Mobile Hydroacoustic Surveys Research Articles

An Assessment of Hydroacoustic and Electric Fishing Data to Evaluate Long Term Spatial and Temporal Fish Population Change in the River Thames, UK

This paper reports the results from mobile hydroacoustic surveys carried out between 1994 and 2018, to assess the fish stocks in four impounded reaches, covering 19.8 km of the River Thames, England. The data are complemented with electric fishing boom boat results, collected at the same study reaches and time periods. Hydroacoustic surveys used inter-calibrated dual and split-beam scientific echosounders, with the transducers beaming horizontally across the river to provide fish abundance and distribution estimates. Electric fishing surveys provided catch per unit effort estimates and information on size structure and species composition. Catch data from the margins of the study reaches were dominated by roach (Rutilus rutilus), with bleak (Alburnus alburnus) dominant in mid-river. Hydroacoustic data demonstrated patchy spatial distribution, often associated with natural and anthropogenic habitat features. Cyclical peaks and troughs in both hydroacoustic and electric fishing abundance were found. There were periods of correspondence with electric fishing abundance estimates, but also periods of significant divergence. The concept of ‘Shifting Baseline Syndrome’ is discussed with reference to these data, illustrating the importance of viewing long term quantitative information when using meaningful reference points. The potential impact of river temperature and flow on the fish population data are discussed.

Stationary hydroacoustics demonstrates vessel avoidance biases during mobile hydroacoustic surveys of alewife in Lake Ontario

Mobile hydroacoustic surveys are routinely used to estimate pelagic fish abundance. In the Great Lakes, alewife are commonly surveyed with mobile hydroacoustics, however, their behavior often has them associated with epilimnetic habitats which increases the potential for vessel avoidance to bias hydroacoustic observations. Abundance estimates from mobile hydroacoustic surveys are typically made using depth and size thresholds to classify targets to species. In hydroacoustic surveys, fish can appear to be smaller when oriented off horizontal axis, as is common with fish displaying vessel avoidance behaviour. This presents a problem where alewives that are diving may appear too small to be correctly classified. We compared alewife swimming behaviours and target strength distributions between stationary up-looking and mobile down-looking hydroacoustics to quantify how vessel avoidance may bias hydroacoustic observations. Alewives from the mobile survey were found to be diving away from the surface, moving faster and in more linear paths than the undisturbed fish from the stationary survey. In the mobile survey, alewives were observed at smaller target strength values than would be expected if boat avoidance was not occurring. Our results suggest that alewife behavioral changes associated with vessel avoidance affect the number and size of targets classified as alewife from mobile hydroacoustic surveys in Lake Ontario.

Gizzard Shad Target Strength‐to‐Body Size Equations at Multiple Hydroacoustic Frequencies

AbstractSpecies‐specific target strength (TS)‐to‐length (L) and TS‐to‐weight (W) equations can reduce bias in biomass estimates from hydroacoustic surveys, yet these equations do not exist for most fishes. Equations specific to the Gizzard Shad Dorosoma cepedianum, a wide‐ranging and often highly abundant prey fish in North American reservoirs and rivers, do not exist. Herein, we sought to develop TS–L and TS–W equations for Gizzard Shad by insonifying free‐swimming individuals of known sizes (36–209 mm TL) in a net cage at three transducer frequencies (70, 120, and 200 kHz). We derived TS–size relationships using major‐axis regression (MAR) and least‐squares regression (LSR), comparing our resultant TS–L equations to a commonly used multispecies equation (Love 1971). To determine how our Gizzard Shad‐specific equations affected estimates of prey fish biomass, we conducted mobile hydroacoustic surveys in four small, shallow Midwestern reservoirs and then estimated biomass using each equation. In general, for TS–L equations, MAR produced the highest estimates of biomass, followed by LSR and then the multispecies equation. Similarly, the TS–W equation derived using MAR produced greater biomass estimates than the equation using LSR. Our findings highlight the value of using species‐specific TS–size equations over multispecies equations in ecosystems dominated by a single fish species (e.g., Gizzard Shad in Midwestern reservoirs). They also demonstrate the value of using MAR to develop TS–size equations, owing to its ability to account for fish size measurement error. The use of species‐specific TS–size equations and MAR should lead to robust estimates of biomass in single‐species‐dominated ecosystems, thus benefiting fisheries assessment and decision making.

Behavioral responses of fish to a current-based hydrokinetic turbine under mutliple operational conditions.

There is significant international interest in developing current-based marine and hydrokinetic (MHK) technologies to capture the power of tidal energy. However, concerns have been raised regarding the ecological effects of these projects on fish, including the risk of blade collision and behavioral impacts such as the disruption of migratory behavior and food acquisition and displacement from preferred habitats. We conducted mobile hydroacoustic surveys to track fish as they approached a tidal turbine deployed in Cobscook Bay, Maine. There was a significant decline in fish numbers with decreasing distance to the turbine, beginning approximately 140m from the turbine. Similar declines were not observed at control transects or when the turbine was not spinning. The decline in fish numbers appeared to be the result of horizontal displacement, not vertical, movements to avoid the turbine. Noise rather than visual cues or flow field disturbance seemed to be a likely explanation for the reduced number of fish near the turbine. This finding, combined with near-field blade collision studies indicating a low probability of encounter, suggests that a single turbine poses a low collision risk to pelagic fish and that a single turbine is likely to result in minimal behavioral responses by fish. However, the risk may be different with additional devices, which will become more relevant as commercial-scale MHK arrays come under consideration. Therefore, the risks associated with commercial-scale operations will ultimately have to be evaluated to fully understand the ecological impacts of MHK devices.

Possible unintended effects of management at an invasion front: Reduced prevalence corresponds with high condition of invasive bigheaded carps

Limiting the prevalence of invasive species is a global conservation priority. Invasive species can have varying ecosystem effects and responses to control throughout an invaded range, and removal near invasion fronts may inadvertently alter these characteristics. Bigheaded carp (bighead carp (Hypophthalmichthys nobilis Richardson) and silver carp (H. molitrix Valenciennes)) are invasive fishes from Asia invading North American freshwater ecosystems. We used mobile hydroacoustic surveys to examine bigheaded carp population characteristics from 2012 to 2015 across an invasion gradient in the Illinois River (USA), one of the most likely pathways to the Laurentian Great Lakes. These bigheaded carp species comprised 23–46% of fish community abundance and 45–78% of fish biomass across reaches, with lower contribution near the invasion front where intensive management by harvest occurs. Bigheaded carp prevalence in the community did not differ by habitat and comprised >50% of community abundance and biomass throughout the river for most size classes. We identified negative relationships between density and relative weight (an index of body condition) of bigheaded carp, suggesting evidence of potential density-dependent intraspecific competition. Efforts to reduce invasive species abundances near invasion fronts may reduce prevalence. However, this could inadvertently release individuals from density-dependent competition and could enhance reproductive potential, growth or movements. By employing a suite of control efforts, including continuous removal efforts (including novel approaches) and by limiting movements (e.g., utilizing roads, fences, dams), it may be possible to offset undesired consequences of increased condition.

Using Hydroacoustics to Describe Pelagic Fish Distribution in the Penobscot Estuary, Maine

AbstractTemperate estuaries are inherently variable and productive ecosystems that provide nursery habitat, migration pathways, and forage areas for diadromous, estuarine, and marine fish. We used multifrequency scientific echo sounders (SIMRAD EK60 split‐beam, 38 and 120 kHz) to describe the distribution of pelagic fish in the Penobscot River estuary, Maine, in 2012 and 2013. Differences in responses between frequencies were used to distinguish fish from other biota. Acoustic area backscatter from echo integration (sA [m2/nautical mile2], a common measure proportional to fish density) and target strength (TS; dB re 1 m2, an acoustic measure of fish size) distributions varied with season and salinity. Overall, the sA and TS distributions were similar in both years, with detectable spatial and temporal patterns. The highest value of sA occurred in July of both years, when dense schools of fish were detected in higher‐salinity areas of the lower estuary. The middle estuary had high sA values in April both years, particularly in the vicinity of the seawater–freshwater interface. The mixing area in the middle estuary stratum appears to be important fish habitat; we found fish in this area throughout the year. Fish of variable TS were using this mixing zone throughout the survey period. In full freshwater, upstream from the salinity mixing area, sA was generally low. The majority (~77%) of discrete fish detected had TS values less than −42 dB. The TS distributions varied seasonally, with the highest TS measurements occurring more frequently in April and May and the lowest ones occurring most frequently in July and August. This study demonstrates the efficacy of using a mobile hydroacoustic survey to assess pelagic fish distribution in a complex estuary and may provide a template for long‐term monitoring in dynamic estuarine ecosystems.Received November 3, 2016; accepted March 15, 2017 Published online June 20, 2017

Estimating the probability of fish encountering a marine hydrokinetic device

Strong tidal currents in eastern Maine, USA, make that region attractive for tidal power development. Little is known about the effects of marine hydrokinetic (MHK) devices on fish, yet many fish species use tidal currents for movements. We used empirical data from stationary and mobile hydroacoustic surveys to examine the probability that fish would be at the depth of an MHK device and may therefore encounter it. The probability was estimated using three components: 1) probability of fish being at device-depth when the device was absent; 2) probability of fish behavior changing to avoid the device in the far-field; and 3) probability of fish being at device-depth in the near-field when the device was present. There were differences in probabilities of fish encountering the MHK device based on month, diel condition and tidal stage. The maximum probability of fish encountering the whole device was 0.432 (95% CI: [0.305, 0.553]), and the probability of fish encountering only device foils was 0.058 (95% CI: [0.043, 0.073]). Mobile hydroacoustics indicated that fish likely avoided the device with horizontal movement beginning 140 m away. We estimated the encounter probability for one device, but results can be applied to arrays, which may have bay-wide implications.

Integrating Hydroacoustic and Optical Video Technologies to Identify the Riverbed Substrate at the Spawning Reach of Chinese Sturgeon

Riverbed substrate is important to many riverine organisms, however, it is normally difficult to study the substrate intensively especially in large and fast flowing rivers. The Chinese sturgeon Acipenser sinensis is a critically endangered fish species, it spawns on a specific riverbed substrate. In this paper, the hydroacoustic and underwater optical video technologies were integrated to study the riverbed substrate at the only remaining spawning area of the fish. Sixteen samples were firstly studied to verify the relationship between acoustic backscattering characteristics (hardness and roughness) and video observed characteristics (embeddedness and medium diameter of the grain). Then eight vertical mobile hydroacoustic surveys were conducted to acoustically map the 16 km spawning reach. The results revealed that the heterogeneous mix of boulder/cobble and sand was the dominant substrate at the spawning reach. However, the embeddedness and medium diameter of the grain varied within the area which tend to affect the spawning site selection of the fish. This study indicated that the combination of hydroacoustic and optical video technologies could be very useful to study the riverbed substrate in river ecological issues.

Quantifying fish avoidance of small acoustic survey vessels in boreal lakes and reservoirs

AbstractMobile hydroacoustic surveys are increasingly used to assess the distribution and abundance of freshwater fish; yet, fish may avoid moving vessels, potentially introducing bias in these assessments. In this study, avoidance in boreal lakes and reservoirs was quantified by developing a simple method based on paired drift:drift (D:D) and drift:motor (D:M) transects. Two systems in eastern Manitoba, Canada were studied: Lac du Bonnet reservoir and Nopiming. Acoustic data were collected using a digital DTX echosounder (BioSonics, Seattle, WA, USA), with a downward facing 200‐kHz split‐beam transducer, deployed from 5.5‐m vessels (Boston Whalers) modified for acoustic research. An avoidance coefficient (Ac) was developed based on comparisons of acoustic fish densities while the vessel moved over the same transects by drifting, and by motoring at survey speeds. Ac did not differ significantly from 1 (no avoidance) at Nopiming (median of 0.81, n = 13), but did at Lac du Bonnet (median of 0.51, n = 31, P < 0.05). Variability in Ac was as high in transect pairs and was unrelated to fish depth (mean 6.9 m at Lac du Bonnet; 13.1 m at Nopiming) or survey speed (up to 3.70 m·s−1, 7 knots). Results indicated that fishes did not dive in the presence of the motoring vessel, nor was avoidance size‐based. We did not detect any evidence of fish attraction to our drifting vessel. Our results suggest that boat avoidance during acoustic surveys of shallow boreal lakes may vary in relatively similar water bodies but can be quantified experimentally.

Comparison of vertical mobile hydroacoustic survey strategies for monitoring fish distributions in the Gironde estuary (France)

Today, hydroacoustic technologies are able to monitor fish populations and assess fish biomass by providing data of a high spatio-temporal resolution, and without damaging the environment. Such techniques are widely used in lakes and marine environments, but they remain much less tested in shallow waters – especially in estuarine habitats. Our study was carried out using a strictly methodological approach. This was necessary in order to take into account the highly changeable nature of the ecosystem in question. Hydroacoustic surveys were conducted in the mesohaline part of the Gironde estuary using SIMRAD EK60 split-beam echosounders, operating simultaneously at two frequencies (70 kHz and 120 kHz). Different mobile hydroacoustic surveys were tested in different seasons, with vertical acquisition, in order to compare variability of results due to the sampling strategy, and to validate the relevance of our design by repeating the surveys. The results obtained on survey design choices gave similar outcomes when sampling was carried out with or against the current and between two mobile designs. The comparison between flood and ebb tides gave different results from one day to another but we observed the same evolution for each flood tide or for each ebb tide on several successive days. This acoustic study in the Gironde estuary was used to validate a reliable sampling mobile design. It is the first step in the process of gaining a better understanding of estuarine ecosystems, an understanding that will be enhanced by combining our data with data from a variety of other sources.

Assessment of fish spatial distribution and biomass in Lake Taihu using hydroacoustic method

利用BioSonics DT-X科学回声探测仪(208 kHz)在太湖2011年开捕前的8月对东部和北部湖区的鱼类进行了走航式水声学调查,并结合地理信息系统(GIS)模型对调查湖区的鱼类大小组成、空间分布和资源量进行了评估.结果表明,调查湖区的鱼类平均目标强度(目标鱼类对声波的反射能力)为-51.85±0.02 dB,平均体长在6 cm左右,体长范围为2.35~89.33 cm,不同区域间的鱼类目标强度差异性显著,表明不同区域间鱼类大小存在差异,其中鱼类的最小平均目标强度(-53.94±0.10 dB)出现在洞庭东西山之间,最大平均目标强度(-50.27±0.14 dB)出现在光福湾.调查湖区的鱼类密度在0.43~3.90 ind./m³之间,采用地理信息系统(GIS)对调查湖区进行建模得到鱼类密度均值为2.27±0.57 ind./m³,不同区域间鱼类密度差异性显著,鱼类密度在敞水区较高.基于建模的栅格化数据评估调查湖区鱼类资源量约为5.3×10⁹ind.,其中目标强度在-45 dB(体长约13 cm)以下的鱼类占98.49%.本文对水声学方法在大型浅水湖泊中的应用进行了初步探索,水声学方法可在一定程度上突破传统鱼类资源调查方法在较大空间尺度上的局限性,但在调查时易受风浪、水生植物、船速的影响.;Before the fishing of Lake Taihu,a mobile hydroacoustic survey was performed in eastern and northern of Lake Taihu in August of 2011,with using BioSonics DT-X scientific echo-sounder (208 kHz).Combining Geographic Information System (GIS) model,then fish size component,spatial distribution and biomass are assessed.The results show that the mean target strength (acoustic reflectivity of target fish) in the surveying lake areas is-51.85 ± 0.02 dB and the mean length is about 6 cm,ranging from 2.35 to 89.33 cm.The fish target strength in different areas is significantly different,which means there is significant difference of fish size,with the minimum mean target strength (-53.94 ± 0.10 dB) in the middle of Dongshan Island and Xishan Island and the maximum mean target strength (-50.27 ± 0.14 dB) in Guangfu Bay.The mean fish density is 2.27 ± 0.57 ind./m³, ranging from 0.43 to 3.90 ind./m³ in all survey areas,where a high fish density occurred in open water zone.Based on the raster data gained from fish distribution GIS model,the total amount of fish mantissa biomass are estimated to be 5.3×10⁹ ind.,in which the fish with target strength lower than-45 dB (length about 13 cm) is 98.49%.The present study provided a preliminary application of the hydroacoustic method and performed in big shallow lake for fish resources investigation.This can break through the limitations of the traditional investigation methods for fish resource assessment on large spatial scales,to a certain extent.The application is still influenced by stormy waves,aquatic plants and speed.

Use of Gill Nets for Target Verification of a Hydroacoustic Fisheries Survey and Comparison with Kokanee Spawner Escapement Estimates from a Tributary Trap

AbstractThe focus of this study was to determine whether gill nets are a valid method for assessing species composition for a hydroacoustic survey and whether the hydroacoustic and gill‐net survey could be used to forecast the spawn escapement of kokanee Oncorhynchus nerka so as to allow fisheries managers to plan ahead for egg takes at Sullivan Lake, Washington. We conducted a mobile hydroacoustic survey of the limnetic zone of Sullivan Lake in September 2003. Species composition was estimated using floating, sinking, and suspended horizontal and vertical gill nets. Spawning escapement was estimated from a weir, trapping, and carcass recovery effort in Harvey Creek, the only spawning tributary of Sullivan Lake. Fish captured in gill nets ranged from 110 to 579 mm total length (TL), but 82% of the fish captured were between 150 and 290 mm TL. Kokanee were the dominant fish species captured in the limnetic gill nets, comprising 77% of the fish captured between 150 and 290 mm TL and 90% of the fish captured between 240 and 290 mm TL. We derived four alternative estimates of age‐3 kokanee abundance to account for the uncertainty in estimating the target strength of individual fish and the percentage of kokanee from the gill‐net catch. The acoustic and gill‐net abundance estimates that did not take into account the uncertainty in estimating kokanee length from target strength were relatively consistent (1–16%) with the Harvey Creek spawning escapement estimate (11,923). When abundance estimates were expanded by the average SE (25 mm) of individually tracked fish targets, the correspondence with the tributary spawn escapement was not as good (110–148%). This study showed that gill nets could be an effective means of verifying the acoustic targets of larger fish (>150 mm) and were adequate for forecasting spawn escapement for management purposes in our situation.

Assessing Fish Populations in Remote Subarctic Lakes Using Hydroacoustics

High latitudes of North America and Asia have many unstudied small lakes. The remoteness of these lakes presents a challenge to biologists who manage these systems. At Togiak National Wildlife Refuge in Alaska we evaluated the use of mobile hydroacoustic surveys as a tool for assessing unstudied lakes and setting priorities for further study. We sampled 50-ha Hole Lake in July 2002 with a 120-kHz split-beam hydroacoustic system, completing four surveys at different times throughout daylight and darkness. Despite day-night changes in distribution of fishes in the lake we found no significant differences in relative biomass, density, or in the detection of larger fish targets that may be of importance from a fisheries management perspective. However, between-transect variability in acoustic measures was high and may have masked the ability to detect these changes. Nonetheless, a simple design bisecting the study lake that was completed in 25 min was capable of detecting fish populations of potential interest to fisheries managers. We suggest a simple design (bisecting the lake) for scanning such lakes for the presence of fish populations of interest in these remote areas.

Hydroacoustic observations indicating swimbladder volume compensation during the diel vertical migration in coregonids ( Coregonus lavaretus and Coregonus albula)

The diel vertical migration of whitefish ( Coregonus lavaretus) and vendace ( Coregonus albula) was studied in a lake using bottom mounted echosounder transducers beaming upwards. Significant gas release was observed when the fish were ascending towards the surface during the dusk. From mobile hydroacoustic surveys it was found that the target strength (TS) did not decrease with depth, as would be expected if the fish had no possibility to fill the swimbladder. Our observations suggest swimbladder volume compensation during the diel vertical migration in coregonids.

Simulating Movement Patterns of Blueback Herring in a Stratified Southern Impoundment

J. Strom Thurmond Lake (Georgia-South Carolina) strongly stratifies during the summer, producing a temperature-dissolved oxygen “squeeze” for landlocked blueback herring Alosa aestivalis. A coupled Eulerian-Lagrangian hybrid (CEL hybrid) model was developed to improve understanding of and better predict the in-reservoir movements of blueback herring in response to these limiting conditions. An existing application of CE-QUAL-W2, a two-dimensional, laterally averaged water quality and hydrodynamic model, was used to simulate the spatial and temporal dynamics of summer water temperature, dissolved oxygen, and hydraulics. The biological module was parameterized by using mobile hydroacoustic survey data supplemented with species composition data from gill-net surveys. The simulation accurately described the longitudinal (r2 = 0.67) and vertical (r2 = 0.93) distributions observed for blueback herring. The model results suggest that the longitudinal distribution of blueback herring in summer is best explained by a random term (57%) and horizontal water velocity (43%). The vertical distribution is best explained by the following variables (in order of their importance): water temperature (45%), a random term (44%), dissolved oxygen (6%), horizontal velocity (4%), and vertical velocity (1%). The integration of fish behavior into a flow and water quality modeling framework can be used to gain insight into the response of coolwater species to flow and water quality patterns. This insight can serve as a foundation for population and bioenergetics modeling or be used to improve the management of coolwater fish and their habitats in dynamic reservoir systems. We recommend that additional data be used to further test and refine the model.

A mobile horizontal hydroacoustic fisheries survey of the River Thames, United Kingdom

The River Thames is a shallow (1.5 m to 5 m+) regulated lowland river that forms an important recreational fishery in South East England. The river is divided into 44 contiguous reaches, separated by locks and river control structures that effectively prevent fish movements between them. Thirty-seven reaches were surveyed from a small boat using a BioSonics model 102 dual beam sonar operating at 420 kHz and 40 log R TVG with a circular (6° and 15°) transducer directed horizontally across the river. Both upstream and downstream acoustic runs were conducted on the same night in July and August of 1995 and 1996; fish densities were estimated by echo counting. Over 180 km of river was surveyed with an overall density of 33 fish 1000 m −3. Upstream and downstream runs of the same reach showed similar fish densities. Although fish densities were variable along the whole length of the river, densities were tenfold greater in the upper, more natural reaches than in the lower, more engineered reaches. The river was narrower, shallower with more submerged macrophyte beds in the upper reaches, conditions which were not ideal for mobile acoustic surveys, resulting in runs with low sampled volume, shortened ranges and more variable densities. In general, mobile hydroacoustic surveys promise to be a valuable, cost-effective tool for monitoring fish abundance and distribution in this type of river.