Gill nets are transparent fences, suspended by top floats and stretched taught by a weighted bottom.
Longliningone of the most common fishing methodssets out miles of baited hooks that snag or entangle unwanted species, including at least forty seabird species.
The Scope of "Dirty Fishing"
"The enormity of the problem still isn't understood," said Jeremy Jackson, a marine biologist at Scripps Institution of Oceanography in San Diego, California.
All seven species of marine turtle are endangered. With better-protected nesting beaches, scientists believe bycatch plays a big role in population declines.
The rarest, the leatherback (Dermochelys coriacea), has declined by 95 percent oceanwide. The animals must navigate a gauntlet of coastal gill nets off Peru and Chile, at great cost, said Larry Crowder, a marine biologist at Duke University in Durham, North Carolina.
Research suggests that longlines take hundreds of thousands of leatherbacks and other turtles each year. "If longline fishing continues unabated, there's a 50 percent chance of turtle extinctions in the next 10 to 30 years."
Fisheries around the world kill seals, whales, dolphins, and other marine mammals in the course of operations. Some of these are endangered species.
The bykill issue is a huge, complex problem. "There is no one-size-fits-all solution," says Lubchenco. "Bycatch must be addressed, fishery by fishery."
Some types of gear, like purse seines and hook and line are less damaging, says Ratana Chuenpagdee, a marine biologist at the Virginia Institute of Marine Science in Williamsburg, Virginia, and co-author of the "Shifting Gears" study.
In some cases, the answer is to modify gear. For example, in the Bering Sea, changing net's mesh size and shape cut bycatch of young pollock by 75 percent, said Ellen Pikitch, director of the Ocean Strategy Program at the Wildlife Conservation Society in New York City.
An abiding success is the dolphin. During the 1960s, 200,000 dolphins a year drowned in drawstring nets used for Pacific yellowfin tuna. Public outcry and a consumer boycott spurred Congress to pass the Marine Mammal Protection Act in 1972. Since then, nets are set to spare dolphins.
Another lifesaving technique is to outfit gill nets with acoustic alarms called "pinger," which reduced capture of harbor porpoises by 92 percent in a British Department for Food, Environment, and Rural Affairs study.
The world's largest flying bird, the wandering albatross, is in serious trouble because of longline tuna fishing in the sub-Antarctic Ocean. But an innovation by Japanese fishermen is keeping birds away from some operations. They attach metallic red streamers to nets that scare the birds away while nets are submerged.
But, Pikitch says, "we need to ban the most destructive fishing methods."
Growing scientific evidence shows that some marine species are threatened with extinctionand others will beunless fishing practices and regulations change.
Sometimes the only answer is to limit fishing. Fisheries have been closed where populations are "economically extinct," like the North Atlantic cod fishery.
Recent Pew Oceans Commission recommendations call for a new approach to managing fisheries that preserves habitat in addition to setting catch limits. Lubchenco advocates for a network of fully protected marine reserves, linked by corridors, to protect breeding and nursery grounds.
"The bottom line is that we need to come to grips with the bycatch issue," she said. "The answers are going to have to be fishery-specificbut the answers must come from leadership at the highest levels"requiring both national regulations and international agreements.
Regulations can save species. One conservation success is Kemp's ridley turtle (Lepidochelys kempii), once the most endangered marine turtle. By the 1970s, shrimpers in the Gulf of Mexico had fished them nearly to extinction. Only 300 nesting females remained.
Then in the mid-1980s, the Turtle Excluder Device, or TED, a turtle escape hatch, was introduced. Since 1990, TEDs are required in U.S. waters, though compliance varies by region. Today, nesting females have jumped to 3,000. "If they enforce it, TEDs work," Crowder says.
Given a measure of protection, sea creatures can rebound.
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