Decoys

Shark decoys have been shown to work as sea turtle 'scarecrows', though these decoys also frightened-off target finfish species (tunas, billfish, mahi-mahi). However, there remains potential to develop decoys which maintain target species catch rates while deterring sea turtles from approaching baited longline hooks.
 
In tank trials, shark shapes triggered an innate flight response in captive-bred sea turtles that had not been exposed to sharks or other predators. In more recent at-sea trials, shark shapes reduced the number of turtles caught on nets.
 
Research is required to identify the shark characteristics most repulsive to sea turtles. It has been suggested that, for example, adding motion or sound may make the decoy appear more lifelike.
 
Exploiting the difference in visual systems between turtles and tunas (and other commercially important fish species such as billfish and mahi-mahi) may be a way to decrease turtle bycatch while maintaining target species catch. Turtles can see into the ultraviolet light (UV) spectrum while tunas etc can't. For example, by constructing decoys from transparent, UV-absorbent plastic, shark shapes may appear as black silhouettes and trigger avoidance behaviors in sea turtles while remaining transparent and undetected by target fish species.
References
  1. Southwood, A., Fritsches, K., Brill, R. and Swimmer, Y. 2008. Sound, chemical, and light detection in sea turtles and pelagic fishes: sensory-based approaches to bycatch reduction in longline fisheries. Endangered Species Research 5: 225-238.
  2. Swimmer, Y., and Brill, R. (eds.). 2006. Sea Turtle and Pelagic Fish Sensory Biology: Developing Techniques to Reduce Sea Turtle Bycatch in Longline Fisheries. NOAA Technical Memorandum NOAA-TM-NMFS-PIFSC-7.
  3. Swimmer, Y. and Wang, J.H. (eds). 2006. Sea Turtle and Pelagic Fish Sensory Physiology Workshop. NOAA Technical Memorandum NOAA-TM-NMFS-PIFSC-12.
  4. Wang, J.H., Fisler, S. and Swimmer, Y. 2010. Developing visual deterrents to reduce sea turtle bycatch in gill net fisheries. Marine Ecology Progress Series 408: 241-250.