Impacts of shipping underwater radiated noise on the behavior of aquatic animals

Roee Diamant, Dept. of Marine Technologies. Aviad Scheinin, The Morris Kahn Marine Research Station. University of Haifa.

 

  • Aquatic animals rely on underwater sound for critical life functions such as localization, communication, foraging, and mating.
  • With the significant increase in human marine activity, our seas have become populated with boats and ships that project high-powered underwater radiated noise (URN) that propagate over large areas up to 20 square kilometers.
  • The effects of shipping URN on animals’ behavior include communication disorders, loss of navigation capability, and decreased foraging activity.
  • Current investigations are biased towards physiological impacts, and a systematic study for the accumulated effects of shipping URN on the behavior of aquatic species has not yet been performed.
  • The main goal of our project is to quantify the impacts of shipping disturbance on the behavior of the Bottlenose dolphin (Tursiops truncatus). 
  • This species occurs in almost all tropical and temperate regions and can be found in coastal and offshore waters. 
  • Their extensive range of distribution makes them ideal representatives for this study, as they exhibit plasticity in their choice of habitat and can migrate to another environment in case of a strong disturbance - like sound. 
  • Dolphin vocalization served as a proxy for behavioral implications. For example, no clicks and many whistles are characteristic of social behavior, while low-frequency clicks typically indicate navigation or traveling, and high frequency indicates foraging activity. However, statistical comparison of passive acoustic recordings and shipping URN has never been explored. Thus, we could not determine the dolphin’s vocalization characteristics that reflect behavioral changes.
  • Considering this, in our project, we compare dolphin whistles emitted in and without the presence of vessels. These will include the signal’s duration, bandwidth, maximum and minimum frequency, curving up, curving down, symmetrical shape characteristics, and signal strength variance across the bandwidth. 
  • This pilot project was completed near the Dolphin Reef in Eilat, which houses four bottlenose dolphins in the facility. 
  • Four hydrophones were set on the bottom nearby simultaneously sampled at 96kHz and we recorded continuously for a month. Two one-month deployments took place.
  • The analysis focused on 3 elements:
  1. Detection and characterization of dolphin emissions (expected detection distance was 500 m).
  2. Detection and description of nearby vessels (expected detection distance was 5 km).
  3. Comparison of features in dolphin vocalization based on the existence of vessels.

The results showed that the dolphins alter their whistle production in the presence of vessel noise.  

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