A COMPARATIVE STUDY OF LONGLINE BAITS 

 By 



Richard S. Shomtira 



Fishery Research Biologist 



Pacific Oceanic Fishery Investigations 



Honolulu, T. H. 



The Pacific Oceanic Fishery Investigations (POFI) of the U. S. Fish and 

 Wildlife Service Is surveying the tuna resources of the central equatorial Pacific. 

 Its investigations have proven the existence of a large population of deep-swimming 

 yellowfin tuna, Neothunnus macropterus (Temminck and Schlegel) , in the vicinity of 

 the Equator south of Hawaii" The only practicable method of sampling or harvest- 

 ing these tuna is by the use of longline (also known as flagline) fishing gear, 

 which consists of a mainline supported in the water at Intervals by buoys and bear- 

 ing a series of branch lines with baited hooks (Shapiro 1950). This fishing method, 

 developed by the Japanese £Lnd used by fishermen in Hawaii, has been adopted as a 

 sampling tool by POFI researchers. 



In adapting the fishing gear used In the Hawaiian longline fishery to 

 its purposes, POFI has introduced a number of modifications In the technique, one 

 of the most significant of which has been a change In the kind of bait used. 

 Hawaiian fishermen have traditionally used locally caught opelu, Decapterus 



f innulatus (Eydoux and Souleyet), for bait, and have preserved it prior to fishing 

 y packing it in rock salt (June 1950). Opelu, which brings a good price in the 

 fresh fish market, has not often been readily available in the areas in which POFI 

 vessels were fishing. It has, therefoire, been more convenient and cheaper to use 

 frozen West Coast sardine, Sardlnops caerulea (Girard) , herring, Clupea pallasll 

 (Valenciennes), and squid, a practice which has also been followed In recent years 

 by the Hawaiian commercial fleet. 



This use of sardines and herring, and less often of squid, for longline 

 bait has raised questions with regard to such matters as the comparative attrac- 

 tiveness of different baits to the various species of tuna taken on longllnes, 

 the comparative durability of the various baits while on the hook and "soaking", 

 i.e., fishing Immersed in the sea, and the effects of such preserving techniques 

 as dry salting or brining and finally of different ways of impaling the bait on 

 the hook. These questions are Important from two points of view. First, it is 

 desirable to determine by experimentation, if possible, what is the most effective 

 bait and what is the best way of handling it, in order to be able to provide 

 guidance to American fishermen who may wish to engage in tuna longline fishing. 

 Second, it is essential to ascertain what effects, if any, variations in the kind 

 of bait and the manner of its use have had on the catching efficiency of the gear 

 employed on POFI fishing cruises, since the catch rates (tiona per 100 hooks per 

 day) of this gear have been the primary index used by POFI in assessing the geo- 

 graphical and seasonal abundance of deep-swimming timas. Thus the main objective 

 of this study is to determine any adjustments that might be necessary to insure 

 the comparability of POFI's basic longline fishing survey data. 



The successful completion of the experiments was due to the efforts of 

 the scientific personnel and crew members of the vessels Cavalleri , John R. 

 Manning , and Hugh W. Smith . The author is also grateful to fellow staff members 

 i"or their constructive criticisms of this report. 



FISHING GEAR AND METHODS 



The longline gear!/ used in these experiments was made up of a number 

 of 1,260-foot sections (known as "baskets") joined end to end to make up a set. 

 With the exception of one experiment, each basket had 6 hook lines or droppers 

 attached to the mainline at ISO-foot intervals (fig. 1). Floats were attached by 

 60-foot lines at basket junctures to support the mainline. A total of 40-50 

 baskets were set each day at dawn and retrieved in the afternoon commencing at 

 or shortly after noon. This procedure resulted in a range of fishing times for 



i/ Detailed accoiants of the construction of the longline gear have been given by 

 various authors (Shapii»o 1950, Shimada 1951, and Nlska 1953) . 



