Comparison of three seabird bycatch avoidance methods in Hawaii-based pelagic longline fisheries

Abstract

KEY WORDS: albatross, bycatch, Hawaii, longline fishery, seabird.Capture in longline fisheries is a critical threat to most albatross and large petrel species. 1-3 Blackfooted Phoebastria nigripes and Laysan P. immutabilis albatrosses are the predominant seabird species incidentally caught in Hawaii longline fisheries. This study reports results of a trial in the Hawaii pelagic longline tuna and swordfish fisheries comparing four experimental treatments' seabird capture rates and commercial viability. Two research fishing trips were conducted between 1 April and 17 May 2003 on a Hawaii-based pelagic longline vessel, at traditional fishing grounds south of the Northwestern Hawaiian Islands, between 21°41′N and 25°08′N, 173°58′W and 167°43′W.Two of the treatments employed were setting branch lines through 9 m and 6.5 m long underwater setting chutes, which release baited hooks beneath the sea surface, in an attempt to prevent diving seabirds from reaching them. The design of the underwater setting chute, illustrated in Molloy et al., 4 is similar to that used in this present trial. When setting with the 9 m and 6.5 m chutes on the research vessel, 5.4 m and 2.9 m of the chute's shaft was underwater, respectively.A third treatment, called side-setting, entailed setting from the side of the vessel, with other gear design the same as conventional approaches when setting from the stern. The crew throwing baited hooks was 8 m forward from the port-stern corner. Baited hooks were thrown forward, close to the side of the vessel's hull, to protect baits from seabirds. A bird curtain was used, 4.9 m forward from the portstern corner, when side-setting to increase the effectiveness of this mitigation method by preventing birds from establishing a flight path along the side of the boat where baited hooks were being deployed. The hypothesis is that when side-setting, baited hooks will be set close to the side of the vessel hull where seabirds will be unable or unwilling to pursue the hooks. By the time the stern passes the hooks, the hooks will have sunk to a depth where seabirds cannot locate them or cannot dive.A fourth treatment was blue-dyed bait. Bait was completely thawed and dyed blue by soaking in a large tub with dissolved blue food coloring (Virginia Dare FD & C Blue no. 1) powder at a concentration of 4 g/L of water for 1-4 h to achieve regulatory-required darkness. The hypothesis is that dyed bait is difficult for birds to detect because it reduces the contrast between bait and sea color.Research on the efficacy of blue-dyed bait and underwater setting chutes for pelagic longline fisheries at reducing seabird bycatch has been conducted previously. 5,6-10 This present study is the first assessment of the effectiveness of side-setting at reducing seabird capture.Setting occurred only during daylight to enable observations of seabird interactions with fishing gear. Both tuna and swordfish gear used 60 g swivels attached within 1 m of the hook, a weighting design selected by the Hawaii Longline Association. Gilman et a...

Reducing seabird bycatch in the Hawaii longline tuna fishery

“…Based on results from controlled and comparative experiments of seabird avoidance methods in the Hawaii longline fleet (McNamara et al 1999, Boggs 2001, Gilman et al 2007a, fishery management authorities adopted and amended regulatory measures for the Hawaii longline fleet to reduce seabird catch rates. Since regulations were first adopted in June 2001, total seabird captures in the combined Hawaii longline tuna and swordfish fisheries dropped 96% from an estimated 2433 in 2000 to 88 in 2006(Van Fossen 2007.…”

“…When implemented to prescription, crew throw baited hooks forward and close to the side of the vessel hull where seabirds, such as albatrosses, are unable or unwilling to pursue them. Ideally, by the time the stern passes, the hook has sunk beyond the reach of seabirds (Gilman et al 2007a). Employment of a bird curtain in combination with…”

Are deep-sea cephalopods really common preys for oceanic seabirds?

“…Nowadays, almost whole oceans are explored by longliners, from equatorial to circumpolar waters, which supply with available and abundant food resources through the discharges from the fishing boats, and consequently, an apprenticeship of the seabirds in take advantage of this easy food resource. A tragic consequence that resulted from this apprenticeship was the serious increase of the mortality rate of albatrosses hooked on longlines in the last decades, when the birds eat the baits, normally cephalopods, and die hooked (Brothers 1991, Vaske Jr. 1991, Neves & Olmos 1997, Neves et al 2006, Gilman et al 2007.…”

Best practices to mitigate seabird bycatch in longline, trawl and gillnet fisheries—efficiency and practical applicability

“…Side setting, as opposed to traditional stern setting, reduces the time baited hooks remain within the reach of seabirds. Lines set at the side of the vessel enter the water several meters in front of the stern, and thus commence sinking sooner and have sunk to a certain depth when they emerge clear of the stern (see Yokota & Kiyota 2006, Gilman et al 2007.…”

“…The line weighting regime, appropriate sink rate and combination of other mitigation measures need to be determined for a specific fishery. Future research should also include the concepts of underwater setting and side setting (see Kiyota 2006 andGilman et al 2007 for side setting).…”