Hawaii FEP - Western Pacific Fishery Council

sources have been used to assess bycatch rates in this fishery. Logbook data compiled by theHawaii Division of Aquatic Resources (HDAR) indicate the reported disposition of the catchfrom all trips. Data were also compiled from 26 NWHI fishing trips that carried observersbetween October 1990 and December 1993 (Nitta 1999). The observer coverage represented 12percent of the 209 trips made during that period. In Table 9 is a summary of the 1990–1993observer data and the logbook data for the 1997–2001 period. The logbook figures are annualaverages, while the observer figures are aggregates of all data collected during the 3-yearprogram. 16 The two datasets indicate the same general discard patterns. Two species, kahala(Seriola dumerili) and butaguchi (Pseudocaranx dentex), made up the majority of the bycatch.Less than 5 percent of the catch of kahala was retained, and between about 50 and 75 percent ofthe catch of butaguchi was retained. Relatively large percentages of the catch of certain otherspecies, including white ulua (Caranx ignobilis), were discarded, but these species’ contributionto the catch was relatively small, so their contribution to absolute discards was relatively small.Non-BMUS that had relatively high-percentage discard rates (but relatively low absolute discardrates) in the observer data included opelu (Decapturus spp.), sharks, and a number of reefassociatedspecies.Target species are often discarded if they are damaged by predators. Sharks are responsible formost damage, but Hawaiian monk seals and bottlenose dolphins also cause damage. Thecarangids tend to be discarded because of their short shelf life and low market value. Butaguchi,for example, is palatable but of generally low value. Kahala, once a major component ofcommercial and recreational landings, is now seldom retained because it has been implicated inincidents of ciguatera poisoning (Kasaoka 1989).Although the logbook and observer data represent two different time periods and cannot bestrictly compared, substantial differences between the two indicate probable shortcomings in thelogbook data. The average overall discard rate indicated by the logbook data is 13 percent,compared with 25 percent for the observer data (Table 14). The differences suggest that thelogbook data—at least for some species—probably do not reliably reflect actual bycatch rates.The biggest differences were for the two most commonly discarded species: butaguchi andkahala.The two datasets indicated similar percentage discard rates for kahala, but the logbookdata indicated a substantially lower contribution of kahala to the total catch. The same was truefor butaguchi, but the percentage bycatch rates indicated in the two datasets were alsosubstantially different. Thus, as is common in many fisheries, underreporting of commonlydiscarded species appears to be a shortcoming of the logbook data. In 2003, NMFS redeployedobservers to the NWHI bottomfish fishery, in part, to collect additional bycatch observations andto calibrate the shortfall in discard reporting.16 HDAR logbook data report “number released” and “number damaged.” Assuming that all damaged fish werediscarded, these two categories were combined to estimate total bycatch. The observer data report the numberdiscarded and unknown disposition.Assuming that the discard rate where the disposition was unknown equaled therate where the disposition was known, the values in the unknown category were reduced by the proportion of knowndiscards to retained-plus-known discards. NWHI bottomfishing vessels often engage in pelagic trolling in additionto bottomfishing. The logbook data presented here include only fish recorded as being captured with bottomhandline gear; the observer data include relatively small numbers of troll-caught fish.94