Fish Pens Research Articles

An automated offshore fish farm comes to Norway: Giant remote-controlled pens will tend to millions of salmon - [News

Tucked within Norway's fjord-riddled coast, nearly 3,500 fish pens corral upwards of 400 million salmon and trout. Norway exports more such fish than any other country in the world (1.1 million tons in 2018), and farmed salmon is one of its top three exports. With the global industry expected to quintuple by 2050, farmed salmon is a fine kettle of fish.

Difficulties for cost-benefit analysis in the 2020 environmental impact statement to recover the endangered wild salmon and steelhead in the Columbia River Basin.

Runs of the endangered wild salmon/steelhead in the Columbia River basin may be only two to seven percent of historic levels. These fish are a common-pool resource, where stakeholders over-consume, pollute rivers and oceans, block passage with dams and culverts, operate net pen fish farms, and plant huge numbers of hatchery fish that compete with and hybridize wild fish. Rivers provide free or subsidized services that stakeholders covet, however recovery of the endangered wild fish requires that peoples utilizing the rivers and the ocean must constrain their behavior, often reducing their profit. A new Environmental Impact Statement (EIS) and cost-benefit analysis are in progress for recovery of the endangered wild salmon/steelhead in the Columbia River basin. New regulations require surveys of U.S. households to measure the non-use benefits of salmon/steelhead recovery that can be important for endangered species. We review the 2002 EIS for juvenile salmon migration on the lower Snake River tributary to find mistakes to avoid in the new EIS and in other recovery studies.

Preliminary evaluation of ecological effects of silver and bighead carps to control cyanobacterial blooms in the early eutrophication lakes

放养鲢（Hypophthalmichthys molitrix）、鳙（Aristichthys mobilis）控制富营养化湖泊蓝藻水华暴发是当前最有效的手段之一.为评估富营养化初期湖泊鲢、鳙控藻的生态效果，2016年在洱海红山湾开展原位围栏鲢、鳙控藻实验，对围栏内外的浮游生物群落结构及水环境因子的变化进行对比分析，同时测定了围栏内鲢、鳙的生长及摄食节律.结果表明：围栏内鲢、鳙呈现匀速生长，围栏生存环境适宜.根据Egger's模型估算鲢、鳙的日摄食量分别为24.96%和18.18%，鲢的日粮高于鳙；滤食率结果表明，鲢对浮游植物的摄食率高于鳙（分别为3.01和2.19 L/（g·h），而鳙对浮游动物的滤食率高于鲢（分别为18.61和13.54 L/（g·h））.研究期间，围栏内外水体理化因子无显著差异；但围栏内外微囊藻生物量差异明显，并且在7月达到生物量峰值（围栏内为1.7 mg/L，围栏外为2.4 mg/L）.鲢、鳙对浮游植物的优势种类——微囊藻和隐藻有明显的削减效果，6-8月逐渐上升并在8月达到最高（64%）；当浮游植物优势种由微囊藻替换为硅藻门和绿藻门的种类时，鲢、鳙的削减效率不明显（10-11月为负值）.此外，鲢、鳙放养显著降低了浮游甲壳动物的总生物量和枝角类生物量.因此，结合实验结果得出，鲢具有更高的控藻能力，尤其对微囊藻水华，但同时具备了较高对浮游甲壳动物的削减能力，需要进一步分析富营养化初期湖泊——洱海中实施非经典生物操纵的适宜性.;It is one of the most effective ways to control the outbreak of cyanobacteria blooms in eutrophic lakes by stocking silver and bighead carps. In order to evaluate the ecological effects of controlling algae by silver and bighead carps in early eutrophication lakes. In 2016, a little biomanipulation in-situ pen with the stock of silver and bighead carps was built to control cyanobacterial blooms in Hongshan Bay of Lake Erhai. The changes of plankton community structure and water environmental factors were compared and analyzed within and outside the pen. Meanwhile, the growth and feeding rhythm of silver and bighead carps were measured. The pen-cultured silver and bighead carp all displayed normal growth, the survival environment of the pen is suitable. Daily rations of silver and bighead carp were estimated by Egger's model in the main growing season. Filtration rate was calculated from the daily ration and the density plankton in the lake. Daily rations of silver and bighead carp was 24.96% and 18.18%. The daily rations silver carp is higher than that of bighead carp. Filtration rates of silver and bighead carp for phytoplankton were 3.01 L/(g·h) and 2.19 L/(g·h), respectively, and filtration rates for zooplankton were 13.54 L/(g·h) and 18.61 L/(g·h), respectively. Silver carp had a stronger ability of eliminating phytoplankton than bighead carp. Bighead carp had a stronger ability of eliminating zooplankton than silver carp. During the study, there was no significant difference in the environmental parameters within and outside the pen. The biomass of Microcystis reached its peak in July (1.7 mg/L in the fish pen and 2.4 mg/L in the surrounding lake water). The Microcystis biomass was significantly lower in the pen. The present stocking density of silver and bighead carp(about 20 g/m³ in June)was effective to control Microcystis. From June to August, the reduction rate of the phytoplankton in the silver and bighead carp gradually increased, and the rate of reduction was up to 64% in August. When phytoplankton's dominant species Chlorophyta and diatom replace Microcystis, the rate of reduction decreased gradually, with negative values in October and November. Furthermore, the biomass of crustacean zooplankton biomass and cladocerans biomass were significantly lower in the pen. Therefore, in combination with several experimental results, silver carp had a stronger ability of eliminating phytoplankton than bighead carp. Especially for Microcystis blooms, silver carp at the same time have the higher on the reduction ability of crustacean zooplankton. We need to further analyze the suitability of non-traditional biological manipulation in the early stage of eutrophication Lake Erhai.

Captive-Reared Dusky Grouper (Mycteroperca marginata) As an Alternative to Repopulation of Degraded Reef Habitats

1. Abstract Captive fish have been extensively used for stock enhancement and conservation of coastal and marine habitats. Evaluation of the effectiveness of this practice, however, has not been as extensively demonstrated. Here we assessed acclimation of captive-reared dusky grouper to reef habitats as an indication of introduction success. Fish were reared in laboratory from eggs obtained from wild local stocks to early juvenile stage (approximately 5 cm total length). Early juvenile fish were transported to fish pens for grow out to approximately 20 cm total length. Fish were individually tagged with acoustic transmitters and released after the grow out phase. Tagged fish were released at three reef habitat stations. Two stations received five fish each and one received 15 fish. Tagged fish were monitored for 7 months. We observed high mortality at the station receiving 15 fish and low mortality at the other stations. Behavior of fish demonstrated a pattern of refuge use according to time-of-day following approximately 5 days of release. Tagged fish behavior indicated adaptation to new habitat, demonstrating that captive groupers are a viable option in population recovery of degraded reef habitats. 2. Keywords: <span style=font-size:10.0pt;font-family: times= new= roman,serif=> Conservation; Dusky Grouper; Mari Culture; Recovery; Reef Restoration; Telemetry 3. Abbreviations: IUCN : International Union for Conservation of Nature <span lang=PT-BR style=font-size:10.0pt; font-family: times= new= roman,serif;mso-ansi-language:pt-br=>GnRHa : Gonadotropin-Releasing Hormone Agonist IBAMA : <span style=font-size:10.0pt; font-family: times= new= roman,serif=>Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renov a veis (Brazilian Environment and Renewable Natural Resources Institute) <span lang=PT-BR style=font-size:10.0pt; font-family: times= new= roman,serif;mso-ansi-language:pt-br=> <span lang=PT-BR style=font-size:10.0pt; font-family: times= new= roman,serif;mso-ansi-language:pt-br=>Vemco : Acoustic Telemetry Company <span lang=PT-BR style=font-size:10.0pt; font-family: times= new= roman,serif;mso-ansi-language:pt-br=>V9 : Vemco 9 mm transmitter <span lang=PT-BR style=font-size:10.0pt; font-family: times= new= roman,serif;mso-ansi-language:pt-br=>VR2W : Vemco 69 kHz receiver

Do Natural Disasters Affect the Poor Disproportionately? Price Change and Welfare Impact in the Aftermath of Typhoon Milenyo in the Rural Philippines

This paper illustrates the sharp contrast in welfare impacts between the rich and the poor caused by typhoon Milenyo in a Philippine village. We find that fish prices dropped sharply due to the damage caused to fish pens near the village, leading to positive net welfare gains among the wealthy. In contrast, the poor do not consume much fish and thus did not gain from the sharp decline in prices. Finally, consumption reallocation played an important role as an ex post risk-coping measure, albeit only among the wealthy, who are relatively well-protected against typhoons.

Forecasting the Genetic Impacts of Net Pen Failures on Gulf of Mexico Cobia Populations Using Individual-based Model Simulations

Offshore net pen fish farming provides a cost-efficient means for production of marine finfish, and there is great interest in development of net pen operations in domestic waters. However, there are concerns over the possible genetic and ecological impacts that escaped fish may have on wild populations. We used individual-based simulations, with parameter values informed by life history and genetic data, to investigate the short-term (50 yr) impacts of net pen failures on the genetic composition of cobia, Rachycentron canadum, stocks in the Gulf of Mexico. Higher net pen failure rates resulted in greater genetic impacts on the wild population. Additionally, the use of more genetically differentiated source populations led to larger influxes of non-native alleles and greater temporal genetic change in the population as a result of net pen failure. Our results highlight the importance of considering the appropriate source population for broodstock collection in net pen aquaculture systems and help to provide a general set of best management practices for broodstock selection and maintenance in net pen aquaculture operations. A thorough understanding of the genetic diversity, stock structure, and population demography of target species is important to determine the impact escapees can have on wild populations.

THE APPLICATION OF SUPPORT VECTOR MACHINE (SVM) USING CIELAB COLOR MODEL, COLOR INTENSITY AND COLOR CONSTANCY AS FEATURES FOR ORTHO IMAGE CLASSIFICATION OF BENTHIC HABITATS IN HINATUAN, SURIGAO DEL SUR, PHILIPPINES

Abstract. This study demonstrates the application of CIELAB, Color intensity, and One Dimensional Scalar Constancy as features for image recognition and classifying benthic habitats in an image with the coastal areas of Hinatuan, Surigao Del Sur, Philippines as the study area. The study area is composed of four datasets, namely: (a) Blk66L005, (b) Blk66L021, (c) Blk66L024, and (d) Blk66L0114. SVM optimization was performed in Matlab® software with the help of Parallel Computing Toolbox to hasten the SVM computing speed. The image used for collecting samples for SVM procedure was Blk66L0114 in which a total of 134,516 sample objects of mangrove, possible coral existence with rocks, sand, sea, fish pens and sea grasses were collected and processed. The collected samples were then used as training sets for the supervised learning algorithm and for the creation of class definitions. The learned hyper-planes separating one class from another in the multi-dimensional feature space can be thought of as a super feature which will then be used in developing the C (classifier) rule set in eCognition® software. The classification results of the sampling site yielded an accuracy of 98.85% which confirms the reliability of remote sensing techniques and analysis employed to orthophotos like the CIELAB, Color Intensity and One dimensional scalar constancy and the use of SVM classification algorithm in classifying benthic habitats.

THE APPLICATION OF SUPPORT VECTOR MACHINE (SVM) USING CIELAB COLOR MODEL, COLOR INTENSITY AND COLOR CONSTANCY AS FEATURES FOR ORTHO IMAGE CLASSIFICATION OF BENTHIC HABITATS IN HINATUAN, SURIGAO DEL SUR, PHILIPPINES

This study demonstrates the application of CIELAB, Color intensity, and One Dimensional Scalar Constancy as features for image recognition and classifying benthic habitats in an image with the coastal areas of Hinatuan, Surigao Del Sur, Philippines as the study area. The study area is composed of four datasets, namely: (a) Blk66L005, (b) Blk66L021, (c) Blk66L024, and (d) Blk66L0114. SVM optimization was performed in Matlab&amp;lt;sup&amp;gt;®&amp;lt;/sup&amp;gt; software with the help of Parallel Computing Toolbox to hasten the SVM computing speed. The image used for collecting samples for SVM procedure was Blk66L0114 in which a total of 134,516 sample objects of mangrove, possible coral existence with rocks, sand, sea, fish pens and sea grasses were collected and processed. The collected samples were then used as training sets for the supervised learning algorithm and for the creation of class definitions. The learned hyper-planes separating one class from another in the multi-dimensional feature space can be thought of as a super feature which will then be used in developing the C (classifier) rule set in eCognition&amp;lt;sup&amp;gt;®&amp;lt;/sup&amp;gt; software. The classification results of the sampling site yielded an accuracy of 98.85% which confirms the reliability of remote sensing techniques and analysis employed to orthophotos like the CIELAB, Color Intensity and One dimensional scalar constancy and the use of SVM classification algorithm in classifying benthic habitats.

Phytoplankton composition and diversity in response to abiotic factors in Lake Buhi, Camarines Sur, Philippines

Phytoplankton were collected from eight sampling stations around Lake Buhi (Camarines Sur, Philippines) in September and November 2013. The eight sites represented varied zonation and resource uses. A total of 29 species were identified belonging to five major taxonomic groups: the diatoms (Heterokontophyta), green algae (Chlorophyta), cyanobacteria (Cyanophyta), eustigmatophytes (Heterokontophyta) and dinoflagellates (Dinophyta). Diatoms were the most abundant group (50%), followed by the green algae (41%). Sampling station with high concentration of fish pens generated high diversity (Shannon-Wiener diversity index 2.65) with dominance of pollution tolerant taxa, while the site near the outlet of the lake has the highest phytoplankton abundance (0.139 cells/ml). Results revealed significant differences in relative abundance of phytoplankton among sampling sites and between sampling months within each site. These differences were attributed to the variation in physico-chemical parameters among the sites. Canonical Correspondence Analysis (CCA) showed that nitrate, depth and turbidity positively influenced phytoplankton abundance. Variation in the abiotic factors, including resource use, affected spatial and temporal distribution of the phytoplankton community. Remediation measures on the lake must be directed towards the primary sources of these variations.

Exploring larval development and applications in marine fish aquaculture using pink snapper embryos

This biology investigation on Pristipomoides filamentosus larval development, survival, and aquaculture research was developed with three educational objectives: to provide high school students with (1) a scientific background on the biology and science of fisheries as well as overfishing, its consequences, and possible mitigations; (2) exposure to field and laboratory techniques in marine science; and (3) practical skills in scientific inquiry and investigation. We teach this investigation at the Hawai‘i Institute of Marine Biology, where we have access to captive broodstock of the pink snapper, P. filamentosus. During this investigation students follow several steps scientists take to study aquaculture: collecting spawn from outdoor fish pens, quantifying the number of eggs, determining the percentage of fertilisation, and estimating the time of spawning and hatching. Additionally, students perform hypothesis-driven science activities with the embryos to test the effects of water quality on their development and survival. In this paper we discuss background information of aquaculture, specifically of P. filamentosus, and thoroughly describe the several components of delivering the investigation. Lastly, we provide possible outcomes of students’ performances in the laboratory activities, and discuss how effectively the exercise met its educational objectives.

Transformation of The Fishery Subsector of Nigeria: The Need for Fishery Extension Program

The inclusion of fishery subsector as one of the priority subsectors in the agricultural transformation plan of Nigeria stems from the increasing demand-supply gap for fish; which continues to constitute a colossal loss of foreign exchange in Nigeria. In view of the foregoing, this study was carried to examine the programs of the fishery subsector transformation plan in the achievement of self-sufficiency in fish production which is the principal goal of the fisherysubsector transformation plan. Secondary data were employed in this study. Despite the laudable programs of the fishery transformation plan namely: (i) fish farm estate development program (ii) fish seeds and feed mill development program (iii) fish pen and cage culture development program(iv) fish post-harvest management and marketing program, the exclusion of fishery extension program in the programs of the fishery transformation plan was identified as a major weakness of the fishery transformation plan that could mar the achievement of the goal of achieving selfsufficiency in fish production. Therefore, it is recommended that fishery extension program should be included as a component of the fishery transformation plan of Nigeria so as to facilitate the delivery of fishery extension services to fish farmers, fish marketers, fish feed millers and other actors in the fish value chain.

Growth and survival of California sea cucumbers (Parastichopus californicus) cultivated with sablefish (Anoplopoma fimbria) at an integrated multi-trophic aquaculture site

In a 12-month field trial we examined the growth and survival of California sea cucumbers (Parastichopus californicus) in suspended culture underneath net pens of sablefish (Anoplopoma fimbria) at an experimental integrated multi-trophic aquaculture (IMTA) site. We tested the effects of sea cucumber size (small: 7–99g and large: 100–565g whole wet weight) and stocking density (12, 17, and 21indm−2) on growth and survival in a completely-crossed experimental design. We also compared growth and survival of experimental animals cultured directly under the fish pens with control sea cucumbers grown ~250m away from the farm. The ability of the sea cucumbers to reduce total organic carbon and total nitrogen from the sablefish faeces was also examined. Small experimental animals grew significantly faster than large experimental individuals, the former increasing in whole wet weight by 27–56% over the 12months and the latter decreasing by 10–33% over the same period. It was concluded that stocking densities of large animals were too high to produce net positive growth. Stocking density had a significant effect on growth of both size classes, lower densities producing higher growth rates, or less negative growth rates in the case of large animals. Small sea cucumbers suspended directly below the sablefish net pens grew significantly faster than control individuals grown ~250m away from the farm, which had negative growth over the 12-month period. The small sea cucumbers cultured under the net pens had a high survival rate (mean: 99.5%) and their feeding reduced the total organic carbon and total nitrogen contents of the sablefish faeces by an average of 60.3% and 62.3%, respectively, demonstrating their potential as an important organic-reducing component in IMTA. Suspending sea cucumbers below fish net pens, as opposed to growing them on the seabed, makes their collection and monitoring easier and moves them away from potential seabed predators such as sea stars. This study demonstrated that P. californicus is well suited to utilise the heavy fraction of waste from a sablefish farm while providing an additional valuable harvestable product.

The influences of silver carp and bighead carp in bio-manipulation pen on the community structure of cladocera in Lake Gehu

As a dominant group of zooplankton in fresh water worldwide,Cladocera plays an important role in the material circulation and energy flow of water ecosystem,and it is not only a consumer for small animals and algae,but also food for zooplanktivorous fish.Many current studies have showed that non-classical bio-manipulation,a way to prevent water bloom and improve water environment by controlling fierce fish and stocking planktonivorous filter-feeding fish(such as Hypophthalmichthys molitrix and Aristichys mobilis),can be effective.However,to some extent,phytoplankton and community structure of cladocera may be varied with different stocking patterns,fish density and lake type.Lake Gehu,a total area of 164 km2 crossing Wujin and Yixing,is located in the south of Jiangsu province.In recent years,more attention was paid to the researches about the influence of H.ypophthalmichthys molitrix and Aristichys mobilis on lake ecosystems,of which the past domestic studies were mainly focused on aquatic plants,physical and chemical factors,the control of eutrophication and phytoplankton,however,no reports have been made in the bio-manipulation fish pen of Lake Gehu about the influences of abiotic environmental factors and filter-feeding fish on cladocera,and that is our work to fill in the blanks.Thus,from December 2009 to November 2010,a large bio-manipulation fish pen with the stock of silver carp(H.molitrix)and bighead carp(A.mobilis)inside was built to control the cyanobacterial bloom in Lake Gehu,an investigation and laboratory analysis was carried out to compare the variation of the cladoceran community structure between region A outside of the fish pen and regions B,D,C with different ratios of fish(1∶ 4,1∶ 2,1∶ 1.5),which was combined to discuss the influences of bio-manipulation fish pen on cladocera and the effects on improving eutrophic water.Through the identification,32 species of cladocera,belonging to 7 families,14 genera were collected inside and outside of the fish pen where there were no differences between species,and the annual average density and biomass of region A were both higher than any region inside of the fish pen,having a significant difference(P0.05)with region B,respectively.The main dominant species were Bosmina longirostris,Ceriodaphnia cornuta and Moina sp..In August,the density of Moina sp.in region A had significant differences from region B and D,while 3 regions inside of fish pen had no apparent differences,et al.,the results of which indicated that Moina sp.with a larger volume was easier to be preyed by fish than the other two small species.Moreover,some characteristic parameters of water were investigated to depict the correlation between cladoceran and environmental variables.CCA(Canonical Correspondence Analysis)showed that water temperature,permanganate index(CODMn),nitrate nitrogen(NO3-N)and water transparency(SD)were the main abiotic factors affecting the community structure of cladocera.

Factors affecting fish yield and profit in fish pen culture in flooded ricefields

In recent years, a rotational system consisting of two rice crops followed by a fish pen culture during the monsoon flood period was adopted in parts of the flood-prone region of the Mekong Delta. In this paper, we use the survey data from 51 fish pen farmers at Co Do and Vinh Thanh district, Can Tho City, to investigate the factors affecting fish yield and profit in such fish pen culture system. The net yield of all stocked fish varies from 377 to 3,782 kg/ha/crop while the return above variable costs varies from −5.3 to 9.8 million VND/ha/crop. Low fish price at harvest and the difficulty to sell below market sized fish at a period of oversupply are the main problems for fish pen culture. Fish net yield significantly increases with stocking density and is linked with specific polycultures. Common carp and bighead carp perform best in fish pen culture, both in production and profit considerations. Harvest body mass of common carp is mainly limited by increasing common carp stocking density. Therefore, a stocking density of common carp of about 6,000 fish/ha is recommended to obtain the optimum combination of reasonable body masses, and a good price, as well as a high return above fingerling costs.

Response of double‐crested cormorants to a large‐scale egg oiling experiment on Lake Huron

AbstractWe report on a management experiment examining the effects of large‐scale egg oiling on double‐crested cormorant nest abundance and measures of seasonal cormorant density (bird‐days/km2) from 2000 to 2005. We employed the staircase design to distinguish transient responses to management treatments from site and year effects that generally contribute to variation in populations. The response to egg oiling in Georgian Bay was as expected with a decline in nest abundance attributable to egg oiling. In the North Channel, nest abundance did not decline because of egg oiling but increased, reflecting either retention of nesting adults or recruitment to colonies. This surprising outcome may stem from fish escapement from pen rearing facilities in the vicinity of the oiling experiment in the North Channel. We observed no effect of egg oiling on the July–August seasonal density of cormorants. The strongest effect size was associated with site effects followed by year effects for nest abundance and seasonal density. The effect size of egg oiling on variation in nest abundance did not exceed 5% for any year in both the North Channel and Georgian Bay. Fish pen culture appears to affect coastal distribution of cormorants. © 2011 The Wildlife Society.

Feeding preference of recaptured Atlantic salmon Salmo salar following simulated escape from fish pens during autumn

Escapes of farmed fish from coastal farms around the world are believed to have genetic and ecological consequences for wild fish populations. Each year there are numerous escapes of adult farmed Atlantic salmon Salmo salar. However, survival until maturity appears to be low. One possible explanation is that many of these salmon have difficulties switching to live prey. To address this possibility, growth rate and dietary preference were recorded in recaptured salmon released in 3 groups from August to October 2008 within a small fjord in south-western Norway (Masfjord). The fish were primed with a commercial diet containing 11% of the 'vegetable oil marker' 18:2n-6 before release. In the 14.5 to 35.1% of fish recaptured, growth rates were generally good (0.21-1.23% d -1 of fish recaptured in main fjord >2 mo after release), with body weight doubled or more for fish recap- tured after 19 wk and thereafter. However, fish recaptured in a small arm of Masfjord (Hopsvag) had a growth rate close to zero and were in poor condition. While stomachs of recaptured fish were gen- erally empty in the first weeks after release, pellets from fish farms were found in more than 80% of the stomachs after 12 wk and thereafter. Additionally, the level of 18:2n-6 in depot lipids (11% of fatty acids) of the muscle indicated that none of the fish recaptured the following autumn and winter in the vicinity of the release site had switched to wild prey diets. Salmon that escape during autumn are unlikely to compete for prey with wild fish in the vicinity of the release site.

Impact of Seepage from Land Treatment of Pulp and Paper Effluent on Water Quality and Aquaculture

Pulp and paper mill wastewater has been treated by biological treatment, but the secondary effluent still contains high lignin, chem - ical oxygen demand, color and total dissolved solids. Tertiary treatment by land application, referred to as 'Project Green,' has been implemented to treat such high quantities of undesirable matters. The impacts of seepage from Project Green diffusing into receiving streams on the water quality and fish pen aquaculture were studied via the integration of technical and social approaches. The determi - nation of the water quality was performed for 13 sampling stations along the receiving stream, including the Chot stream, Chot lagoon and the Pong River. The water quality was generally at normal levels, with the exception of total dissolved solids. The levels of matter were higher at the Chot stream, but became more diluted at the Chot lagoon and the Pong River, respectively. The social approach was conducted through the voluntary participation of the villagers as research assistants for the fish aquaculture study. Fish could grow at three fish pens within the study sites at the location of Project Green, the Chot lagoon and the Pong River. Fish growth at the Chot lagoon was better at the site of Project Green and the Pong River. The integration of technical and social approaches was a meaningful tool not only for the technical feasibility but in helping to solve the conflict between the community and industry.

Prymnesium parvum: The Norwegian Experience1

Johnsen, Torbjørn M., Wenche Eikrem, Christine D. Olseng, Knut E. Tollefsen, and Vilhelm Bjerknes, 2010. Prymnesium parvum: The Norwegian Experience. Journal of the American Water Resources Association (JAWRA) 46(1):6‐13. DOI: 10.1111/j.1752‐1688.2009.00386.xAbstract: In Norwegian waters, Prymnesium parvum has been reported from Oslofjorden in the south to Spitzbergen in the north. However, blooms of P. parvum have only been reported from the Sandsfjorden system in Ryfylke, Western Norway where the salinity of the permanent brackish layer (2‐5 m) typically is in the range of 4‐7 psu during the summer months. The first bloom on record occurred in 1989, and it killed 750 metric tons of caged salmon and trout which was a significant economic loss to the fish farming industry. Toxic blooms occurred as well in subsequent years and the number of fish farms in the area decreased considerably as did the occurrence of P. parvum. In 2005, fish farming was reintroduced to the area and again, in 2007 a toxic bloom of P. parvum killed 135 metric tons of caged fish. The Norwegian Institute for Water Research has, in collaboration with “Erfjord Stamfisk” fish farm, set up a monitoring program that includes light microscopy cell counts of Prymnesium, water quality measurements, and observation of the caged fish. A submergible fish net was mounted over the fish pens and during the toxic outbreak of P. parvum in July‐August 2007, which was as previous years confined to the upper brackish water layer, the fish nets were lowered to 10 m depths below the surface and fish feeding was temporarily stopped. Despite substantial weight loss, the fish survived the toxic bloom and the economic loss was minimal. Monitoring of P. parvum bloom dynamics in 2007 revealed that populations were initially dominated by the nonmotile forms which were gradually replaced by the flagellated forms. Toxicity was observed when the flagellated cells dominated populations in the summer. Chrysochromulina, solitary small Chaetoceros species, and small centric diatoms co‐existed with P. parvum during the monitoring period (June‐October).

Seasonal variations in stable isotope ratios of two biomanipulation fishes and seston in a large pen culture in hypereutrophic Meiliang Bay, Lake Taihu

This paper reports on seasonal changes in stable carbon and nitrogen isotope ratios of seston and muscle tissue of silver carp and bighead carp during 2004 and 2005, focusing primarily on the carbon sources and trophic relationships among phytoplankton, zooplankton and silver carp and bighead carp in a large fish pen of Meiliang Bay (Lake Taihu, China). δ 13C showed a minimal value in March 2005 and a maximal value in August 2005 in seston both inside and outside the pen, whereas δ 15N of seston showed the minimum in winter and the maximum during algal blooms. A positive correlation between δ 13C of silver carp and that of seston suggested that temporal variation of δ 13C in seston was preserved in fish via the food chain. The differences of δ 13C among seston, zooplankton and muscle tissue of silver carp and bighead carp ranged only 0.2–1.7%, indicating that plankton production was the primary food source of filter-feeding fishes. According to a mass balance model, we estimated that the contributions of zooplankton to the diets of silver carp and bighead carp were 45.7% and 54.3%, respectively, based on the δ 15N values of zooplankton and planktivorous fishes.

Impacts of two biomanipulation fishes stocked in a large pen on the plankton abundance and water quality during a period of phytoplankton seasonal succession

Silver and bighead carp were stocked in a large pen to control the nuisance cyanobacterial blooms in Meiliang Bay of Lake Taihu. Plankton abundance and water quality were investigated about once a week from 9 May to 7 July in 2005. Biomass of both total crustacean zooplankton and cladocerans was significantly suppressed by the predation of pen-cultured fishes. There was a significant negative correlation between the N:P weight ratio and phytoplankton biomass. The size-selective predation by the two carps had no effect on the biomass of green alga Ulothrix sp. It may be attributed to the low fish stocking density (less than 40 g m −3) before June. When Microcystis dominated in the water of fish pen, the pen-cultured carps effectively suppressed the biomass of Microcystis, as indicated by the significant decline of chlorophyll a in the >38 μm fractions of the fish pen. Based on the results of our experiment and previous other studies, we conclude that silver and bighead carp are two efficient biomanipulation tools to control cyanobacterial ( Microcystis) blooms in the tropical/subtropical eutrophic waters. Moreover, we should maintain an enough stocking density for an effective control of phytoplankton biomass.