A brigade specialized in studies of conservation and aquatic fauna will comb the urban section of the Onyar river, as it passes through Girona, in order to remove the maximum number of carp and other species that proliferate in these waters. . They will do so using the electric fishing method, a system that allows the specimens to be stunned and makes their removal easier.
The objective is none other, according to the person in charge of the operation, the biologist Quim Pol Rovira, than to avoid a “sudden and massive” mortality of the species that inhabit this stretch of river caused by the reduction of the flow and the bad conditions of the water.
Two elements that have been aggravated by the current episode of drought. Pol Rovira explains that the quality of the water has already caused the death of some fish and could cause suffocation or toxicity problems for the rest in the coming weeks or months.
On the other hand, the flow in this section, which goes from the Pedret bridge to the urban exit of Girona, in the south of the city, is estimated to be less than 200 l/second. In a normal rainfall year, it would have double or triple the amount of water.
Figure to which should be added the contribution of the Monar ditch, with water from the river Ter, now non-existent. “In this section there is usually a flow between 10 and 20 times higher than the current one,” explained Pol Rovira, director of the Sorelló company, to which the City Council has commissioned.
The brigade uses the electric fishing method to capture the specimens. Through the use of devices, they create electric fields in the water that stun fish that are within reach of the generated field, the amplitude of which can range from one to six meters.
“The electric field generates an electronarcosis in the species that makes them immobilized for seconds or minutes and can be more easily removed from the water,” explains the biologist.
The person in charge of the operation and hopes to finish the day having captured a minimum of one hundred adult carp, approximately fifty kilos, an invasive species introduced in Catalonia 120 years ago that is the most numerous in the Onyar river.
As it is an invasive species, the regulations require it to be sacrificed. In this way, all the specimens that are withdrawn will be destined for an animal biomass treatment company. The carp is not the only foreign species that inhabits the Onyar River. Percasols, introduced a century ago, could also appear; rutiles or minnow.
However, native species such as mountain barbel, eel or catfish will be transported to the River Ter, with a higher cabal, to thus guarantee their survival. Although it is not native to Girona but to other parts of Catalonia, the Ebro catfish is also present in the Onyar river. In this case, it will not be sacrificed either.
If this action is not carried out, the massive mortality of fish in the river could cause public health problems. “The risk to people is minimal, but it is a matter of hygiene. It is not advisable to expose large dead fish outdoors in an urban area,” he said. The operation could be repeated in May and June.
