Use noise aversive conditioning to deter mammals from fishing gear
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Aversive conditioning is the process of associating a negative stimulus with a secondary behaviour or outcome. For this intervention, it involves associating a negative stimulus (a loud startling sound) with a neutral one (a non-startling sound) when marine and freshwater mammals are carrying out undesirable behaviour (predating on fish catches) to the extent that the neutral stimulus alone deters this behaviour. This may reduce the risk of mammals becoming entangled or captured in fishing gear. Mammal predation on fish catches may also decrease, which may reduce human-wildlife conflict at wild fisheries. The study summarised below tested the effects of the first step of this approach only, i.e. pairing a negative stimulus with a neutral one.
Supporting evidence from individual studies
A controlled study in 2013–2014 of five pelagic areas in the North Pacific Ocean, off the coast of California, USA (Schakner et al. 2017) found that attempts to condition California sea lions Zalophus californianus to avoid fishing lines by pairing a ‘startle’ sound with a ‘neutral’ sound did not reduce bait foraging behaviour. Playing ‘startle’ sounds alone reduced sea lion bait foraging behaviour by 83% and sea lions surfaced three times further from fishing vessels compared to when no sounds were played (data reported as statistical model results). However, there was no significant difference in sea lion behaviour when ‘startle’ sounds were played after a ‘neutral’ tone. Commercial passenger fishing vessels carried out fishing stops (each 0.1–2 h) across five areas with sounds played back through an underwater speaker (98 stops) or with no sounds (48 stops). Sounds were either a ‘startle’ pulse (200 ms of white noise at 10–11 kHz) or a ‘startle’ pulse played 2 seconds after a ‘neutral’ tone (6-second tone at 1–2 kHz with a 1.5 second long fade-in). Sound treatments were randomly selected during each fishing stop. Two observers on board each of the fishing vessels recorded bait foraging (sea lions taking bait from fishing lines during at least 50% of the time spent fishing) and distances of surfacing sea lions from vessels during each of the 146 fishing stops in May–September 2013 and 2014.Study and other actions tested