Sexual maturity, sex ratio, and size composition of swordfish, Xiphiasgladius, caught by the Hawaii-based pelagic longline fishery

摘要

Swordfish (Xiphias gladius) caught by the Hawaii-based pelagic longline fishery during March 1994-June 1997 were examined at sea by observers of the National Marine Fisheries Service, Southwest Region. Observers provided unbiased size and sex composition data for 4.8% of the swordfish catch and 4.9% of the effort in number of hooks of the fishery during the 40-mo. period. Observers measured body lengths for more than 8600 swordfish brought aboard participating vessels; sex, based on macroscopic appearance of gonads, was identified aboard ship for 77% of measured fish. Sex identifications were later verified (0.5% error rate) and gonadal developmental stage described for 1336 fish whose sex was identified in the field. Logistic regression was used to estimate sex-specific, median body size at sexual maturity (L-50) by using microscopic morphological evidence for gonadal development. L-50 was 102 cm +/-2.5 (95% CI) cm eye-to-fork length (EFL and 144 +/- 2.8 cm EFL for males (n=506) and females (n=822), respectively. Sex ratios were an increasing power function between 100 and 220 cm, and nearly all fish >220 cm EFL were females. Sex composition and body size varied temporally and spatially, especially the latter. Relatively more males were caught south of 27 degrees N: females dominated catches north of 27 degrees N. Small-bodied fish of both sexes prevailed year-round below 22 degrees N. A greater percentage of large-bodied (>156-cm [males], >172-cm [females] EFL fish were caught north of 35 degrees N during the late summer-early Minter. The latter observations are consistent with several nonmutually exclusive hypotheses of migration energetics and body muscle heat conservation, both of which ale discussed.