Fish Biomanipulation Research Articles

Water quality in a shallow eutrophic lake is unaffected by extensive thinning of planktivorous and benthivorous fish species

Ambitious to fulfill the European Water Framework Directive obligations, the European governments support projects to rehabilitate lakes with poor water quality. However, most lake restorations having relied on biomanipulation by fish thinning have failed to improve or even maintain water quality. Previous attempts removed all target fish species simultaneously, thus making it impossible to assess the specific impact of each feeding group on water chemistry. Lake Bromme was selected for extensive, time-selective fish biomanipulation to improve water clarity and promote submerged macrophytes and piscivorous fish stocks over a three-year monitoring period. Thinning of adult benthivorous bream (Abramis brama) and tench (Tinca tinca) was conducted throughout year one while thinning in years two and three targeted planktivorous roach (Rutilus rutilus), juvenile bream, and small perch (Perca fluviatilis). Yearly fish surveys assessed changes in fish population structure and biomass. Water quality parameters were monitored continually, and the cover of submerged macrophytes was surveyed annually via sonar. We found no improvement in water clarity or reductions of nutrients, organic particles, chlorophyll concentrations, or watercolor, despite a 6-fold thinning of total estimated fish biomass, from 112 to 19 kg ha−1. Over the period, the macrophyte cover increased from 0.8 to 13.5 %, but no recruitment of large piscivorous fish (perch and pike (Esox lucius) > 10 cm) was detected. We found higher correlations of particle concentration and water clarity to water temperature than to wind speed, which indicates sediment particle resuspension by the remaining fish community (mostly carp Cyprinus carpio) that forage on benthos in shallow lakes. Further system-ecological research in Lake Bromme should evaluate whether thinning the stock of carp and increasing plant cover may improve water quality and test which optical properties sustain high water turbidity and prevent shallow, eutrophic lakes like Lake Bromme from responding to intense fish thinning.

Primary production modeling identifies restoration targets for shifting shallow, eutrophic lakes to clear-water regimes

Benthic primary production (BPP) plays an important functional role in lakes, improving water quality by stabilizing clear-water regimes. Shallow, eutrophic lakes lacking BPP communities can be difficult to restore because self-stabilizing feedbacks of phytoplankton dominance can impede the establishment of BPP. BPP in lakes is light limited, and ecosystem models can provide guidance for determining the water clarity necessary to re-establish BPP dominance. We developed a multi-tiered framework for the restoration of shallow, eutrophic lakes that incorporates multiple turbidity sources, lake morphometry, and water-level fluctuations to determine water-clarity thresholds above which BPP dominance may be established. We present a case study applying this restoration target framework to a large, shallow lake (Utah Lake, Utah, USA), where water clarity was greatly impeded by sediment resuspension and high algal biomass. Our analysis, which used commonly available lake-monitoring data, indicated that a return to BPP dominance is possible in Utah Lake, particularly if external nutrient loading to its shallow, wind-protected bays is reduced. Our novel framework incorporates regime shift theory to improve shallow, eutrophic lake restoration efforts. By incorporating ecological feedbacks when identifying the restoration targets necessary for returning a lake to a self-stabilizing, clear-water regime, this restoration target framework offers economical and logistical advantages over strategies that focus solely on phytoplankton management or fish biomanipulation.

Ecosystem stability and water quality improvement in a eutrophic shallow lake via long-term integrated biomanipulation in Southeast China

Biomanipulation is one of the most promising measures in ecological restoration and used to mitigate eutrophication in water bodies. Current biomanipulation methods, such as traditional biomanipulation (based on large-size zooplankton) and non-traditional biomanipulation (based on filter-feeding fish), are often carried out independently and focus on algae control. Integrated biomanipulation, including traditional and non-traditional biomanipulation, was implemented in Longhu Lake, a drinking water source, to successfully control cyanobacterial blooms and improve water quality for 20 years. In order to study the mechanism of algae control and the ecosystem stability, we analysed the effects of integrated biomanipulation and single-biomanipulation on the phytoplankton community and the ecosystem via model simulation. The results revealed that compared with the other single-biomanipulation scenarios of ‘filter-feeding fish biomanipulation’, ‘omnivorous fish biomanipulation’, ‘piscivore biomanipulation’, and ‘without biomanipulation’, integrated biomanipulation combined the advantages of traditional and non-traditional biomanipulation. In this case, cyanobacteria biomass (4.5 ton/km2) was kept at a low level, although the biomass of small phytoplankton was high. The slope of trophic-levels spectrum was low (18.54%), and the biomass distribution of the community was balanced (less ‘up-and-down’). The energy flow transfer efficiency of food web was as high as 14.1% and the ratio of grazing food chain and detrital food chain was close to 1:1. The ascendency was better than other scenarios. These data indicated that the ecosystem after integrated manipulation was more stable and mature than that other single-biomanipulation. Moreover, integrated biomanipulation could substantially increase fishery income. Integrated biomanipulation can therefore be used to meet the requirements of sustainable development, especially in tropical and subtropical eutrophic lakes used as drinking water source.

Long-term effects of fish biomanipulation and macrophyte management on zooplankton functional diversity and production in a temperate shallow lake

Eutrophication still is one of the greatest anthropogenic impacts affecting aquatic ecosystems. Food web manipulations to reverse eutrophic conditions have been applied, mainly by reducing fish stocks. However, the long-term results of biomanipulation are still ambiguous. The objective of this study was to evaluate biomanipulation effects on zooplankton functional diversity and production during 24 years of monitoring a shallow temperate lake. Temporal variation in crustacean biomass (CB), zooplankton resource use efficiency (RUE), limnological variables, functional diversity indices and functional traits were assessed using the Mann–Kendall test. The effects of the limnological and functional variables on zooplankton production (CB and RUE) were analyzed by generalized least squares models (GLSs). We found decreasing trends for almost all the limnological variables, indicating a reduction in lake eutrophic conditions. We also observed a decreasing trend in functional traits related to pelagic habitat, filter-feeding mode, herbivore feeding preference and body size. The GLS results showed that functional dispersion and chlorophyll a are important determinants of zooplankton production. The effects of fish biomanipulation produced no significant temporal trends in zooplankton biomass. In fact, the increase in submerged macrophytes promoted littoral food webs, which was likely the main determining factor of the changes in zooplankton functional traits and production.

Water environment change over the period 2007-2016 and the strategy of fishery improve the water quality of Lake Taihu

太湖水环境是国内外关注的焦点，其生态环境质量影响到流域经济社会发展.2007年太湖水危机事件，催生了对太湖的综合整治.本文基于2007-2016十年对太湖水质与蓝藻水华面积等的监测，分析了太湖水环境的演变趋势.太湖十年水质变化阶段性明显，2008-2012年各项水质指标下降明显，而后趋于平缓，近3年个别指标如总磷、叶绿素a浓度等呈现快速上升的反弹趋势；另外，水质指标在空间上的差异性逐步缩小，原来污染严重的西北部水域水质改善效果较为显著，其正从污水湖向自然湖状态过渡，而原来水质相对较好的东南部水域水质却逐步下降.本文也综述分析了太湖鱼类群落结构变化与水质环境变化的相关性，基于太湖局部水域的鱼类调控实践，提出了太湖现阶段以渔改水的鲢鳙控藻非经典生物操纵与鱼类结构调控的经典生物操纵结合的渔业途径.湖泊富营养化治理需要充分关注到鱼类对湖泊浮游生物和水质变化的重要驱动效应，需要充分考虑到鱼类群落结构优化和食物网调控对环境的改善作用.;Currently,water environment in the Lake Taihu has become one of the focuses due to its importance to the rapid growth of economy and the process of society in the Lake Taihu Basin. Water Crisis of the Lake Taihu in 2007 has resulted in a series of comprehensive treatment program for its eco-environmental improvement. Based on the water quality data from 2007 to 2016, the characteristics and dynamic variation of water environment in the last decade were analyzed. The results showed that the periodic change of water quality in Lake Taihu was obvious. All water quality indexes continued to decline and then leveled off over the period of 2008 to 2012, while certain indexes, such as total phosphorus and chlorophyll-a concentration, showed a rapidly increasing trend in nearly three years. Additionally, the spatial heterogeneity of water quality in the Lake Taihu decreased. As for the heavily polluted northwestern waters, changing from contaminated to natural status, had acquired a massive improvement in the ecological environment, while the water quality of the southeastern waters had gradually deteriorated. Based on the correlation analysis between the fish community structure and water quality variation in Lake Taihu, and combined with the practice of certain fish bio-manipulation projects in local lake regions, a bio-manipulation approach Fishery improve the water quality combined using traditional and non-traditional bio-manipulations was proposed. Eutrophication control in lakes requires sufficiently concern the irreplaceable role of fish in driving plankton community and water quality modification, as well as considering the advantageous effects of structural optimization of fish community and food web manipulation.

Fish community and fisheries management of Brno Reservoir following revitalisation measures

Brno Reservoir (259 ha) is one of the most intensively utilised waterbodies in the Czech Republic, being used simultaneously for recreation, sport, fisheries, boating and electric power production. Despite this, no consistent fish survey has yet been performed at the reservoir. Between 2009 and 2012, a number of measures, including fish biomanipulation, were applied to improve water quality. Large cyprinids (mainly common bream Abramis brama) were removed and predatory fish (e.g. pike Esox lucius, zander Sander lucioperca) stocked. In September 2012 and 2013, we carried out an extensive study of the fish community in order to describe the present fish assemblage and evaluate the success of biomanipulation. Fish were sampled at 11 locations using electrofishing (inlet zone) and beach seining (lake zone). Twenty-three species and one hybrid were recorded (inlet zone — 20, lake zone — 14), with roach Rutilus rutilus and bleak Alburnus alburnus (plus perch Perca fluviatilis) dominant in inlet samples, but carp Cyprinus carpio dominant by biomass; and white bream Blicca bjoerkna and roach dominant in the lake zone, both by abundance and biomass. Predatory species represented 14-17 % of biomass in both the inlet and lake zones in both years. The final results of biomanipulation were questionable. While a low proportion of adult bream suggests successful removal, populations of small cyprinids, such as roach and white bream, increased in compensation. There was little evidence for an increase in predatory fish following stocking, probably due to angling pressure. Our results indicate that biomanipulation to improve ecological water quality in reservoirs is unlikely to be successful when they are managed specifically for carp and predator angling.

Use of multiple fish-removal methods during biomanipulation of a drinking water reservoir – Evaluation of the first four years

The improvement of water quality in recreational and drinking water reservoirs has been a main priority of river basin authorities for some time. One measure commonly applied is biomanipulation, which aims to improve water quality by adjusting fish community structure. Effective reduction of cyprinid density, with a resultant increase in filtering zooplankton development, has already proved successful in many lakes. In this paper, we document progress in a project to evaluate the feasibility and efficiency of biomanipulation through parallel use of age-selective fish removal and predator stocking to improve water quality in a 42ha drinking water reservoir. Between 2009 and 2012, cyprinid and young perch (Perca fluviatilis) density was reduced through removal of early-stage planktonophagous fish and perch eggs, along with removal of adult bream (Abramis brama) and roach (Rutilus rutilus) during spawning. Predatory fish were also stocked to increase juvenile mortality of the target species. As a result, cyprinid biomass was significantly reduced (ca. 2/3 of adult bream removed; biomass now estimated at <25kgha−1).This study showed that biomanipulation was successful at the reservoir and that it is a feasible method for other water bodies of similar area and depth with suitable capture sites. While reduced cyprinid biomass has resulted in a continuous increase in zooplankton density and biomass, however, phytoplankton dynamics appear to be dependent on additional factors such as nutrient input (especially phosphorus). Over the coming years, therefore, attention will focus on both external (catchment) and internal (sediment) nutrient sources, in addition to continuing fish biomanipulation.

Restoration of a shallow Mediterranean lake by biomanipulation complicated by drought

Whether fish biomanipulation is an efficient restoration technique in eutrophic warm sub/tropical lakes has been subject to recent debate. Our investigations undertaken in warm Lake Eymir, Turkey show that fish re- moval increased water clarity during a five-year period. Rapid re-colonisation of submerged plants, Potamogeton pectinatus and Ceratophyllum demersum, occurred. This recovery was achieved at higher total phosphorus (TP) levels than the suggested threshold for stability, probably owing to the nitrogen-limited condition of the lake. Re- establishment of vegetation coincided with significantly reduced concentrations of TP and dissolved inorganic nitrogen (DIN). Abundance of the large-bodied Daphnia pulex was low and it later disappeared completely from the zooplankton community, probably due to increased fish predation. A severe drought, occurring two years after the fish removal, significantly lowered the water level, increased the hydraulic residence time and caused an expan- sion of the vegetation. The drought was also associated with a significant increase in salinity, conductivity, nutrient concentrations (TP and DIN) and in the abundance of Arctodiaptomus bacillifer. The in-lake nutrient amounts became more dependent on internal processes rather than on the external loading, which was very low during the drought period. When the water level rose to normal values, the concentrations of TP and soluble reactive phosphate (SRP) decreased. However, the DIN concentration significantly increased due to slowed denitrification processes in consequence of the low availability of dissolved oxygen. This increase in ammonium concentrations may have contributed to the instability of clear-water conditions by releasing the lake from its former nitrogen-limited state, since the TP levels in the lake had already surpassed critical levels. Along with this, tench (Tinca tinca ) biomass in- creased to pre-biomanipulation levels and the pike (Esox lucius) to planktivorous fish ratio decreased with increased chlorophyll-a concentrations, largely by inedible cyanobacteria, which led to a decline in summer water clarity but not to disappearance of submerged plants. The early growth of plants was probably controlled by the spring water clarity, which remained high, and the lake maintained its macrophyte-dominated state, despite the relatively turbid conditions prevailing in summer. The highly positive effect of the Lake Eymir restoration effort contradicts the experiences from other subtropical lakes. This could be due to the fact that warm Lake Eymir being at high latitude with a strong presence of predatory fish and limited abundance of planktivorous fish species, as opposed to low altitude warm lakes. However, drought as an inherent feature of the arid region may be even more important in the future as drier conditions are predicted for the Mediterranean region in consequence of the global climate change.

The importance of drawdown and sediment removal for the restoration of the eutrophied shallow Lake Kraenepoel (Belgium)

Lake Kraenepoel (Belgium) is a shallow lake (22 ha), divided in two basins since 1957 by a shallow dike. The lake was used for fish farming until World War II and was drawn down about every 5 years to harvest fish. Despite its dense historical carp population, it had clear water and a rich Littorelletea vegetation. During the course of the 20th century, the lake became eutrophic and the Littorelletea vegetation degraded. The northern basin, which was still drawn down about every decade after 1957, retained its clear water and had a dense submerged macrophyte vegetation. The southern basin, which was never drawn down after 1957 and which received direct surface water inputs, had become a turbid shallow lake with phytoplankton blooms in summer. In 2000, efforts were taken to restore the lake: the entire lake was drawn down, the fish community was biomanipulated, nutrient-rich surface water inputs were diverted from the southern basin and sediments were removed (only in the northern basin). Fish biomanipulation and sediment removal were successful in the northern basin, as nutrient levels declined and the Littorelletea vegetation recovered. In the southern basin, sediment analyses indicated that drawdown resulted in sediments with a lower water and organic matter content and water column turbidity decreased after the drawdown. But pH in the southern basin declined to <4, probably because sulphides in the sediment were oxidized during drawdown and sediment desiccation. In contrast, desiccated sediments were removed from the northern basin and pH did not decline below 6 after restoration. In spite of the still high dissolved nutrient concentrations, phytoplankton biomass declined significantly in the southern basin, probably due to acidification. However, no Littorelletea species colonised the lake bottom in the southern basin. Thus, lake drawdown may be a useful management technique to promote clear water conditions in shallow lakes. However, acidification due to sulphide oxidation may be an undesirable outcome and should be considered in drawdown and sediment desiccation manipulations.

Excess propagation and biological control of zooplanktonic Cyclops in drinking water sources

Starting with the occurrence of Cyclops in drinking water sources and its danger to drinking water safety, we extensively investigated the nature of its excess propagation by analyzing the effect of living space and predator pressure in the food chain on its survival. Then we developed an ecological project using fish biomanipulation, different to the conventional fishery culture technique, to control excess propagation of Cyclops. The control effects on Cyclops of four species of fish were investigated experimentally at a stocking density of 30 g/m3 of water. Results showed that the food habit of the fish had a significant influence on the biological control of Cyclops. The propagation of Cyclops could be controlled effectively and also the water quality improved simultaneously by stocking filter-feeding fish, such as silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis). However, herbivorous Ctenopharyngodon idellus and omnivorous Cyprinus carpio had no obvious biological effects on controlling the growth of Cyclops and restoring water quality. The results further proved that under conditions of proper poly-culture densities of silver carp and bighead carp, the number of Cyclops might be controlled at very low levels and eutrophication might be abated by removing nutrients from the water body.

Internal phosphorus loading in Lake Ringsjön

Lake Ringsjon did not respond with decreased algal production following a substantial reduction in external phosphorus loading. This is typical of many shallow lakes which for decades have received excessive amounts of nutrients. The inertia is due to large amounts of phosphorus (P) stored in sediments and biota, causing internal phosphorus loading. Much of this phosphorus is thought to be released from the organic-rich profundal sediments. In Lake Ringsjon, only one third of the total bottom area is covered by such sediments, the rest being dominated by sand and silt. In the profundal sediments bulk P content was not exceptionally high (approximately 2 mg P·g DW−1), while the pore water phosphate concentrations, especially in Satofta Basin, were very high, indicating large potential for phosphorus release to the water. This is also indicated by the large proportion of Fe- and Al-bound P in the sediments of Satofta Basin. Although there are no direct quantifications of phosphorus release from the sediments in Lake Ringsjon, measurements of phosphorus concentrations in the water mass as well as budget calculations for the three basins clearly show a high capacity for internal loading. Phosphorus concentrations generally increase during summer, when external additions are minimal. Until 1980, the annual external phosphorus addition to Lake Ringsjon greatly exceeded the output, showing that the lake was an efficient phosphorus trap. Since then, input and output have been balanced, but in recent years signs that the lake is once again retaining phosphorus on an annual basis are evident. There are marked differences between the three basins, with Western Basin generally retaining phosphorus, while the upstream Eastern Basin and Satofta Basin during the 1980s often exported phosphorus. It is not possible to evaluate the effects of the fish biomanipulation on the internal loading of phosphorus from the sediment.