Background | Green Sticks | Buoy Gear | Surface Longline Gear Modification – Weak Hook | A Reliable Solution | References | Vietnamese Translation
Surface longline fishing gear consists of a five to 45 mile long mainline suspended near the surface by buoys. Fishermen tether approximately 25 baited hooks per mile to the mainline by short sections of line called “gangions.” The gear is then left to float independent of the vessel for 10-12 hours, during which time it interacts with a variety of target and non-target marine animals (National Marine Fisheries Service [NMFS], 2010, p. 44).
Surface longlines were first introduced to the Gulf of Mexico at a commercial scale in the 1950’s. Foreign fishing fleets and, increasingly, U.S. fishermen used the gear to target yellowfin tuna and Western Atlantic bluefin tuna until regulations came into effect in 1983 that prohibited directed fishing for bluefin in the Gulf of Mexico (Beerkircher, Brown, & Restrepo, 2009, p. 1-2). This action aimed to protect depleted Western Atlantic bluefin tuna in their only known spawning area – the Gulf of Mexico (Rooker et al., 2007, p. 266).
The U.S. excludes foreign fishing vessels from fishing within U.S. waters of the Gulf of Mexico; however, U.S. commercial surface longline vessels continue to target yellowfin tuna and swordfish in the Gulf. These vessels fish surface longlines averaging 30 miles long that contain hundreds of baited hooks. These lines sit unattended for 10-12 hours, during which time they injure and kill a variety of non-target marine life (Beerkircher et al., 2009, p. 2-3). Government observer program data from 2007 through 2009 indicates that 50.1% of the Gulf surface longline catch was discarded, with 65% these discards thrown back dead.
The National Marine Fisheries Service (NMFS) has instituted a number of measures to reduce incidental catching and killing of non-target marine animals, otherwise known as bycatch, by Gulf surface longlines. These include areas closed to fishing, prohibition on the use of live bait, and surface longline gear modifications, such as mandatory circle hooks, to prevent catching non-target ocean wildlife (Beerkircher et al., 2009, p. 2). Despite past management actions, the U.S. Gulf of Mexico surface longline fleet continues to capture, injure and kill significant numbers of severely depleted non-target marine animals, such as Western Atlantic bluefin tuna, blue marlin and leatherback sea turtles.
Swordfish buoy gear and green sticks have been identified by scientific research and anecdotal reports from commercial fishermen as two promising alternatives to surface longlines in the Gulf. These highly selective fishing gears reduce incidental catch of non-target species, while preserving the fishermen’s access to target fish species (Bayse & Kerstetter, 2010; NMFS, 2010). These alternative gears could more reliably decrease the incidental catching and killing of non-target marine animals than modifying surface longline gear to reduce incidental catch.
Green stick fishing rigs consist of one or more 35 to 45 foot long fiberglass poles that are mounted to the stern of the boat deck. The green stick tows a mainline behind the vessel with no more than 10 hooks attached to it. Each hook is connected independently to the mainline so that the fishermen can selectively retrieve them. Hooks are baited with plastic squid and trolled across the surface, mimicking flying fish skipping across the water. At the end of the mainline, is a fish-shaped weight, known as a “bird”, that holds the mainline taught while the boat is moving. When a fish is hooked, its corresponding line breaks away from the mainline and is retrieved by the fishermen (Wescott, 1996, p. 2; NMFS, 2010, p. 106).
Fishermen use green sticks to target yellowfin, bigeye, albacore, skipjack and bluefin tuna. The Japanese introduced the gear to Hawaii in the 1980’s and since then it has been adapted for use in mainland U.S. commercial and recreational tuna fisheries in New England, North Carolina, South Carolina and the Gulf of Mexico. Preliminary research by NMFS, as well as anecdotal reports and logbook data from commercial fishermen using the gear, highlight the green stick’s effectiveness at catching tunas. According to logbook data from 2000-2002, the total green stick catch was 81.9% yellowfin tuna. The ability to reel in each fish separately allows the fishermen to bring them to the boat immediately after they are hooked. This quick retrieval allows fishermen to bring fresher tuna to market, while significantly reducing the killing of non-target marine animals, like bluefin tuna, because the fish are the hook for minutes rather than hours on longlines (Wescott, 1996, p. 2; NMFS, 2008, p. 215-218).
Swordfish buoy gear (SBG) functions like a very small section of surface longline. Each piece of SBG has one or two branch lines attached to a mainline, which varies in length according to moon phase. The mainline is then attached to a lighted float or radar-reflecting buoy that allows fisherman to track the gear. No more than 35 individual buoy gears are allowed per vessel, with a maximum of two hooks per buoy. SBG must be free floating and not connected together in any way (NMFS, 2010, p. 104).
SBG was developed to target swordfish following the 2001 prohibition on the use of surface longlines in large expanses of the southeast Atlantic, including the east coast of Florida (Bayse & Kerstetter, 2010). Scientific research shows this gear to be far more effective at targeting swordfish than surface longlines, with little or no incidental catch of non-target marine animals, such as sea turtles and blue marlin (Bayse & Kerstetter, 2010). According to 2007-2009 logbook data, for every 1,000 hooks fished, SBG caught approximately 322 swordfish, while surface longlines only caught approximately 8 swordfish (NMFS, 2010, p. 105-106). Equally impressive is that SBG catch during this three-year period was 94% swordfish. Since each SBG is free floating, fishermen are able to remove fish from the line and get a freshly baited hook back in the water quickly (Bayse & Kerstetter, 2010). Because fishermen actively fish SBG it produces fresher swordfish, while reducing injury to incidentally caught non-target marine animals.
Surface Longline Gear Modification – Weak Hook
The National Marine Fisheries Service (NMFS) is testing a modified version of the circle hooks mandated for use by surface longline fishermen to reduce the incidental catch of spawning Western Atlantic bluefin tuna by Gulf surface longlines. The diameter of the metal wire used to make these experimental hooks is smaller than a conventional circle hook. The pressure created by struggling large fish like bluefin tuna is supposed to straighten these weak” hooks and allow the fish to escape (NMFS, 2009, p. 2).
The ability of weak hooks to release large bluefin spawners alive and in good condition is questionable. The physiological stress created by the high surface water temperatures where surface longlines are used, spawning activities and inadequate oxygen caused by their impeded ability to swim bring fatigued hooked bluefin to the point of death or limit their ability to escape before the gear is hauled back (Teo et al., 2006, p. 2). Variable haul back methods, ocean currents and gear arrangements can limit the hook’s effectiveness (NMFS, 2009, p. 12). If the weak hook does straighten and release the fish, there is no way to know whether the fish survived the encounter.
In addition to the weak hook’s questionable performance for bluefin tuna, it also provides little or no protection for other non-target marine animals, such as leatherback sea turtles, that may be incapable of producing the force necessary to straighten the hook and release themselves (NMFS, 2009, p. 6). In fact, large, commercially valuable swordfish may be one of the only other marine animals that can bend these weak hooks (NMFS, 2009, p. 8). Therefore, the widespread use of weak hooks may increase the catch rate of undersized swordfish and other non-target marine animals, while reducing the catch of commercially valuable swordfish.
A Reliable Solution
Based on existing scientific research, the only reliable way to protect spawning Western Atlantic bluefin tuna or other non-target marine animals from being incidentally killed by surface longline gear is to switch to selective alternative gear like green sticks and buoy gear.
Bayse, S.M., & Kerstetter, D. W. (2010). Characterization of swordfish buoy gear catches in the Florida Straits. Poster session presented at the annual meeting of the Florida Chapter of the American Fisheries Society, Altoona, FL.
Beerkircher, L., Brown, C. A., & Restrepo, V. (2009). Pelagic observer program data summary, Gulf of Mexico bluefin tuna (Thunnus thynnus) spawning season 2007 and 2008; and analysis of observer coverage levels. NOAA Technical Memorandum NMFSSEFSC-588, 33 p.
National Marine Fisheries Service. (2008). 2008 project report Gulf of Mexico pelagic longline bluefin tuna mitigation research.
National Marine Fisheries Service. (2009). 2009 project report update Gulf of Mexico pelagic longline bluefin tuna mitigation research.
National Marine Fisheries Service. (2008). Stock assessment and fishery evaluation (SAFE) report for Atlantic highly migratory species 2008. Retrieved from www.nmfs.noaa.gov/sfa/hms/Safe_Report/2008/
National Marine Fisheries Service. (2010). Stock assessment and fishery evaluation (SAFE) report for Atlantic highly migratory species 2010. Retrieved from www.nmfs.noaa.gov/sfa/hms/Safe_Report/2010/
Rooker, J. R., Bremer, J., Block, B. A., Dewar, H., de Metrio, G., Corriero, A., et al. (2007). Life history and stock structure of Atlantic bluefin tuna (Thunnus thynnus). Reviews in Fisheries Science, 15(4), 265-310. doi:10.1080/10641260701484135
Teo, S. L., Boustany, A., Dewar, H., Stokesbury, M. J., Weng, K. C., Beemer, S., et al. (2006). Annual Migrations, diving behavior, and thermal biology of Atlantic bluefin tuna, Thunnus thynnus, on their Gulf of Mexico breeding grounds. Marine Biology, 151, 1-18. doi: 10.1007/s00227-006-0447-5
Vietnamese Translation — Switching gears in the Gulf of Mexico – Alternatives to Surface Longlines
Chuyển đổi dụng cụ đánh bắt tại Vịnh Mexico – Các Biện pháp Thay thế cho Giăng dây câu Dài trên Mặt Biển
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