This week we have reported the first underwater images recorded in the Western Mediterranean and Iberian Peninsula of common bottlenose dolphins feeding in trawl nets. The images have been obtained within the framework of the project “COSTtERA: Comportamiento Submarino de Tursiops truncatus En Redes de Arrastre en el Norte de Cataluña”, which is carried out with the support of the Fundación Biodiversidad, of the Ministerio para la Transición Ecológica y el Reto Demográfico, through the Programa Pleamar, cofinanced by the European Maritime and Fisheries Fund (FEMP).

We have already observed that bottlenose dolphins (Tursiops truncatus) follow the trawl fishing boats, mainly showing a feeding behaviour. However, until now we had not information of their underwater behaviour; we did not know if the animals entered the moving net, if they fed on the fish stirred up by the net, or if they ate the trapped fish from outside the net.

As part of the COSTtERA project, and thanks to the collaboration of the vessels Galandu, Roca Forne and Nova Armonia, of the Roses Fishermen’s guild and the Llançà Fishermen’s guild, we have now been able to obtain underwater records of bottlenose dolphins swimming around the net, searching for food and extracting trapped from outside the nets. However, no dolphins have been observed swimming completely inside the net. One individual has been observed swimming at the beginning of the net, with half of its body inside and half outside. So far, no interaction of risk for the animals has been observed, although it is necessary to continue obtaining records.

These are the first images from the Western Mediterranean and the Iberian Peninsula showing the type of interaction that occurs underwater when dolphins follow the trawl nets, and many  media have reported the news. Recording this type of underwater images has not been easy, given that this happens at around 100 metres of depth.

Throughout the month of September, we will continue to record images and collect data in order to identify the preferred areas of the nets and to see if there are differences in the behaviour of the dolphins depending on the type of net, as well as to determine the risk of this behaviour.