PROBLEMSLike 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...