Line of action:

Status:

Execution date:

Specific objectives:

• To qualitatively and quantitatively describe the diet and trophic requirements of the entire population of Common Tern, Sandwich Tern, Little Tern, Audouin’s Gull and Yellow-legged Gull that breed in the breeding colonies adjacent to SPA ES0000512 (colonies located in the Ebro Delta, and the ports of Tarragona and Castellón)
• Obtaining information on the movements and distribution of these species to describe their foraging areas in the SPA
• Analysis of the Good Environmental Status (BEA) of the populations of these species both at sea (SPA ES0000512) and on land (ES0000020): abundance, demographic parameters and food webs.
• Dissemination of the results of the project, both for the general public and for professionals in the fishing activity. To this end, an animation will be edited and disseminated on social networks and on the project’s website, where the actions of the project and its results will also be explained

The following results have been achieved in the implementation of the SteLar_Delta project:

Movements and foraging

This action aims to obtain information on the movements and distribution of the five species selected in the study to describe their foraging areas in the SPA, the delimitation of the important areas for these species in the sea and description of the use of the habitat within the SPA (feeding areas, areas for foraging and/or transit, rest areas, etc.).

30 specimens of Audouin’s gull have been tagged in the colonies of the Ebro Delta and Castellón, the two most important adjacent to the marine SPA. (15 in Punta de la Banya and 15 in the port of Castellón); 18 yellow-legged gulls in the Ebro Delta, 12 little terns, 13 sandwich terns and 12 common terns. In total, data have been obtained from 29 Audouin’s gulls, 18 yellow-legged gulls, 11 sandwich terns, 8 common terns and 3 little terns, as well as 5 Cory’s shearwaters. These markings have made it possible to define very precisely the habitats used by seabirds and also their interactions with the fishing fleet.

Interactions with the fishing fleet

The identification of possible interactions between birds and ships has been done in a multi-step process. First, the distance to all VMS positions within 2 km of each bird GPS position has been calculated. Secondly, applied to the positions that met the previous criterion, the bird positions that occurred in a time window of 1 hour and a half around each VMS position have been identified. Then, again on the positions identified in previous steps, those bird positions that were at an angle of between -30º and +30º with respect to the course of the boat in its VMS position have been identified. This procedure replicates the one used in Soriano-Redondo et al. (2016). To exclude possible false interactions, VMS positions in ports were excluded from the procedure, as well as those in which the speed of the bird calculated between points was higher than that recorded by the ships in their VMS data, since these take instantaneous speeds. Interactions in which the bird flew at a speed at which no ship can sail (in this case 15 km/h) have been removed.

Feed availability

Thanks to the collaboration of the ICM-CSIC, it has been possible to obtain an estimate of the available/present biomass of the main prey of small pelagic fish, a very important food source for seabirds during the 2022 breeding period in the SPA. This analysis has been carried out based on various probabilistic models of spatial projection of the biomass carried out.

The spatial distribution in terms of biomass and probability of occurrence of the three main species of small pelagic fish (anchovy -Engraulis encrasicholus-, sardine –Sardina pilchardus– and alacha –Sardinella aurita-) on the Iberian continental shelf within the geographical subarea (GSA) 06, and particularly within the SPA ES0000512, has been evaluated.

Diet

From photographs of fattening of the three species of terns, the use by the birds of the fishing discards and the analysis of regurgitated chicks, a very detailed analysis of the diet of each of the species has been carried out. The results have made it possible to quantify, qualitatively and quantitatively, the diet of these species, in order to relate it to the amount of food available in the environment, calculated from the estimates of biomass in the sea, the biomass extracted by the fishing fleet and the discards contributed.