A section of the Sevillian river Guadaira appeared lined with dead fish over a week ago. In the pile of corpses, the expert eye was able to confirm a fact: almost all the specimens belonged to exotic species. Among thousands of dead fish, a single specimen of a native species appeared, an eel, also cataloged Endangered in the entire Europe.
Not in vain, a recently published study reveals that in the course of the river basin Guadalquivir, of the 18 fish species detected, 9 were exotic. And, almost worse, fish richness, unlike normal, is reduced in the lower course of the rivers due to their poor ecological status.
Joseph Clothing, Professor of Zoology at the University of Huelva and researcher Pedro Saez are the authors of this scientific work. “This result indicates a truly depleted state of fish in the Guadalquivir basin, as they show a very restricted distribution compared to what there should have been a few decades ago and due to the extraordinary presence of alien species, many of them character invasive”, says EL MUNDO the expert.
Basin Plan of the Hydrographic Confederation of the Guadalquivir
Already the Basin Plan of the Hydrographic Confederation of the Guadalquivir (CHG) indicates in its documents an analysis of the current situation. 14 fish, 5 molluscs, 4 crabs, 4 plants and 1 reptile, the Florida turtle, of exotic origin, live in its rivers. Some generate an industry, like the red crab, others harm the economy, and all alter the natural ecosystem.
Although many studies have been conducted in this basin on its hydrological regime or water quality, “the fish biodiversity, as well as its distribution and state of conservation, have not been approached globally as in other Iberian basins”, adds José Prenda. The work was based on field sampling and bibliographic research.
“Throughout the 20th century and up to the present day, the presence of 40 species of fish, 20 native and 20 exotic. However, in the field, only 18 species were captured, 9 native and 9 exotic, with a prevalence for native species of less than 23% », except Andalusian barbel.
According to the International Union for Conservation of Nature (IUCN), approximately 50% of fish species Guadalquivir is threatened. several decrease “at an alarming rate and others are likely extinct and/or their current status is unknown”says Pedro Saez, “to jeopardize spaces so emblematic, so necessary and so affected by other conservation problems such as Donana».
The CHG report indicates that of the 14 exotic fish detected, 10 have a category of invaders, and they are present in 78 water bodies (river sections or swamps). Some are old acquaintances, like carp or pike, and others have recently been incorporated, such as the bullhead or the catfish, Famous for its voracity. There are images of the latter engulfing an unsuspecting baby duck.
Something very singular is that the greatest species richness has occurred in the the middle sections, while that of the lower sections was very poor. “One would expect fish richness to increase from top to bottom, but as the deterioration of the basin’s streams also increases downstream, this natural pattern is significantly changed”.
threats to fish
Hydrological alterations, water availability and quality, intensive farming and introduced species are the main threats to the fish fauna of the Guadalquivir. All of this is a direct result of human disturbances and over the past decades.
There are premeditated presentations. The almost certain action of fishermen releasing the gigantic catfish, at least in the Iznajar Swamp and in the field of Alcala del Rio, It is due to the desire to have fun capturing animals of two meters and one hundred kilos, devastating the waters in which they live.
Highly aggressive invasive species are not just fish. The most recent is the tropical plant camalote, water hyacinth. In Extremadura they wear worn 50 millions euros to control, and not eradicate, this dangerous plant, which completely covered parts of the Guadiana. It appeared last year in Andalusia, first in a stream in the park of The Alcornocales, and around May Port of Seville.
Faced with this gloomy panorama, the study of University of Huelva stresses the urgent need to identify areas of importance for the conservation of the Guadalquivir basin, which will guarantee the long-term persistence of the rare biodiversity that remains, in particular its fish.
Character font: JORGE MOLINA / THE WORLD
Reference article: https://www.elmundo.es/andalucia/2022/10/15/634ab4d1fdddffbe908b457f.html