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Feature Article

Partnering with Commercial Shipping for Cetacean Research
Scientists Detect Marine Mammals by Deploying Passive Acoustic Recording System from Barge

By Alexis Rudd
Graduate Student
Dr. Whitlow W.L. Au
Chief Scientist
Marine Mammal Research Program
Hawaii Institute of Marine Biology
University of Hawai'i at Manoa
Kaneohe, Hawaii

Among the greatest challenges to cetacean research is that whales and dolphins are difficult to find and often dispersed over great distances. As a result, research cruises cover large areas with variable success locating animals along their route. Boats that are suitable for dealing with multiday deep-sea voyages are uncommon and can cost upwards of $10,000 per day to charter, making it difficult for researchers to obtain sufficient funding to study the distribution of marine organisms at ecologically significant intervals. As a result, these studies often occur infrequently or are focused on accessible areas. Such is the case in Hawaii, where cetacean surveying efforts are often sporadic or limited to the calm-water leeward sides of the islands.

The equipment used in this study, including the modified Ecological Acoustic Recorder.

Partnering with commercial shipping enterprises that make regular trips among ocean ports is one method of increasing cetacean survey coverage. Although platforms of opportunity have been used by researchers for some cetacean studies, most tend to rely on various visual observation methods. Visual detection of cetaceans decreases markedly with increasing wind and swell, making this method less useful in rough seas. Acoustic detection of cetaceans is less affected by sea state than visual detection and can actually increase detection rates for some species. The challenges of sea state and accessibility are particularly prevalent in the deepwater channels between the Hawaiian Islands.

Through a partnership with shipping company Young Brothers Ltd. (Honolulu, Hawaii), researchers at the Hawaii Institute of Marine Biology have created an acoustic recording system that allows them to detect cetaceans in the challenging working conditions of offshore Hawaiian waters.

Firstly, because this company makes more than 90 trips across each deepwater channel per year, there are ample opportunities to collect data. Secondly, since the barges are towed at approximately 1,500 feet from the tug, the amount of engine noise recorded by the hydrophone is minimized. In order to make an effective system, several changes needed to be addressed to existing array technologies.

Cetacean Acoustics
Acoustic recording methods can be extremely useful in rough waters. Because sound recordings are less affected by surface conditions, such as wind and swell, acoustic effort is a reliable source of survey data. Dolphins and whales use sound for communication, navigation and foraging. Sounds travel five times farther underwater than in air and can be used very reliably to locate animals for many miles. There can be a great deal of overlap between acoustic and visual detections for many cetacean species. For some, such as beaked whales, which spend a majority of their time underwater, acoustic methods may be more accurate for localization and density estimation.

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Alexis Rudd is a graduate student in zoology at the Hawaii Institute of Marine Biology and the University of Hawai'i at Manoa. Her research specializes in the use of sound to study the behavior and distribution of marine mammals and birds.

Dr. Whitlow W.L. Au is the chief scientist of the Marine Mammal Research Program at the Hawaii Institute of Marine Biology at the University of Hawai'i at Manoa. He is a former president of the Acoustical Society of America and the author of the book
The Sonar of Dolphins and senior author of Fundamentals of Marine Bioacoustics. He is also a former member of the Ocean Studies Board of the National Research Council.

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