Abstract
Marine mammal interactions with fisheries create conflicts that can threaten human safety, economic interests and marine mammal survival. A deterrent that capitalizes on learning mechanisms, like fear conditioning, may enhance success while simultaneously balancing welfare concerns and reduce noise pollution. During fear conditioning, individuals learn the cues that precede the dangerous stimuli, and respond by avoiding the painful situations. We tested the efficacy of fear conditioning using acoustic stimuli for reducing California sea lion Zalophus californianus interactions from two fishing contexts in California, USA; bait barges and recreational fishing vessels. We performed conditioning trials on 24 individual sea lions interacting with bait barges. We tested for acquisition of conditioned fear by pairing a neutral tone with a startle stimulus. Avoidance was strongest in response to the startle stimulus alone, but low when paired with a neutral tone. From actively fishing vessels, we tested for fear conditioning by exposing sea lions to a neutral tone followed by a startle pulse, a startle pulse alone or a no sound control. We conducted playbacks from 146 (including 48 no sound control) stops over two summer fishing seasons (2013, 2014). The startle stimulus decreased surfacing frequency, reduced bait foraging and increased surfacing distance from the vessel while the conditioned stimulus only caused a mild reduction in surfacing frequency with no other behavioral change. Exposing animals to a pair of a conditioned stimulus with a startle pulse did not achieve the intended management outcome. Rather, it generated evidence (in two study contexts) of immediate learning that led to the reduction of the unconditioned response. Taken together, our results suggest that for fear conditioning to be applied as a non‐lethal deterrent, careful consideration has to be given to individual behavior, the unconditioned/conditioned responses and the overall management goals.
Abstract
Autonomous reflexes enable animals to respond quickly to potential threats, prevent injury andmediate fight or flight responses. Intense acoustic stimuli with sudden onsets elicit a startle reflex while stimuli ofsimilar intensity but with longer rise times only cause a cardiac defence response. In laboratory settings,habituation appears to affect all of these reflexes so that the response amplitude generally decreases with repeatedexposure to the stimulus. The startle reflex has become a model system for the study of the neural basis of simplelearning processes and emotional processing and is often used as a diagnostic tool in medical applications.However, previous studies did not allow animals to avoid the stimulus and the evolutionary function and long-term behavioural consequences of repeated startling remain speculative. In this study we investigate the follow-upbehaviour associated with the startle reflex in wild-captured animals using an experimental setup that allowsindividuals to exhibit avoidance behaviour.Results:We present evidence that repeated elicitation of the acoustic startle reflex leads to rapid and pronouncedsensitisation of sustained spatial avoidance behaviour in grey seals (Halichoerus grypus). Animals developed rapidflight responses, left the exposure pool and showed clear signs of fear conditioning. Once sensitised, seals evenavoided a known food source that was close to the sound source. In contrast, animals exposed to non-startling(long rise time) stimuli of the same maximum sound pressure habituated and flight responses waned or wereabsent from the beginning. The startle threshold of grey seals expressed in units of sensation levels wascomparable to thresholds reported for other mammals (93 dB).Conclusions:Our results demonstrate that the acoustic startle reflex plays a crucial role in mediating flightresponses and strongly influences the motivational state of an animal beyond a short-term muscular response bymediating long-term avoidance. The reflex is therefore not only a measure of emotional state but also influencesemotional processing. The biological function of the startle reflex is most likely associated with mediating rapidflight responses. The data indicate that repeated startling by anthropogenic noise sources might have severeeffects on long-term behaviour. Future, studies are needed to investigate whether such effects can be associatedwith reduced individual fitness or even longevity of individuals.
Carnivore depredation on human livestock is a worldwide problem with few viable solutions. Non‐lethal management tools such as acoustic devices show highly varying success and often pose a conservation risk due to noise pollution and habitat degradation. We tested the long‐term effectiveness of a deterrence system which harnesses an autonomous reflex (startle) to selectively inflict avoidance responses in a target species (phocid seals) by emitting band‐limited noise pulses with sharp onset times. Seal predation was monitored at a marine salmon farm (test site) over a full production cycle (19 month) with a multi‐transducer deterrent system deployed for the final year. Predation was also monitored for several months at two control sites and additional short‐term tests were carried out at sites which suffered higher predation rates.
Carnivore depredation on human livestock is a worldwide problem with few viable solutions. Non‐lethal management tools such as acoustic devices show highly varying success and often pose a conservation risk due to noise pollution and habitat degradation. We tested the long‐term effectiveness of a deterrence system which harnesses an autonomous reflex (startle) to selectively inflict avoidance responses in a target species (phocid seals) by emitting band‐limited noise pulses with sharp onset times. Seal predation was monitored at a marine salmon farm (test site) over a full production cycle (19 month) with a multi‐transducer deterrent system deployed for the final year. Predation was also monitored for several months at two control sites and additional short‐term tests were carried out at sites which suffered higher predation rates.
