Effects of Underwater Sounds on Escape Behavior of Steller Sea Lions

Akamatsu Tomonari, Nakamura Koji, Nitto Hiroshi, Watabe Mitsuru

doi:10.2331/fishsci.62.503

The reactions of 10 captive Steller sea lions Eumetopias jubatus, including one adult male, four adult females and five juvenile animals to underwater sounds, with and without the presence of a baited fishing net, were observed. Two narrow spectrum sounds, an 8 kHz pure tone and a 1 kHz to 4 kHz frequency sweep, three broad spectrum sounds, two mechanically generated impulse sounds, and the recorded vocalization of a killer whale were used. The reactions of Steller sea lions were divided into three categories. Category Ο: Both adult and juvenile Steller sea lions landed on a side of their pool during a one-minute period timed from the start of the sound projection. Category Δ: More than two juvenile Steller sea lions landed. Category ×: A single juvenile Steller sea lion or no animals landed.<br> Impulsive sounds transmitted at high source level (210 dB re 1 μPa at 1m) or pure tone sounds(165 dB source level) were found to repel adult Steller sea lions. Broad band spectrum sounds did not repel adult and juvenile Steller sea lions after successive sound projections.<br> The male Steller sea lion was only deterred from eating the fish entangled in the net by the high source level impulsive sound.<br> The acoustic characteristics required to repel Steller sea lions are thought to be narrow spectrum with-in the sensitive range of a Steller sea lion's audible frequency and above 165 dB sound pressure level. However, Steller sea lions appear to acclimatize to repeated sound projections, and a sound pressure level below 165 dB does not appear to be enough to repel Steller sea lions from a fishing net.

Effects of Underwater Sounds on Escape Behavior of Steller Sea Lions

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