Deep / shallow setting

Deep setting is a longline fishing technique where hooks are set below a critical depth, out of range of most bycatch species, but within the range that target species are usually captured. In early trials at sea, deep setting was shown to decrease bycatch of sea turtles, however, subsequent research has challenged these findings [2]. Deep-set buoy gear has been trialed recently in a US swordfish fishery.
 
'Set Your Longline Deep' outlines the technical details of adopting this fishing technique. Deep setting uses a longline boat's existing gear with some slight modifications.
 
Recent trials of deep-set buoy gear in a swordfish, Xiphias gladius, fishery have had good results when the gear has been set during daytime, rather than nocturnally - see Sepulveda et al 2019.
References
  1. Beverly, S. 2004. New deep setting longline technique for bycatch mitigation. SeaNet report number R03/1398. Noumea, New Caledonia: Secretariat of the Pacific Community.
  2. Miller, P. and Domingo, A. 2014. Update on sea turtle bycatch on deep set pelagic longlines in Uruguayan Waters.
  3. Sepulveda CA, Aalbers SA (2018) Exempted Testing of Deep-set Buoy Gear and Concurrent Research Trials on Swordfish, Xiphias gladius, in the Southern California Bight. MFR 80:17–29. doi: 10.7755/MFR.80.2.2
  4. SPC. 2005. Set your longline deep:  Catch more target fish and avoid bycatch by using a new gear design.