After more than thirty years of absence, otter has returned to the rivers Guadarrama and Manzanares, which until recently they were the sewer of the largest urban agglomeration in the country. A new instance of that nature may be appreciated even in environments very Humanized.
Text and photos: Carlos Sunyer
In the mid-sixties otter it was still a widespread species well in the middle basin of the Tagus. A decade later the situation seemed to have changed and the first warnings that was disappearing in much of Spain were given, which it coincided with the trend being followed in other European countries. In order to better understand the situation of the species and establish the basis for conservation, in 1984 a national sampling otter allowed to know in detail organized, for the first time, distribution throughout the country and has been repeated in 1994 (5) and 2004 (6).
Evolution of otters in the Community of Madrid
The first national survey 1984 He revealed that the otter had disappeared from most of the Community of Madrid. In fact, He had been relegated to the Lozoya river and a small stretch of the Jarama. The situation in the environment was not unflattering, because the nearest populations vanished as he approached the Community of Madrid (Figure 1). It was a time when there were hardly any wastewater treatment plants and rivers down as true sewers after crossing the main urban and industrial centers. The final collector all discharges of Madrid, Toledo and Guadalajara was the Tagus River, so it is not surprising that here the otter was absent on a stretch of 230 kilometers, between Tielmes and Malpica de Tajo, where the river was beginning to show signs of some recovery.
He had also disappeared from some well-preserved rivers, as the Alberche and some tributaries of the Jarama and Henares, so besides pollution there were other factors that were negatively impacting on the otter, probably hunting and trapping.
If the results of the first survey offered a pessimistic view, with a big gap of the species around Madrid, polls 1994 and 2004 invited optimism. They are showing the gradual recovery of the species in most river basins and, Besides, in those where it still was absent was the most likely cause water pollution, as in the Guadarrama and Manzanares rivers.
In the sixties the otter was present throughout the course of the Guadarrama, including its main tributary, the Aulencia. At that time the river was clean and was very popular bathing areas in La Navata, Las Rozas, Batres and Recas. But in 1984 the situation had completely changed, the river was heavily polluted and the otter had disappeared, situation remained polls 1994 and 2004. Although the results of the first three national surveys had been negative, there was evidence of the occasional presence of otters in the cattle pastures located in the foothills of the Sierra de Guadarrama. Where they could have reached these otters?