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

Issue:

Author(s): 
DeMartini, Edward E., James H. Uchiyama, and Happy A. Williams
Cover date: 
2000
PDF: 
Pages: 
489-506
Abstract: 

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 (L50) by using microscopic morphological evidence for gonadal development. L50 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°N; females dominated catches north of 27°N. Small-bodied fish of both sexes prevailed year-round below 22°N. A greater percentage of large-bodied (>156-cm [males], >172-cm [females] EFL) fish were caught north of 35°N during the late summer–early winter. The latter observations are consistent with several nonmutually exclusive hypotheses of migration energetics and body muscle heat conservation, both of which are discussed.