Circumglobal, in tropical and subtropical waters
Longlines, gillnets, trawls, traps and pots, and dredges
The main cause of the decline of loggerhead turtles, and the current primary threat to global populations is bycatch in longlines, gillnets, trawls, traps and pots, and dredges. Loggerhead can be hooked in the mouth or another part of their body when trying to consume bait, entangled in gillnets or ropes, or caught in a trawl or dredge. Longlines, gillnets, and trawls are responsible for the majority of sea turtle bycatch events around the world (Wallace et al, 2010). Commercial longlines incidentally caught an estimated 200,000 loggerhead turtles in 2000 (Lewison et al, 2004). At the same time, small-scale, coastal fisheries may have an even larger impact, but incidents are not well recorded. In one study, researchers found that loggerheads were caught in very high numbers (1,500 to 2,950 per year from 2003 to 2007) in gillnet and bottom-set longline fisheries in Baja California Sur, Mexico.
There are several fishing gear modifications that have had varying degrees of success for reducing sea turtle bycatch. In hook and line fisheries, the circle hook has replaced traditional J-hooks, and has been shown to reduce loggerhead capture and increase post-release survival. Turtle excluder devices (TEDs) have been successful in preventing the capture of sea turtles in trawls. Other devices and techniques include: changing the configuration of gillnets, introducing novel bait species, adding chain mats, and putting in trap guards.
Wallace, BP, RL Lewison, SL McDonald, RK McDonald, CY Kot, S Kelez, RK Bjorkland, EM Finkbeiner, S Helmbrecht, and LB Crowder. 2010. Global patterns of marine turtle bycatch. Conservation Letters 3: 131-142.
Lewison, RL, SA Freeman, and LB Crowder. 2004. Quantifying the effects of fisheries on threatened species: the impact of pelagic longlines on loggerhead and leatherback sea turtles. Ecology Letters 7(3): 221-344.
Peckham, SH, DM Diaz, A Walli, G Ruiz, LB Crowder, and WJ Nichols. 2007. Small-scale fisheries bycatch jeopardizes the endangered Pacific loggerheads. PloS ONE 2(10).