Longline Fishing’s Unintended Victims: Billfish, Sharks, and Tuna

What's good for protecting some species from longlines can lead to disaster for others.


Like anchors, circle hooks work well for one bycatch class but harm another. “They’re wonderful for turtles,” says Russell Nelson, The Billfish Foundation’s chief scientist. “But [because they work better on fish than J hooks] they can increase longline bycatch of blue marlin by 30 percent or 40 percent. High-seas longlining bycatch is a major problem, accounting for 90 percent to 95 percent of the fishing mortality of marlin.”

Large sharks are being annihilated by longliners. For example, as bad as Canada’s Northwest Atlantic swordfish longlining industry is for turtles, it’s worse for sharks. It kills two for every swordfish caught.

It’s hard to think of a shark in worse shape than the dusky. They take almost twice as long as humans to reach sexual maturity and then bear only 3 to 14 pups every third year. The NMFS banned dusky retention in 2000. But partially because people, longliners included, have trouble distinguishing them from other species, they aren’t recovering. So late in 2012 the NMFS proposed an eight-foot limit and closing dusky bycatch hotspots to shark longlining. The agency got eaten alive—not just by longliners but by recreational anglers—so it backed off.

Because of their high value, bluefin tuna are even more critically depressed than sharks and billfish. In 2012 Atlantic longliners targeting fish other than bluefins killed and were required to discard 239.5 metric tons of bluefin bycatch because the NMFS wants to discourage a de facto bluefin fishery. The worst bycatch occurs in the Gulf of Mexico, the western Atlantic stock’s only known spawning area. Adding to the problem is that the NMFS allows Gulf longliners targeting abundant yellowfin tuna to sell some of their bluefin bycatch. So the valuable bluefins are caught “accidentally on purpose.” It’s a grotesque ruse that threatens to usher western bluefins into commercial extinction.


For billfish: In 2012 the International Commission for the Conservation of Atlantic Tunas (which also manages billfish) implemented the first retention cap for white and blue marlin.

For sharks: Longliners not targeting sharks are getting away from wire leaders in favor of monofilament that hooked sharks can bite through and thereby escape. In fact, Australia, Ecuador, Micronesia, New Caledonia, Papua New Guinea, South Africa, Tonga, and the Marshall Islands have banned wire. And last March the Convention on International Trade in Endangered Species, goosed by the United States, protected the oceanic whitetip shark, the porbeagle, and three species of hammerheads—great, scalloped, and smooth—by banning export unless the nation’s scientific authority determines that international trade won’t pose a threat.

For bluefin tuna: “Greensticking” is mitigation that works as well for bluefins as streamers work for birds. A fiberglass, graphite, or wooden stick (originally green but now any color) elevates and tows a weight about 400 yards behind the boat. The weight has the dual function of serving as an attractor for the targeted yellowfins and keeping the mainline taut so the attached squid lures can fly in and out of the water. The yellowfins hit them, get hooked, and are then winched to the boat. Like buoy gear, greensticking is catching on because of its efficiency, but its use needs to be mandated.

In the Gulf a possible fix is at hand with the NMFS’s proposed Amendment 7 to its Atlantic Highly Migratory Species Plan. The rule may be out by the time you read this, and a 60-day public comment period will follow publication. The NMFS needs to implement a strict bycatch cap, ban surface longlining in the Gulf when spawning bluefins are present, and require 100 percent NMFS observer coverage.

This story originally ran in the September-October issue as "Fishing Failures."