- Status: In Progress
The Mira-chub (Squalius torgalensis) and the Southwestern arched-mouth nase (Iberochondrostoma almacai) are two freshwater fish species endemic to the Mira basin that are on the edge of extinction. The primary cause of this alarming situation is the severe reduction and degradation of freshwater habitats caused by recurring droughts, intensified by climate change and unsustainable water abstraction. Compounding this crisis are the spread of invasive species and water pollution, which further threaten their survival. This project seeks to reverse this alarming trend through five key actions: ex-situ reproduction programmes, habitat restoration efforts, aquatic invasive species control, ecological education initiatives and rigorous monitoring. Together, these efforts aim to secure a future for these unique species and their fragile ecosystem.
Project Timeline
June-September 2025
Targeted control actions of invasive aquatic species, such as the blue-crab (Callinectes sapidus) or the common bleak (Alburnus alburnus).
May-June 2025
Pilot of ‘Native Fishes’ (Peixes Nativos) pedagogic activity with school kids from Odemira.
Conservation Status
Freshwater fishes account for 51% of the world’s known fish species, an astonishing diversity given that freshwater ecosystems make up just 1% of aquatic habitats. Yet, 25% of the 14,898 freshwater fish species assessed globally (3,086 species) are at risk of extinction. In Portugal, the situation is even grimmer: 60% of native freshwater fish taxa (26 out of 43) are currently threatened, making freshwater fish 32% of the country’s endangered vertebrate species.
The Mira-chub and the Southwestern arched-mouth nase are small cyprinid fishes (10–15 cm) teetering on the brink of extinction. Although their conservation status was recently downgraded from Critically Endangered to Endangered, many expert biologists and the Red List of Freshwater and Diadromous Fishes of Continental Portugal caution that this change reflects updated IUCN criteria rather than a genuine reduction in extinction risk. In fact, many argue that their situation has worsened.
Shrinking Freshwater Habitats
The Mira-chub is found exclusively in the Mira basin, while the Southwestern arched-mouth nase inhabits the Mira basin and two smaller neighbouring basins. Both species depend on oxygenated flowing freshwater in Mediterranean streams for reproduction and species survival. However, a significant drop in freshwater availability has transformed permanent streams into intermittent ones and intermittent streams into ephemeral streams, devastating their habitats.
One critical stronghold for these species, the Torgal stream, which has historically flowed year-round, dried up for the first time during the summer of 2023, signalling an urgent threat to their survival.
The Problem
The sharp decrease in freshwater availability and the disruption of watercourse continuity in the Mira Basin result from several interconnected factors. Climate change plays a significant role by reducing rainfall and increasing evapotranspiration. At the same time, the intensification of agriculture heightens water consumption, while intensive silviculture, overgrazing and other unsustainable land management practices exacerbate soil erosion. This erosion diminishes water infiltration and leads to the sanding of waterlines. Adding to these challenges, water pollution further degrades the limited remaining freshwater, leaving these habitats severely damaged.
Waterlines in the Mira Basin are on the verge of becoming novel ecosystems. Human-induced environmental changes to hydrological regimes are not only altering flow patterns but also increasing water temperature and salinity, reshaping ecological conditions for native flora and fauna. Compounding these pressures, the introduction of new species that swiftly enter these new niches and establish altered food chains is driving dramatic ecosystem shifts, effectively displacing native species.
The Severe Threat of Invasive Species
Invasive species already present in the Mira Basin exert significant well-known pressure on the Mira-chub and the Southwestern arched-mouth nase. The largemouth bass (Micropterus salmoides), for instance, is a voracious predator, while the pumpkinseed or sun perch (Lepomis gibbosus) not only competes fiercely with both species for food and habitat but also preys on their juveniles.
Another critical way invasive species endanger native populations is through hybridization, which disrupts the genetic integrity of native species. For example, the common bleak (Alburnus alburnus) and the species known as bordalo in Portuguese, or calandino in Spanish (Squalius alburnoides), pose a substantial threat to the survival of the Mira-chub due to this possible interspecies reproduction.
The Cost of Inaction
This scenario suggests that, without intervention, these two fish species, along with other native freshwater species, soon face conditions that make their survival in the Mira Basin impossible. This project is dedicated to preventing such an outcome by leveraging all available knowledge and resources to halt the extinction of these two freshwater fish species and avert the collapse of an entire ecosystem - one that is crucial to the vitality and sustainability of a much larger territory.
Our Project Plan
Given the multifactorial nature of the problem, this project is structured around five main pillars:
Step 1 - Monitoring
The first step is a comprehensive assessment of the current distribution and status of both species in the Mira Basin. This will begin with an eDNA analysis across various sections of the Mira River and its tributary streams, providing a detailed understanding of where the species are present and where they are absent. This approach will also allow us to screen for other species, both native and invasive, broadening the scope of our data collection.
Surveys & habitat mapping
Once we establish where these species are still surviving, we will conduct fishing surveys to estimate population sizes and analyse individual characteristics to infer their overall health.
Another crucial aspect of monitoring is habitat mapping and characterization. Initially, the focus will be on the habitats currently occupied by the target species, with subsequent efforts directed toward identifying and evaluating other potentially suitable areas.
Step 2 - Habitat Restoration
The mapping and evaluation of current and potential freshwater habitats will provide essential insights into where to prioritise stream or river restoration efforts, a critical step for securing the future of these species.
Interventions may focus directly on the riverbed, such as reconfiguring channel shapes, de-sanding certain areas, creating step pools or stabilizing banks using natural engineering techniques. Equally important is restoring the riparian forest, which plays a vital role in ecological processes necessary for healthy streams, including water depuration, infiltration, erosion control and the creation of microhabitats. Supporting the natural regeneration of riparian galleries can be achieved through measures like fencing to exclude grazing animals and employing applied nucleation plantations.
In terms of increasing freshwater flow in the watercourses, our broader Mira Basin restoration project will prioritise improving aquifer recharge by fostering large-scale soil regeneration, revegetation and landscape hydration. Simultaneously, efforts will aim to bring water extraction back to sustainable levels.
Step 3 - Aquatic Invasive Control
Currently, there are 19 exotic fish species identified in Portugal and, in the Mira Basin alone, over 9 invasive aquatic animal species have already been recorded. These include significant invasive invertebrates as well, such as the blue crab (Callinectes sapidus), the Louisiana crawfish (Procambarus clarkii) and the Asian mussel (Corbicula fluminea). It is not only critical to manage and control the populations of invasive species already present - many of which continue to thrive at the expense of native species - but also to prevent the introduction and establishment of new species. This is particularly urgent given the extensive alert list of potential future invasives. This component will become a new standalone project as part of our wider restoration efforts in the Mira Basin.
Step 4 - Ex-Situ Reproduction
This initiative serves as a critical and last-resort measure when wild populations of a species face an exceptionally high risk of extinction, as is currently the case with the Mira-chub and the Southwestern arched-mouth nase. In the past, a captive breeding project for endangered Portuguese endemic freshwater fish led to the release of thousands of individuals, contributing to a measurable increase in wild populations. Unfortunately, this programme was discontinued.
We aim to establish a sustainable long-term initiative that adheres to best practices in animal welfare. This programme will ensure the preservation of a viable population of these endangered species, safeguarding their survival irrespective of the challenges they face in their natural habitats.
Raising Awareness
An equally crucial aspect of this project is fostering a sense of stewardship within the local community, encouraging people to care for and protect these two species. Our experience reveals that most people are unaware of the existence of these fish, let alone that they are found exclusively in this region.
We will organise activities to connect the community with these species on a deeper level. For instance, we will bring school children to the river, allowing them to observe these animals up close while learning about their habitats, survival needs and the actions they can take - or avoid - to support conservation efforts. Similarly, we will engage with local fishermen and other river users, such as nature sport enthusiasts and tourism operators, to raise awareness about the native fish species, the challenges posed by invasive species and practical ways to minimise negative impacts on the former while avoiding unintentional support for the latter.
In addition to these targeted initiatives, we will launch a broader public awareness campaign throughout the region, leveraging various local media outlets. The goal is to make these fish "famous" within their hometown, inspiring pride and recognition of their unique role as endemic species of the Mira basin. By fostering a strong local connection to these fish, we aim to ensure their long-term protection and survival.
Our Partner
Peixes Nativos is a Portuguese project launched in 2017 to monitor and conserve native freshwater fish species while raising awareness about their importance through environmental education for schools. Primarily based in the Oeste region, north of Lisbon, the project’s scientific lead, Carla Sousa Santos, and her team have also expanded efforts to study and protect native fish in the drier regions of Alentejo and Algarve.
Their expertise makes them ideal partners for our Mossy Earth initiative. Beyond shaping our strategy with valuable feedback and consultancy, they are training us for school activities, drawing from their pedagogic engaging program that takes children to rivers to observe fish first-hand. This approach has proven impactful and we are thrilled about the positive influence this partnership will bring.
Project Discussion
Our Conservation Site Manager, Teresa, gives more background on this project.
the team behind the project
Teresa Santos, Conservation Site Manager, Mossy Earth
Flora Hentz, Partnership Project Coordinator, Mossy Earth
Carla Sousa Santos, Scientific Coordinator, Peixes Nativos
Sources & further reading
- “Livro Vermelho dos Peixes Dulciaquícolas e Diádromos de Portugal Continental” - FCiências.ID & ICNF.I.P. Lisboa (2023)
- “Uma ribeira que secou e uma espécie única que desapareceu. O peixe alentejano que poderá estar extinto por causa das alterações climáticas” - Observador (2023)