Vertical distribution pattern of CPUE of Atlantic billfishes and associated species estimated using longline research data

A longline research cruise was conducted in August–October 2002 in the tropical Atlantic Ocean to investigate the vertical pattern of catch per unit effort (CPUE) of Atlantic marlins. The vertical CpUE patterns of four Atlantic billfishes (Makaira nigricans Lacépède, 1802, Tetrapturus albidus Poey, 1860, Istiophorus albicans Latreille, 1804, and Tetrapturus pfluegeri Robins and de Sylva, 1963) were estimated using data from micro-time temperature depth recorders attached to the top of the hook line. Vertical CPUE patterns of billfishes estimated in this study were different from the vertical distribution pattern of billfishes reported by previous telemetry and electronic tag studies. This indicates that the catchability of longline gear on billfishes changes vertically, and vertical CPUE is more adequate for the calculation of effective fishing effort of billfishes caught by longline gear. Vertical CPUE patterns were also estimated for bigeye tuna Thunnus obesus Lowe, 1839, yellowfin tuna Thunnus albacares Bonnaterre, 1788, and blue shark Prionace glauca Linnaeus, 1758, to compare these patterns with those of billfishes. The results indicated that the main hooking depth of billfishes is shallower than that for bigeye tuna and blue shark, and similar to that of yellowfin tuna.