conduit near the surface of a shallow (<1 km) submarine volcanic edifice, allowing for efficient release of acoustic energy into the ocean sound channel. During periods of peak energy radiation the tremor could be clearly detected on hydrophones in the western Aleutians, Hawaii, west coast of the United States, and eastern equatorial Pacific and was detected by the French Polynesian seismic network, covering a maximum distance of ∼14,000 km.

Mapping of seagrass and seaweed beds using hydro-acoustic methods

Mapping of seagrass and seaweed beds using hydro-acoustic methods

A comparison of three methods for assessing the abundance of Arctic charr, Salvelinus alpinus, in Windermere (northwest England)

Windermere, the largest natural lake in England, is divided by shallows and islands into North and South Basins. The lake supports an important sports fishery for Arctic charr, Salvelinus alpinus (L.), with some of the catches sold locally. The chief objectives of this comparative study were: (i) to examine the relationships between data obtained by three sampling methods (gill-nets, angling, hydroacoustic surveys), (ii) to discover if the simpler methods of gill-netting or anglers’ catches provided an adequate method for assessing the charr stock compared with the more extensive echo-sounding (hydroacoustic methods). There was a significant correlation ( r=0.59, P<0.01) between the annual catch per unit effort (CPUE) for two anglers. The annual CPUE for angler A, but not for angler B, for the whole lake correlated significantly ( r=0.41, P<0.05) with the gill-net CPUE for one site in the North Basin, but the relationship for both the anglers was not significant ( P>0.05) when only the catches for the North Basin were used in the comparisons. Gill-net CPUE for one site in the North Basin correlated significantly ( r=0.85, P<0.01) with the annual mean density of large ( length>20 cm) pelagic fish in both the North Basin and the whole lake, both densities being estimated by hydroacoustic methods. Anglers’ catches (annual CPUE for angler A and B) for the whole lake and for the North Basin, but not the South Basin correlated significantly ( r=0.80–0.90, P<0.01) with the annual mean density of large pelagic fish in the upper water layers ( depth<20 m) during the day. It was concluded that both gill-net and anglers’ CPUE could be used as an approximate annual index of abundance for the charr stocks for the whole lake; and for the North, but not the South Basin of the lake, they were not as reliable as the more extensive hydroacoustic methods.

Use of the stratified-Petersen estimator in fisheries management: estimating the number of pink salmon (Oncorhynchus gorbuscha) spawners in the Fraser River

The simple-Petersen estimator is a well-known mark-recapture method to estimate animal abundance. Two key assumptions are equal catchability in both samples and complete mixing of tagged and untagged animals. If these are violated, severe bias can occur. The stratified-Petersen estimator can be used to account for some of the heterogeneity in catchability or mixing. In this paper, we first review recent developments in the stratified-Petersen experiment for fisheries audiences and demonstrate some of the practical problems that can occur that have not been discussed in the theoretical literature. Second, we present a case study to estimate the gross escapement of Fraser River pink salmon (Oncorhynchus gorbuscha) in 1991. The motivation for this study is a discrepancy of over 5 million fish between the estimates as derived by the Pacific Salmon Commission (PSC) (7.5 million fish based on a hydroacoustic method) and the Department of Fisheries and Oceans (DFO), Canada (13.0 million fish based on a mark-recapture method). One hypothesis put forward was that the discrepancy may be due to the use of a pooled-Petersen estimator when there is differential migration over time. The stratified-Petersen model suggests that little of this discrepancy can be explained by differential migration.

Monitoring microseismicity in the northeast Pacific using hydroacoustic techniques

On 29 August 1991, NOAA/PMEL began collecting ocean acoustic signals from the U.S. Navy’s Sound Surveillance System (SOSUS) in the northeast Pacific Ocean. SOSUS consists of linear arrays of underwater hydrophones deployed on the seafloor within the sound channel that are directly cabled to shore. The NOAA/PMEL-developed system digitizes the acoustic signals directly from the underwater cables and passes the information via the phone line to NOAA laboratories in Newport, OR for analysis. The hydroacoustic method allows small submarine earthquakes (mb≳1.8) to be routinely detected and located throughout the North Pacific. The primary advantages of this method are the large areal coverage from relatively few sensors and the low detection threshold and improved accuracy of the derived epicenter locations relative to land-based systems. Several significant discoveries have been made using the hydroacoustic method over the past 5 years, including (1) a better understanding of the distribution of seismicity in the northeast Pacific; (2) detection of volcanic activity and magma dike injection supported by extensive field observations; (3) detection of periodic volcanic tremor; and (4) the discovery of a band of low-level seismicity within the Gorda plate that may offer a precursor to subduction zone earthquakes.

Do diel changes in patchiness exhibited by schooling fishes influence the precision of estimates of fish abundance obtained from hydroacoustic transect surveys?

Rainbow smelt (Osmerus mordax) were studied using hydroacoustic methods (echo integration and dual-beam) to determine whether fish patchiness resulting from diel vertical migrations and schooling behavior cause lowered precision in estimates of fish abundance when assessed with hydroacoustic technique. A parallel transect design with randomly selected transect locations was applied. Cluster sampling analysis was used to assess sample error. Smelt were dispersed at night and patchily distributed during the day. The observed changes in fish distribution had no influence on the precision of abundance estimates. However, when compared seasonally, sample errors were found to decrease in association with an increase in fish abundance and in relation to a decrease in the large-scale heterogeneity of fish.

The behaviour of Atlantic salmon in relation to efficient cage-rearing

To maintain salmon farming as a viable industry it is necessary to continue to focus on the well-being of the fish from hatching to harvesting. This requires intimate knowledge of all aspects of salmon biology. Understanding the behaviour of farmed salmon is an essential part as this could suggest ways of preventing stress and diseases rather than merely treating their symptoms. This review attempts to summarize current knowledge of salmon behaviour in sea cages. Major modes of behaviour have been described and possible control mechanisms have been suggested. Behavioural studies of salmon in this particular system, however, are still at an early stage. Further research is needed to verify and deepen the current understanding. In future research the behavioural ontogeny of cultured salmon from hatching to harvesting should receive more attention. For example, the effect of smolt-rearing procedures on subsequent behaviour in sea cages is unclear. An ontogenetic approach would probably pay off in terms of a better holistic understanding of the mechanisms controlling the behaviour of cultured salmon in different stages of the production process. The present level of understanding should provide a basis for developing simple models of behaviour in cages from which meaningful hypotheses can be formulated. Experiments should primarily be carried out in a realistic rearing environment, but the inherent methodological problems of carrying out full-scale experiments make it difficult to test hypotheses that require detailed description of the behaviour of individuals. The transfer of a small number of individuals from larger groups subjected to different treatments to an experimental arena, might overcome these problems. This approach proved fruitful in an unpublished study that tested the competitive ability of individuals reared under different feeding regimes. This paper proposes several ways to improve the management of salmon behaviour and growth in sea cages. Some of these suggestions should be further investigated before they are adopted by the salmon industry in general. Daily management would be improved by methods to observe the fish complementary to visual inspection. Continuous hydroacoustic monitoring of sea cages provides this and would be especially helpful in large cages holding a considerable value of fish. In addition to demand feeding and routine behavioural observations (e.g. early warning of disease), this would provide useful information about the accumulation of dead fish on the cage bottom and the abundance of wild fish under cages (predators, food-waste eaters). Another important application could be to monitor the fish biomass. Fish counters are sometimes used during stocking of sea cages with smolts, but the error in estimated numbers remains unknown. Unregistered theft, escapees and mortality in the period prior to harvesting can easily increase errors in such estimates. A reliable hydroacoustic method of estimating biomass would thus significantly improve management control. Such work is in progress (Furuzawa et al., 1984; Burczynski et al., 1990; Bjordal et al., 1993; Dunn and Dalland, 1993).

Application of hydroacoustic techniques to exploitation of biological resources of the sea

The paper discusses application of hydroacoustic methods in fishing techniques, with a particular reference to exploitation of biological resources of the sea. Application of hydroacoustic methods in exploitation of living marine resources is considered with respect to the following areas:- determination of marine environmental parameters,- determination of the nature and behaviour of fish shoals and fish resource assessment,- determination of fishing gear performance parameters and magnitude of catch,- application of hydoacoustic techniques in ichthyology.

Scattering of underwater sound by algae

The theoretical investigation of scattering underwater sound waves by algae has been performed. The dependencies of sound level in the reflection waves upon parameters of the algae (sizes, biomass) are determined. For this purpose physical models corresponding to the typical kinds of the algae are developed. Scattering of sound by the algae are considered as the diffraction of the sound wave on the random set of the three-dimensional curved elastic bodies. By solving Helmholtz equation for the definite boundary conditions on the surface of the bodies, sound pressure in the waves scattered by the acoustic semi-transparent curved plates and rods corresponding to the plates and stems of the algae are computed. The obtained results can be used for the development of hydroacoustic methods of investigation of the continental shelf and also for reconnaissance of the algae abundance.

Fish Abundance and Fish Migration in Gravel-Pit Lakes Connected with the River Rhine

The total fish abundances of two gravel-pit lakes connected with the River Rhine have been observed by a hydro-acoustic method (echo-sounder: Lowrance X16) for about one year. Diel (24-hour-period) as well as seasonal changes in fish distribution and aggregation behaviour have been established. Concerning the assessment of the fish stocks, these changes in fish behaviour have to be considered. Some clear fluctuations of fish numbers, which coincide with flood events of the river are interpreted as indications of fish migration from the river into the lentic water.

The spacial organization of aquatic populations as observed using hydroacoustic methods

The spacial organization of aquatic populations as observed using hydroacoustic methods

Hydroacoustic measurement of the density of the Baikal macrozooplankter Macrohectopus branickii

Experimental studies and statistical analyses were performed to evaluate hydroacoustic methods for assessing the density of Macrohectopus branickii (Amphipoda, Gammaridae) in Lake Baikal. Minimal registered abundance (expressed as volume) appeared to be &lt;1 mg m−3(echosounder at a frequency of 200 kHz). Patterns of Macrohectopus diel vertical migration varied with individual age, size, and sex. It is preferable to assess abundance of Macrohectopus at night when the population is distributed primarily in the upper 100 m. Under these conditions, acoustic estimates of animal densities can be made by applying calculated data on the scattering ability of Macrohectopus within the size range of 1–30 mm: TS(kg) = −36.8±0.5 dB kg−1 (mean ±95% C.I.).