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Anthropogenic noise and its impact on bottlenose dolphin (Ttursiops Truncatus) distribution in the Lošinj dolphin reserve (Croatia)

The primary source of the sea ambient noise (SAN) is sea traffic, which dominates the range of low frequencies (10-1000 Hz). This is especially so in areas with strong nautical tourism. The Lošinj Dolphin Reserve is an important area for nautical tourism, located in the northern Adriatic, Croatia. This study aims to assess the extent of the anthropogenic pressure in the Reserve, looking at the relationships between boat traffic and underwater noise, and their relationship with bottlenose dolphin distribution. SAN was made sampled on 10 acoustic stations, between November 2004 and October 2005, within the Reserve by using a Reson TC4032 hydrophone and Pioneer DC-88 DAT recorder. Cool Edit and Matlab software were used to calculate the average Root mean square (RMS) value (intensity of the energy of each acoustic sample, in relative dB), and to obtain octave bands analyisis for each acoustic sample. Recordings of noise, and data on vessel presence were compared to the spatial distribution of bottlenose dolphins’ groups collected in the same period. Results show a clear correlation between the areas of high anthropogenic pressure, and strong dolphin avoidance. This was particular so on the ‘boat highways’ within the Reserve, and during the summer months. Data collected on vessel presence indicates how this dolphin displacement can be attributed to a significant seasonal increment in the number of very fast and noisy vessels, such as motor cruisers, and medium or large speed boats, with high powered engines. This study shows the existence of a direct link between anthropogenic noise and traffic on the habitat use of the Kvarneric bottlenose dolphin population. Moreover, it is demonstrated that the SAN is a good indicator of anthropogenic impact due to the presence of sea traffic.

sea ambient noise; acoustics; vessels; anthropogenic noise

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