Rebecca Pond B.S., Katie Starke B.S., Sara Tremblay B.S.
Department of Animal Science, University of Connecticut
In an effort to determine the integrity of the Beluga Whale exhibit at Mystic Aquarium, we measured the sound levels of potentially damaging background noise using a specialized hydrophone and recorder. Results indicate that the intensity of the noise for a wide range of frequencies is not detrimental to the animals’ well being.
One of the dilemmas involved in keeping beluga whales in captivity is the effect of external sound on their confined lifestyle. All aquaria use machinery like pumps and motors that produce various background levels of noise. This abiotic noise, coupled with pool architecture, structural material, and bottom type all impact and determine the ambient noise level of the whales’ habitat. When judging the well-being of beluga kept in a maintained pool, one must consider the acoustic properties of the exhibit to determine if the animals are being exposed to any interfering and potentially damaging sounds.
In this study, we examined the soundscape in the beluga whale holding pool in Mystic Aquarium. This soundscape included the combined sound of the living organisms and the geophysical sounds of the environment, as well as any human-generated mechanical sounds. Our goal was to use the intensity levels of various measured frequencies to identify possible introduced elements that could cause stress or change in the animals’ lifestyle otherwise unnoticed by traditional evaluation techniques.
MATERIALS & METHODS
Noise recordings were made using an Aquarian hydrophone, a preamplifier and a Sony TCD-D8 Digital Audio tape recorder. The Aquarian hydrophone has a flat free-field sensitivity of 120v, and a frequency range of 100Hz to 12,000Hz, flat to 8,000 Hz. Recordings were made on a Sony TCD-D8 digital audio (DAT) tape recorder with a 48,000 Hz sampling frequency and 16-Bit linear quantization. The TCD-D8 recorder had a flat frequency response from 20 Hz to 20,000 Hz. The total recording was 210 minutes in duration. The recordings were edited and then previewed on a PC using ATSpec Pro (Taquis Corp.). Acoustic recordings were taken using a single Aquarian Hydrophone. The hydrophone was attached to the gate between the beluga holding pool and the main exhibit pool (Fig. 1). Recordings were taken for 210 minutes. Using ATSpec Pro, ten one-minute samples were cut from the original recording. Only samples that did not include beluga vocalizations were selected. Peak recordings for each sample were taken at 100 Hz, 500 Hz, 1000 Hz, 5000 Hz, and 10000 Hz. Various peaks for each one-minute sample were also taken. Upon completion of spectral analyses of the noise from each sample, the mean intensity level for each frequency (100 Hz, 500 Hz, 1000 Hz, 5000 Hz, and 10000 Hz) was calculated.
The overall mean noise levels were calculated as marginal means (Fig. 2). Frequency is on the x-axis and is measured in Hertz and the mean dB re 1µpa is on the y-axis. At 100Hz the mean noise level is 75.946dB re 1µpa. At 500Hz the mean noise level is 84.528dB re 1µpa. At 1000Hz the mean noise level is 71.48dB re 1µpa. At 5000Hz the mean noise level is 40.042dB re 1µpa. At 10000Hz the mean noise level is 36.177dB re 1µpa. The greatest intensity levels re 1µpa occurred at 500Hz, 1000Hz, and 100Hz. The lowest intensity levels occurred at 5000Hz and 10000Hz (Fig. 3).
Normally we should see the lowest frequency with the highest intensity, but we do not. 500Hz is greater than 100Hz. This is probably due to the hydrophone being attached to gate that divides the main pool from the holding pool, and the gate movement was emitting high frequency noise.
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