An alert study on the ecological impact of native species in waters that do not correspond to them

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Exotic fish are a threat to river ecosystems, but what happens when invasive species are native to one territory and have been introduced to waters that are not their native territory? A new study carried out by the UB and published in the journal Total Environmental Scienceanalyzed the impact that native fish receive from these species, called cash transferredin relation to the effects of invasive alien species, that is, those that are not native to any basin in the territory.

The study’s findings show that habitat quality is the most important factor for the well-being of native fish, but the study also points out that translocated species can become as problematic as alien species.

According to the researchers, these results may have implications for river management, especially in the context of climate change, since species translocation is a common effect of interregional water transfers carried out by some countries to mitigate the consequences of global warming. .

“What our data suggest is that invasions of displaced native species should be taken at least as seriously as those of alien species in the systems we studied, i.e. streams and typical medium-sized Mediterranean rivers”, notes Alberto Maceda, researcher at Biodiversity. Research Institute (IRBio) of the University of Barcelona and first author of the article. The study included the participation of Adolfo de Sostoa, researcher at IRBio, and experts Ralph Mac Nally and Jian DL Yen, from the University of Melbourne (Australia).

A pioneering study on the effects of translocated species

The researchers studied the characteristics of different fish species in fifteen sites in the basins of the northeast of the Iberian Peninsula, but they mainly focused on cyprinid species (Cyprinidae), one of the most species-rich in the world and the most widespread in Europe.

Specifically, the researchers analyzed indicators of high ecological relevance, such as the diversity of native species, the abundance and size distribution of native fish when exposed to invasion by exotic native species or transferred. “Before our study, there were studies that highlighted the problem of mixing of Mediterranean and Atlantic trout populations, and some examples of competition between native and translocated species, but ours is the first study that has analyzed the problem. from a broader point of view and combined different indicators”, explains Alberto Maceda, lecturer at the Faculty of Biology of the UB.

Negative effects on native fish

The results, consistent with previous studies, indicate that habitat quality is essential for the conservation of native species. In other words, environmental characteristics, such as temperature, water depth or velocity, pH or nutrient levels, are the variables that best explain the variability of characteristics such as abundance or weight of native species analyzed. However, the main novelty of the study is that, after taking these environmental variables into account, the results suggest that translocated species had potentially greater impacts on native fish than exotic species, despite the fact that the latter contained some widely recognized alien species, such as carp (Cyprinus carpio) or bleaks (Alburnus alburnus).

As reported by the authors in the paper, the presence of translocated fish was associated with lower abundance and richness of native fish and smaller native individuals, while the presence of exotic fish was associated with greater abundance and richness of native fish and generally to larger individuals. people.

There are still many unanswered questions about transferred cash

In view of the results, the researchers stress the need to study in more detail the ecological impact of the displaced native species. “There is no point in assuming that the impacts of alien species are worse because they come from outside our borders, because we don’t yet have enough information to make such claims. In fact, we we have a great lack of knowledge about the diseases, hybridization problems, trophic competition, etc. that translocated species can bring”, emphasizes the researcher.

Legislative and river management challenge

The conclusions of this study present a considerable challenge for current legislation and the management of watercourses, such as finding oneself in the situation of having to protect and eradicate the same species depending on the hydrological basin in which it is found. Alberto Maceda notes that “Species are usually declared problem species in a political territory, but we may find that a species is native and has invasive populations in the same political area. To make matters worse, we may even find that a species is declining in its source basin, but it is expanding into basins where it was previously introduced.”

In this context, the researcher indicates that habitat conservation is the aspect on which managers should focus the most in order to conserve native fish. “Generally, we believe action needs to be taken with respect to habitat conservation, as the benefits have multiple dimensions which, in turn, may even make native species better competitors against alien species” , he said.

Despite this general recommendation, Alberto Maceda adds that sometimes intervention against introduced species can also be a solution, especially if they are displaced natives, since they may have similar habitat requirements as natives. “Rivers with poorly conserved habitats also experience the most biological invasions, and it is often difficult to distinguish between the effects of alien species and habitat. However, in some cases the main adverse effect is that of transferred native or alien species, and therefore acting on them, if complete eradication is feasible, will certainly benefit the river,” he concludes.

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