NOAA Fisheries Southeast Fisheries Science Center, Galveston, Texas
NOAA Fisheries conducted studies to test how deeply turtles take bait into their mouths using different sized hooks, different baits, and different baiting techniques. These studies were conducted using captive reared loggerhead turtles raised at the NOAA Fisheries sea turtle facility in Galveston, Texas. The studies were conducted by “fishing for turtles” with a short piece of monofilament line attached to a hook. The hooks were baited and presented to a sea turtle, and the turtle was allowed to take the bait. A score was given to each turtle as to how deeply the turtle takes the bait into its mouth. Some turtles deeply swallowed the hooks (see first turtle in video), and others only got the hook partially in their mouths (see second turtle in video). Results indicated that larger hooks lead to a lower incidence of deep hooking, and turtles are less likely to be deeply hooked if bait is threaded onto the hook versus single baiting. In addition, turtles are less likely to deeply swallow sardine baits than squid baits.
Experiments conducted by NOAA Fisheries in the Northeast Distant waters of the North Atlantic Ocean have shown that using larger-sized circle hooks in conjunction with using mackerel as bait have significantly reduced the capture of sea turtles while still retaining target catch. It appears that larger (wider) circle hooks reduce the incidence of deep ingestion in sea turtles, therefore reducing post-hooking mortality rates. Studies are ongoing, and it appears that the location in which a sea turtle is hooked greatly impacts their rate of post-hooking mortality, with deeply ingested hooks (gut hooked) more likely to be fatal than mouth-hooked turtles.
Sea turtles are incidentally caught by fishing methods such as longlining throughout the temperate and tropical oceans of the world. All seven species of marine turtles are listed under the Endangered Species Act. Research is ongoing to attempt to mitigate these captures while still retaining target species in these fisheries.