PIFSC Sea Turtle Longline Research EA June 1, 2009
species such as sharks, some marketed and some not, and some longline fisheries may target species considered bycatch in other fisheries, again, such as sharks.
Pelagic longline fishing generally occurs in open ocean areas beginning several miles from shore (at least outside the 6.6 km limit of state waters (3 nmi) and can often extend well offshore into international waters outside the Exclusive Economic Zone (EEZ) of any nation (200 nmi).
Pelagic longline fleets range in size from small-scale traditional domestic artisanal fisheries, to small domestic commercial fleets, to modern mechanized industrialized fleets from nations distant from the fishing grounds. Longline fishing involves suspending a mainline from floats at the sea-surface to which is attached branch lines with terminal hooks. The configuration of the gear, including the length of the mainline, the number of branch lines between floats, the maximum depth of branch lines, the size of hooks, the bait, and other characteristics vary with the specific target fishery. At the extreme, a longline may be nearly 100 km (60 miles) in length with up to 2,400 hooks. Depending on their target species, longline fisheries may deploy hooks at depths ranging from near the surface to 400 m (1,312 feet) in depth (Beverly and Chapman 2007, NMFS 2008a (Figure 1). Mainlines are typically 33 km (18 nmi) to over 100 km (60 nmi) long.
Depending on the fishery and the size and type of vessel, the main line of pelagic longline gear generally drifts freely near the surface in the high seas for approximately 12 hours between the time they are set and the time they are hauled back out (soaking time). The Hawaii-based pelagic longline fishing can be roughly divided into two categories, (recognizing that other fisheries also are conducted, such as that for mahi mahi in South America; Figure 1):
Shallow-set gear, where the hooks are typically within 100 m (300 feet) of the surface and are generally set at night, deploying between 700 and 1,000 hooks, targeting either broadbill swordfish or night-swimming bigeye tuna;
deep-set gear, where the majority of the hooks are set much deeper (140 m to 370 m; 450 to 1200 feet below the surface) during the day, typically deploying between 1200 to 1900 hooks, targeting albacore and bigeye tuna (because the underwater lines typically form a “U-shape” between the floats, hooks nearer the floats may actually be in the same water layer as shallow-sets).
Pelagic longline sets of both types are often deployed where target fish are expected to be found near temperature breaks (thermal fronts) or eddies that can be identified by available sea surface temperature and height charts or color charts showing phytoplankton concentrations that are readily available to fishers worldwide. Sea turtles, especially loggerhead (Caretta caretta) turtles are highly vulnerable to pelagic longline fishing because they typically forage within 60 m (<180 feet) of the surface and occupy the same fronts and eddies as targeted fish, due to the abundance of prey inthese nutrient-rish waters. Therefore, most sea turtle encounters in pelagic longline fisheries involving either hooking or entangling turtles happen on shallow sets for swordfish that are set at night using squid baits near thermal fronts or eddies. In addition, in deep sets, up to 30% of the hooks may be set within the upper 100 m (300 feet) of the water column near the