YeonJoon Cheong – yjcheong@umich.edu
K. Alex Shorter – kshorter@umich.edu
Bogdan-Ioan Popa – bipopa@umich.edu
University of Michigan, Ann Arbor
2350 Hayward St
Ann Arbor, MI 48109-2125

Popular version of 2pAB4 – Acoustic scene modeling for echolocation in bottlenose dolphin
Presented Tuesday Morning, November 30, 2021
181st ASA Meeting
Click here to read the abstract

Dolphins are excellent at using ultrasound to discover their surroundings and find hidden objects. In a process called echolocation, dolphins project outgoing ultrasound pulses called clicks and receive echoes from distant objects, which are converted into a model of the surroundings. Despite significant research on echolocation, how dolphins process echoes to find objects in cluttered environments, and how they adapt their searching strategy based on the received echoes are still open questions.

Fig. 1. A target discrimination task where the dolphin finds and touches the target of interest. During the experiment the animal was asked to find a target shape in the presence of up to three additional “distraction” objects randomly placed in four locations (red dashed locations). The animal was blindfolded using “eye-cups”, and data from the trials were collected using sound (Dtag) and motion recording tags (MTag) on the animal, overhead video, and acoustic recorders at the targets.

Here we developed a framework that combines experimental measurements and physics-based models of the acoustic source and environments to provide new insight into echolocation. We conducted echolocation experiments at Dolphin Quest Oahu, Hawaii, which consisted of two stages. In the first stage, a dolphin was trained to search for a designated target using both vision and sound. In the second stage, the dolphin was asked to find the designated target placed randomly in the environment in the presence of distraction objects while “blind-folded” using suction cups, Fig. 1. After each trial, the dolphin was rewarded with a fish if it selected the correct target.
Target discrimination tasks have been used by many research groups to investigate echolocation. Interesting behavior has been observed during these tasks. For example, animals sometimes swim from object to object, carefully inspecting them before making a decision. Other times they swim without hesitation straight to the target. These types of behavior are often characterized using measurements of animal acoustics and movement, but how clutter in the environment changes the difficulty of the discrimination task or how much information the animals gather about the acoustic scene before target selection are not fully understood.
Our approach assumes that the dolphins memorize target echoes from different locations in the environment during training. We hypothesize that in a cluttered environment the dolphin selects the object that best matches the learned target echo signature, even if it is not an exact match. Our framework enables the calculation of a parameter that quantifies how well a received echo matches the learned echo, called the “likelihood parameter”. This parameter was used to build a map of the most likely target locations in the acoustic scene.

During the experiments, the dolphin swam to and investigated positions in the environment with high predicted target likelihood, as estimated by our approach. When the cluttered scene resulted in multiple objects with high likelihood values, the animal was observed to move towards and scan those areas to collect information before the decision. In other scenarios, the computed likelihood parameter was large at only one position, which explained why the animal swam to that position without hesitation. These results suggest that dolphins might create a similar “likelihood map” as information is gathered before target selection.
The proposed approach provides important additional insight into the acoustic scene formulated by echolocating dolphins, and how the animals use this evolving information to classify and locate targets. Our framework will lead to a more complete understanding of the complex perception procedure used by the echolocating animals.

Krista Trounce, krista.trounce@portvancouver.com
Vancouver Fraser Port Authority
999 Canada Place, Vancouver, British Columbia, V6C 3T4

Popular version of 4aAB7 – Managing vessel-generated underwater noise to reduce acoustic impacts to killer whales
Presented at the 181st Acoustical Society of America Meeting at 10:40 AM PST on Thursday, December 2, 2021
Click here to read the abstract

Every year, thousands of ships en route to Canada’s largest port, the Port of Vancouver, transit through the Pacific Ocean’s richly biodiverse Salish Sea, home to a vast array of marine life including the endangered Southern Resident killer whale.

As Southern Resident killer whales rely on sound to survive, underwater noise from commercial ships can interfere with their ability to hunt, navigate, and communicate, which is why both the Canadian and U.S. governments recognize “acoustic disturbance” as one of the key threats to the species’ recovery.
To better understand and reduce the effects of vessel-generated noise on local whale populations, the Vancouver Fraser Port Authority launched the Enhancing Cetacean Habitat and Observation (ECHO) Program in 2014. The ECHO Program coordinates research projects to advance our understanding of underwater vessel noise and since 2017, has led seasonal initiatives encouraging ships to slow down or stay distanced to reduce underwater vessel noise while transiting through Southern Resident killer whale foraging areas.

To achieve high levels of participation in its voluntary initiatives, the ECHO Program works closely with both Canadian and US marine transportation industry, vessel traffic management agencies and pilots and captains aboard commercial vessels. During the last two seasonal slowdowns, over 90% of piloted commercial vessels voluntarily reduced speed in Haro Strait and Boundary Pass, key areas of Southern Resident killer whale critical habitat. In-water measurements collected on behalf of the ECHO Program and the Government of Canada have shown that for the vast majority of ships plying the waters of the Salish Sea, reduced speeds result in measurable reductions in underwater noise generated both at the ship source, and in nearby whale habitats.
Hear the difference: Underwater sound from the same container ship operating at regular and reduced speeds

MP3: Container ship at regular speed (19.4 knots)*

MP3: Container ¬¬¬ship at reduced speed (10.6 knots)*

To date, more than 6,000 ships have participated in the ECHO Program’s voluntary underwater noise reduction initiatives, by either slowing down, or moving away from key areas, across 74 nautical miles of shipping routes in the Salish Sea. During the summer of 2020, these initiatives helped achieve a nearly 50% reduction in underwater sound intensity from commercial shipping, in key Southern Resident killer whale foraging areas.
The endangered Southern Resident killer whales face many challenges to their recovery, and underwater noise from vessel traffic is just one of these challenges. Through science-based decisions and regional collaboration, the ECHO Program partners are proving that voluntary efforts can help make a difference.

A killer whale (orcinus orca) nearby a commercial ship transiting through the Salish Sea, off British Columbia’s southern coast. (Photo credit: Joan Lopez)

A pod of killer whales (orcinus orca) travel nearby a commercial ship in pod formation. The southern resident killer population is made up of three matrilineal pods (J, K, L), which are led by the eldest female. (Photo credit: Joan Lopez)