Auditory detection of ultrasonic coded transmitters by seals and sea lions

Abstract

Ultrasonic coded transmitters (UCTs) are high-frequency acoustic tags that are often used to conduct survivorship studies of vulnerable fish species. Recent observations of differential mortality in tag control studies suggest that fish instrumented with UCTs may be selectively targeted by marine mammal predators, thereby skewing valuable survivorship data. In order to better understand the ability of pinnipeds to detect UCT outputs, behavioral high-frequency hearing thresholds were obtained from a trained harbor seal (Phoca vitulina) and a trained California sea lion (Zalophus californianus). Thresholds were measured for extended (500 ms) and brief (10 ms) 69 kHz narrowband stimuli, as well as for a stimulus recorded directly from a Vemco V16-3H UCT, which consisted of eight 10 ms, 69 kHz pure-tone pulses. Detection thresholds for the harbor seal were as expected based on existing audiometric data for this species, while the California sea lion was much more sensitive than predicted. Given measured detection thresholds of 113 dB re 1 μPa and 124 dB re 1 μPa, respectively, both species are likely able to detect acoustic outputs of the Vemco V16-3H under water from distances exceeding 200 m in typical natural conditions, suggesting that these species are capable of using UCTs to detect free-ranging fish.

Grey seals use anthropogenic signals from acoustic tags to locate fish: evidence from a simulated foraging task

“…Similarly, tagged predator species may experience a decrease in foraging success. Acoustic tags are becoming more widely used on sharks [ 30 – 32 ] and could make them more detectable by prey species such as seals [ 16 ]. Even recently published reports of acoustically tagged seals meeting at sea [ 33 ] could be caused by a tag attraction effect, as the tags used produced sounds similar to the fish tags used in the area.…”

“…In an experimental study, sensitivity thresholds for a Vemco 69 kHz fish tag signal were measured and used to estimate detection distances for a harbour seal ( Phoca vitulina ) and California sea lion ( Zalophus californianus ). Both species were found to be capable of detecting the signal (source level of 165 dB re 1 µPa) at simulated distances of greater than 200 m [ 16 ].…”

Beat Keeping in a Sea Lion As Coupled Oscillation: Implications for Comparative Understanding of Human Rhythm

“…Following data collection for Cook et al ( 2013 ), Ronan received intermittent “practice” sessions (typically no more than one per week) with familiar simple stimuli and several novel musical stimuli. During this time, Ronan also participated in several other cognitive and perceptual studies unrelated to rhythm (Reichmuth et al, 2013 ; Cunningham et al, 2014a , b ; Cook et al, 2015 ; Cunningham and Reichmuth, 2016 ).…”

Predator-prey interactions between harbor seals and migrating steelhead trout smolts revealed by acoustic telemetry

“…Thus far, 'association studies' have not revealed evidence of predation by pinnipeds on any fish species and detection rates have generally been quite low. Recent work has shown that harbor seals in particular can hear the sound generated by Vemco 69 kHz tags (Cunningham et al 2014), and they can learn to associate the sound from the tags with food in a laboratory setting. This raises the question of whether the sound of the tag rings a 'dinner bell' that puts tagged fish at greater risk of predation (Stansbury et al 2015).…”