Southern Stingray Photo by Hilary Jaffe
In 2019, Mickle et. al studied 20 different Southern stingrays (Hypanus americanus) in the waters surrounding the Bimini Biological Field Station. They placed underwater speakers in the pen with the stingrays and using a Sony Walkman, they played 5 different low frequency tones.
The 9 males and 11 females were tested individually and were exposed to 5 sound frequencies- 50Hz, 90Hz, 200Hz, 500Hz, and 1000HZ. Using a hydrophone they measured the sound level (in decibels) at 27 different locations inside the stingray’s enclosures.
Since a sound threshold for the rays was previously unknown, they started with 140dB , then depending on the stingray’s swimming behavior** , the sound was increased or decreased by 10dB or 5dB respectively making the levels tested- 130dB, 135 dB, 140dB, 150dB, and 160 dB.
What they found was both male and female stingrays exhibited behavioral differences. The average tone males responded to was 160dB while females responded more to 140dB.
With regard to frequency, males swimming activity increased at 50Hz, 90Hz, 200Hz, and 500 Hz and the females increased their activity at 50Hz, 90Hz, 200Hz, and 1000Hz.
The study looked at the following stingray behaviors- surface breaches, time spent resting, and side-swimming. Both males and females had significant increases in breaching events at 50 Hz, 90 Hz, and 200Hz. Resting rates for males and females decreased at 50Hz, 90Hz, and 200Hz and 50Hz, 90 Hz, 200Hz, and 500Hz respectively. At frequencies of 50Hz, 90 Hz, 200Hz, and 500Hz, both males and females showed increased rates of side-swimming.
If you would like to read their full article, you can find it here.
Mickle, Megan F et al. “Field assessment of behavioural responses of southern stingrays (Hypanus americanus) to acoustic stimuli.” Royal Society open science vol. 7,1 191544. 22 Jan. 2020, doi:10.1098/rsos.191544
** Animal trainers use similar observation to determine their animals level of enrichment and engagement.