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Delta del Ebro / Columbretes - March Campaign - Submón/Fundación Biodiversidad

Bajando el sonar ©Submon

SUBMON is undertaking the project “Complementary activities to the LIFE+ INDEMARES inventory of sea turtles and cetaceans in the three marine areas proposed by the Natura 2000 Network in the North-west Mediterranean” as part of the Fundación Biodiversidad’s call for grants. As its name suggests, this project is not to be found within the LIFE+ INDEMARES project, but its studies are conducted in three of the INDEMARES areas so as to complete the scientific information necessary for their inclusion in the Natura 2000 Network.

Two campaigns in different fields have been undertaken, using acoustic technology as the chief research tool in both cases. On the one hand, a study of cetaceans was begun by means of passive acoustic monitoring; and on the other hand, a study of turtles was carried out using side scan sonar.

Turtle campaign in the Ebro Delta

The importance of this area for sea turtles in the warm months of spring and summer has long been known, through direct sightings of specimens, beaching of dead animals or accidental catches by local fishermen. However, data from transmitters attached to loggerhead sea turtles in other studies and the beaching of dead animals in winter suggest that the Ebro Delta may be an important area for this species in winter too.

In February and March 2010, with the aid of high-frequency side scan sonar, a comprehensive survey of the bay was conducted using a systematic sampling design that followed a pattern of parallel transects and closed transects. The sonar sends sound at continuous high frequency (various frequencies were used, up to 900 kHz) and receives the echo in real time. This is interpreted by the control unit and transformed into a “sonogram”, in which shapes and textures of the seabed may be perceived (according to the intensity of the echo received) in high definition. In this way a highly detailed image is generated of the entire bed of the water mass being surveyed, making it possible to “see” objects under the surface. This was the first time this technique was used in the study of turtles under water and has been very useful in studying large areas. As this is a study with a significant experimental component, a series of calibrations and trials was carried out (soundings and identification of different known objects), which allowed the technique to be refined. It is now available for fresh studies in other areas and for establishing its optimisation criteria.

Cetacean campaign in the off-shore area

The monitoring of cetaceans by means of acoustic recording is an emergent discipline, but despite certain limitations it proves very helpful for the purposes of making inventories and discovering seasonal patterns and use of habitat on the part of some species.

With this aim, an EAR (Ecological Acoustic Recorder) has been anchored in the area of the Columbretes Delta where the continental shelf ends, at a depth of 350 metres. The device will be left anchored for three months, during which time it will constantly record at a programmed time and frequency. Subsequently, the probe will be collected, thanks to an acoustic release system that will allow it to rise to the surface. Then the data will be analysed in search of cetacean sounds, particularly those of the rorqual and the sperm whale.

The results will be contrasted and compared with similar studies conducted previously, allowing us to discover the seasonal patterns of the common rorqual in the area, as well as the presence of sperm whales.

Sónar de baja frecuencia ©Submón
Bajando el sónar al mar para la toma de datos ©Submón