The incidental catch of sea turtles is a big issue in commercial longline fisheries. Some scientists estimate that every year fishing lines ensnare over a quarter of a million sea turtles. One way to decrease sea turtle by-catch is to change the type of hook and bait used on fishermen’s lines. The most popular type of hook employed is the J hook or Japanese tuna hook. However, if fishermen adopted the circle hook, it would both reduce capture rate and post-release mortality for sea turtles. Circle hooks have barbs that are pointed back towards the shaft of the hook and are wider than the J hooks.
Why would a fisherman want to switch tactics to help sea turtles? Circle hooks catch fish on the side of the mouth allowing fish to stay alive longer which equals a higher quality product. With circle hooks being larger than J hooks, they often increase the size and quaintly of the targeted catch by up to 30%. If you think it would be costly to switch to circle hooks, you’re wrong, as longline hooks are routinely replaced and the cost difference is negligible.
A recently published paper investigated the effects of changes in hook and bait type in the swordfish industry of the Southern Atlantic Ocean (Santos et al. 2013). Overall, the study shows that when circle hooks were baited with mackerel bait, rather than squid, sea turtle catches decreased by 87.5% and 100% for loggerheads and leatherbacks, respectively. Between the two sea turtle species caught, loggerheads were far more likely to be caught than leatherbacks no matter the hook type. Loggerheads had a higher chance of swallowing the J hook and it catching on their esophagus, but if caught with the circle hook it was hooked near its jaw. Leatherbacks were almost exclusively hooked on their flipper with all hook types, which is mainly due to differences in feeding behavior.
This is all good news, but something to keep in mind is the novelty of these circle hooks. Parga (2012) suggest an uncertainty regarding the benefits of loggerheads being hooked on the mouth rather than in the esophagus. She argues that while being hooked in the mouth is generally considered low risk, there are sensitive parts. But the esophagus is a strong muscular wall that, unless the hook is lodged near the heart or large blood vessels, can withstand such lesions.