Longline Fishing's Unintended Victims: Turtles
Many sea turtles die each year from longline fishing, but circle hooks and buoy gear help protect loggerheads and leatherbacks.
What works as mitigation for one class of bycatch may harm another. Anchors reduce bird bycatch by taking bait quickly to the bottom. But when they hold it there they increase lethal bycatch of sea turtles, especially loggerheads that eat longline bait and are then held underwater until they drown. Other sea turtles, especially leatherbacks, tangle or get snagged in unanchored pelagic longlines, but if the lines aren't too deep, at least they can make it to the surface to breathe.
The U.S. fleet kills a lot of turtles, but nothing compared with foreign fleets. Some of the worst offenders are Spain, Japan, China, Ecuador, Peru, and Canada. Canada's Atlantic swordfish longliners annually catch, injure, or kill something like 1,200 loggerheads and at least a hundred leatherbacks. There are no bycatch caps, and no restrictions on area, bait, depth, or time bait stays in the water. And only about 5 percent of the boats have government observers.
In the Pacific, loggerhead and leatherback populations are much smaller and in even steeper decline. So the NMFS prohibits West Coast-based swordfish longliners from the North Pacific high seas. And it requires shallow-water pelagic longliners based in Hawaii to carry a NMFS observer so the agency can shut down fishing when an annual cap of 34 loggerheads or 26 leatherbacks is reached.
"Circle hooks" (rounder and with smaller gaps than traditional "J hooks" and no more expensive) are required where the U.S. fleet operates in major turtle habitat. They help because turtles get hooked in the mouth rather than the throat. U.S. longliners have to carry dip nets and line cutters so they can cut the line near the hook, generally enabling turtles to survive. And in much of the North Atlantic they have to use fish instead of squid for bait because turtles tend to nibble the former off the hook and gulp the latter whole.
Most loggerheads die on lines held to the bottom by anchors. The most effective mitigation method for turtle bycatch is "buoy gear," developed for swordfish in the Gulf of Mexico. It also works better--about 300 swordfish caught per 1,000 hooks compared with 8 per 1,000 for longlines. It's catching on because of its efficiency, but it needs to be mandated. About 15 buoys, often illuminated and hanging on baited hooks near the bottom, are deployed from a tethered line at night. When a fish takes the bait the buoy moves, and the fisherman hauls in his catch. Turtle bycatch is virtually nonexistent; non-target fish are released alive; and the quality of the catch is improved because it doesn't die the way it does on longlines.
This story originally ran in the September-October 2013 issue as "Turtle Troubles."