A client/server architecture remote fish finder system for a set net fishery

In order to monitor the fish volume entrapped over time in a set net in real time, a new remote fish finder system based on a mobile network was developed and tested. This system was designed with a client/server architecture including an echo sounder terminal, a web server, and some end user display terminals, which allowed fishermen to monitor the fishing state of a set net via any display device. In addition, in order to transfer the echo data smoothly via a mobile network, a fish echo extraction method based on image processing and a data organization structure were proposed, which can significantly reduce the data volume for transmission, supply sufficient information to reconstruct the high resolution echogram at the user terminals, and calculate the positional and morphometric parameters of fish echoes. Furthermore, a semiautomatic data recording method for use with a database was proposed to manage the extracted fish echo data and the fishing records. The functions and capabilities of the new system were demonstrated by a sea trial.     

Measurement of sea bottom surface backscattering strength by quantitative echo sounder

ABSTRACT:   Measurement theory and method of the bottom surface backscattering strength (SS) using a quantitative echo sounder (QES) are discussed and applied in the ocean near Java, Indonesia. The frequencies of the QES were 38, 70, and 120 kHz. The measurements of bottom echoes and sampling of bottom material by a dredge were done simultaneously. Bottom characterization was based on analysis of particle size distribution for bottom samples taken during the survey. The SS value increases with the increase of the mean diameter of the bottom particles. The SS decreased with increasing frequency. The effectiveness of QES for measurement of the SS along with observation of the depth topography were demonstrated.     

Point-source violations: split-beam tracking of fish at close range

Split-beam positional estimates of fish detected in a river at close range often do not correspond to the actual position of the target. These inaccuracies create problems in determining whether a fish is moving upstream or downstream. We hypothesize that these positional estimates are degraded by two factors: size of target relative to beam diameter, and the complex scattering of the fish. These parameters create a near-field effect, within which the phase measurements of the returning echoes are corrupted. Examples of fish tracks from near and far range fish detected by a split-beam echo sounder are provided to illustrate these inaccuracies. Experimental data from tethered spheres and complex targets show increasing distortion with target complexity and proximity to the transducer.     

Observations of controlled moving targets with split-beam sonar and implications for detection of migrating adult salmon in rivers

When measuring the flux of migrating salmon in rivers there are often multiple fish in the beam simultaneously. To obtain accurate measurements of flux, an understanding of the effects of multiple targets is required. Multiple targets in various configurations were passed through a horizontally-oriented 4° × 10° beam from a split-beam echo sounder. The effects on target strength, detection probability, spatial and temporal patterns of echoes, and measurement of target position are presented. When multiple targets were in the beam at the same range, the target strength was positively biased, whereas, when they were in-line at different ranges, the target strength and detection probability were negatively biased for the shadowed targets. Targets at the same range, but separated in the vertical or horizontal direction, produced characteristic patterns in the X vs. ping and Y vs. X plots. Similar patterns were found in routine observations of migrating salmon, allowing the identification of some multiple-target events. Identification of these events can aid in the correct interpretation of migrating fish data for flux measurement.     

基于单回波检测跟踪的深水网箱生物量评估模型研究

构造了基于声纳信号处理的深水网箱生物量评估数学模型。运用单回波脉宽检测和跟踪方法，结合二维低通滤波器，对声纳数据进行处理，去除背景噪声和其他回波，在单体鱼连续的回波踪迹中可以检测出鱼的游速和方向。同时，结合图像分析有效压缩噪声，提取有用特征来识别检测到的鱼迹，形成一种自动计数方法，提高生物量的检测概率。该方法通过提取和使用原始的回声图像，检测出运动目标，同时压缩回声图中的噪声，从而在低信噪比数据中实现对网箱中生物量的检测和估计，适合实际工程应用。     

An acoustic approach to study tuna aggregated around fish aggregating devices in French Polynesia: methods and validation

The behaviour and spatial distribution of tuna, aggregated beneath fish aggregating devices (FADs), have been studied through ultrasonic tagging experiments but, surprisingly, very few studies on FADs have used underwater acoustic devices. We present techniques, and their limits, incorporating a scientific echo sounder connected to a split-beam transducer to observe and characterise tuna aggregations around FADs, and propose a general approach for future studies. Experiments were conducted in French Polynesia between December 1995 and February 1997. Two methods, echo-counting and echo integration, were used. Echo-counting is possible when individual fish are sufficiently scattered so that each target can be discerned. On the other hand, echo integration can be used with both scattered and aggregated fish schools. The knowledge of tuna target strength is useful for separating targets for echo-counting, and essential for obtaining absolute estimates of densities by echo integration. Sonar performances and settings should be considered when choosing the most suitable method to determine fish density or assessing spatial structure of a tuna aggregation. These techniques allow one to study an entire tuna aggregation, its behaviour in space and time at very fine time–space scales (about a nautical mile and over a few hours), and open up a new scientific field to study the spatial structure and behaviour of tuna aggregations around anchored or drifting FADs.     

Seasonal hydro-acoustical observations of small pelagic fish behaviour in Bahía Magdalena,Mexico

Bahía Magdalena, located on the southwest coast of Baja California Sur, Mexico (24°20'N, 111°30'W), is an important area for fishing of small pelagic fish. The Pacific sardine (Sardinops caeruleus) comprises more than 75 % of the total catch in the bay. Hydro-acoustic surveys were carried out in this bay using a single-beam echo sounder, Simrad EY-200 (200 kHz), during three oceanographic surveys (March, July and December 1996). Results demonstrate that in July more than 75 % of the positive observations (those echograms with more than 100 echoes in the volume sampled) and most of the echo counts were recorded in the 5–10-m-deep layer. During March and December, positive echograms in the upper stratum were below 50 % and most of the echo counts were detected in the lower layer (10–20 m). These results were related to the availability of Pacific sardine to the commercial fleet, specifically to the capture-per-unit-effort. Results support the hypothesis that sardines migrate during late summer and autumn and that a new recruitment occurs during the winter within the bay.     

Diel interactions between sprat and mackerel in a marine lough and their effects upon acoustic measurements of fish abundance

We have investigated how diel changes in fish behaviour may affect acoustic estimates of fish abundance in a marine system. Studies in Lough Hyne (Ireland), a marine lake with only a narrow and shallow connection to the sea, showed the presence of large numbers of sprat (Sprattus sprattus), mackerel (Scomber scombrus), and zooplankton. Fish species were identified from regular rod and line fishing. Zooplankton were identified from net hauls. Acoustic measures of zooplankton were low with little diel variation. The sprat formed dense schools during the day and dispersed into the water column at night. The acoustic estimate of sprat abundance at night, obtained by means of a standard hydroacoustic technique and protocol, was more than double the estimated biomass during the day. We have considered whether the lower fish estimate during daytime resulted from acoustic shadowing due to aggregation of the fish into dense schools. However, no decrease in echo energy was evident from the top to the bottom of the schools, and there was no reduction in the seabed echo beneath the schools. Acoustic shadowing was therefore not responsible for the diel differences in the estimates of abundance. Instead, we suggest that the target strength of individual sprat diminished during the day as a result of attacks from predatory mackerel. We observed echoes from gas released by the sprat as they gathered into dense plumes close to the seabed. Compression of the gas remaining within the swim bladder as the fish were moving deeper would also reduce swim bladder volume. Finally, negative buoyancy due to reduced swim bladder volume may in addition have forced the fish to change tilt angle to compensate for sinking. All these effects will reduce the target strengths of individual fish and lead to underestimation of fish abundance based on daytime surveys.     

Causes and effects of underwater noise on fish abundance estimation

The power of modern research vessels using diesel engines means significant levels of noise may be radiated underwater. At low frequencies a surveying vessel must not cause fish avoidance behaviour when it is using trawl or acoustic assessment methods. All the main mechanisms that form the essential propulsion system are described and discussed in terms of underwater radiated noise. Diesel engines, generators and propulsion motors contribute significantly to the low frequency spectrum and an illustration is given of underwater noise when an unsuitable propulsion system is used. Avoidance behaviour by a herring school is shown due to a noisy vessel, by contrast there is an example of no reaction of herring to a noise-reduced vessel. Propellers are major sources of both low and high frequency noise. The latter should not reduce echo sounder detection range, nor contaminate echo integrator recordings. Underwater noise levels from four vessels with different machinery and propulsion characteristics are seen in relation to ambient noise levels at 18 kHz. Fish detection is examined in relation to sea background noise and vessel self-noise. Calculated detection ranges for fish target strength classes from –30 to –60 dB at 38 kHz are shown for six vessels travelling at 11 knots, based on self-noise measurements. Echo sounder noise levels from several vessels at 120 and 200 kHz are tabulated. Beyond 100 kHz the effect of vessel-radiated noise is usually insignificant; levels up to that frequency are proposed in the International Council for the Exploration of the Sea (ICES) Cooperative Research Report No. 209 of 1995.     

Hydroacoustic assessment of pelagic stages of freshwater insects

Two independent surveys showed that aquatic insects can generate echoes comparable with the echoes of small fish. In the open water of two fishless mountain acidic waters of the Czech Republic, a very distinct population of well-defined single targets resembling fish (target strength –66 to –50 dB at 120 kHz) was discovered. These targets were found in the depth range of 5–7 m during the day (June–July 1997). At night, most targets were recorded by horizontal beaming (depth < 3 m). Towing of ichthyoplankton nets in these horizons revealed the presence of ‘water bugs’, Corixidae (Hemiptera), mostly genus Glaenocorisa. Target strengths of corixids was also verified by direct observations in an experimental tank, where it was possible to track side, dorsal and ventral aspects. In three Dutch reservoirs, Petrusplaat, Honderd-en-Dertig and De Gijster (area 100–300 ha, maximum depth 15–28 m, with fish presence) the targets of ascending dipteran pupae (Chironomidae, Procladius signatus) with target strength of –74 to –65 dB were observed by vertical beaming. The presence of pupae was verified by horizontally towed ichthyoplankton nets and by vertical plankton hauls inside the echosounder beam. The contribution of aquatic insects to the fish biomass was small but they can interfere in juvenile fish assessment.     

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.     

用于渔业资源调查评估的两种声学手段的比较

采用数字回声探测仪Bio Sonics DT-X(430 KHz)和双频识别声呐DIDSON(低频1.1 MHz、高频1.8MHz)对青草沙水库的渔业资源量、空间分布特征等进行了为期2 d的水声学调查。在调查过程中两种仪器同步工作,并采用放网捕捞的方法对青草沙水库中的鱼类样本进行采集,并测量其体重与体长。利用Echoview软件对两种仪器采集所得的声学数据进行分析处理。DIDSON的调查结果显示:水库鱼类总数约为936万尾,总的资源量约为705万kg,鱼类主要分布于水库的东部、中部地区。Bio Sonics DT-X的调查结果显示:水库鱼类总数约为1 079万尾,总的资源量约为604.24万kg,鱼类主要分布于水库的东北部地区。     

Determination of effective tow duration for estimation of fish and shellfish abundance in deeper-water bottom trawl surveys

Experimental trawl surveys were conducted to determine effective tow durations for estimating fish and shellfish abundances in deeper-water bottom trawl surveys. A total of 304 hauls were conducted in Kagoshima Bay, southern Japan, for preset tow durations of 10 and 20 min, using a simple trawl net fitted with depth loggers. Towing durations were recorded at the ship’s bridge based on the shooting, towing and hauling times of the trawl net, using pre-established warp lengths for different water depths. Effective tow durations were computed by plotting depth logger and echo sounder data against tow time, and compared with preset tow durations. Trawled distances and swept areas were calculated using the Euclidean distance method. Effective tow durations ranged from 9 to 23 and from 19 to 37 for the 10 and 20 min preset tow durations, respectively. Preset tow duration estimations for abundance were highly biased: −10 to 130% and −5 to 85% biases relative to the effective tow duration estimations, respectively. Moreover, the biases were more pronounced in the shorter tow durations in deeper-water trawl hauls. The computation of effective tow durations using depth loggers and the ship’s onboard instrumentation presents a simple approach for correcting inadvertent estimations of effective tow duration, swept area and abundance indices.     

Bioturbation of sediments by benthic macroinvertebrates and fish and its implication for pond ecosystems: a review

Bioturbation of bottom sediments at the sediment–water interface is currently gaining more attention in studies dealing with the functioning of aquatic ecosystems. Such bioturbation can be caused by a variety of benthic macroinvertebrates or benthivorous fish that forage and burrow various bottom tubes, holes and pits. Thus, the processes involved may either be a result of direct interception by benthic animals, e.g., through bioresuspension of particles or through food ingestion and biodeposition, or of other indirect effects, e.g., changes in the physical properties of sediments or through the constructions mentioned above, along with corresponding changes in pond ecosystem functioning. The most distinct effect of benthivorous fish bioturbation activities is an increase in the turbidity of the water, which can lead to many subsequent knock-on effects, including inhibition of phytoplankton and submersed macrophyte growth with resulting alterations in physico-chemical water conditions. The importance of benthic macroinvertebrates and fish in bioturbation processes is also indicated by an increase in the numbers of resting cyanobacterial colonies recruited due to bioturbation of bottom sediments.     

Development of automatic system for monitoring fishing effort in conger-eel tube fishery using radio frequency identification and global positioning system

ABSTRACT:   In this study, we developed a new automatic system, comprised of a radio frequency identification (RFID) system and global positioning system (GPS), for monitoring fishing effort, and effectiveness of effort, in fisheries using many pieces of fishing gear, such as hooks of longlines. The outline of this system is as follows. A single RFID tag with an identification (ID) number is attached to each piece of fishing gear. The RFID tag on the fishing gear passes the antenna of the RFID reader before being shot into the sea and after being hauled up from the sea. Data on the time and geographic location are measured by the GPS and recorded along with the ID number in a personal computer (PC). When a fish is caught, it is brought close to the fish-sorting table. Then, the second antenna of the RFID reader set at the side checks for a catch in the gear. The advantage of this system is that the fishing operation data can be collected without interfering with the fishermen's usual work. The prototype of the system was tested at a conger-eel tube fishery in Tokyo Bay and was able to record data on the time, the location and the catch of individual conger-eel tubes successfully.     

基于成像声呐的鱼类三维空间分布

针对海洋牧场中鱼群的三维空间分布问题,本研究提出一种利用成像声呐进行位置计算的方法。将成像声呐固定在船舷外侧的水下,并保证波束发射方向和声呐移动方向一致,通过走航的方式采集水下鱼群信息。首先对采集的原始数据进行图像处理,包括图像构建、背景去除、目标提取等,然后利用基于交互式多模型联合概率数据关联算法对水下目标进行关联处理,得到同一个目标在声呐水平视场中不同帧图像中的对应关系,在此基础上根据连续两帧图像中目标位置关系计算目标的空间坐标,最后结合关联算法获得多目标在三维空间中的运动轨迹以及深度分布情况。研究表明,本方法可以有效获取鱼群在水下的三维运动轨迹及其分布情况,这将为鱼类行为分析以及海洋牧场的资源评估提供技术支持。     

鲢、鳙非经典生物操纵作用的研究进展与应用现状

鲢、鳙作为内陆水域主要的滤食性经济鱼类,通过对浮游生物的摄食行为抑制蓝藻水华的发生,这种干预现象在水域生态学领域称为非经典生物操纵。综述了鲢、鳙非经典生物操纵作用的研究与应用进展。目前关于鲢、鳙非经典生物操纵作用存在2种不同的观点。一种观点认为鲢、鳙大量滤食浮游生物,在控制蓝藻水华的同时还可将水中有机物转化为鱼产品移出,能够有效控制水体富营养化;另一种观点认为,放养鲢、鳙实际加快了水体营养盐的周转速率,在抑制蓝藻水华的同时加快了水体的富营养化进程。针对这2种不同观点开展的实验与调查表明,鲢、鳙放养对于抑制藻类水华的爆发作用明确,但同时导致浮游动植物小型化,浮游生物的数量会由于水体营养盐周转速率的加快而出现大幅波动。综合各方观点作者认为,鲢、鳙对于水体蓝藻水华形成的预防和抑制作用证据较为明确,但对于一定时期内水体营养盐变化的影响存在较大的不确定性,与水文条件、鲢鳙存量、集水区状况等有密切的关联。     

Fish biodiversity sampling in stream ecosystems: a process for evaluating the appropriate types and amount of gear

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