The Segura River Basin Authority has launched a ambitious study on populations de peces and eutrophication in the reservoirs within its jurisdictionwith the aim of improving available scientific knowledge and guiding future decisions poblaciones de pecesThe initiative is integrated into the River Basin Management Plan and focuses on analyzing how fish communities influence the ecological and trophic state of these bodies of water.
The service contract for this work, published in the Official State Gazette, has a base budget of €287.044,07, including VAT, and a completion period of 24 months . During this period, the aim is to gather detailed information on species, biomass, trophic dynamics, and risks associated with low water levels , as well as to propose action plans tailored to each reservoir in the Segura River basin.
A strategic contract within the framework of the Segura River Basin Management Plan
The study falls under measure 1136 of the Segura River Basin Management Plan and represents a significant step towards strengthening the management of public water resources. The Segura River Basin Authority aims to obtain up-to-date and consistent data to better understand the relationship between fish populations in reservoirs and eutrophication processes—that is, the excessive enrichment of nutrients that can lead to algal blooms and a decline in water quality.
According to the tender documents published in the BOE (Official State Gazette), the contract includes the conducting a “Study on the population de peces and eutrophication in reservoirs of the Demarcation and proposed action measures, such as the elimination of non-native species”Although the name is very technical, the underlying principle is clear: to have a solid scientific basis for making management decisions that can range from preventative actions to direct interventions on fish communities, including the removal of non-native species.
The Segura Hydrographic Confederation (CHS) emphasizes that this project will help strengthen its functions in analyzing and monitoring the quality of inland waters , as well as in tracking the ecological and trophic status of reservoirs. This information is crucial for planning water use, anticipating critical events, and meeting environmental objectives set at the national and European levels. Monitoring water quality is essential for detecting eutrophication events and algal blooms.
The contract design contemplates a gradual approach: it will start with a broad set of potential reservoirs and, based on the information obtained in a first phase, a small number of them will be selected to carry out more detailed analyses, both from the point of view of the fish and the physical and trophic structure of the aquatic environment.
Improve knowledge about fish and eutrophication in reservoirs
The central objective of the project is to deepen the knowledge of the populations de peces present in the reservoirs of the Segura basin and their relationship with eutrophication processesThis involves identifying which species are present, in what quantities, how they are distributed, and how they are integrated into the food web of each body of water; for this purpose, species such as the catfish when they are present and their impact on the fish farming community.
A significant part of the work will focus on studying the link between fish communities and the ecological and trophic status of reservoirsThat is, the nutrient level, water transparency, and the presence of phytoplankton, macrophytes, and other key organisms. This information will allow us to determine the extent to which the species composition de peces It either promotes or hinders the good ecological status required by European water regulations. Furthermore, solutions based on microalgae combat pollutants as complementary tools in the management of eutrophication.
In addition, the study will include the development of proposals for specific action measures for each reservoirThese include preventative measures against episodes of mortality de pecesThis can occur when high temperatures, low oxygen levels, and reduced water levels are combined, as well as possible actions aimed at controlling or eliminating non-native species that are contributing to ecological imbalances.
The Confederation intends that, once the work is completed, there will be a catalog of measures adapted to the characteristics of each reservoir: managing a reservoir with a strong presence of invasive species is not the same as managing one with more balanced communities, nor does a system subject to frequent sudden drops in level have the same risk as one with a more stable regime.
In this context, the information generated will also serve to guide medium- and long-term monitoring plans , so that it is not merely a snapshot of the current situation, but rather the starting point for more proactive management of fish populations and water quality in the Segura River basin. These initiatives are related to restocking and monitoring programs implemented in other areas.
Study techniques: hydroacoustics, nets and electrofishing
To achieve these objectives, the contract provides for the combined use of hydroacoustic techniques and direct samplingHydroacoustics allows the detection of banks. de peces and estimate their abundance and distribution in the water using sound impulses, a tool especially useful in large reservoirs, where traditional methods would be slower and more expensive.
These techniques will be complemented by net sampling , which allows for the capture of specimens for identification, biometric measurements, and analysis of biological parameters. This will make it possible to determine not only the number of fish present, but also which specific species are dominant, their physical condition, and the age structure of the populations.
Another key tool will be electrofishing from boats , a professional technique that, when applied with the appropriate safety measures and under expert supervision, temporarily immobilizes fish in a specific area without causing permanent harm. This facilitates controlled capture, counting, and subsequent release of the fish, and is very useful for supplementing the information obtained with hydroacoustics and nets.
In addition to these sampling methods, the study will include the calculation of the Minimum Environmental Volume (MEV) in the selected reservoirs. This parameter is fundamental for assessing the risks associated with very low water reserve levels, as it indicates the volume below which the reservoir may begin to present problems for aquatic fauna and for maintaining good ecological status.
The combination of these techniques will allow us not only to estimate the biomass of the different fish species, but also to relate that data to habitat availability, depth, bottom structure and other physical and chemical factors that influence water quality and eutrophication processes.
Reservoirs involved and selection for detailed analysis
The contract's territorial scope includes a broad list of reservoirs in the Segura River basin, among them Cenajo, La Pedrera, Fuensanta, Puentes, Santomera, Talave, Camarillas, Alfonso XIII, Algeciras, Valdeinfierno, La Cierva, Judío, Anchuricas-Miller, Crevillente, Ojós, Argos, and Taibilla . These are key infrastructures for water regulation and supply in the region. The presence of invasive species such as the zebra mussel in other reservoirs highlights the need for specific studies on biological pressure and eutrophication, as in similar cases.
In its first phase, the study will cover this set of reservoirs in order to to obtain an overview of the state of the populations de peces and the levels of eutrophication throughout the basin. From this initial overview, eight reservoirs will be selected for a more thorough analysis, taking into account criteria such as their strategic importance, the presence of recurring problems, or ecological interest.
Of those eight reservoirs, four will be the subject of more detailed studies . In these cases, high-resolution bathymetry is planned, which allows for obtaining a very precise model of the depth and morphology of the bottom, as well as detailed mapping of the substrate to distinguish areas of rock, gravel, silt, or accumulated fine sediments.
In the reservoirs selected for intensive analysis, the characterization of fine sediments is also planned , a relevant aspect because these materials can accumulate nutrients and pollutants that contribute to eutrophication. Where appropriate, a study of submerged macrophytes (aquatic plants) and the structure of the food web will be carried out, analyzing the relationships between producers, consumers, and predators in the ecosystem.
In the specific case of La Pedrera , the study highlights its unique status as the only reservoir in the Vega Baja region included in this project. This infrastructure plays a central role in the irrigation and water supply of the area, and its inclusion in the analysis allows for the incorporation of the perspective of a territory particularly sensitive to changes in water availability and episodes of poor water quality.
Management measures: mortality de peces and non-native species
One of the most practical elements of the contract is the obligation to formulate proposals for action measures adapted to each reservoir Based on the results obtained. Among the possible actions, the CHS expressly mentions the preparation of preventive measures against mortality episodes. de peceswhich can originate from a combination of eutrophication, high temperatures, lack of oxygen and sudden drops in level.
Another important line of work will be the assessment of the role of non-native or invasive species in eutrophication processes and the deterioration of ecological status. The tender specifications contemplate the possible elimination or control of these species as a management measure, provided it is justified based on the data obtained and complies with current regulations on fauna and biodiversity.
These decisions will not be made generically; rather, the aim is for each reservoir to have its own set of recommendations , based on its specific circumstances: the types of pressures it faces, priority water uses, prevailing climatic conditions, and the specific composition of its fish community. These recommendations will be integrated with current regulations and management plans, as is the case with fishing bans and management practices.
Furthermore, calculating the Minimum Environmental Volume and analyzing the food web structure will allow for the definition of risk thresholds and action scenarios . This will make it possible to anticipate, for example, which combinations of water level and temperature could trigger serious problems, helping river basin authorities plan reservoir management strategies or intensive monitoring campaigns during critical periods.
With this type of study, the CHS reinforces its role as the body responsible for controlling the public water domain and monitoring the state of inland waters, aligning itself with the guidelines of the Water Commissioner and with the requirements of European policies on the protection of aquatic ecosystems.
Overall, the project tendered by the Segura River Basin Authority represents a significant investment for better understand how populations interact de peces, eutrophication and reservoir management in the basinOver the next 24 months, the combination of advanced sampling techniques, trophic analysis, and physical characterization of reservoirs will provide an unprecedented information base on these ecosystems, which should translate into management decisions more closely aligned with reality and a greater capacity to prevent water quality problems and mortality events. de peces in Spain.
