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Positive Results In Pilot Study To Reduce Bluefin Tuna By-catch

An American research scientist is in the home stretch of a pilot study showing that substituting two types of fishing gear for pelagic long-lines might eliminate the by-catch of severely overfished bluefin tuna in their northern Gulf of Mexico spawning grounds.

After 150 fishing days beginning in March 2012 using greenstick equipment to target yellowfin tuna and buoy gear for swordfish, researcher David Kerstetter said his group observed more than 16,000 pounds of yellowfin and more than 3,000 pounds of swordfish landed — without a single catch of bluefin tuna, sea turtles or marine mammals. Small numbers of other species were caught — including wahoo, dolphin, blackfin tuna, white marlin and blue marlin — with nearly all released alive, Kerstetter said.

The preliminary findings from the study, which will go on for several more months, emerge as NOAA Fisheries is poised to propose a rule to reduce bluefin tuna by-catch.

Kerstetter says it might be possible for commercial fishers to make more money catching fewer fish using the alternative gear.

“You don’t need as much crew, or boat or gear,” he said. “You can land fewer fish and make the same or more money doing it because the product quality is higher.”

The preliminary findings of David Kerstetter and several graduate students are important because bluefins are the priciest and most exploited fish. Their stocks have plunged over the past several decades despite strict international management measures. The northern Gulf is one of a few spots where bluefins are known to reproduce, and many are caught accidentally by commercial long-line fishermen targeting yellowfin tuna and swordfish. To make matters worse, the 2010 BP oil spill might have taken out large numbers of bluefin larvae because it occurred in the middle of the spawning season.

Kerstetter, who has extensive experience with the commercial buoy gear fishery for swordfish in southeast Florida, wanted to find out whether substituting that equipment — as well as commercial “greenstick” gear — for miles of baited surface hooks in the Gulf would result in less by-catch of bluefins and other species such as sea turtles and billfish. So, for the past year, he and several graduate students have been working with four commercial fishing boats to switch from long-lines in the Gulf.

Buoy gear consists of a floating, lit-up marker attached to a mainline with one or two branch lines, each with a baited hook. When a fish strikes, it pulls the buoy across the surface, alerting the fishermen to retrieve it. Greenstick gear consists of a pole mounted amidships trolling a mainline behind the boat that holds five to 10 “drop lines” baited with plastic squid that skip across the surface. When a fish bites the baits, the mainline breaks away from the greenstick and is retrieved by a hydraulic winch. Both systems are tended immediately when a fish hits, while pelagic long-lines have up to 40 miles of baited hooks dangling just beneath the surface that might not be hauled back until long after hooked fish or other species are dead.