Captain and Observer Perspectives on the Commercial Viability and Efficacy of Alternative Methods to Reduce Seabird Bycatch during Gear Haulback in the Hawaii-based Pelagic Longline Swordfish Fishery
Bycatch of seabirds in longline fisheries threatens the viability of some populations (Anderson et al., 2011). Seabirds are primarily caught while longline gear is being set, and as a result, seabird bycatch mitigation research has appropriately focused on methods to reduce seabird captures during setting and not hauling (Brothers et al., 1999; Gilman, 2011; Clarke et al., 2014).
Since 2001, when requirements to mitigate seabird bycatch during setting in the Hawaii-based longline shallow-set swordfish fishery came into effect, seabird catch rates and levels declined by about 90% (Gilman et al., 2014). Now, about 75% of bird captures occur during gear haulback (Gilman et al., 2014). An average of about 59 seabirds (±9 95% CI) was annually caught during gear haulback in the fishery between 2011 and 2015 (Gilman et al., 2014; NMFS, 2012, 2013, 2014, 2015, 2016).
There are about 20 active vessels in the Hawaii shallow-set longline swordfish fishery (NMFS, 2015). The fishery operates year-round, with the majority of effort occurring between February and April. Vessels fish at grounds in the North Pacific typically between 130 o W to 180o longitude and 22o to 40o N latitude (summarized in Gilman et al., 2014). A study conducted in 2014 analyzed observer data and identified methods that significantly affect seabird bycatch during gear haulback in the Hawaii longline swordfish fishery (Gilman et al., 2014).
Building off of the 2014 study, we interviewed Hawaii longline swordfish captains and conducted a demonstration of a method designed to reduce seabird interactions during gear retrieval. Study aims were, globally, to fill a gap in knowledge of effective and commercially viable methods to mitigate seabird bycatch during haulback in pelagic longline fisheries, and locally, to identify commercially viable solutions that may enable substantial reductions in seabird haul bycatch rates in the Hawaii longline swordfish fishery. Current fishing mortality levels of Laysan and black-footed albatrosses in the Hawaii longline swordfish fishery are very unlikely to pose a risk to these two species at the genetic population level (Laysan albatross estimated absolute abundance has been stable, and there has been an increasing trend in black-footed albatross estimated absolute abundance, ACAP, 2014; IUCN, 2016). Further reductions, however, would directly contribute, albeit slightly, to remediating the cumulative effects from anthropogenic mortality sources, including removals in other pelagic and demersal longline fisheries operating in the north Pacific. Further reductions would also improve fishing efficiency, as it is economically and operationally inefficient to catch, handle and release alive and discard dead seabirds.