Pingers as deterrents of bottlenose dolphins interacting with trammel nets

In north-eastern Majorca (Balearic Islands), an area where dolphin predations on the nets were repeatedly reported by fishermen, specially during the red mullet fishing season, the effectiveness of pingers in discouraging common bottlenose dolphins from approaching trammel nets was addressed in a field study during September–October 2001. The pingers used emit eight wide-band frequency signals that range between 20 kHz and 160 kHz, with mean source levels of 145 dB (re 1 μPa at 1 m) at 70 kHz. In the same study dolphin damage to the nets and economic losses by the fishermen were also evaluated. Though pingers did not stop dolphins from approaching the fishing nets, the nets equipped with functional pingers received less damage (87% fewer holes) than nets with non-functional devices or without pingers. Tested pingers did not appear to have any effect on fishery target species. Nevertheless, the use of pingers may bear unwanted environmental impacts, which are also reviewed here.