Nothing exceptional so far—except that these might be the first Rana temporaria tadpoles to complete metamorphosis in Lake Leità in many decades!

Since the 1960s, the lake had been colonized by an introduced population of brook trout, a salmonid native to North America, introduced into several park lakes at a time when the devastating effects of fish introduction into these ecosystems were still unknown. Among these effects, the presence of fish tends to prevent Rana temporaria from reproducing in the same environments due to predation on both tadpoles and adults.

However, since 2023, an ecological restoration action has been underway at Lake Leità as part of the LIFE RESQUE ALPYR project, aiming to return the lake to its natural, fish-free condition. This year, the project team is working to remove the last remaining brook trout individuals, but the first positive effects of the eradication are already becoming visible. As early as 2024, unusual movements of frogs had been observed around the lake… these few tadpoles might be the first of many new generations of Rana temporaria in this lake!

Image of Lac Leità, in Parco Nazionale del Gran Paradiso

These fish, in addition to being non-native species, are considered invasive because they have a negative impact on the natural ecosystems of these environments.

Fishing in high mountain lakes

In the Pyrenees, the introduction of fish was carried out historically, initially for self-consumption and trade, using native trout from nearby rivers, always in limited lakes. In the Alps, some introductions date back to the medieval period. However, it wasn’t until the second half of the 20th century that the practice of introducing fish became widespread, especially with the popularization of recreational fishing.

Recreational fishing with live bait has led to the introduction, since the end of the 20th century, of the common minnow, a small cyprinid that negatively affects trout, both in the Pyrenees and in the Alps.

Ecological effects of fish introduction

The proliferation of fish in these lakes has had negative consequences on the native fauna, has affected the structure and balance of the entire ecosystem and altered its trophic food web. Furthermore, the consequences of this impact can also affect terrestrial fauna populations, such as birds, bats, and small mammals like the shrew, which depend on aquatic insects as a food source.

In a natural lake without fish, the ecosystem remains balanced: the water is crystal clear, and the food web functions without alterations. However, when species like trout are introduced, other amphibian species begin to disappear, and significant alterations occur in the food web of the littoral zone, where fish dominate over larger macroinvertebrates.

The ecological impact becomes more severe when, in addition to trout, the minnow is also introduced. This cyprinid species, which has been used as live bait for recreational fishing, causes aggressive predation on trout nests and overfishing, which may lead to the disappearance of this species. This significantly alters the food web of the lake.

In lakes where only the minnow is found, the impact not only affects the littoral zone but also alters the pelagic zone, due to the increase in nutrients that promote the growth of microalgae and cause a decrease in water transparency.

The scientific meeting was held in Tortosa and Vic on June 18 and 21, 2024. This time, the congress focused on promoting the study and conservation of native fish in the continental and marine aquatic ecosystems of the Iberian Peninsula.

The members of the LIFE RESQUE ALPYR project contributed knowledge obtained from their research in the field of conservation and restoration of high mountain lakes. They did so through presentations and the display of scientific posters.

For example, among other things, they presented work related to the use of genetic tools for the early detection of invasive fish species in lakes. Metabarcoding is an accurate tool for identifying and conducting phylogenetic analysis of species, allowing the detection of bioinvasions in their early stages.

The history of fish introductions in high mountain lakes was also narrated and explained in detail. This history was studied by researcher Marc Ventura along with Didier Galop and Olivier Baudier.

SIBIC congresses are held every two years to address scientific and management challenges related to various aspects of ichthyology. This edition, among other new topics, will include issues such as freshwater and marine fish, and conservation aquaculture.

In addition to being introduced species, they are considered invasive species, as they have a negative impact on the ecosystem.

Salmonids introduced in the Pyrenees include brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis). The European minnow (Phoxinus sp.), a small Cyprinid, has also been introduced in many of the lakes in the Pyrenees, but in this case, the arrival is related with its use as live bait for fishing trout.

The species introduced in Mont Avic Natural Park are Arctic char (Salvelinus alpinus), the European minnow (Phoxinus spp.), the Italian riffle dace (Telestes muticellus), brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss); and the species introduced in Gran Paradiso National Park are brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta).

The proliferation of fish in these lakes has had negative consequences on the native fauna, has affected the structure and balance of the entire ecosystem and altered its trophic food web. Furthermore, the impact of introductions can also have consequences on terrestrial fauna populations such as birds, bats and small mammals such as the Pyrenean desman, which depend on aquatic insects as a food source.

The brochure can be consulted in digital format on the project’s website, but it can also be found at the tourist offices of the Alt Pirineu Natural Park and the Aigüestortes and Sant Maurici National Park in Catalonia, and the Mont Avic Natural Park and Gran Paradiso National Park in Italy.

Although the effects of the introduction of trout have been the subject of many studies, the effects of minnows are poorly understood. One of the objectives of the thesis has been to investigate the effects of the introduction of non-native fish, and especially minnows, on the littoral macroinvertebrate communities of Pyrenees high mountain lakes.

Through the study of 54 lakes, he evaluated the impact of minnow and trout densities on macroinvertebrates community compositions and abundacnce, relative to other biotic and abiotic factors In the lakes with veron, the macroinvertebrate community was tipically limited to a small number of taxa, predominantly composed of small, semi-sessile burrower organisms. Metabarcoding tools have been used to explore the impact of trout and minnows.

The recovery of macroinvertebrate communities in eight lakes where fish populations were eradicated or controlled has also been evaluated over nine years. A few years after eradication, rapid signs of recovery were already observed, with communities gradually resembling those typical of fishless lakes.

The thesis has been directed by Dr. Marc Ventura from the CEAB-CSIC and Dr. Maria Àngels Puig from the CEAB-CSIC and Dr. Teresa Elena Vigues, professor at the University of Barcelona.

The data and results from the BIOOCULT project directly contribute to LIFE RESQUE ALPYR, particularly in the characterization of biodiversity. This information provides a solid foundation for identifying hidden biodiversity and assessing its sensitivity to global change, including climate change and the introduction of invasive species. This enables a better description of the effects of fish introduction and their recovery.

The Research Conference of the National Parks Network

This year’s conference featured the results of research projects funded under the 2020 call, as well as unique management experiences shared by the management team of the protected area and researchers associated with the Tablas de Daimiel National Park, coinciding with its 50th anniversary. The specific objectives of the conference were as follows:

• Evaluate the degree of compliance and quality of the results of the projects selected in the 2020 call of the National Parks Research Program.
• Present specific research projects from the Tablas de Daimiel National Park funded alternatively to the Program and unique management experiences by the park’s technical team.
• Foster a network of exchange and knowledge among park managers and researchers working in different parks.
• Stimulate the research aspect and its value for conservation at the Tablas de Daimiel National Park.
• Promote and raise awareness about the National Parks Research Program and its impact and value for adaptive management.