Performance assessment of underwater setting chutes, side setting, and blue-dyed bait to minimize seabird mortality in Hawaii pelagic longline tuna and swordfish fisheries
Mortality in longline fisheries is the most critical global threat to some seabird species. Research and a commercial demonstration were conducted on three methods designed to avoid seabird capture in the Hawaii pelagic longline swordfish and tuna fisheries. An assessment is made of each method's effectiveness at avoiding seabird interactions, practicality and convenience, effect on fishing efficiency, cost to employ, and enforceability when limited resources for enforcement are available. A number of seabird avoidance methods have the capacity to nearly eliminate bird captures when employed effectively. However, to resolve the global problem of seabird mortality in longline fisheries, there is a need to identify and mainstream methods that not only have the capacity to minimize bird interactions, but are also practical and convenient, and provide crew with incentives to employ them consistently and effectively.
A seabird avoidance method called side setting, which entails setting gear from the side of the vessel, with other gear design the same as conventional approaches when setting from the stern, showed the highest promise of the tested seabird mitigation treatments. 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 attempt to pursue them, and by the time the stern passes the hooks, hooks will be too deep for seabirds to see or reach them. Side setting had the lowest mean seabird contact and capture rates of the seabird avoidance treatments tested when used with both Hawaii longline tuna and swordfish gear. Side setting provides a large operational benefit for certain types of vessels, and was perceived to be practicable for use by crew. The incentive for broad industry uptake and voluntary compliance is realistic, reducing the necessity for significant resources for compliance enforcement. Side setting requires a nominal amount of initial expense to employ. After the initial conversion to side setting is made, there is no additional effort required to implement the bird avoidance method. Side setting resulted in high fishing efficiency relative to the other treatments, based on bait retention and hook setting rates. Assessment of the feasibility of adjusting the gear to side set from various deck positions, the location of deployment of baited hooks from various side setting positions, sink rates of a range of types of baited hooks, and aspects of vessel conversion to side setting, indicates that side setting would be both feasible and effective at reducing seabird interactions on a wide range of longline vessel deck designs.
Two lengths of an underwater setting chute, a device that is designed to release baited hooks underwater, out of sight and reach of diving seabirds, were relatively effective at reducing bird interactions but performed inconsistently and were inconvenient due to a manufacturing flaw and design problems. Design and manufacturing improvements are needed and are likely feasible. Consideration could then be made to make the chute commercially available and possibly integrate the chute into deck hulls of the next generation of longline vessels. Two chutes, one 9m long and one 6.5m long, which deployed baited hooks 5.4m and 2.9m underwater, respectively, were used in this trial. The 9m chute had the second lowest mean seabird interaction rates when used with swordfish gear, and the 6.5m chute had the second lowest mean seabird interaction rates when used with tuna gear. However, the results from this comparative performance is affected by the technical problems encountered with the chutes in this trial, and does not reflect the chute's potential. The underwater setting chute is relatively expensive, costing U.S.$5,000 for the hardware. The chute is not commercially available for pelagic longline fisheries. Use of the underwater setting chute may be effectively enforced if combined with relevant tec