One of the greatest environmental challenges today is the proliferation of invasive species, responsible for a great biodiversity loss throughout the world. Some years ago, in the Sierra de Guadarrama aquatic ecosystems has been located a population of feral American Mink (Neovison vison), an invasive specie that has colonized many of the Spanish rivers. In the past few years has also been detected the American signal crayfish –“Pacifastacus leniusculus”- in the lower Lozoya River areas. Both species are virtually confined to the Peripheral Protection Zone, though their distribution in the Sierra has been tracked, and their trend and populations size is being analyzed.
In any case, the Sierra de Guadarrama is one of the few successful examples in the eradication of an introduced specie: the Arctic char (Salvelinus Fontinalis), eradicated from the Peñalara Lake and the Hoya de Peñalara stream. The arctic char is a salmonid native to the NE of North America, living in lakes and cold, clear, and oxygenated water rivers. It is a very voracious carnivore, which feeds on great invertebrates, zooplankton, juvenile fishes, and amphibians larvae. Adults are usually about 20-35 cm length and under 0.5 kg weight. It was introduced around 1970 in the Peñalara Lake , where there was previously no fish, and it colonized the Hoya de Peñalara stream by migration.
Eradication of Arctic char
The introduction of the arctic char in the Peñalara Lake originated the disappearance of numerous aquatic organism species, as well as changes in the densities of some other species. For example, the presence of the arctic char caused greater densities of rotifers (Asplachna priodonta, Keratella quadrata) when compared to cladocerans and copepods of medium size (Ceriodaphnia reticulata, Alona quadrangularis, Serrulatus Tropocyclops prasinus, Eucyclops). At the same time, the large cladocerans (Daphnia pulicaria) practically disappeared. In the same manner disappeared aquatic macroinvertebrates large species (Tricoptera, heteropteros, odonates).
The eradication project was carried out between summer 1999 and summer 2004, although with different effort in different years. Five gill nets were used (30 m long) composed of 12 panels of 2.5 m x 1.5 m, with a 5 to 55 mm mesh size. It began with an active fishing, nets were thrown and reviewed every 2-48 hours. As reducing the success of captures, passive-fishing started, by placing the networks at the bottom of the lake for a long time (months), except for short periods, for the networks repair and cleaning. The last scan was conducted in the spring of 2002, counting from the start of the eradication a total of 550 individuals, aged up to 4 years.
The eradication has been a remarkable change in the populations of aquatic organisms, with a rapid settlement of new species. As well, it has gone from 9-13 aquatic family organisms with arctic char living in the lake, to 23-26 families following the eradication project. All these species appear in ponds, which have served as recolonization farms.
On the other hand, the arctic char colonized streams located downstream the lake, in the Hoya de Peñalara. In this case, eradication has been performing from 2002 to 2012 with two battery-powered backpack electric fishing equipment, splitting the task in two sessions. In each session, each stream was covered twice. In 2008 the collapse of arctic char was already observed the Large Lagoon and the Dos Hermanas stream, and in 2013 was confirmed the definitive eradication of this specie.
The complete eradication of arctic char in these streams is of special interest, given the suitability of this water course as habitat for the R. Ibérica. As well, it is being used as a place of reception of the Iberian frog copies translocation.