Each of the methods of fishing outlined is known to be responsible for the incidental catching of a large number of turtles. By-catch is the incidental capture of species other than those specifically targeted.
Long term studies on the incidental catching of turtles on long lines has shown that, though some turtles may be incidentally snagged on the hooks, most are hooked in the oesophagous, stomach or mouth as they swallow the fish bait. This is usually mackeral Scomber scombrus or Scomber japonicus or flying squid (Todarodes sagittatus) (Muntingh 1988; Panou 1988). It is likely that this mostly affects Caretta caretta.

Three fishing hooks and line found in the oesophagous of a stranded loggerhead turtle: the cause of death to the stranding.
Photo: C.Morris 1996 - Kefalonia