A study by the Balearic Ministry of Agriculture and Fisheries has shown that the use of British disuasory acoustic devices known as pingers reduce dolphin attacks on fishing nets which have been set to catch red mullet by some 70 percent. The Balearic Government's director of Fisheries, Miquel Angel Calviño, explained yesterday that this study was done with the aim of stopping the accidental deaths of dolphins. These dolphins gather around the nets for the purpose of eating the fish which have been caught in them.
At the same time, he said, this measure will also protect the professional fishermen.
The study will be continued in August and September to get more information, the purpose of this being to try the effectiveness of this system and to assist the fishermen with the use of the pingers. The use of pingers is strictly regulated by a 2005 decree, which was brought in to stop people using them unwisely, added Calviño.
Calviño said that the red mullet fishermen, who make numerous complaints every year about the damage caused to their nets by the dolphins, lose approximately 6.5 percent of their catch to these dolphins. In addition to this, an average of some 30 dolphins die every year as a result of being caught in the fishermen's nets. One of those responsable for the study, Txema Brotons, said that three types of pingers had been tried, one British, one Dutch and one American. Pingers emit low frequency sounds which are not perceptible to the human ear.
The use of the pingers, said Brotons, had reduced the dolphin attacks by 44 percent.
Brotons said that the model which gave the best results emits eight types of random frequencies.
This is best because it stops the dolphins learning the sound sequence and coming in to eat the fish during the quiet times.
During the investigations, the first of their type to be carried out in Spain, pingers without batteries were used so that the fishermen would not know, when choosing the depth for the nets, where the pingers were, and therefore the study would be more reliable. Other factors, such as contamination, sea traffic and overfishing have also drastically reduced the population of this species of mammal in the last few years. The study, which came from a proposal by the Balearic Federation of Fishermen, took place between July and December 2005.
It had the voluntary participation of 59 boats throughout all of the islands.
In total, all of these boats made 1'075 fishing trips using 806.25 kilometres of controlled nets which stayed in the water for 3'995 hours, and with which 13'035 kilos of fish were caught. During this time 50 dolphin attacks were recorded, which is a frequency of 4.65 percent.
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