Net Cage Aquaculture Research Articles

Measuring the swimming behaviour of a reared Pacific bluefin tuna in a submerged aquaculture net cage

The swimming path of a reared Pacific bluefin tuna, Thunnus orientalis, was measured in a submerged aquaculture net cage to understand how reared fish use the space in such a cage. A bluefin tuna (fork length, FL, 0.51 m) was captured by angling in the cage, and two micro data loggers (PD3GT, Little Leonardo; DST Comp-Tilt, Star-Oddi) were attached to its body. The fish was then released back into the net cage. The PD3GT measured its swimming speed and depth at 1-s intervals and recorded these in flash memory. The DST Comp-Tilt measured the magnetic field strength at 1-s intervals and recorded the heading estimated from the magnetic field strength in flash memory. The fish moved through the water in the cage at speeds of 0.7–0.8 m s-1 and attained a maximum speed of 3.6 m s-1. Burst swims exceeding 2 m s-1 were confirmed only after dark and a significant difference was found between the daytime and night-time swimming speeds (p < 0.001). The fish moved at depths between 2 and 22 m, swimming near the bottom during the day and at 10–15 m at night, with a significant difference in swimming depth between day and night (p < 0.001). The swimming path reconstructed by dead reckoning was visualised using night-time data. For this period, the absolute speed was corrected from 0.75 ± 0.09 m s-1 to 0.71 ± 0.15 m s-1 by removing the accumulated error from the reconstruction vector. This study allowed us to examine the behaviour of a tagged tuna in three dimensions and is the first to monitor the behaviour of a bluefin tuna in a submerged net cage. Although only one fish was analysed, this study provides useful information on the space use of reared fish in aquaculture net cages. Future studies must obtain sufficient data to understand the underlying generalities of tuna behaviour.

Structural analysis of aquaculture net cages in current

A method for structural analysis of aquaculture net cages has been developed and verified for a netting solidity of 0.23, water current velocities from 0.1 to 0.5 m/s and relatively large deformations (volume reduction up to 70%) by comparing the numerical results to tests in a flume tank. Strength analysis was performed using commercial explicit finite element software to calculate distribution of loads in the net cage due to current, weights and gravity. The net cage was modelled using truss elements that represented several parallel twines. Sub-elements allowed the trusses to buckle in compression, and only negligible compressive forces were seen in the numerical results. Resulting drag loads and cage volume were shown to be dependent on the net cage size and weight system. Drag loads increased almost proportional to the current velocity for velocities in the range of 0.2–0.5 m/s, while the cage volume was reduced proportional to the current velocity. The calculated forces in ropes and netting of full-size net cages were well below the design capacity for current velocities up to 0.5 m/s. However, netting seams in the bottom panel of the net cage were identified as a potential problem area as the forces could reach the design capacity.

Resistance of aquaculture net cage materials to biting by Atlantic Cod ( Gadus morhua)

Cod bite on aquaculture net cages has resulted in damages like frayed netting and holes, which in part can explain why cultured cod have escaped more frequently than salmon over the last years. We describe damages found on various netting materials subjected to cod bite through field experiments at commercial cod farms. Further, a method to test local cod bite resistance of traditional netting structures is suggested and initial results from a test jig prototype are given. Results from field experiments indicated that cod may have been attracted by types of netting that made it possible to draw filaments out of the twine, while stiff, coated netting structures and thick filaments showed no sign of bite damage during the test period. We concluded that netting materials for cod aquaculture must be resistant to cod bite or be repellent or uninteresting for cod. Based on the present findings, the better choice among the traditional netting materials seemed to be hard-laid netting materials, preferably with a primer that glues the filaments together.

A mesocosm fish farming experiment and its implications for reducing nutrient load on a regional scale

This work presents results from a mesocosm fish farming experiment. The main aim of the work was to put the results from the experiment into a wider context dealing with an approach to get zero – or even – negative nutrient fluxes from fish cage farms on a regional scale. To quantify the nutrient loading of phosphorus and nitrogen from net cage aquaculture, a standard dynamic mass-balance model approach was used. A comparison was made between responses from two feeding scenarios with rainbow trout ( Oncorhynchus mykiss). One set was given a commercial pelleted fish food the other food with fresh herring inclusion. We have shown that on a regional scale, a zero nutrient load situation may be achievable if the wild fish from the given region account for about 11% of the fish food. In the mesocosm experiment, we also tested different approaches to calculate the growth of the cultivated fish and one can conclude that there are no major differences in using the different sub-models for the interpretations to get zero emissions but different growth functions do give different dynamic responses for the fish growth. We have also tested if it is important to account for denitrification. Under the given conditions this is not the case. Critical testing of the modelling has been performed with uncertainty and sensitivity analyses and the major uncertainties were identified in the growth pattern of the fish and the mesocosm biomass nutrient uptake rate. We argue that these results imply that, from an eutrophication point of view, fish farming in open net cages can be viewed as an environmental sustainable industry, if the fish feed includes nutrients that originate from the surrounding waters.

Technological solutions and operational measures to prevent escapes of Atlantic cod (Gadus morhua) from sea cages

The main goal of this PhD project was to develop a method for non-linear strength analysis of net structures applied in the aquaculture and fishing industries, e.g. net cages and trawls. The work focused on the aquaculture net cage, which was applied in experiments and analyses, and included research to establish knowledge within material properties and failure modes of traditional netting materials for aquaculture. It was chosen to focus on tensile properties and to study elastic and plastic behaviour, fracture, creep behaviour and cod bite damage. The project consisted of three main activities: tensile testing of netting materials, studies and testing of cod bite damage and resistance, and structural analysis of aquaculture net cages. Net cages are built as a system of ropes and netting. They are designed to transfer and carry all major forces through the ropes. Loads from current, waves, weights and handling induce forces in the net cage, which must be dimensioned to withstand this. Analyzing an aquaculture net cage is both complex and time consuming due to non-linear effects, detailed geometry and dynamic loads. The behaviour of the net cage is dominated by very large deformations and displacements, and materials with non-linear properties. There is a need for verified analysis methods and specific guidance on how to reduce the complexity of a net cage analysis. In order to perform a strength analysis of a net cage, it is crucial to know the material properties of the netting material. Traditionally, the material property of major interest for the aquaculture industry has been the tensile breaking strength of netting (mesh) and ropes, and comparatively little focus has been on their detailed stiffness properties and general behaviour prior to fracture. A new test method was established to determine the uniaxial tensile properties of knotless netting materials. It was applied on a variety of netting materials and stress-strain relations were developed. Data on temporary creep properties, recovery of strain post creep and post creep tensile properties of a selection of Raschel knitted netting materials was presented. Post creep tensile testing showed that the length and force at break were not significantly affected by the creep load history. Cod farmers have reported that cod interact with the cage netting through biting and thereby create wear and tear. The nature of the cod bite attack on traditional, multifilament netting materials was described based on studies of cod interaction with traditional knotless netting and resulting fracture damage on netting fibres. Field experiments were performed, subjecting panels of netting to cod bite in commercial cod cages. In addition, a test method was developed to simulate damage on traditional netting from cod bite, and a prototype bite-jig was designed and assembled. It was concluded that netting materials for cod aquaculture must be resistant to cod bite or be repellent or uninteresting for cod. A method for numerical analysis of net cages in constant uniform current was developed and verified for limited solidity, deformations and current velocities. Various new designs for aquaculture net cages were presented and compared to a traditional net cage with regard to stresses in the netting material and deformation of the net cage.

Ildır Koyu’nda (İzmir-Ege Denizi) Açık Deniz Ağ Kafeslerde Yapılan Balık Yetiştiriciliğinin Su Kalitesi Üzerine Etkilerinin İzlenmesi

Türkiye kıyılarında ağ kafeslerde balık yetiştiriciliği 1980’lerin ortalarında başlamıştır. Hızlı ve plansız gelişim bazı çevresel sorunları da beraberinde getirmiştir. Yetiştiriciliği yapılan türler tarafından tüketilmeyen yemler ve dışkılar özellikle kapalı ve yarı kapalı koylarda su sütununda ve sedimentte olumsuz etkilere yol açmıştır. Günümüzde ağ kafes teknolojisindeki gelişmelere paralel olarak daha yoğun ve verimli üretim yapılmasına olanak sağlayan açık deniz ağ kafes sistemlerinin kurulması, ağ kafes yetiştiriciliğine yeni bir yön vermiştir. Bu çalışmada Ildır Koyu’nda açık deniz ağ kafeslerde gerçekleştirilen çipura ve levrek yetiştiriciliğinin su kolonunda oluşturması olası etkilerin izlenmesi amaçlanmıştır. Bu amaçla Mayıs 2000, Temmuz 2000, Ekim 2000, Şubat 2001 ve Şubat 2004, Mayıs 2004, Ağustos 2004, Kasım 2004 tarihlerinde üç istasyonda yüzeyve dip suyunda 8 kez mevsimsel örnekleme yapılmıştır. Alınan örneklerde fiziko-kimyasal parametreler ve besleyici elementlerin değişimleri incelenmiştir. Örneklerin analizi sonucunda; su sıcaklığının 14,0-24,5 ºC, pH’ın 7,858,48, çözünmüş oksijenin 5,2-9,2 mg/L, tuzluluğun ‰33,97-41,00, Secchi derinliğinin 10,5-32,9 m, nitrit azotunun nd ölçüm limitinin altında -0,44 µgat/L, nitrat azotunun nd-1,12 µgat/L, amonyum azotunun nd-9,07 µgat/L, fosfat fosforunun nd-0,61 µgat/L arasında değişimler gösterdiği saptanmıştır. Sonuç olarak, ağ kafeslerin anakaradan oldukça uzak olması, dolayısı ile derinliklerin yüksek oluşu ve yemlemenin kontrollü olarak yapılması nedeni ile su kalite kriterlerinde önemli boyutta değişim gözlenmemiştir

Microbial hydrolytic enzyme activity in the sediments of a net cage aquaculture area

Potential microbial extracellular leucine-aminopeptidase (LAP) and β-glucosidase (βGlc) activity in the sediments of a red sea-bream (Pagrus major) aquaculture area were measured. Temporal variations in these enzymatic activities were low and stable from December 1999 to April 2000. They rose but fluctuated widely from May to November 2000. LAP activity in the sediments ranged from 334 to 4461 nmol/g per h in the 0–1-cm layer and from 106 to 258 nmol/g per h in the 4–5-cm layer. βGlc activity ranged from 221 to 4121 nmol/g per h in the 0–1-cm layer and from 18 to 238 nmol/g per h in the 4–5-cm layer. These values were higher than others reported and the organic matter load from the fish farms appeared to promote these enzymatic activities, although the relationship was not linear. The ratio of LAP to βGlc was smaller than other reported values in marine sediments or in water samples from the same aquaculture area, suggesting that not only quantitatively but qualitatively an aspect of organic matter degradation in the sediment might be changed by the heavy supply of organic materials from fish farms.

Development of net cage acoustic alarm system

In recent years, the fishery production has been drastically decreased in Taiwan, mainly due to overfishing and coast pollution; therefore, fishermen and corporations are encouraged by government to invest in ocean net cage aquaculture. However, the high-price fishes in the net cage are often coveted, so incidences of fish stealing and net cage breaking were found occasionally, which cause great economical loss. Security guards or a visual monitoring system has limited effect, especially in the night when these intrusions occur. This study is based on acoustic measure to build a net cage alarm system, which includes the sonobuoy and monitor station on land. The sonobuoy is a passive sonar that collects the sounds near the net cage and transmits the suspected signal to the monitor station. The signals are analyzed by the control program on the personal computer in the monitor station, and the alarms at different stages could be activated by the sound levels and durations of the analyzed data. To insure long hours of surveillance, a solar panel is applied to charge the battery, and a photodetector is used to activate the system.

Simultaneous measurement of swimming speed and tail beat activity of free-swimming rainbow trout Oncorhynchus mykiss using an acceleration data-logger

A recently developed motion detector (acceleration data-logger), based on accelera- tion measurements, was used to monitor the swimming behavior of two free-swimming captive rainbow trout Oncorhynchus mykiss in an aquaculture net cage. Depth, swimming speeds and two- direction acceleration data were collected continuously for approximately 20 h per fish. To define relationships between swaying acceleration profiles and tail beat activity of rainbow trout, the tail beat activity of trout was monitored using a video camera in a small tank with the simultaneous use of the acceleration data-logger. During steady swimming, there were sharp, distinct peaks of swaying acceleration. When compared with the data from the video camera, the frequency of swaying acceleration was synchronized with the sequences of swimming activity. In addition, the tail beat frequency of the fish could be identified within the cycle of swaying acceleration during steady swimming phases. Mean tail beat frequency was 1.27 ± 0.40 and 1.40 ± 0.5 Hz (mean ± SD). Using the relationship between tail beat frequency and swimming speed, the 'preferred' swimming speed of trout was estimated to be between 0.48 and 0.58 body length (BL)/s, and trout rarely swam in excess of 2.0 BL/s. The present study shows that acceleration data-loggers used to record sponta- neous measurements of swimming speed and tail beat activity represent a useful and reliable system for accurately estimating both the rate of activities and movements of free-ranging fish.

Effects of nitrogen and phosphorus from fish cage-culture on the communities of a shallow lake in middle Yangtze River basin of China

In recent decades, net-cage aquaculture has become one of the main patterns of the intensive fish-culture in the lakes, reservoirs and even rivers in China. This aquaculture pattern results in enriching exogenous nutrients in water and, consequently, accelerates the process of lake eutrophication. To ensure that normal environmental conditions and fisheries in a lake remain sustainable, qualitative estimations of nutrients in relation to ecosystem changes are essential. A study, mainly on nitrogen (N) and phosphorus (P) influences due to cage fish-culture was carried out in a shallow 35.5 ha bay in Niushanhu Lake, a shallow lake located in middle Yangtze Basin, during the period from March to December 2000. Net-cages in total covered an area of 1000 m 2 and the annual fish yield was 16.0 metric tons (MT). Fish feeding residue entering the water during the period was equivalent to 1532.9 kg of total N and 339.2 kg of total P. Sampling and analyses of the total N and total P concentrations, diversity and biomass of plankton and Chl a were made monthly, while data on zoobenthos were collected twice, respectively, at the beginning and the end of the study. Results showed that the Chl a content in water was correlated negatively to distance from the cage. The Chl a content that is converted into wet biomass of phytoplankton may be expressed by the regression: B=2.673−0.0016 D ( B, biomass in mg/l; D, distance in km; r=0.9362; n=7). The biomass of rotifers inside or near the cages was higher than that in areas more distant, while that of the cladocerans was the opposite. No significant difference of copepod density or biomass was detected between cages and open water. Changes of zoobenthic community were remarkable. At the beginning of fish farming, there were nine zoobenthic taxa inside and 13 outside the cages. Only two saprophilous taxa, chiefly oligochaetes, were present in the cages at the end of the culture. Density and biomass of benthic animals decreased as well. Several bio-indices, such as Shannon-Wiener index, Simpson index, and Margelef index, also exhibited a declining tendency. Through this study, the authors are of the opinion that mass-input of exogenous nutrients may cause negative effects on water quality in areas from the cage to a distance of 50 m outwards.

Describing benthic impacts of fish farming with fuzzy sets: theoretical background and analytic methods

Summary Diver observations have been recorded over a period of several years at a site severely impacted by finfish niariculture. The logged data were analysed using fuzzy logic in order to address the problem of interpreting sometimes qualitative and sub- jective information. The underlying methodology based on fuzzy set theory is developed and described in this paper, along with the techniques used to quantify the relationship between the information recorded by the divers, which was usually of a verbal descriptive nature, and a numerical index of benthic impact. Fuzzy logic proved to be a valuable tool for translating the dive log data into quantitative form. Introduction A 3-year time series of more than 100 dive logs describing the status of the benthic environment beneath a net cage farm in the northern Gulf of Aqaba (Red Sea) has been collected and analysed. These logs cover the productive life of a fish farm site, including observations made after the cages were removed. The original purpose of these logs was an informal collection of qualitative observations made during the frequent dives under the fish farm, in the course ofa geochemical and microbiological study on benthic implications of net cage aquaculture in the oligotrophic Gulf of Aqaba (Angel el al. 1995a). During this study it became evident that valuable information about the sediment dynamics and benthic processes involved in organic enrichment and recovery of the site could be gleaned from the observations. These observations include information that cannot be easily collected quantitatively due to the dynamic nature of the environment. Moreover, the use of diver obser- vations enables sampling of larger areas than would be tech- nically feasible by conventional quantitative measurements of such variables as sediment organic carbon or porewater nutri- ents. Owing to the complexity of events occurring in the benthos, it is not possible to give a clear-cut diagnosis of the health of a site by just looking at the dive logs. This is due to several factors, including the extreme patchiness of the benthic environment, occasionally incomplete dive logs and the apparent con- tradictory nature of certain observations regarding the health of the benthos on any one day. Faced with informative obser- vations that are also semiquantitative, sometimes incomplete, or subjective and conflicting in nature, we decided

単純化した網生す模型に作用する流体力について

In this experiment, we measured the fluid force on simplified models of aquaculture net cage in steady flow and wave. Then we calculated the drag coefficient and added mass coefficient from the measured fluid force. The main results are as follows:The added mass coefficient of models in wave was 12. The ratio of the drag force to the maximum wave force became small as the wave height-length ratio increased. However, the ratio of the mass force to the maximum wave force became large as the wave heightlength ratio increased. Therefore, we cannot disregard the mass force and consider only the drag force, when we calculate the fluid force acting on aquaculture net cage in wave.

平面網地に作用する波力について

The drag force action on plane nets of steady current flow has been investigated both analytically and experimentally by many researchers. Although wave force is a very important factor that should be considered in designing aquaculture net cage in the marine environment, there are few studies on the wave force action on plane nets. Moreover, many problems still remain unsolved regarding wave force action. In this experiment, the wave force action on plane nets was measured in a wave tank, and the drag and added mass coefficients were obtained. The main results are as follows: 1) The drag coefficient obained from the wave force and from the drag force under the steady flow were similar. The drag coefficient could be expressed as a founction of the Reynold's number (Rn).2) When the Kenlegan Carpenter, KC number was larger than 35, the horizontal added mass coefficient was about 6, and vertical one about 2.