Fish Pens Research Articles

The heat is on: sensitivity of goldsinny wrasse to global climate change.

Unsustainable harvesting practices have drastically reduced fish populations globally and developments in aquaculture have increased. Unexpectedly, Atlantic salmon farming caused the opening of a new fishery in northern European countries, where previously unharvested mesopredatory species, like the goldsinny wrasse (Ctenolabrus rupestris), are captured for use as cleaner fish in pens along the coast and fjords. The goldsinny wrasse is widespread in coastal areas where it plays an ecologically important role as a predator of small invertebrates. Since climate change effects are particularly pronounced in coastal waters, it becomes urgent to understand how fish like the goldsinny will respond to global climate change, including the increasing frequency and intensity of marine heatwaves (MHWs), ocean freshening (OF) and ocean acidification (OA). To address this, we conducted a multi-stressor experiment exposing adult goldsinny to each stressor individually, as well as to all three combined. The results indicated that the goldsinny is highly affected by MHWs and extremely sensitive to a multi-stressor environment, with 34% and 53% mortality, respectively. Additionally, exposure to a MHW event, OF and multi-stressor conditions affected fish metabolism, with the highest standard metabolic- and maximum metabolic-oxygen consumption rates observed for the MHW treatment. Increases in oxidized glutathione (GSSG) and percent oxidized glutathione (% GSSG) in the livers, indicative of oxidative stress, were also seen in the MHW, OF and multi-stressor treatments. As a single stressor, OA showed no significant impacts on the measured parameters. This information is important for conservation of coastal marine environments, given the species' important role in shallow-water habitats and for management of goldsinny or other mesopredatory fish harvested in coastal ecosystems. The sensitivity of the goldsinny wrasse to future stressors is of concern, and any potential reductions in abundance as a result of climate change may lead to cascade effects with ecosystem-wide consequences.

Hydroelastic Responses of a Submersible Ring Structure for Offshore Seaweed Cultivation under Wave Action

This paper investigates the hydroelastic response of a submersible circular ring structure, designed for offshore seaweed cultivation, under wave action and during the submergence process. The ring structure comprises two circular HDPE pipes connected to each other by equally spaced brackets. The structure carries seaweed grow-out lines, and is kept in position by a mooring-line system used for fish pens. The HDPE collar is equipped with multiple inlet and outlet valves, allowing it to be submerged to avoid strong waves and to be raised to the water surface when the strong waves die down. The software AquaSim was used for the hydroelastic analysis of the moored structure. It is found that we can significantly reduce the von Mises stresses in the ring structure as well as the mooring-line forces by submerging. However, the structure can experience significant increase in stress during the submergence process due to bending from combined wave action and non-uniform distribution of filled water in the ring structure. This stress increase may cause structural damage or even failure. Therefore, it is important to submerge the ring structure in calm waves ahead of predicted storms and to control the distribution of seawater into the ring structure. For the latter, it is best to use at least two inlet valves and two outlet valves to minimize the likelihood of damage of the ring structure during the submergence process.

SeaFisher—A Submersible High-Density Polyethylene Offshore Fish Pen

Moving offshore for fish farming poses challenges due to the more energetic sea environment. In this paper, a novel offshore fish pen design named SeaFisher has been proposed. The SeaFisher comprises modular cubic pens that are assembled to form a large 2 × n array offshore fish pen. Its frame structure is made from HDPE, making it flexible and durable against the harsh sea environment. Specially tailored connection brackets and connector pods are designed to assemble bundles of HDPE pipes forming the SeaFisher structure. The SeaFisher is moored using a single point mooring to minimize environmental and collision loads, and for improved waste dispersal. More importantly, the SeaFisher possesses ballast tubes positioned on the top surface to allow it to submerge to a desired water depth to dodge the strong surface waves during severe weather events. This paper presents the engineering design details and hydroelastic analysis of the SeaFisher. Based on a hydrostatic analysis, suitable materials were chosen for the various components of the SeaFisher, and the components were appropriately sized up. By using the software AquaSim v.2.17.3, the SeaFisher’s hydroelastic responses under different sea-state conditions were investigated. It is found that the designed SeaFisher structure and mooring system are adequate with respect to strength and stiffness for the considered sea-state conditions of up to 8 m significant wave height and 0.8 m/s current speed. It is expected that the SeaFisher will be a game changer for offshore fish farming due to its cost-effectiveness and ability to survive in severe storms.

Biodeposit dispersion around a deep cage finfish farm in the Northern Persian Gulf

Due to increasing demand for food, intensive mariculture of finfish is a fast developing industry in the Iranian part of the Persian Gulf (PG). The environmental impacts of cage fish farming largely involve release of excessive organic matter (biodeposits). Careful monitoring of fish farms to avoid anoxia and bottom “dead zones” is an essential part of a sustainable mariculture industry.Monitoring data were collected for a fish farm north of Kish Island that had been in full operation for a period of one year. The data were then incorporated into a hydrodynamic model in order to estimate the quantity and dispersion pattern of biodeposits around the farm.Our results show that the farm had significant impacts on local environmental conditions, including water transparency, sulfide levels, and Eh values. Bottom water clarity near the cages was >15 NTU. Underneath the cages, sediment sulfide values are >800 μmole, Eh is usually -100 or less, and the sedimentation rate is 6.8 g/m2/day. The number of live benthic foraminifera near the cages was 4.5/10 g aliquot, as opposed to 20 at a control site.Numerical modeling, combined with data from sediment traps, shows that the farm “footprint” is much larger than the actual area of the farm, and is elongated by tidal currents. Considering the relatively short operation of the farm, it is already close to generating anoxic bottom conditions over a 2 km wide area. This can potentially impact the fragile habitats of the Persian Gulf. Continued expansion of net pen fish farms in sensitive areas such as the PG should be carefully monitored.

Offshore Fish Farms: A Review of Standards and Guidelines for Design and Analysis

While moving fish farms to offshore sites can be a more sustainable way to expand farmed fish production, the fish pens have to contend with a harsher environment. Thus, it is necessary to draw on offshore engineering competences for designing and analysing the offshore fish farming infrastructure. This paper reviews existing design and analysis guidance from maritime classification and national/international authorities that can be applicable for offshore fish farms. Based on the existing design guidelines, a review of design criteria for offshore fish farms under the following subtopics is provided: design life, design environmental loads, combining environmental loads, and miscellaneous load conditions. This review on the global performance analysis procedures and methods is presented based on practices used for neighbouring industries, such as offshore oil and gas and wind energy production, under the following subtopics: hydrostatic analysis, hydrodynamic analysis, and mooring system analysis with introducing theoretical background and modelling techniques. This paper also highlights limitations and cautions when using these design and analysis methods. Providing this comprehensive information, as well as commentary on their applications, will help engineers and designers to develop offshore fish farming infrastructure with confidence.

Modelling the response of offshore aquaculture fish pens to environmental loads in high-energy regions

Offshore aquaculture is a burgeoning sector, but operating in offshore environments can be difficult, especially in areas with high energy conditions such as strong currents and waves. The purpose of this study was to understand the effects of these environmental loads on slender gravity salmon fish cages, which are commonly used in offshore aquaculture operations. By simulating the responses of the cages to different load conditions, this study aims to provide useful data for the design of anchors and other structural elements of offshore aquaculture operations. A structural Finite Element Method (FEM) model was used to simulate the responses of the salmon cages to environmental loads. An extensive sensitivity analysis was conducted, examining the responses of the salmon model to current-only and combined current and wave scenarios under various conditions. These conditions included different magnitudes and angles of attack for the current and waves. The results showed that symmetrical orientations of the cages experienced lower anchor line tensions than those with lesser symmetry. In the farm with the highest number of cages, the anchor line tension reached a value of 2.9 MN. This study provides valuable data for the design of offshore aquaculture anchors, particularly in high-energy regions where environmental loads can be severe, through a series of large-scale sensitivity analyses, specifically for the purpose of determining the largest expected anchor loads.

Simulating fish farm enrichment and fallowing impacts reveals unequal biogeochemical recovery of benthic variables

Finfish aquaculture is playing an increasing role in global food provision, with accompanying increases in benthic impacts under intensive pen production systems. Deposited faeces under and near fish pens affect the seafloor environment and biogeochemical functioning. To maintain healthy coastal environments, many fish farms operate by alternating input and fallowing periods to allow benthic coastal receiving environments to recover from excess organic matter inputs. Here, we used flow-through annular flume mesocosms to simulate sustained organic matter inputs to the benthos with a subsequent fallowing period of no inputs. To quantify the effects of excess organic matter loading on benthic receiving environments, we carried out repeated closed-system flux studies to quantify the benthic carbon mineralisation processes, with a focus on benthic oxygen, inorganic and organic carbon, nitrogen, phosphate, and sulphide fluxes, along with the redox state throughout the input and recovery period. We found that recovery periods were input-dependent, with parameters requiring longer fallowing periods to recover following larger inputs. While some benthic parameter fluxes such as dissolved organic carbon, sulphide, and ammonium returned to their pre-input state relatively rapidly (1-2 mo) following cessation of inputs, others such as sediment oxygen demand, ammonium, and redox required longer (>7 mo) to recover. Our results suggest that in situations where the benthic macrofaunal community has been severely impaired, extended fallowing periods may be required in order to permit the biogeochemical composition of the seabed to return to a more natural state, with implications for farm-consenting permits and planning as well as operational fallowing practices.

Effects of stocking density on growth performance, feed utilization and economic profitability of juvenile Heterotis niloticus reared in a pen fish farming

Effects of stocking density on growth performance, feed utilization and economic profitability of juvenile Heterotis niloticus reared in a pen fish farming

Analysis of the Sustainability, Vulnerability, and Challenges of Aquaculture Livelihood Projects

Background: Aquaculture is the best source of sustainable livelihood for communities, as long as the technology is in place and environment friendly. The aquaculture in southern Negros Occidental continues to experience a crisis that includes this recent COVID-19 pandemic, in addition to rapid financial and structural changes and awareness of farming's enormous influence on ecosystem health. Oyster and fish cages farmers were familiar with and associated terms such as environmental protection, small-scale aquaculture, profitability, and productivity with sustainable oyster and fish production. Furthermore, the researcher, who has experience in the aquaculture industry, desires to investigate sustainability and recognizes this aquaculture owners/operators' vulnerability and challenges in their livelihood. Thus, the paper analyzed the sustainability, vulnerability, and challenges of aquaculture livelihood projects in Southern Negros. Methods: Using a descriptive quantitative research design, 50 aquaculture operators/owners answered a checklist questionnaire to analyze the sustainability, vulnerability, and challenges of aquaculture livelihood projects. Frequency count and percentage distribution were used in analyzing the quantitative data. Results: In human capital, the operators/owners have at least a high school graduate to engage in aquaculture livelihood and range 0-1 year of experience. They are aware of health and safety practices, and the skills they know are feeding and harvesting. They are sole workers, and the physical skill they perform is swimming. For natural capital, all operators/owners gained access to the Nanunga River permit from the Local Government Unit of Municipality of Hinigaran. The size of the fishing ground and fish pens is at 5x5meters, and they conduct monthly coastal cleaning for the maintenance of the surroundings. The timeline and growth and water sensitivity affect the timeline growth of the oyster shell and fish species, respectively. They are also given an action plan to prepare the climate change and initiate the monthly coastal cleanup to maintain cleanliness in the coastal. In terms of financial capital, the income of operators/owners is higher compared to expenses, debt, and taxes paid per harvest. As a result, they can set aside a net amount for savings. Also, they received support from the government every year. They were given a three-year projected financial statement to know the income, expenses, debt, savings, and taxes. Regarding social capital, the aquaculture livelihood helps their community by providing livelihood to their families, providing food supplies, and contributing to economic gain. The operators/owners are trusted, and they follow norms in the community. They are also involved in the monthly meetings to discuss the concerns about their aquaculture livelihood projects. They also avail of the financial assistance loan from the government through the Department of Labor and Employment (DOLE) Pangkabuhayan Program. These imply scheduling a mandatory monthly meeting for the Aquaculture owners/operators, which is also open to the community. In physical capital, most operators/owners have fish pen infrastructure, fish boats, materials for oyster farming, and fish cage fishing. They also used electricity and fuel as a source of energy. They sent an application for financial aid to the Department of Labor and Employment (DOLE) to purchase new materials for Aquaculture. The major vulnerabilities are the Covid-19 pandemic, climate change, oil spills, seasonality, and technological changes. The major challenges that the Aquaculture operators/owners face are lack of knowledge, high/low tide, no preparation of unforeseen expenses, lack of participation among members in monthly association meetings, and cannot afford to purchase new materials for fish pens and fishing boats. Overall, the findings in the light of the Department for International Development (DFID) Sustainable Livelihood Framework, the results were validated as aquaculture livelihood projects are sustainable in terms of human, natural, financial, social, and physical capital. Conclusion: The aquaculture livelihood projects of aquaculture growers in Southern Negros were sustainable in terms of human, natural, financial, social, and physical capital. It shows that the aquaculture operators/owners have various knowledge and skills in the industry, preservation of water resources and cleanliness of coastal areas, more income and less expenses and debts growers, improve the economy and the people's standard of living and relationships and more fish pens infrastructure and increase of supplies of materials. Notwithstanding the existing vulnerabilities and challenges, the aquaculture livelihood projects were manageable and could easily cope with unforeseen events. Practical Value of the Paper: The local government agency may explore the possibility of assisting aquaculture livelihood projects in gathering information for periodic evaluation and monitoring of the financial status of aquaculture livelihood projects for reporting purposes. It is hoped that future researchers utilize this study as the basis for further research, especially studies focusing on the sustainability, vulnerability, and challenges of other livelihoods like agriculture industries. Also, the Aquaculture owners/operators can use the strategic plan to present to the Department of Labor and Employment (DOLE) and other organizations to avail the financial assistance and funding in the future.

Ecotoxicological Assessment of Water and Sediment in Areas of Taal Lake with Heavy Aquaculture Practices Using Allium cepa and Daphnia magna Assay

Aquaculture is one of the main livelihoods of people living near Taal Lake. However, the quality of the lake is deteriorating due to the increasing number of fish cages and fish pens. In this study, ecotoxicological assessment of water and sediment in three areas (Gonzales, Bañaga, and Balakilong) of Taal Lake were conducted using Allium cepa and Daphnia magna assay. The result of A. cepa assay showed that areas with heavy aquaculture practices have a higher percentage of chromosomal aberrations (CAs) such as anaphase bridge, precocious chromosome, sticky chromosome, C-mitosis, and micronucleus (MN). This indicates the presence of cytotoxic and genotoxic compounds in the lake water. On the other hand, assessment of sediment samples using D. magna assay showed that the population exposed to samples from areas with heavy aquaculture practice showed a significantly lower number of offsprings compared to the control area. The result of our study shows the effectiveness of the two bioassays on the evaluation of ecotoxicity of water and sediment samples.

Engineering A Low-Cost Kelp Aquaculture System for Community-Scale Seaweed Farming at Nearshore Exposed Sites via User-Focused Design Process

For over 50 years, government fishery agencies have recognized the need to transition excess fishing capacity in coastal waters to aquaculture. For the most part, investment strategies to move wild capture and harvest efforts into aquaculture have failed since the technology and capital expense for entry, such as large fish pens, was not conducive for acceptance. In contrast, low trophic level aquaculture of shellfish and seaweeds is suitable as an addition to the livelihoods of seasonal fishing communities and to those displaced by fishery closures, especially if vessels and gear can be designed around existing fishing infrastructures, thus allowing fishers to maintain engagement with their primary fishery, while augmenting income via aquaculture. In this study, an inexpensive, lightweight, and highly mobile gear for kelp seaweed farming was developed and tested over a 3-year period in southern Maine, USA. The system was different from existing kelp farming operations used in nearshore waters that use low-scope mooring lines, and heavy, deadweight anchors. Instead, a highly mobile, easy to deploy system using lightweight gear was designed for exposed conditions. The entire system fit into fish tote boxes and was loadable onto a standard pickup truck. The seaweed system had small but efficient horizontal drag embedment anchors connected to a chain catenary and pretensioned with simple subsurface flotation. The system was able to be deployed and removed in less than 4 h by a crew of three using a 10 m vessel and produced a harvest of 12.7 kg/m over an 8-month fall-winter growth period. The target group for this seaweed research and development effort were coastal fishing communities who move seasonally into non-fishing occupations in service industries, such as construction, retail, etc. An economic assessment suggests farmers would realize an 8% return on investment after3 years and $13.50/h greater income as compared to a non-farming off season job at minimum wage. This low-cost seaweed farming system for fall-winter operations fits well into a “livelihood” strategy for fishing families who must work multiple jobs in the offseason when their main fishery is unavailable.

Slosh Suppression Blocks - A concept for mitigating fluid motions in floating closed containment fish pen in high energy environments

This paper introduces a new concept to mitigate sloshing, tailored to floating closed containment aquaculture systems, termed slosh suppression blocks. Slosh suppression blocks reduce the natural sloshing periods by contracting the free surface area without any significant reduction of the operational volume in the tank, and can be retrofitted to existing systems. Sloshing energy is dissipated on top of the suppression blocks, out of the fluid domain to reduce the spread of turbulent eddies in the main body of the fluid in the tank. The fundamental idea and working principles of the slosh suppression blocks are illustrated with an experimental setup representing a 2D section of a closed-containment system under forced horizontal excitations. Maximum sloshing amplitudes are compared for 25 different test configurations for a range of excitation frequencies, using cubic slosh suppression blocks of different sizes. For selected configurations, the fluid's internal state is assessed by visualising the fluid motions both experimentally and by numerical simulations. The results show that slosh suppression blocks reduce the total sloshing volume and turbulent motions within the main body of the tank, providing a much calmer, controlled low energy living environment which is regarded essential for fish wellbeing. It is found that positioning the top of the slosh suppression blocks flush with the still water level mitigates and damps internal sloshing most effectively. To quantify and characterise the degree of slosh suppression, three slosh indices are introduced; the slosh reduction index, the slosh overtopping index and the slosh free surface index. The novel concept of slosh suppression blocks provides an important step forward in the design of floating closed containment aquaculture tanks that minimises sloshing and internal fluid motions in energetic environments.

Heavy Metal Pollution Reduced the Potentiality of Pen Culture in the Wetland Aquaculture in an Urban Area of Bangladesh

The Belai beel serves as an important aquatic resource for the livelihood of the local community of the Gazipur district in Bangladesh. However, water pollution in recent times, mainly from industrial wastes and sewage effluents, may disrupt its aquatic environment. Thus, the purpose of the present study was to assess the potential area of pen fish culture in the Belai beel. The study was performed in the Rajbagan (L1), Kamaria (L2) and Rewla (L3) areas of the Belai beel. Grass carp, silver carp, common carp, catla and rui of 20–30 cm in size were stocked at a rate of 15,000 fish/ha and reared for 150 days in pens installed in the L1, L2 and L3 areas, respectively. The fishes were fed with mustard oil cake and rice bran. Maximum fish production was found in Rewla (12.97 ton/ha/150 days) compared to Rajbagan (8.85 ton/ha/150 days) and Kamaria (10.67 ton/ha/150 days) due to it having comparatively good quality water. There were significant differences in metal ion concentrations (p < 0.05) among the three fish pens. In the Rajbagan area, concentrations of Cd and Cu in the water coming from the industrial effluent canal exceeded the acceptable limit. Results indicated that the Rewla area was better than Rajbagan and Kamaria due to it having relatively good quality water for pen fish culture.

Laguna De Bay: A Case Study for Sustainable Fisheries Development

Laguna Lake is the largest source of fish catch from all lakes in the country providing food and livelihood to millions of people. Recently, there were attempts to remove all fish pens and cages from the lake, presumably because of their adverse impact on water quality and pollution. In this paper, we provide an overview of the lake ecology and we identify ways to manage the lake sustainably. For some time, it has been clear that the lake’s ecosystem is deteriorating putting at risk the food source and livelihoods of millions of people. The LLDA, the local government units, and various stakeholders have formulated concrete steps to ensure sustained fish production in the lake.

Cage aquaculture in the Persian Gulf: A cautionary tale for Iran and the world

Around the world, coral reefs are in decline. Recent interest has focussed on the impacts of global warming/climate change, but the decline started long before the influence of climate change became apparent, driven by anthropogenic factors such as sedimentation, nutrient increase, and overfishing. These continue with no real signs of abatement, as does concomitant reef damage.The Persian Gulf supports widespread coral growth, especially on the Iranian side. Responding to issues of food security, the Iranian government has proposed large-scale aquaculture (open-net fish pens) along their coastline, with an eventual production of 200,000 t/year. Nutrient discharge will be a major issue.We developed a hydrodynamic circulation model for the Persian Gulf which allows us to follow the path of dissolved material. We estimated the amount of nitrogen that would be produced by the projected farms and modelled nitrogen distribution over time, using production rates of 44kgN released/t of fish. In a model run simulating one year at full operation of the proposed number of fish farms, we estimate that most of the reefs on the Iranian side will be bathed in waters with nutrient levels higher than will allow for reef survival. We used a trigger value of 20 μg/l total N. Mangroves will also be affected. There is significant trans-border movement of nutrients, to the waters of neighbouring countries. In fact, withing a few years the entire Gulf will be affected.These planned aquaculture projects have the potential to damage the mangroves and kill every reef in the Persian Gulf in a very short period of time. There is a high probability of affecting fisheries resources in neighbouring countries-a situation to be avoided in politically volatile regions.There seem only two solutions: 1. either run the fish farms so that nutrient discharge is kept to acceptable levels, using an ironclad monitoring system, or 2. bring the operations on land by establishing recirculating aquaculture systems.

Lake water level variability determination from SAR backscatter of discrete objects, GNSS levelling and satellite altimetry

In the absence of enough gauging stations for monitoring lake water level, three (3) methods are presented in this research: (1) Synthetic Aperture Radar (SAR) backscatter from discrete object; (2) Global Navigation Satellite System (GNSS) levelling; and (3) satellite altimetry. The results showed that the Laguna Lake water level is not homogeneous but instead varies at different locations. The GNSS leveling showed that water level varies from −0.64 to 1.26 m from water gauge data. Using the fish pen guard house as discrete object for double bounce scattering a correlation of 0.86 was computed between the gauge data and sigma 0 the equation derived through linear regression was used to predict water level from SAR images at different periods. The satellite altimeter data correlated with water level from graduated staff at 0.97 with a difference of about 0.29 m. It also showed an increasing water level trend from north to south.

Geochemical speciation of metals (Cu, Pb, Cd) in fishpond sediments in Batan Bay, Aklan, Philippines.

Batan Bay in Aklan, Philippines supports a population largely dependent on coastal fisheries. The development of aquaculture technologies coupled with over-crowded fish pens has negatively affected its natural dynamics and environmental quality. Land-use activities including ports and shipyard further aggravate the problem by contributing to chemical pollution. The present study applied sequential extraction techniques to determine the geochemical speciation of metals in fishpond sediments. Samples were processed and analyzed for Cu, Cd, and Pb using flame atomic absorption spectroscopy. Copper (Cu) showed the highest concentration (10.61-66.81μg/g-dry weight of sediment). Lead (Pb) content ranged from below detection limit to 15.14μg/g, while Cd concentration ranged from below detection limit to 2.50μg/g. Fractionation study showed that the Cu present in the fishpond sediments is mostly non-residual (50.03-73.34%) and significantly associated with the oxidizable fraction (33.89-64.75%). In contrast, the residual fraction served as the dominant host of Pb (33.55-62.68%) in the sediments. Comparison of the results with US EPA and NOAA sediment quality guidelines also revealed that the Batan Bay sediments may be considered generally non-polluted with respect Cu, Pb, and Cd, and not expected to cause adverse effects to aquatic organisms under normal conditions. However, under certain redox conditions, most of the sites may be considered moderately polluted as a result of Cu mobilization from the non-residual fractions of the sediments. Overall, geochemical speciation studies in an important fishery area like Batan Bay will provide valuable insights into the availability of metal contaminants to aquatic organisms under certain environmental conditions.

Field and flume tank experiments investigating the efficacy of a bubble curtain to keep harmful jellyfish out of finfish pens

In recent years, salmon aquaculture has struggled to mitigate the impact of harmful jellyfish species in northern Europe and beyond. Typically, large aggregations of jellyfish are carried by currents through salmon pens, leading to unsustainable mortality levels in some years. One potential solution that has been regularly proposed is the creation of a ‘bubble curtain’ around fish pens. A bubble curtain is created by releasing compressed air from a perforated tube at depth, forming a plume of bubbles that entrain the water to create a vertical current. This study investigated the efficacy of a bubble curtain as a jellyfish barrier at several aquaculture locations in Ireland and in a controlled flume tank. Field tests on bubble curtains provided mixed results: a high air flow 8 m linear bubble curtain set at 5 m depth effectively deflected large compass jellyfish (Chrysaora hysoscella), whereas, a low air flow ca. 800 m circular bubble curtain set at 5 m depth, around a salmon farm, did not significantly impact the abundance of small hydromedusae on either side of the bubble curtain. Flume tank experiments demonstrated that increased wave height and increased air flow increased jellyfish transport through the curtain and the lateral movement was consistent with Stokes drift, i.e. an elliptical motion that includes forward movement with each wave. These results suggest that sites with relatively high wave energy may be unsuitable for bubble curtain use and that the variable size and shape of jellyfish may be an important factor in jellyfish and bubble curtain interactions.

The spatial distribution of nitrate and phosphate in Sempor Reservoir, Kebumen Regency, Central Java

Sempor Reservoir is used for irrigation, domestic, industrial, and tourism purposes, as well as hydroelectric power plant and inland fish farming in pens. The land use in its catchment area is mainly plantation (74%) and, followed by, rice field (8.13%), dry farmland (7.74%), and settlement (5.69%). Agricultural activities, both in irrigated and rainfed farming systems, apply fertilizers to maintain crop quality, but when these substances washed away by surface runoff and transported through the drainage system, they end up increasing nutrients in water bodies. Excess nutrients like nitrate and phosphate induce a rapid growth of algae and aquatic plants, disrupting the ecosystems. This study was designed to identify the spatial distribution of nitrate and phosphate in Sempor Reservoir by field observation, water sampling, and laboratory analysis. The water was collected from 25 sampling points distributed at the outlet (close to the spillway), in the middle and the upstream of the reservoir, and around the fish pens (near the check dam). The results showed that nitrate was present on the reservoir water surface and at a depth of 1 meter at varying concentrations, i.e., <0.01-0.36 mg/L. The phosphate levels were <0.01-0.31 mg/L on the surface and <0.01-4.78 mg/L at a depth of 1 meter. The upstream had very high nitrate concentrations both on the surface and at a depth of 1 meter, while the outlet had very high content only at a depth of 1 meter. As for phosphate, very high concentrations were identified in the middle surface of the reservoir (near the pier) and at 1m depth around the fish pens.

ESTIMATION OF CHLOROPHYLL-A CONCENTRATION IN SAMPALOC LAKE USING UAS MULTISPECTRAL REMOTE SENSING AND REGRESSION ANALYSIS

Abstract. Sampaloc Lake is providing livelihood for the residents through aquaculture. An increase in the quantity of fish pens inside the lake threatens its water quality condition. One parameter being monitored is microalgal biomass by measuring Chlorophyll-a concentration. This study aims to generate a chlorophyll-a concentration model for easier monitoring of the lake. In-situ water quality data were collected using chl-a data logger and water quality meter at 357 and 12 locations, respectively. Using Parrot Sequoia+ Multispectral Camera, 1496 of 2148 images were acquired and calibrated, producing 18x18cm resolution Green (G), Red(R), Red Edge (RE) and Near Infrared (NIR) reflectance images. NIR was used to mask out non-water features, and to correct sun glint. The in-situ data and the pixel values extracted were used for Simple Linear Regression Analysis. A model with 5 variables – R/NIR, RE2, NIR2, R/NIR2, and NIR/RE2, was generated, yielding an R2 of 0.586 and RMSE of 0.958 μg/l. A chlorophyll-a concentration map was produced, showing that chl-a is higher where fish pens are located and lowers as it moves away from the pens. Although there are apparent fish pens on certain areas of the lake, it still yields low chlorophyll-a because of little amount of residential area or establishments adjacent to it. Also, not all fish pens have the same concentration of Chlorophyll-a due to inconsistent population per fish pen. The center of the lake has low chlorophyll-a as it is far from human activities. The only outlet, Sabang Creek, also indicates high concentration of Chlorophyll-a.