The sea gives out the illusion of a serene place to either relax or work in. The tranquility of the sea depth is what most of us expect to hear and see. However, the open seas are realistically noisy and contaminated. Archipelagos Marine Mammal team is working to prove how noisy the Aegean Sea and the Icarian sea are. Specifically, our objective is to show a direct correlation between the difference in cetacean communication sounds and the increase in marine traffic in the waters around Samos using bioacoustics.
Bioacoustics is a multi-disciplinary science that combines biology and acoustics, thus referring to the investigation of sound production, dispersion and reception in animals. Massive human presence in the Mediterranean area and inadequate management of marine resources have become an avoidable threat to the survival of the cetaceans in this region. With the increase in trawlers (commercial fishing vessel) in the month of October, the sound pressure levels in and around the shipping routes are very likely to cause a traumatic effect on these gentle creatures. This makes the cetaceans adapt and modulate their frequency levels to those far from normal, hence disrupting their normal social behavior. Thus recent developments in the field of marine bioacoustics could provide information highly relevant to the conservation of cetaceans in the open seas.
The Marine Mammal Bioacoustics Team has developed strict protocols on monitoring and accumulation of viable data during our boat surveys. As we work towards recording the communication sounds of the resident cetaceans, we have adopted methods to avoid disrupting their natural behavior. During our boat surveys, we have collected many hours of recordings including different cetacean species. The data includes whistles, echolocation and the burst pulses from cetaceans, which are the primary sounds emitted during foraging, socializing and communication for cetaceans. Our project concentrates on the complex communication whistles, which include signature whistles from the resident cetaceans. These signature whistles are subjected to a constant frequency, and thus the disruption from marine traffic noise creates a stressful environment for individual identification. The multiple species of cetaceans recorded include the short-beaked Common Dolphin (Delphinus delphis), Striped Dolphin (Stenella coeruleoalba), Common Bottlenose Dolphin (Tursiops truncatus), Risso’s Dolphin (Grampus griseus), Cuvier’s Beaked Whale (Ziphius cavirostris) and the Sperm Whale (Physeter macrocephalus).
The added advantage of these recordings is accumulation of ambient ocean noise, which is louder than one would expect. We are in the process of analyzing the whistles and comparing the ambient noise two seconds prior to the emission of the individual whistle. Audacity, Raven pro and MATLAB are primarily used for sound analysis and data cleaning. The current data shows that the whistle range of the primary subjects (D. delphis and T truncatus) is 3 kHz to 23 kHz. The broadband frequency-modulated whistles from specific groups have been categorized along with the concurrent ambient noise data. These condition-specific frequencies will be useful for comparison with the data collected during the trawling season in order to understand how this human impacting activities can affect the presence of these extraordinary marine cratures.
Karthik Ashok, B.Tech, Electronics and Communication Engineering, VIT University, India