COSTtERA-1

The interaction between bottlenose dolphins and trawlers occurs in areas where there is a spatial overlap between their distribution ranges, as in many cases the target species of fisheries are also prey species for cetaceans. This type of interaction has been described in multiple areas of the Mediterranean and is regularly observed in Catalan coastal waters, which represent an important habitat for bottlenose dolphins. However, the impact of these interactions on both fishing operations and dolphin populations in this area remains largely unknown.

Although SUBMON has documented this interaction in northern Catalonia since 2017, the degree and risk associated with these interactions for both dolphins and fishing activities are still not fully understood.

COSTtERA aims to improve knowledge of the dolphin population in this area and to study its interaction with trawl fisheries. The project is divided into two main components: on the one hand, a surface study analysing the presence, distribution and surface behaviour of bottlenose dolphins, as well as the level of association with fishing activity in northern Catalonia; and on the other hand, an underwater study of the species in trawling nets through the installation of underwater cameras.

To analyse how dolphins behave when following fishing nets and to determine whether they enter the nets to feed and how they do so, underwater cameras were installed in the trawling nets of three vessels from the fishing guilds of Llançà and Roses, with the aim of recording the feeding behaviour of bottlenose dolphins during trawling operations. The selected vessels operate at depths of less than 200 metres, corresponding to the typical range of occurrence of the species.

The participation of the fishing sector in the study area has been essential. The project has been carried out in collaboration with local fishing guilds and, from the outset, has involved trawling fishermen willing to participate. They have worked closely with the SUBMON team in designing the study, helping to define the most suitable equipment and materials, as well as the optimal timing and locations for camera deployment within the nets.

Furthermore, the collected footage has been reviewed together with the fishermen, integrating their experience with the data gathered. This collaborative work has made it possible to assess the impact of these interactions and to evaluate the need to define good fishing practices aimed at minimising their effects on the local bottlenose dolphin population.

The results provide key insights into the habits of bottlenose dolphins in the area and support the development of future conservation measures.

Implementation year: 2022.

Boat-based surveys

Study of bottlenose dolphin distribution and association with fisheries

Boat surveys are carried out within the study area to systematically collect data on presence, relative abundance, behaviour and environmental conditions associated with each sighting, following standardised sampling protocols.

Photo-identification catalogue

Photographs are systematically taken at each sighting and incorporated into the organisation’s photo-identification catalogue, enabling individual identification, temporal monitoring and the analysis of residency patterns and area use.

Recording and analysis of surface behaviour

Surface behaviour data are collected in a standardised manner and subsequently analysed in order to identify recurring patterns and establish correlations between behaviours observed at the surface and those recorded underwater.

Onboard monitoring on trawling vessels

Installation of underwater cameras

Video cameras are installed in trawling nets to record the feeding behaviour of bottlenose dolphins during fishing operations, placing them in different sections of the net and on vessels operating at depths below 200 metres, which correspond to the species’ typical distribution range.

Participation of the fishing sector

Participatory analysis of results

Regular meetings are held with the fishing sector to review and analyse the recorded footage. The audiovisual records are compared with fishing activity data (fishing grounds, catch logs, etc.) and behavioural records. In addition, collaboration with local fishing guilds supports the active involvement of fishers in interpreting results and identifying measures aimed at ensuring compatibility between fishing activities and species conservation.

Explore the COSTtERA project and its different phases