WHAT THE EVIDENCE SAYS
In a field experiment using a dummy bottom-set gillnet, researchers filmed and recorded harbour porpoises approaching the net with and without an acoustic alerting device. Animals often crossed above the float line and avoided direct contact at observed distances of roughly 0.8–16.4 m; speed, breathing and echolocation changed little.
WHY IT MATTERS / OUR READ
Bycatch prevention may need to improve how animals choose evasive paths, rather than only making a net detectable. An audible signal is not evidence that a dangerous encounter has been prevented.
CAVEATS / UNCERTAINTY
A dummy net under observation is not an operational catch trial. The experiment did not measure real-world bycatch reduction or all commercial net configurations.
SOURCE
Journal of Applied Ecology · harbour porpoise field experiment
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