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Sexual maturity, sex ratio, and size composition of swordfish, Xiphias gladius, caught by the Hawaii-based pelagic longline fishery
DeMartini, E.E.; Uchiyama, J.H.; Williams, H.A. (2000). Sexual maturity, sex ratio, and size composition of swordfish, Xiphias gladius, caught by the Hawaii-based pelagic longline fishery. Fish. Bull. 98(3): 489-506
In: Fishery Bulletin. US Government Printing Office: Washington, D.C.. ISSN 0090-0656, more
Peer reviewed article  

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  • DeMartini, E.E.
  • Uchiyama, J.H.
  • Williams, H.A.

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 = 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. 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.

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