Abstract: Little is known of the sounds produced by bottlenose dolphins (Tursiops truncatus) along the coast of Uruguay, South America. The small population that inhabits the Atlantic Uruguayan coast has been estimated at approximately 40 individuals, with a substantial decrease in occurrence in the estuarine coast of Uruguay over the last two decades. A total of 4,152 whistles and 409 clicks were recorded from free-ranging bottlenose dolphins in five locations along the Atlantic coast of Uruguay with five Passive Acoustic Monitoring (PAM) buoys. Bottlenose dolphins emitted a varied repertoire of whistles. They were categorised as ascending in their contour pattern as the most common, corresponding to 44% of all whistles, whereas multi-looped (more than one inflection point) represented 23%. Ascending-descending (12%) and descending (8.1%) whistles were also frequently documented, while descending-ascending (7.5%) and constant (5.5%) whistles were less frequent. Whistles recorded had a wide frequency range, between 1.6 and 22.4 kHz, and whistle duration was 628 ± 293 ms. Click train duration had a mean of 1,105 ± _59.6 ms, and the mean click number per train was 11.4 ± _1.64. Mean click duration was 63.2 ± _4.06 μs, and the interclick interval was 129.4 ± _3.94 ms. Click trains had a mean peak frequency of 52.02 ± 12.09 kHz. Overall, bottle-nose dolphins seemed to be more vocal during the summer months, and declined in vocalizations during the winter months. Whistles showed strong seasonal variability associated with fluctuation in sea surface temperatures (SST). During the winter and early spring (SST < 15° C), the average number of whistles was low. Coincident with water temperatures warming from 16º to 20º C in mid-spring and early summer, the average number of whistles increased to reach maximum values in summer. Meanwhile, a decreasing trend in whistle numbers was found in late summer (N = 1,279) and early autumn (N = 660). In autumn, the water temperature decreased, and the average number of whistles dropped sharply. This study provides the first description of the acoustic characteristics of bottlenose dolphins on the coast of Uruguay, which also assists conservation management efforts for this species that is disappearing from the Uruguayan coast.
Key Words: tonina, whistles, clicks, bottlenose dolphin, Tursiops truncatus, southwestern Atlantic Ocean
Document Type: Research article
DOI: 10.1578/AM.40.2.2014.173
Page Numbers: 173-184