First acoustic detection of franciscana dolphin (Pontoporia blainvillei) in Mar del Plata coast, Argentina

GISELA V GIARDINO; GIUSEPPA BUSCAINO; ELENA PAPALE; MARIA CERAULO; RICARDO O. BASTIDA; DIEGO H. RODRIGUEZ

Palm Beach, Florida

Congreso; 24th BIENNIAL CONFERENCE ON THE BIOLOGY OF MARINE MAMMALS; 2022

The Society for Marine Mammalogy

Franciscana dolphin (Pontoporia blainvillei) is the most affected dolphin species in the Southwestern Atlantic Ocean. It is classified as Vulnerable A3D by IUCN and SAREM (national level) and only in northern coast of Argentina (Buenos Aires Province) around 400 dolphins are entangled every year in coastal gillnets. However, until now little is known about the operation of Franciscana echolocation systems during entanglenments, so more studies need to be carried out to improve possible conservation solutions. Passive acoustics could be a good tool to study the presence of Franciscana in a given area. Franciscana is characterized by a cryptic behavior and it is known to produce narrowband high-frequency (NBHF) pulsed signals with a peak frequency of 130kHz which may be lower in juveniles and calves. Therefore, two passive acoustic loggers (F-PODs; Chelonia Limited) were deployed 100 m apart to record cetacean activity in a marine coastal area of Buenos Aires Province with the aims of studying the acoustic presence of the Franciscana dolphins and to identify possible circadian rhythms in relation with environmental variables. Two acoustic detectors was located at a depth of between 5 and 7 meters during the summer months of 2020 and 2021. We collected a total of 1485 hours of recordings. On 29% of the days recorded, we detected high frequency and narrow band click trains compatible with those emitted by the Franciscana dolphins. Positive detection of NBHF clicks showed a significant relationship with atmospheric pressure, temperature, and the percentage of bottom sediments noise. However, no hourly preference patterns were evidenced, as well as the solar inclination associated with underwater luminosity. These first results show us the potential importance of passive acoustics as a complementary tool to improve conservation regulations of this Vulnerable dolphin.